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<article id="post-ADB-命令整理" class="article article-type-post" itemscope itemprop="blogPost">
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<a href="/2020/05/14/ADB-%E5%91%BD%E4%BB%A4%E6%95%B4%E7%90%86/" class="article-date">
<time datetime="2020-05-14T02:45:27.000Z" itemprop="datePublished">2020-05-14</time>
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<a class="article-category-link" href="/categories/Android/">Android</a>
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<h1 itemprop="name">
<a class="article-title" href="/2020/05/14/ADB-%E5%91%BD%E4%BB%A4%E6%95%B4%E7%90%86/">ADB 命令整理</a>
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<h2 id="显示当前的-Activity-栈"><a href="#显示当前的-Activity-栈" class="headerlink" title="显示当前的 Activity 栈:"></a>显示当前的 Activity 栈:</h2><figure class="highlight sh"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">adb shell dumpsys activity activities | sed -En -e <span class="string">'/Running activities/,/Run #0/p'</span></span><br></pre></td></tr></table></figure>
<h2 id="设置-prop"><a href="#设置-prop" class="headerlink" title="设置 prop"></a>设置 prop</h2><figure class="highlight sh"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">adb shell setprop <name> <value></span><br></pre></td></tr></table></figure>
<p>Firebase 是使用这个来控制是否开启 DebugView</p>
<figure class="highlight sh"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">adb shell setprop debug.firebase.analytics.app <package_name></span><br></pre></td></tr></table></figure>
<p>读取的使用 getprop</p>
<figure class="highlight sh"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">adb shell getprop debug.firebase.analytics.app</span><br></pre></td></tr></table></figure>
<p>在代码里面也可以读取：</p>
<figure class="highlight kotlin"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">fun</span> <span class="title">readProp</span><span class="params">(prop: <span class="type">String</span>)</span></span>: String? {</span><br><span class="line"> <span class="keyword">try</span> {</span><br><span class="line"> <span class="keyword">val</span> process = Runtime.getRuntime().exec(<span class="string">"getprop <span class="variable">$prop</span>"</span>)</span><br><span class="line"> <span class="keyword">val</span> ir = InputStreamReader(process.inputStream)</span><br><span class="line"> <span class="keyword">val</span> input = BufferedReader(ir)</span><br><span class="line"> <span class="keyword">return</span> input.readLine()</span><br><span class="line"> } <span class="keyword">catch</span> (e: IOException) {</span><br><span class="line"> e.printStackTrace()</span><br><span class="line"> }</span><br><span class="line"> <span class="keyword">return</span> <span class="literal">null</span></span><br><span class="line">} </span><br></pre></td></tr></table></figure>
<p>这样就可以通过 adb 命令来控制某个功能的开关</p>
<h2 id="获取设备版本号"><a href="#获取设备版本号" class="headerlink" title="获取设备版本号"></a>获取设备版本号</h2><figure class="highlight sh"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line"></span><br></pre></td></tr></table></figure>
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<article id="post-Kotlin-补坑" class="article article-type-post" itemscope itemprop="blogPost">
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<a href="/2020/04/27/Kotlin-%E8%A1%A5%E5%9D%91/" class="article-date">
<time datetime="2020-04-27T03:50:37.000Z" itemprop="datePublished">2020-04-27</time>
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<a class="article-title" href="/2020/04/27/Kotlin-%E8%A1%A5%E5%9D%91/">Kotlin 补坑</a>
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<p>Kotlin 的 Iterable 遍历基本上都是使用 forEach，在 for 语句中可以方便的使用 break 跳出循环，但是 forEach 代码块中不能使用 break，之前一直以为使用 <code>return@forEach</code> 能够跳出遍历，起到和 break 一样的作用，其实这是非常错误的，<code>return@forEach</code> 只能跳出本次 forEach 的代码块，相当于 continue。</p>
<p>究其原因，先看 forEach 的函数声明：</p>
<figure class="highlight kotlin"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">public</span> <span class="keyword">inline</span> <span class="function"><span class="keyword">fun</span> <span class="type"><T></span> Iterable<span class="type"><T></span>.<span class="title">forEach</span><span class="params">(action: (<span class="type">T</span>) -> <span class="type">Unit</span>)</span></span>: <span class="built_in">Unit</span> {</span><br><span class="line"> <span class="keyword">for</span> (element <span class="keyword">in</span> <span class="keyword">this</span>) action(element)</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<p>forEach 是一个 inline 函数，action 是一个高阶函数，<em>Kotlin的 return 只能返回具名函数或者匿名函数，并且在 Lambda 表达式内禁止使用 return</em>，但是如果 Lambda 表达式是内敛的，return 也可以内敛，那么就可以使用 return，不过这个 return 也只能跳出具名函数或者匿名函数，要跳出 Lambda，需要使用 return 加标签的形式，也就是 <code>return@forEach</code> 的形式，例如：</p>
<figure class="highlight kotlin"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">fun</span> <span class="title">main</span><span class="params">()</span></span> {</span><br><span class="line"> listOf(<span class="number">1</span>, <span class="number">2</span>, <span class="number">3</span>, <span class="number">4</span>, <span class="number">5</span>).forEach {</span><br><span class="line"> <span class="keyword">if</span> (it == <span class="number">3</span>) {</span><br><span class="line"> <span class="keyword">return</span><span class="symbol">@forEach</span></span><br><span class="line"> }</span><br><span class="line"> println(it)</span><br><span class="line"> }</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<p><code>return@forEach</code> 的标签 forEach 是编译器自动生成的，有一定的误导性，如果我们自己加标签的话就是：</p>
<figure class="highlight kotlin"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">fun</span> <span class="title">main</span><span class="params">()</span></span> {</span><br><span class="line"> listOf(<span class="number">1</span>, <span class="number">2</span>, <span class="number">3</span>, <span class="number">4</span>, <span class="number">5</span>).forEach <span class="symbol">action@</span>{</span><br><span class="line"> <span class="keyword">if</span> (it == <span class="number">3</span>) {</span><br><span class="line"> <span class="keyword">return</span><span class="symbol">@action</span></span><br><span class="line"> }</span><br><span class="line"> println(it)</span><br><span class="line"> }</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<p><code>return@action</code> 跳出的是 <code>inline fun <T> Iterable<T>.forEach(action: (T) -> Unit): Unit</code> 的 action 的 匿名函数，如果把 action 单独声明，就更加明了：</p>
<figure class="highlight kotlin"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">fun</span> <span class="title">main</span><span class="params">()</span></span> {</span><br><span class="line"> <span class="keyword">val</span> action = <span class="function"><span class="title">fun</span><span class="params">(item: <span class="type">Int</span>)</span></span> {</span><br><span class="line"> <span class="keyword">if</span> (item == <span class="number">3</span>) {</span><br><span class="line"> <span class="keyword">return</span></span><br><span class="line"> }</span><br><span class="line"> println(item)</span><br><span class="line"> }</span><br><span class="line"> listOf(<span class="number">1</span>, <span class="number">2</span>, <span class="number">3</span>, <span class="number">4</span>, <span class="number">5</span>).forEach(action)</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<p>action 中的 return 是结束本次的匿名函数，是不可能跳出 forEach 遍历的。</p>
