As mentioned in the previous section, you can define bean properties and constructor arguments as references to other managed beans (collaborators), or as values defined inline. Spring’s XML-based configuration metadata supports sub-element types within its <property/> and<constructor-arg/> elements for this purpose.
如上一节所述，您可以将bean属性和构造函数参数定义为对其他托管bean（协作者）的引用，或者作为内联定义的值。 Spring通过配置基于XML的元数据来支持它的<property />和<constructor-arg />元素中的子元素类型。
The value attribute of the <property/> element specifies a property or constructor argument as a human-readable string representation. Spring’s conversion serviceis used to convert these values from a String to the actual type of the property or argument.
<property />元素的value属性指定一个属性或构造函数参数作为一个人为可读的字符串表示。 Spring的转换服务用于将这些值从 一个String转换到属性或参数的实际类型。
<bean id="myDataSource" class="org.apache.commons.dbcp.BasicDataSource" destroy-method="close">
<!-- results in a setDriverClassName(String) call -->
<property name="driverClassName" value="com.mysql.jdbc.Driver"/>
<property name="url" value="jdbc:mysql://localhost:3306/mydb"/>
<property name="username" value="root"/>
<property name="password" value="masterkaoli"/>
</bean>The preceding XML is more succinct; however, typos are discovered at runtime rather than design time, unless you use an IDE such as IntelliJ IDEA or the Spring Tool Suite (STS) that support automatic property completion when you create bean definitions. Such IDE assistance is highly recommended.
You can also configure a java.util.Properties instance as:
前面的XML更简洁; 但是，除非您使用IntelliJ IDEA或Spring Tool Suite (STS)等IDE，否则会在运行时而不是设计时间(也就是在敲代码的时候)发现打字错误，在创建bean定义时支持自动属性完成。 强烈推荐此类IDE帮助。
您还可以将java.util.Properties实例配置为：
<bean id="mappings"
class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">
<!-- typed as a java.util.Properties -->
<property name="properties">
<value>
jdbc.driver.className=com.mysql.jdbc.Driver
jdbc.url=jdbc:mysql://localhost:3306/mydb
</value>
</property>
</bean>The Spring container converts the text inside the <value/> element into a java.util.Properties instance by using the JavaBeans PropertyEditor mechanism. This is a nice shortcut, and is one of a few places where the Spring team do favor the use of the nested <value/> element over the value attribute style.
Spring容器通过使用JavaBeans的PropertyEditor机制将<value />元素内的文本转换为java.util.Properties实例。 这是一个很好的快捷方式，并且是Spring团队喜欢在“value”属性样式上使用嵌套的<value />元素的几个地方之一。
The idref element is simply an error-proof way to pass the id (string value - not a reference) of another bean in the container to a<constructor-arg/> or <property/> element.
idref元素只是一种将容器中另一个bean的* id *（字符串值 - 不是引用）传递给<constructor-arg />或<property />元素 。
<bean id="theTargetBean" class="..."/>
<bean id="theClientBean" class="...">
<property name="targetName">
<idref bean="theTargetBean" />
</property>
</bean>The above bean definition snippet is exactly equivalent (at runtime) to the following snippet:
上面的bean定义代码片段与下面的代码片段完全相同（在运行时）：
<bean id="theTargetBean" class="..." />
<bean id="client" class="...">
<property name="targetName" value="theTargetBean" />
</bean>The first form is preferable to the second, because using the idref tag allows the container to validate at deployment time that the referenced, named bean actually exists. In the second variation, no validation is performed on the value that is passed to the targetName property of the client bean. Typos are only discovered (with most likely fatal results) when the client bean is actually instantiated. If the client bean is a prototype bean, this typo and the resulting exception may only be discovered long after the container is deployed.
![[Note]](http://docs.spring.io/spring/docs/5.0.0.M4/spring-framework-reference/htmlsingle/images/note.png) |
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The local attribute on the idref element is no longer supported in the 4.0 beans xsd since it does not provide value over a regular bean reference anymore. Simply change your existing idref local references to idref bean when upgrading to the 4.0 schema. |
A common place (at least in versions earlier than Spring 2.0) where the <idref/> element brings value is in the configuration of AOP interceptors in aProxyFactoryBean bean definition. Using <idref/> elements when you specify the interceptor names prevents you from misspelling an interceptor id.