<p>如果先结束遍历，可以再外层添加一个匿名函数，用 return加 Label 来返回这个函数</p>
<figure class="highlight kotlin"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br></pre></td><td class="code"><pre><span class="line">run {</span><br><span class="line"> listOf(<span class="number">1</span>, <span class="number">2</span>, <span class="number">3</span>, <span class="number">4</span>, <span class="number">5</span>).forEach <span class="symbol">action@</span>{</span><br><span class="line"> <span class="keyword">if</span> (it == <span class="number">3</span>) {</span><br><span class="line"> <span class="keyword">return</span><span class="symbol">@run</span></span><br><span class="line"> }</span><br><span class="line"> println(it)</span><br><span class="line"> }</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
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<article id="post-Kotlin的非空断言调用" class="article article-type-post" itemscope itemprop="blogPost">
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<a href="/2020/04/22/Kotlin%E7%9A%84%E9%9D%9E%E7%A9%BA%E6%96%AD%E8%A8%80%E8%B0%83%E7%94%A8/" class="article-date">
<time datetime="2020-04-22T01:08:33.000Z" itemprop="datePublished">2020-04-22</time>
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<a class="article-title" href="/2020/04/22/Kotlin%E7%9A%84%E9%9D%9E%E7%A9%BA%E6%96%AD%E8%A8%80%E8%B0%83%E7%94%A8/">Kotlin的非空断言调用</a>
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<p>Kotlin 中使用 if 进行判空后就可以在 if 代码块中安全使用了，但这只针对 val 类型的变量，非空的 var 类型变量在 代码块中使用还是会显示编译错误，但是在 let 代码块内就可以安全使用，原因有可能是变量可以在其他线程置为 null，例如：</p>
<figure class="highlight kotlin"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">import</span> java.util.concurrent.ThreadLocalRandom</span><br><span class="line"></span><br><span class="line"><span class="keyword">class</span> <span class="title class_">Foo</span> {</span><br><span class="line"> <span class="keyword">val</span> name = <span class="string">"bar"</span></span><br><span class="line">}</span><br><span class="line"></span><br><span class="line"><span class="keyword">var</span> foo: Foo? = Foo()</span><br><span class="line"></span><br><span class="line"><span class="function"><span class="keyword">fun</span> <span class="title">main</span><span class="params">()</span></span> {</span><br><span class="line"> Thread(Runnable {</span><br><span class="line"> test1()</span><br><span class="line"> }).start()</span><br><span class="line"> Thread.sleep(<span class="number">1000</span>)</span><br><span class="line"> foo = <span class="literal">null</span></span><br><span class="line"> Thread.sleep(<span class="number">3000</span>)</span><br><span class="line">}</span><br><span class="line"></span><br><span class="line"><span class="function"><span class="keyword">fun</span> <span class="title">test1</span><span class="params">()</span></span> {</span><br><span class="line"> foo?.let {</span><br><span class="line"> Thread.sleep(<span class="number">2000</span>)</span><br><span class="line"> println(it.name)</span><br><span class="line"> }</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<p>在 <code>println(foo!!.name)</code> 一定会抛出空指针异常。<br>如果把 if 换成 let， 程序就能正常打印了：</p>
<figure class="highlight plaintext"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br></pre></td><td class="code"><pre><span class="line">fun test2() {</span><br><span class="line"> foo?.let {</span><br><span class="line"> Thread.sleep(2000)</span><br><span class="line"> println(it.name)</span><br><span class="line"> }</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<p>通过反编译来生成 Java 代码：</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">public</span> <span class="keyword">static</span> <span class="keyword">final</span> <span class="keyword">void</span> <span class="title function_">test1</span><span class="params">()</span> {</span><br><span class="line"> <span class="keyword">if</span> (foo != <span class="literal">null</span>) {</span><br><span class="line"> Thread.sleep(<span class="number">2000L</span>);</span><br><span class="line"> <span class="type">Foo</span> <span class="variable">var10000</span> <span class="operator">=</span> foo;</span><br><span class="line"> <span class="keyword">if</span> (var10000 == <span class="literal">null</span>) {</span><br><span class="line"> Intrinsics.throwNpe();</span><br><span class="line"> }</span><br><span class="line"> <span class="type">String</span> <span class="variable">var0</span> <span class="operator">=</span> var10000.getName();</span><br><span class="line"> System.out.println(var0);</span><br><span class="line"> }</span><br><span class="line">}</span><br><span class="line"></span><br><span class="line"><span class="keyword">public</span> <span class="keyword">static</span> <span class="keyword">final</span> <span class="keyword">void</span> <span class="title function_">test2</span><span class="params">()</span> {</span><br><span class="line"> <span class="type">Foo</span> <span class="variable">var10000</span> <span class="operator">=</span> foo;</span><br><span class="line"> <span class="keyword">if</span> (var10000 != <span class="literal">null</span>) {</span><br><span class="line"> <span class="type">Foo</span> <span class="variable">var0</span> <span class="operator">=</span> var10000;</span><br><span class="line"> Thread.sleep(<span class="number">2000L</span>);</span><br><span class="line"> <span class="type">String</span> <span class="variable">var5</span> <span class="operator">=</span> var0.getName();</span><br><span class="line"> System.out.println(var5);</span><br><span class="line"> }</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<p>两个方法的主要区别是 <code>test2()</code> 首先执行了一次赋值 <code>Foo var10000 = foo;</code>，我的理解是 Foo 对象是保存在堆上，foo 是一个静态的引用，<code>Foo var10000 = foo;</code> 这一步操作确保了在函数使用的是函数内的临时变量，不会被修改。</p>
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<article id="post-Java-Time" class="article article-type-post" itemscope itemprop="blogPost">
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<time datetime="2019-11-01T16:05:11.000Z" itemprop="datePublished">2019-11-02</time>
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<h2 id="Java-Time-简介"><a href="#Java-Time-简介" class="headerlink" title="Java Time 简介"></a>Java Time 简介</h2><p>Java Time 是 Java8 新加入的一个包，用来替换 Calendar、Date 这些 Java 类。Java Time 符合 JSR310 规范，JSR310 实际上有两个日期概念。第一个是Instant，它大致对应于<code>java.util.Date</code>类，因为它代表了一个确定的时间点，即相对于标准Java纪元（1970年1月1日）的偏移量；但与<code>java.util.Date</code>类不同的是其精确到了纳秒级别。第二个对应于人类自身的观念，比如<code>LocalDate</code>和<code>LocalTime</code>。他们代表了一般的时区概念，要么是日期（不包含时间），要么是时间（不包含日期），类似于<code>java.sql</code>的表示方式。此外，还有一个<code>MonthDay</code>，它可以存储某人的生日（不包含年份）。每个类都在内部存储正确的数据而不是像<code>java.util.Date</code>那样利用午夜12点来区分日期，利用<code>1970-01-01</code>来表示时间。</p>
<p>Java Time 中所有的时间对象都是 <strong>Immutable</strong> 的，是不可变的，和 <code>String</code> 一样，对象一旦生成就不能修改它的属性，这个保证了它们都是线程安全的。</p>
<p>在 Android 开发中使用 Java Time 需要 minSdkVersion 最低 Android O，api level 26，这基本是不可能的，现阶段使用 Java Time 需要使用替代方案，这个推荐两种：joda-time 和 Threetenabp。joda-time 的开发者也是 JSR310 的制定者，和 JSR310 api 基本一致，有少许差别，Threetenabp 是一个 backport 版本，和 JSR310 api 完全一致。为了以后迁移方便，最好还是使用 Threetenabp。Threetenabp 引入方法很简单，添加 dependencies</p>
<figure class="highlight gradle"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">implementation <span class="string">'com.jakewharton.threetenabp:threetenabp:1.2.3'</span></span><br></pre></td></tr></table></figure>
<p>在 Application 中进行初始化</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta">@Override</span> <span class="keyword">public</span> <span class="keyword">void</span> <span class="title function_">onCreate</span><span class="params">()</span> {</span><br><span class="line"> <span class="built_in">super</span>.onCreate();</span><br><span class="line"> AndroidThreeTen.init(<span class="built_in">this</span>);</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<h2 id="Java-Time-使用"><a href="#Java-Time-使用" class="headerlink" title="Java Time 使用"></a>Java Time 使用</h2><p>Java Time 由5个包组成：</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line">java.time <span class="comment">// 基础包</span></span><br><span class="line">java.time.chrono <span class="comment">// 年表，用于不同的日历系统</span></span><br><span class="line">java.time.format <span class="comment">// 格式化和解析时间和日期</span></span><br><span class="line">java.time.temporal <span class="comment">// 包括底层框架和扩展特性</span></span><br><span class="line">java.time.zone <span class="comment">// 包含时区支持的类</span></span><br></pre></td></tr></table></figure>
<p>我们主要使用的是基础包和 format，如果要使用农历、伊斯兰历会用到 chrono。我们从最常用的类开始介绍。</p>
<h3 id="LocalDateTime、LocalDate、LocalTime"><a href="#LocalDateTime、LocalDate、LocalTime" class="headerlink" title="LocalDateTime、LocalDate、LocalTime"></a>LocalDateTime、LocalDate、LocalTime</h3><p>这三个类都是无时区的本地时间，分别表示时间日期、日期、时间，最简单的构造方法是通过 <code>now()</code> 方法：</p>
<figure class="highlight kotlin"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">val</span> localDateTime = LocalDateTime.now() <span class="comment">// 当前日期和时间 2020-04-21T09:55:27.429053</span></span><br><span class="line"><span class="keyword">val</span> localDate = LocalDate.now() <span class="comment">// 当前日期 2020-04-21</span></span><br><span class="line"><span class="keyword">val</span> localTime = LocalTime.now() <span class="comment">// 当前时间 09:55:27.429661</span></span><br></pre></td></tr></table></figure>
<p>它们之间可以通过一些方法转换：</p>
<figure class="highlight kotlin"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line">localDateTime.toLocalDate() <span class="comment">// LocalDateTime 转 LocalDate</span></span><br><span class="line">localDateTime.toLocalTime() <span class="comment">// LocalDateTime 转 LocalTime</span></span><br><span class="line"></span><br><span class="line">localDate.atTime(localTime) <span class="comment">// LocalDate 转 LocalDateTime</span></span><br><span class="line">localTime.atDate(localDate) <span class="comment">// LocalTime 转 LocalDateTime</span></span><br></pre></td></tr></table></figure>
<p>简单来说就是 LocalDateTime 可以提取时间和日期，LocalDate 填上时间成为 LocalDateTime， LocalTime 填上日期成为 LocalDateTime。</p>
<p>日期操作可以总结为以下几个：</p>
<ul>
<li>加 plus</li>
<li>减 minus</li>
<li>设置 with</li>
<li>转换 to</li>
<li>结合 at</li>
</ul>
<h3 id="at-系列方法"><a href="#at-系列方法" class="headerlink" title="at 系列方法"></a>at 系列方法</h3><p><code>localDate.atTime(localTime)</code> 就是一个日期结合时间成为一个 LocalDateTime，同样，LocalDateTime 结合时区成为 ZonedDateTime ：</p>
<figure class="highlight kotlin"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">val</span> localDateTime = LocalDateTime.now()</span><br><span class="line">println(localDateTime)</span><br><span class="line"><span class="keyword">val</span> zonedDateTime = localDateTime.atZone(ZoneId.of(<span class="string">"UTC"</span>))</span><br><span class="line">println(zonedDateTime)</span><br></pre></td></tr></table></figure>
<p>ZonedDateTime 的输出就有时区了：</p>
<figure class="highlight plaintext"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line">2020-04-21T10:16:44.938773</span><br><span class="line">2020-04-21T10:16:44.938773Z[UTC]</span><br></pre></td></tr></table></figure>
<p>at 系列方法就是对内容的扩展。</p>
<h3 id="plus-x2F-minus-系列方法"><a href="#plus-x2F-minus-系列方法" class="headerlink" title="plus/minus 系列方法"></a>plus/minus 系列方法</h3><p>使用 plus/minus 开头的方法是对当前对象加/减一个单位生成一个新的对象，例如：</p>
<figure class="highlight kotlin"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">val</span> localDateTime = LocalDateTime.now()</span><br><span class="line"><span class="keyword">val</span> nextMonth = localDateTime.plusMonths(<span class="number">1</span>) <span class="comment">// 加一个月</span></span><br><span class="line"><span class="keyword">val</span> yesterday = localDateTime.minusDays(<span class="number">1</span>) <span class="comment">// 减一天</span></span><br><span class="line"><span class="keyword">val</span> preHour = localDateTime.minusHours(<span class="number">1</span>) <span class="comment">// 减一小时</span></span><br></pre></td></tr></table></figure>
<h3 id="with-系列方法"><a href="#with-系列方法" class="headerlink" title="with 系列方法"></a>with 系列方法</h3><p>with 开头的方法是设置对应的属性的值生成一个新的对象，例如：</p>
<figure class="highlight kotlin"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">val</span> localDateTime = LocalDateTime.now()</span><br><span class="line"><span class="keyword">val</span> jan = localDateTime.withMonth(<span class="number">1</span>) <span class="comment">// 设置为一月</span></span><br></pre></td></tr></table></figure>
<h3 id="to-系列方法"><a href="#to-系列方法" class="headerlink" title="to 系列方法"></a>to 系列方法</h3><p>to 开头的方法是转换的操作，例如：</p>
<figure class="highlight kotlin"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">val</span> localDate = localDateTime.toLocalDate()</span><br></pre></td></tr></table></figure>
<p>转换只能是同级或者向下转换，例如同级转换:</p>
<figure class="highlight kotlin"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">val</span> nanoOfDay = LocalTime.now().toNanoOfDay()</span><br><span class="line"><span class="keyword">val</span> epocSecond = ZonedDateTime.now().toEpochSecond()</span><br></pre></td></tr></table></figure>
<p>LocalTime 只能转换为从今天0点开始的多少纳秒，ZonedDateTime 可以转换为 epoc 时间戳。</p>
<p><strong>需要注意，所有对象都是 Immutable 的，以上的操作都是在原始对象的基础上生成一个新的对象，不会修改原来的对象。</strong></p>
<h3 id="时间对比"><a href="#时间对比" class="headerlink" title="时间对比"></a>时间对比</h3><p>Java Time 都实现了 equals 方法和 Comparable，想比较两个时间的先后，可以直接通过 <code>compareTo()</code> 方法：</p>
<figure class="highlight kotlin"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">val</span> dateTime1 = LocalDateTime.now()</span><br><span class="line"><span class="keyword">val</span> dateTime2 = dateTime1.minusNanos(<span class="number">1</span>)</span><br><span class="line"></span><br><span class="line">dateTime2.compareTo(dateTime1) <span class="comment">// 0 相等，负数 dateTime2 在 dateTime1 之前，正数 dateTime2 在 dateTime1 之后</span></span><br></pre></td></tr></table></figure>