第一种形式优于第二种形式，因为使用idref标签允许容器在部署时验证被引用的命名bean实际存在。在第二个变体中，不对传递给client bean的targetName属性的值执行验证。当client bean实际被实例化时，只有发现了typos（而且可能是致命的结果）。如果client bean是一个prototype bean，这个打印错误所生成的异常只能在容器部署后很久才被发现。
| ！[Note] |
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idref元素上的local属性在4.0 bean xsd中不再支持，因为它不再提供超过正则bean引用的值。在升级到4.0模式时，只需将现有的“idref local”引用更改为“idref bean”。 |
<idref />元素带来的一个常见的价值（至少在Spring 2.0之前的版本中）是在AOP拦截器 的配置中。在一个ProxyFactoryBean bean定义中，当指定拦截器名称时，使用<idref />元素可防止拼写拦截器ID。
The ref element is the final element inside a <constructor-arg/> or <property/> definition element. Here you set the value of the specified property of a bean to be a reference to another bean (a collaborator) managed by the container. The referenced bean is a dependency of the bean whose property will be set, and it is initialized on demand as needed before the property is set. (If the collaborator is a singleton bean, it may be initialized already by the container.) All references are ultimately a reference to another object. Scoping and validation depend on whether you specify the id/name of the other object through the bean, local, or parentattributes.
Specifying the target bean through the bean attribute of the <ref/> tag is the most general form, and allows creation of a reference to any bean in the same container or parent container, regardless of whether it is in the same XML file. The value of the bean attribute may be the same as the id attribute of the target bean, or as one of the values in the name attribute of the target bean.
ref元素是<constructor-arg/>或<property/>定义元素中的最后一个元素。在这里，你将bean的指定属性的值设置为对容器管理的另一个bean（协作者）的引用。引用的bean是将设置其属性的bean的依赖关系，并且在设置属性之前根据需要对其进行初始化。 （如果协作者是单例bean，它可能已经由容器初始化。）所有引用最终都是对另一个对象的引用。范围和验证取决于您是通过“bean”，“local”还是“parent”属性指定其他对象的id / name。
通过<ref/>标签的bean属性指定目标bean是最通用的形式，允许创建对同一容器或父容器中的任何bean的引用，而不管它是否在同一个XML文件。 “bean”属性的值可以与目标bean的“id”属性相同，也可以与目标bean的“name”属性中的值之一相同。
<ref bean="someBean"/>Specifying the target bean through the parent attribute creates a reference to a bean that is in a parent container of the current container. The value of the parentattribute may be the same as either the id attribute of the target bean, or one of the values in the name attribute of the target bean, and the target bean must be in a parent container of the current one. You use this bean reference variant mainly when you have a hierarchy of containers and you want to wrap an existing bean in a parent container with a proxy that will have the same name as the parent bean
.
通过parent属性指定目标bean将创建对当前容器的父容器中的bean的引用。 “parent”属性的值可以与目标bean的“id”属性相同，也可以与目标bean的“name”属性中的一个值相同，并且目标bean必须位于父容器中 的当前一个。 你使用这个bean引用变体主要是当你有一个容器的层次结构，并且你想用一个与父bean同名的代理在一个父容器中包装一个现有的bean。
<!-- in the parent context -->
<bean id="accountService" class="com.foo.SimpleAccountService">
<!-- insert dependencies as required as here -->
</bean><!-- in the child (descendant) context -->
<bean id="accountService" <!-- bean name is the same as the parent bean -->
class="org.springframework.aop.framework.ProxyFactoryBean">
<property name="target">
<ref parent="accountService"/> <!-- notice how we refer to the parent bean -->
</property>
<!-- insert other configuration and dependencies as required here -->
</bean>![[Note]](http://docs.spring.io/spring/docs/5.0.0.M4/spring-framework-reference/htmlsingle/images/note.png.pagespeed.ce.9zQ_1wVwzR.png) |
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'ref元素的local属性在4.0 beans xsd中不再支持，因为它不再提供超过正则范围bean引用的值。 在升级到4.0模式时，只需将现有的ref local引用更改为ref bean` |
A <bean/> element inside the <property/> or <constructor-arg/> elements defines a so-called inner bean.