<p>使用 Kotlin 的话就更加直观：</p>
<figure class="highlight kotlin"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">if</span> (dateTime1 > dateTime2) {</span><br><span class="line"> <span class="comment">// dateTime1 在 dateTime2 之后</span></span><br><span class="line">} <span class="keyword">else</span> <span class="keyword">if</span> (dateTime1 == dateTime2) {</span><br><span class="line"> <span class="comment">// dateTime1 dateTime2 相同</span></span><br><span class="line">} <span class="keyword">else</span> {</span><br><span class="line"> <span class="comment">// dateTime1 在 dateTime1 之前</span></span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<h3 id="计算时间差"><a href="#计算时间差" class="headerlink" title="计算时间差"></a>计算时间差</h3><p>时间差可以使用 <code>ChronoUnit</code> 计算：</p>
<figure class="highlight kotlin"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">val</span> localDate = LocalDate.of(<span class="number">2012</span>, <span class="number">12</span>, <span class="number">1</span>)</span><br><span class="line"><span class="keyword">val</span> localDate2 = LocalDate.of(<span class="number">2012</span>, <span class="number">11</span>, <span class="number">1</span>)</span><br><span class="line"><span class="keyword">val</span> days = ChronoUnit.DAYS.between(localDate2, localDate)</span><br><span class="line"><span class="keyword">val</span> months = ChronoUnit.MONTHS.between(localDate2, localDate)</span><br><span class="line"><span class="keyword">val</span> years = ChronoUnit.YEARS.between(localDate2, localDate)</span><br></pre></td></tr></table></figure>
<p>这个时间差计算的是绝对的时间差，一个月是一年的时间除以12，2012-12-1和2012-11-1月份相差1，2012-12-1和2012-11-10月份相差0。</p>
<h3 id="考虑时区的转换"><a href="#考虑时区的转换" class="headerlink" title="考虑时区的转换"></a>考虑时区的转换</h3><p>如果不考虑时区，LocalDateTime、LocalDate、LocalTime 这三个类已经够用了，如果考虑时区，就会遇到这样的问题：</p>
<ul>
<li>服务器接口是 UTC 时间，客户端需要转换为用户本地的世界</li>
<li>用户输入的时间是当前时区的时间，服务器接口要求是 UTC 时间</li>
<li>等等 …</li>
</ul>
<p>这就涉及到一些比较复杂的转换规则，我们先给 Java Time 的类按照包含内容的丰富程度拍个序，从小到大依次为：</p>
<ol>
<li>LocalDate/LocalTime</li>
<li>LocalDateTime/Instant</li>
<li>OffsetDateTime</li>
<li>ZonedDateTime</li>
</ol>
<p>Instant 是指从 0时区1970-01-01 0点的偏移时间，它能表示绝对时间，可以通过打印看一下它和 LocalDateTime 的区别：</p>
<figure class="highlight kotlin"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">val</span> ms = System.currentTimeMillis()</span><br><span class="line"><span class="keyword">val</span> instant = Instant.ofEpochMilli(ms)</span><br><span class="line"></span><br><span class="line">println(<span class="string">"<span class="variable">$instant</span>"</span>)</span><br><span class="line">println(<span class="string">"<span class="subst">${LocalDateTime.now()}</span>"</span>)</span><br></pre></td></tr></table></figure>
<p>输出为：</p>
<figure class="highlight plaintext"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line">2020-04-21T04:03:53.886Z</span><br><span class="line">2020-04-21T12:03:53.947636</span><br></pre></td></tr></table></figure>
<p>Instant 多了一个 <code>Z</code>，用来表示是 UTC 时间，看样子 Instant 的内容应该丰富些，但是 Instant 不能进行日期计算，而且通过 LocalDateTime 获取 Instant 使用的是 <code>toInstant()</code>，从 api 命名也显示它们是一个平级的关系。</p>
<p>回到第一个问题，服务器的时间格式如果是标准的 iso 字符串，例如 <code>2020-04-21T04:03:53.886Z</code>，我们直接用 <code>Instant.parse()</code> 就可以，如果是时间戳，使用 <code>Instant.ofEpochMilli()</code> 或者 <code>Instant.ofEpochSecond()</code>，如果是 <code>2012-12-01 12:30:10</code>，使用如下方法：</p>
<figure class="highlight kotlin"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">val</span> instant = LocalDateTime</span><br><span class="line"> .parse(<span class="string">"2012-12-01 12:30:10"</span>, DateTimeFormatter.ofPattern(<span class="string">"yyyy-MM-dd HH:mm:ss"</span>))</span><br><span class="line"> .toInstant(ZoneOffset.UTC)</span><br></pre></td></tr></table></figure>
<p>这样我们成功将服务器接口里面的时间转换为了 Instant 对象，下一步就可以将 Instant 转换为 LocalDateTime 来使用：</p>
<figure class="highlight plaintext"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line">LocalDateTime.ofInstant(instant, ZoneId.systemDefault()) // 默认时区</span><br><span class="line">LocalDateTime.ofInstant(instant, ZoneOffset.ofHours(8)) // 指定时区</span><br></pre></td></tr></table></figure>
<p>同理，用户输入的时间为转换为 UTC，假设用户在东8区</p>
<figure class="highlight kotlin"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">val</span> now = LocalDateTime.now()</span><br><span class="line"><span class="keyword">val</span> instant = now.toInstant(ZoneOffset.ofHours(<span class="number">8</span>))</span><br></pre></td></tr></table></figure>
<p>还有一种简单的方法：</p>
<figure class="highlight plaintext"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">OffsetDateTime.now().toInstant()</span><br></pre></td></tr></table></figure>
<h3 id="OffsetDateTime-和-ZonedDateTime-区别"><a href="#OffsetDateTime-和-ZonedDateTime-区别" class="headerlink" title="OffsetDateTime 和 ZonedDateTime 区别"></a>OffsetDateTime 和 ZonedDateTime 区别</h3><p>OffsetDateTime 和 ZonedDateTime 都能表示绝对时间，都带有时区和时间日期。</p>
<p>我们的知道时区的概念，0 时区 0 点的时候，北京时间是 8 点，OffsetDateTime 对象中就带有这个偏移量，打印 OffsetDateTime：</p>
<figure class="highlight kotlin"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">println(OffsetDateTime.now())</span><br></pre></td></tr></table></figure>
<p>输出为：</p>
<figure class="highlight plaintext"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">2020-04-21T13:00:40.823521+08:00</span><br></pre></td></tr></table></figure>
<p>当前时间是东八区下午一点，如果打印 ZonedDateTime：</p>
<figure class="highlight plaintext"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">println(ZonedDateTime.now())</span><br></pre></td></tr></table></figure>
<p>输出为：</p>
<figure class="highlight plaintext"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">2020-04-21T13:02:56.629844+08:00[Asia/Shanghai]</span><br></pre></td></tr></table></figure>
<p>多了一个 ZoneId，通过这个 ZoneId，同一个时区下也可能时间不同，例如澳大利亚是是实行夏时令的，夏时令（Daylight Saving Time：DST），又称“日光节约时制”和“夏令时间”，在这一制度实行期间所采用的统一时间称为“夏令时间”。一般在天亮早的夏季人为将时间调快一小时，可以使人早起早睡，减少照明量，以充分利用光照资源，从而节约照明用电。澳大利亚夏时令时间为 10-7 到 4-1，我们测试一下：</p>
<figure class="highlight kotlin"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">val</span> zoneId = ZoneId.of(<span class="string">"Australia/Sydney"</span>)</span><br><span class="line">println(Instant.parse(<span class="string">"2018-05-01T08:00:00.000Z"</span>).atZone(zoneId))</span><br><span class="line">println(Instant.parse(<span class="string">"2018-11-01T08:00:00.000Z"</span>).atZone(zoneId))</span><br></pre></td></tr></table></figure>
<p>输出的结果为：</p>
<figure class="highlight plaintext"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line">2018-05-01T18:00+10:00[Australia/Sydney]</span><br><span class="line">2018-11-01T19:00+11:00[Australia/Sydney]</span><br></pre></td></tr></table></figure>
<p>同一个城市，UTC时间都是早上8点，但是5月1号悉尼是18点，11月1号悉尼是19点。这也说明了 ZonedDateTime 包含的内容要比 OffsetDateTime 多。</p>
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<time datetime="2019-07-03T04:35:25.000Z" itemprop="datePublished">2019-07-03</time>
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<a class="article-title" href="/2019/07/03/Tips-Java-Thread/">Tips:Java Thread</a>
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<h2 id="先看一个经典的多线程的例子："><a href="#先看一个经典的多线程的例子：" class="headerlink" title="先看一个经典的多线程的例子："></a>先看一个经典的多线程的例子：</h2><figure class="highlight kotlin"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">class</span> <span class="title class_">A</span> {</span><br><span class="line"> <span class="keyword">private</span> <span class="keyword">var</span> value = <span class="number">0</span></span><br><span class="line"></span><br><span class="line"> <span class="function"><span class="keyword">fun</span> <span class="title">increase</span><span class="params">()</span></span> {</span><br><span class="line"> value++</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> <span class="function"><span class="keyword">fun</span> <span class="title">printValue</span><span class="params">()</span></span> {</span><br><span class="line"> println(<span class="string">"value = <span class="variable">$value</span>"</span>)</span><br><span class="line"> }</span><br><span class="line">}</span><br><span class="line"></span><br><span class="line"><span class="function"><span class="keyword">fun</span> <span class="title">main</span><span class="params">()</span></span> {</span><br><span class="line"> <span class="keyword">val</span> a = A()</span><br><span class="line"> <span class="keyword">for</span> (i <span class="keyword">in</span> <span class="number">0</span> until <span class="number">100</span>) {</span><br><span class="line"> Thread(Runnable {</span><br><span class="line"> <span class="keyword">for</span> (j <span class="keyword">in</span> <span class="number">0</span> until <span class="number">100000</span>) {</span><br><span class="line"> a.increase()</span><br><span class="line"> }</span><br><span class="line"> }).start()</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> <span class="comment">// 等待所有线程执行完，activeCount 根据环境不同，为 1 或 2</span></span><br><span class="line"> <span class="keyword">while</span> (Thread.activeCount() > <span class="number">2</span>) { </span><br><span class="line"> Thread.yield()</span><br><span class="line"> }</span><br><span class="line"> </span><br><span class="line"> a.printValue()</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<p>输出的结果可能每次都不一样<br>同步的方法：</p>
<ul>
<li>synchronized</li>
<li>lock</li>
<li>使用 Atomic</li>
</ul>
<p>加上时间的统计，测试一下速度：</p>
<figure class="highlight kotlin"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">fun</span> <span class="title">main</span><span class="params">()</span></span> {</span><br><span class="line"> <span class="keyword">val</span> start = System.currentTimeMillis()</span><br><span class="line"> <span class="keyword">val</span> a = A()</span><br><span class="line"> <span class="keyword">for</span> (i <span class="keyword">in</span> <span class="number">0</span> until <span class="number">100</span>) {</span><br><span class="line"> Thread(Runnable {</span><br><span class="line"> <span class="keyword">for</span> (j <span class="keyword">in</span> <span class="number">0</span> until <span class="number">100000</span>) {</span><br><span class="line"> a.increase()</span><br><span class="line"> }</span><br><span class="line"> }).start()</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> <span class="keyword">while</span> (Thread.activeCount() > <span class="number">2</span>) {</span><br><span class="line"> Thread.yield()</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> a.printValue()</span><br><span class="line"> println(<span class="string">"spent: <span class="subst">${System.currentTimeMillis() - start}</span>ms"</span>)</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<h2 id="首先使用-synchronized"><a href="#首先使用-synchronized" class="headerlink" title="首先使用 synchronized"></a>首先使用 synchronized</h2><figure class="highlight plaintext"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br></pre></td><td class="code"><pre><span class="line">@Synchronized</span><br><span class="line">fun increase() {</span><br><span class="line"> value++</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<p>花费时间 <code>550ms</code> 左右。</p>
<p>还有一种方式是使用同步代码块：</p>
<figure class="highlight kotlin"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">private</span> <span class="keyword">val</span> lock = Any()</span><br><span class="line"></span><br><span class="line"><span class="function"><span class="keyword">fun</span> <span class="title">increase</span><span class="params">()</span></span> {</span><br><span class="line"> synchronized(lock) {</span><br><span class="line"> value++</span><br><span class="line"> }</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<p>花费时间比使用 synchronized 函数要少一点，在 <code>480ms</code> 左右。</p>
<h2 id="使用-Lock"><a href="#使用-Lock" class="headerlink" title="使用 Lock"></a>使用 Lock</h2><figure class="highlight kotlin"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">private</span> <span class="keyword">val</span> lock = ReentrantLock()</span><br><span class="line"><span class="function"><span class="keyword">fun</span> <span class="title">increase</span><span class="params">()</span></span> {</span><br><span class="line"> lock.lock()</span><br><span class="line"> value++</span><br><span class="line"> lock.unlock()</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<p>花费时间 <code>310ms</code> 左右</p>
<h2 id="最后使用-Atomic"><a href="#最后使用-Atomic" class="headerlink" title="最后使用 Atomic"></a>最后使用 Atomic</h2><figure class="highlight kotlin"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">private</span> <span class="keyword">var</span> value = AtomicLong()</span><br><span class="line"></span><br><span class="line"><span class="function"><span class="keyword">fun</span> <span class="title">increase</span><span class="params">()</span></span> {</span><br><span class="line"> value.incrementAndGet()</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<p>花费时间 <code>230ms</code> 左右。</p>
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<article id="post-Tips-sdkman" class="article article-type-post" itemscope itemprop="blogPost">
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<a href="/2019/06/11/Tips-sdkman/" class="article-date">
<time datetime="2019-06-11T02:32:37.000Z" itemprop="datePublished">2019-06-11</time>
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<h1 id="安装"><a href="#安装" class="headerlink" title="安装"></a>安装</h1><p><code>https://sdkman.io/install</code></p>
<figure class="highlight sh"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line">$ curl -s <span class="string">"https://get.sdkman.io"</span> | bash</span><br><span class="line">$ <span class="built_in">source</span> <span class="string">"<span class="variable">$HOME</span>/.sdkman/bin/sdkman-init.sh"</span></span><br><span class="line">$ sdk version</span><br></pre></td></tr></table></figure>