元素内的<property />或<constructor-arg />元素里面定义了一个所谓的*inner(内部)bean *。
<bean id="outer" class="...">
<!-- instead of using a reference to a target bean, simply define the target bean inline -->
<property name="target">
<bean class="com.example.Person"> <!-- this is the inner bean -->
<property name="name" value="Fiona Apple"/>
<property name="age" value="25"/>
</bean>
</property>
</bean>An inner bean definition does not require a defined id or name; if specified, the container does not use such a value as an identifier. The container also ignores the scope flag on creation: Inner beans are always anonymous and they are always created with the outer bean. It is not possible to inject inner beans into collaborating beans other than into the enclosing bean or to access them independently.
As a corner case, it is possible to receive destruction callbacks from a custom scope, e.g. for a request-scoped inner bean contained within a singleton bean: The creation of the inner bean instance will be tied to its containing bean, but destruction callbacks allow it to participate in the request scope’s lifecycle. This is not a common scenario; inner beans typically simply share their containing bean’s scope.
内部bean定义不需要定义的id或名称; 如果指定，容器不使用这样的值作为标识符。 容器在创建时也忽略scope标志：内部bean 总是匿名的，它们总是用外部bean创建。 将内部bean注入到协作bean中而不是注入到封闭bean中或者独立访问它们是不可能的。
作为一种角落情况，可以从自定义范围接收销毁回调，例如。 对于包含在单例bean内的请求范围内部bean：内部bean实例的创建将绑定到其包含的bean，但销毁回调允许它参与请求范围的生命周期。 这不是一个常见的情况; 内部bean通常简单地共享它们被包含bean的范围。
In the <list/>, <set/>, <map/>, and <props/> elements, you set the properties and arguments of the Java Collection types List, Set, Map, and Properties, respectively.
在<list/>，<set/>，<map/>和<props/>元素中，设置JavaCollection类型List，Set，Map和Properties的属性和参数。
<bean id="moreComplexObject" class="example.ComplexObject">
<!-- results in a setAdminEmails(java.util.Properties) call -->
<property name="adminEmails">
<props>
<prop key="administrator">[email protected]</prop>
<prop key="support">[email protected]</prop>
<prop key="development">[email protected]</prop>
</props>
</property>
<!-- results in a setSomeList(java.util.List) call -->
<property name="someList">
<list>
<value>a list element followed by a reference</value>
<ref bean="myDataSource" />
</list>
</property>
<!-- results in a setSomeMap(java.util.Map) call -->
<property name="someMap">
<map>
<entry key="an entry" value="just some string"/>
<entry key ="a ref" value-ref="myDataSource"/>
</map>
</property>
<!-- results in a setSomeSet(java.util.Set) call -->
<property name="someSet">
<set>
<value>just some string</value>
<ref bean="myDataSource" />
</set>
</property>
</bean>The value of a map key or value, or a set value, can also again be any of the following elements:
一个map键或值或set值也可以是以下任何元素：
bean | ref | idref | list | set | map | props | value | nullThe Spring container also supports the merging of collections. An application developer can define a parent-style <list/>, <set/>, <map/> or <props/> element, and have child-style <list/>, <set/>, <map/> or <props/> elements inherit and override values from the parent collection. That is, the child collection’s values are the result of merging the elements of the parent and child collections, with the child’s collection elements overriding values specified in the parent collection.
This section on merging discusses the parent-child bean mechanism. Readers unfamiliar with parent and child bean definitions may wish to read the relevant section before continuing.