<h1 id="安装-JDK"><a href="#安装-JDK" class="headerlink" title="安装 JDK"></a>安装 JDK</h1><figure class="highlight sh"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">sdk list java</span><br></pre></td></tr></table></figure>
<p>输出：</p>
<figure class="highlight sh"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br></pre></td><td class="code"><pre><span class="line">================================================================================</span><br><span class="line">Available Java Versions</span><br><span class="line">================================================================================</span><br><span class="line"> 19.0.0-grl 11.0.2-zulufx 1.0.0-rc-16-grl</span><br><span class="line"> 13.ea.24-open 10.0.2-zulu</span><br><span class="line"> 12.0.1-sapmchn 10.0.2-open</span><br><span class="line"> 12.0.1-zulu 9.0.7-zulu</span><br><span class="line"> 12.0.1-open 9.0.4-open</span><br><span class="line"> 12.0.1.j9-adpt 8.0.212-zulu</span><br><span class="line"> 12.0.1.hs-adpt 8.0.212-amzn</span><br><span class="line"> 12.0.1-librca 8.0.212.j9-adpt</span><br><span class="line"> 11.0.3-librca 8.0.212.hs-adpt</span><br><span class="line"> 11.0.3-sapmchn 8.0.212-librca</span><br><span class="line"> 11.0.3-zulu 8.0.202-zulu</span><br><span class="line"> 11.0.3-amzn 8.0.202-amzn</span><br><span class="line"> 11.0.3.j9-adpt 8.0.202-zulufx</span><br><span class="line"> 11.0.3.hs-adpt 7.0.222-zulu</span><br><span class="line"> 11.0.2-open 7.0.181-zulu</span><br><span class="line"></span><br><span class="line">================================================================================</span><br><span class="line">+ - <span class="built_in">local</span> version</span><br><span class="line">* - installed</span><br><span class="line">> - currently <span class="keyword">in</span> use</span><br><span class="line">================================================================================</span><br></pre></td></tr></table></figure>
<p>大部分人应该都是使用的 Oracle 版本的 JDK，各个版本的区别可以参考文章：</p>
<figure class="highlight plaintext"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">https://www.oschina.net/news/99836/time-to-look-beyond-oracles-jdk</span><br></pre></td></tr></table></figure>
<p>然后安装：</p>
<figure class="highlight plaintext"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">sdk install java 8.0.212-zulu</span><br></pre></td></tr></table></figure>
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<article id="post-Tips-SpringBoot-Properties" class="article article-type-post" itemscope itemprop="blogPost">
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<time datetime="2019-05-16T02:11:04.000Z" itemprop="datePublished">2019-05-16</time>
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<a class="article-title" href="/2019/05/16/Tips-SpringBoot-Properties/">Tips:SpringBoot Properties</a>
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<p>新建项目里面都有一个 <code>application.properties</code>，我们可以在这个文件中添加一些属性，</p>
<figure class="highlight plaintext"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line">test.foo=Hello</span><br><span class="line">test.bar=World </span><br></pre></td></tr></table></figure>
<p>在组件中可以通过添加 <code>@Value</code> 注解来读取</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta">@RestController</span></span><br><span class="line"><span class="meta">@RequestMapping("/test")</span></span><br><span class="line"><span class="keyword">public</span> <span class="keyword">class</span> <span class="title class_">TestController</span> {</span><br><span class="line"></span><br><span class="line"> <span class="meta">@Value("${test.foo}")</span></span><br><span class="line"> <span class="keyword">private</span> String foo;</span><br><span class="line"> <span class="meta">@Value("${test.bar}")</span></span><br><span class="line"> <span class="keyword">private</span> String bar;</span><br><span class="line"></span><br><span class="line"></span><br><span class="line"> <span class="meta">@GetMapping("/hello")</span></span><br><span class="line"> <span class="keyword">public</span> String <span class="title function_">hello</span><span class="params">()</span> {</span><br><span class="line"> <span class="keyword">return</span> foo + <span class="string">" "</span> + bar;</span><br><span class="line"> }</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<p><code>test/hello</code> 接口输出的是 <code>Hello World</code>，我们可以通过 Java 的 JVM Args 在运行的时候覆盖这些属性：</p>
<figure class="highlight plaintext"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">java -Dtest.bar=bar -jar xxx.jar</span><br></pre></td></tr></table></figure>
<p>这样 <code>test/hello</code> 接口输出的是 <code>Hello bar</code>，那么 SystemProperties 有没有这些属性呢，实验一下，修改 <code>hello()</code> 为</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta">@GetMapping("/hello")</span></span><br><span class="line"><span class="keyword">public</span> String <span class="title function_">hello</span><span class="params">()</span> {</span><br><span class="line"> <span class="keyword">return</span> foo + <span class="string">" "</span> + bar + <span class="string">", from system: "</span> + SystemProperties.get(<span class="string">"test.foo"</span>) + <span class="string">" "</span> + SystemProperties.get(<span class="string">"test.bar"</span>);</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<p>输出结果为：<code>Hello bar, from system: null bar</code>，看来 <code>application.properties</code> 是不会写入 SystemProperties 的，另外 <code>@Value</code> 不是直接读取 <code>application.properties</code> 的值，而是好几个源，有优先级的。<br><code>@Value</code> 可以注入一下的资源：</p>
<ul>
<li>注入普通字符串</li>
<li>注入操作系统属性</li>
<li>注入表达式结果</li>
<li>注入其他Bean属性：注入beanInject对象的属性another</li>
<li>注入文件资源</li>
<li>注入URL资源</li>
</ul>
<p>示例：</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta">@Value("normal")</span></span><br><span class="line"><span class="keyword">private</span> String normal; <span class="comment">// 注入普通字符串</span></span><br><span class="line"></span><br><span class="line"><span class="meta">@Value("#{systemProperties['os.name']}")</span></span><br><span class="line"><span class="keyword">private</span> String systemPropertiesName; <span class="comment">// 注入操作系统属性</span></span><br><span class="line"></span><br><span class="line"><span class="meta">@Value("#{ T(java.lang.Math).random() * 100.0 }")</span></span><br><span class="line"><span class="keyword">private</span> <span class="type">double</span> randomNumber; <span class="comment">//注入表达式结果</span></span><br><span class="line"></span><br><span class="line"><span class="meta">@Value("#{valueTestBean.name}")</span></span><br><span class="line"><span class="keyword">private</span> String fromAnotherBean; <span class="comment">// 注入其他Bean属性：注入beanInject对象的属性another，类具体定义见下面</span></span><br><span class="line"></span><br><span class="line"><span class="meta">@Value("classpath:resources/static/value_test.dat")</span></span><br><span class="line"><span class="keyword">private</span> Resource resourceFile; <span class="comment">// 注入文件资源</span></span><br><span class="line"></span><br><span class="line"><span class="meta">@Value("http://www.baidu.com")</span></span><br><span class="line"><span class="keyword">private</span> Resource testUrl; <span class="comment">// 注入URL资源</span></span><br></pre></td></tr></table></figure>
<p>Properties 的加载顺序可以查看官方文档</p>
<p><a target="_blank" rel="noopener" href="https://docs.spring.io/spring-boot/docs/1.5.9.RELEASE/reference/htmlsingle/#boot-features-external-config">https://docs.spring.io/spring-boot/docs/1.5.9.RELEASE/reference/htmlsingle/#boot-features-external-config</a></p>
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<article id="post-Tips-Mysql-显示-BIT" class="article article-type-post" itemscope itemprop="blogPost">
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<time datetime="2019-05-15T01:41:17.000Z" itemprop="datePublished">2019-05-15</time>
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<a class="article-title" href="/2019/05/15/Tips-Mysql-%E6%98%BE%E7%A4%BA-BIT/">Tips:Mysql 显示 BIT</a>
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<p>在数据库中创建一个表，添加一个 <code>is_new</code> 的 column，类型为 <code>BIT</code>：</p>
<figure class="highlight sql"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">CREATE</span> <span class="keyword">TABLE</span> `test_table`</span><br><span class="line">(</span><br><span class="line"> `id` <span class="type">BIGINT</span> <span class="keyword">NOT</span> <span class="keyword">NULL</span> AUTO_INCREMENT <span class="keyword">PRIMARY</span> KEY,</span><br><span class="line"> `is_new` BIT <span class="keyword">NOT</span> <span class="keyword">NULL</span> <span class="keyword">DEFAULT</span> b<span class="string">'0'</span></span><br><span class="line">);</span><br></pre></td></tr></table></figure>
<p>插入一条数据库：</p>
<figure class="highlight sql"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">INSERT</span> <span class="keyword">INTO</span> `test_table` <span class="keyword">SET</span> `is_new`<span class="operator">=</span><span class="number">1</span>;</span><br></pre></td></tr></table></figure>
<p>然后查询所有的数据：</p>
<figure class="highlight sql"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">SELECT</span> <span class="operator">*</span> <span class="keyword">FROM</span> `test_table`;</span><br></pre></td></tr></table></figure>
<p>显示结果为：</p>
<figure class="highlight sh"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br></pre></td><td class="code"><pre><span class="line">mysql> select * from test_table;</span><br><span class="line">+----+--------+</span><br><span class="line">| <span class="built_in">id</span> | is_new |</span><br><span class="line">+----+--------+</span><br><span class="line">| 1 | |</span><br><span class="line">+----+--------+</span><br><span class="line">1 row <span class="keyword">in</span> <span class="built_in">set</span> (0.00 sec)</span><br></pre></td></tr></table></figure>
<p>数据插入成功了，但是 <code>is_new</code> 的值不显示，换个图形化工具，可以查到这个值是 <code>1</code>，那么在命令行怎么查看呢？两种方法：</p>
<figure class="highlight sql"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">SELECT</span> `id`, bin(`is_new`) <span class="keyword">FROM</span> `test_table`;</span><br><span class="line"></span><br><span class="line"><span class="keyword">SELECT</span> `id`, ord(`is_new`) <span class="keyword">FROM</span> `test_table`;</span><br></pre></td></tr></table></figure>
<figure class="highlight plaintext"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br></pre></td><td class="code"><pre><span class="line">mysql> SELECT `id`, bin(`is_new`) FROM `test_table`;</span><br><span class="line">+----+---------------+</span><br><span class="line">| id | bin(`is_new`) |</span><br><span class="line">+----+---------------+</span><br><span class="line">| 1 | 1 |</span><br><span class="line">+----+---------------+</span><br><span class="line">1 row in set (0.00 sec)</span><br><span class="line"></span><br><span class="line">mysql> SELECT `id`, bin(`is_new`) FROM `test_table`;</span><br><span class="line">+----+---------------+</span><br><span class="line">| id | bin(`is_new`) |</span><br><span class="line">+----+---------------+</span><br><span class="line">| 1 | 1 |</span><br><span class="line">+----+---------------+</span><br><span class="line">1 row in set (0.00 sec)</span><br></pre></td></tr></table></figure>
<p>结果都是一样的，但是这两个函数有什么区别呢？首先是 <code>BIN</code></p>
<figure class="highlight plaintext"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line">BIN(N)</span><br><span class="line">返回N的二进制值的字符串表示，其中N是一个长(BIGINT)数字。这等同于CONV(N，10,2)。返回NULL，如果N为NULL。</span><br></pre></td></tr></table></figure>
<figure class="highlight sh"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br></pre></td><td class="code"><pre><span class="line">mysql> select bin(2);</span><br><span class="line">+--------+</span><br><span class="line">| bin(2) |</span><br><span class="line">+--------+</span><br><span class="line">| 10 |</span><br><span class="line">+--------+</span><br></pre></td></tr></table></figure>
<p>2 显示成了二进制形式 10。</p>
<p><code>ORD()</code> 有点复杂：</p>
<figure class="highlight plaintext"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br></pre></td><td class="code"><pre><span class="line">ORD(str)</span><br><span class="line">如果字符串str的最左边的字符是一个多字节字符返回该字符，用这个公式其组成字节的数值计算的代码：</span><br><span class="line"> (1st byte code)</span><br><span class="line">+ (2nd byte code . 256)</span><br><span class="line">+ (3rd byte code . 2562) ...</span><br><span class="line">如果最左边的字符不是一个多字节字符，ORD()返回相同的值如ASCII()函数。</span><br></pre></td></tr></table></figure>
<p>**<em>这个函数接受的是字符串</em>，我们就认为它的作用是返回参数的第一个字符的 ASCII，</p>
<figure class="highlight sh"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br></pre></td><td class="code"><pre><span class="line">mysql> select ord(1);</span><br><span class="line">+--------+</span><br><span class="line">| ord(1) |</span><br><span class="line">+--------+</span><br><span class="line">| 49 |</span><br><span class="line">+--------+</span><br><span class="line">1 row <span class="keyword">in</span> <span class="built_in">set</span> (0.00 sec)</span><br><span class="line"></span><br><span class="line">mysql> select ord(2);</span><br><span class="line">+--------+</span><br><span class="line">| ord(2) |</span><br><span class="line">+--------+</span><br><span class="line">| 50 |</span><br><span class="line">+--------+</span><br><span class="line">1 row <span class="keyword">in</span> <span class="built_in">set</span> (0.00 sec)</span><br><span class="line"></span><br><span class="line">mysql> select ord(<span class="string">'abc'</span>);</span><br><span class="line">+------------+</span><br><span class="line">| ord(<span class="string">'abc'</span>) |</span><br><span class="line">+------------+</span><br><span class="line">| 97 |</span><br><span class="line">+------------+</span><br><span class="line">1 row <span class="keyword">in</span> <span class="built_in">set</span> (0.00 sec)</span><br></pre></td></tr></table></figure>
<p>那么这个函数为什么能正常显示 <code>is_new</code> 呢，因为 <code>is_new</code> 是 BIT 类型。</p>
<figure class="highlight sh"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br></pre></td><td class="code"><pre><span class="line">mysql> select ord(b<span class="string">'1'</span>);</span><br><span class="line">+-----------+</span><br><span class="line">| ord(b<span class="string">'1'</span>) |</span><br><span class="line">+-----------+</span><br><span class="line">| 1 |</span><br><span class="line">+-----------+</span><br><span class="line">1 row <span class="keyword">in</span> <span class="built_in">set</span> (0.01 sec)</span><br></pre></td></tr></table></figure>
<p>就是说，<code>BIN</code> 是把 <code>is_new</code> 按二进制形式显示，<code>ORD</code> 是显示的 <code>is_new</code> 的 ASCII，或者转成了字符串？</p>
<p><code>BIT</code> 对应 Java 的布尔类型，<code>BIT</code> 默认只有一个比特位，那么 0 就是 false, 其他是 true，下面的设置方式在 mysql 中都是允许的</p>
<figure class="highlight sql"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">INSERT</span> <span class="keyword">INTO</span> `test_table`</span><br><span class="line"><span class="keyword">SET</span> `is_new`<span class="operator">=</span><span class="number">1</span>;</span><br><span class="line"><span class="keyword">INSERT</span> <span class="keyword">INTO</span> `test_table`</span><br><span class="line"><span class="keyword">SET</span> `is_new`<span class="operator">=</span>b<span class="string">'1'</span>;</span><br><span class="line"><span class="keyword">INSERT</span> <span class="keyword">INTO</span> `test_table`</span><br><span class="line"><span class="keyword">SET</span> `is_new`<span class="operator">=</span> <span class="literal">FALSE</span>;</span><br><span class="line"><span class="keyword">INSERT</span> <span class="keyword">INTO</span> `test_table`</span><br><span class="line"><span class="keyword">SET</span> `is_new`<span class="operator">=</span> <span class="literal">TRUE</span>;</span><br></pre></td></tr></table></figure>
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<a class="article-title" href="/2019/04/08/MySql%E9%94%99%E8%AF%AF%E6%8E%92%E9%99%A4/">MySql错误排除</a>
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<h2 id="最大文件打开数量的问题"><a href="#最大文件打开数量的问题" class="headerlink" title="最大文件打开数量的问题"></a>最大文件打开数量的问题</h2><p>使用 <code>ulimit -a</code> 可以查看系统对单个进程的限制</p>
<figure class="highlight sh"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br></pre></td><td class="code"><pre><span class="line">➜ ~ <span class="built_in">ulimit</span> -a</span><br><span class="line">-t: cpu time (seconds) unlimited</span><br><span class="line">-f: file size (blocks) unlimited</span><br><span class="line">-d: data seg size (kbytes) unlimited</span><br><span class="line">-s: stack size (kbytes) 8192</span><br><span class="line">-c: core file size (blocks) 0</span><br><span class="line">-v: address space (kbytes) unlimited</span><br><span class="line">-l: locked-in-memory size (kbytes) unlimited</span><br><span class="line">-u: processes 1418</span><br><span class="line">-n: file descriptors 7168</span><br></pre></td></tr></table></figure>
<p><code>ulimit -n</code> 是打开的最大文件数量限制，在 Mac 上可能是 256，如果是用了分表，默认情况下一个表对应一个文件，如果表的数量超过 256，打开超过256个文件的时候会报错。</p>
<p>解决方法：</p>
<p>1）<br>mysql 的 <code>my.cnf</code> 文件</p>
<figure class="highlight plaintext"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">innodb_file_per_table = OFF </span><br></pre></td></tr></table></figure>
<p>关闭每个 table 建立一个文件，如果还是不行</p>
<p>2）<br>修改最大文件打开数</p>
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<article id="post-Redis命令" class="article article-type-post" itemscope itemprop="blogPost">
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<a href="/2019/03/20/Redis%E5%91%BD%E4%BB%A4/" class="article-date">
<time datetime="2019-03-20T07:36:57.000Z" itemprop="datePublished">2019-03-20</time>
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<a class="article-category-link" href="/categories/Other/">Other</a>
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<a class="article-title" href="/2019/03/20/Redis%E5%91%BD%E4%BB%A4/">Redis命令</a>
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<p>连接：</p>
<figure class="highlight sh"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">redis-cli -h {host} -p {port}</span><br></pre></td></tr></table></figure>
<p>设置一个：</p>
<figure class="highlight sh"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line">127.0.0.1:6379> <span class="built_in">set</span> aaa bbb</span><br><span class="line">OK</span><br></pre></td></tr></table></figure>
<p>获取值，成功的话返回值，失败时 nil</p>
<figure class="highlight sh"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br></pre></td><td class="code"><pre><span class="line">127.0.0.1:6379> get aaa</span><br><span class="line"><span class="string">"bbb"</span></span><br><span class="line">127.0.0.1:6379> get ddd</span><br><span class="line">(nil)</span><br></pre></td></tr></table></figure>
<p>值是否存在，若 key 存在，返回 1 ，否则返回 0：</p>
<figure class="highlight sh"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line">127.0.0.1:6379> exists aaa</span><br><span class="line">(<span class="built_in">integer</span>) 1</span><br></pre></td></tr></table></figure>
<p>获取keys:</p>
<figure class="highlight sh"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line">127.0.0.1:6379> keys aaa</span><br><span class="line">1) <span class="string">"aaa"</span></span><br><span class="line">127.0.0.1:6379> keys ddd</span><br><span class="line">(empty list or <span class="built_in">set</span>)</span><br><span class="line">127.0.0.1:6379></span><br></pre></td></tr></table></figure>
<p>获取过期时间，当 key 不存在时，返回 -2 。 当 key 存在但没有设置剩余生存时间时，返回 -1 。 否则，以秒为单位，返回 key 的剩余生存时间。：</p>
<figure class="highlight sh"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br></pre></td><td class="code"><pre><span class="line">127.0.0.1:6379> ttl aaa</span><br><span class="line">(<span class="built_in">integer</span>) -1</span><br><span class="line">127.0.0.1:6379> ttl ddd</span><br><span class="line">(<span class="built_in">integer</span>) -2</span><br></pre></td></tr></table></figure>
<p>设置过期时间：</p>
<figure class="highlight sh"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line">redis> EXPIRE cache_page 30 <span class="comment"># 设置过期时间为 30 秒</span></span><br><span class="line">(<span class="built_in">integer</span>) 1</span><br></pre></td></tr></table></figure>
<p>列出所有数据库：</p>
<figure class="highlight sh"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line">CONFIG GET databases</span><br><span class="line">1) <span class="string">"databases"</span></span><br><span class="line">2) <span class="string">"16"</span></span><br></pre></td></tr></table></figure>
<figure class="highlight sh"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br></pre></td><td class="code"><pre><span class="line">127.0.0.1:6379[1]> INFO keyspace</span><br><span class="line"><span class="comment"># Keyspace</span></span><br><span class="line">db0:keys=10,expires=10,avg_ttl=140298</span><br><span class="line">db1:keys=3774,expires=3770,avg_ttl=73246701</span><br></pre></td></tr></table></figure>
<p>选择数据库</p>
<figure class="highlight sh"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">select 1</span><br></pre></td></tr></table></figure>
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