The following example demonstrates collection merging:
Spring容器还支持集合的合并。 一个应用程序开发人员可以定义一个父类型 <list/>, <set/>, <map/> 或者<props/>, <list/>``<set/>，<map/>或<props/>元素继承并覆盖父集合中的值。 也就是说，子集合的值是合并父和子集合的元素的结果，子集合元素覆盖父集合中指定的值。
*本节关于合并讨论了父子bean的机制。 不熟悉父和子bean定义的读者可能希望在继续之前阅读相关章节。
以下示例演示集合合并：
<beans>
<bean id="parent" abstract="true" class="example.ComplexObject">
<property name="adminEmails">
<props>
<prop key="administrator">[email protected]</prop>
<prop key="support">[email protected]</prop>
</props>
</property>
</bean>
<bean id="child" parent="parent">
<property name="adminEmails">
<!-- the merge is specified on the child collection definition -->
<props merge="true">
<prop key="sales">[email protected]</prop>
<prop key="support">[email protected]</prop>
</props>
</property>
</bean>
<beans>Notice the use of the merge=true attribute on the <props/> element of the adminEmails property of the child bean definition. When the child bean is resolved and instantiated by the container, the resulting instance has an adminEmails Properties collection that contains the result of the merging of the child’s adminEmailscollection with the parent’s adminEmails collection.
注意在child bean定义的adminEmails属性的<props />元素上使用merge = true属性。 当child bean被容器解析和实例化时，生成的实例会有一个adminEmails``Properties集合，其中包含子集adminEmailscollection与父集合'adminEmails`集合的合并结果。
administrator[email protected]
sales[email protected]
support[email protected]The child Properties collection’s value set inherits all property elements from the parent <props/>, and the child’s value for the support value overrides the value in the parent collection.
This merging behavior applies similarly to the <list/>, <map/>, and <set/> collection types. In the specific case of the <list/> element, the semantics associated with the List collection type, that is, the notion of an ordered collection of values, is maintained; the parent’s values precede all of the child list’s values. In the case of the Map, Set, and Properties collection types, no ordering exists. Hence no ordering semantics are in effect for the collection types that underlie the associated Map, Set, and Properties implementation types that the container uses internally.
子属性Properties集合的值集合从父<props/>继承所有属性元素，support值的子值将覆盖父集合中的值。
这种合并行为类似地适用于<list/>，<map/>和<set/>集合类型。 在<list/>元素的特定情况下，与List集合类型相关联的语义，即ordered集合的值的概念被维护; 父级的值在所有子级列表的值之前。 在Map，Set和Propertie集合类型的情况下，不存在排序。 因此没有排序语义对集合类型有效，这些类型是容器在内部使用的相关联的Map，Set和Properties实现类型的基础。
You cannot merge different collection types (such as a Map and a List), and if you do attempt to do so an appropriate Exception is thrown. The merge attribute must be specified on the lower, inherited, child definition; specifying the merge attribute on a parent collection definition is redundant and will not result in the desired merging.
你不能合并不同的集合类型（例如一个Map和一个List），如果你试图这样做，一个适当的Exception被抛出。 merge属性必须在下层，继承，子定义上指定; 在父集合定义上指定merge属性是多余的，并且不会导致所需的合并。
With the introduction of generic types in Java 5, you can use strongly typed collections. That is, it is possible to declare a Collection type such that it can only containString elements (for example). If you are using Spring to dependency-inject a strongly-typed Collection into a bean, you can take advantage of Spring’s type-conversion support such that the elements of your strongly-typed Collection instances are converted to the appropriate type prior to being added to the Collection.
随着在Java 5中引入泛型类型，可以使用强类型集合。 也就是说，可以声明一个Collection类型，使得它只能包含String元素（例如）。 如果你使用Spring来将一个强类型的“Collection”依赖注入到一个bean中，你可以利用Spring的类型转换支持，这样强类型的“Collection”实例的元素被转换为适当的类型 被添加到Collection。
public class Foo {
private Map<String, Float> accounts;
public void setAccounts(Map<String, Float> accounts) {
this.accounts = accounts;
}
}<beans>
<bean id="foo" class="x.y.Foo">
<property name="accounts">
<map>
<entry key="one" value="9.99"/>
<entry key="two" value="2.75"/>
<entry key="six" value="3.99"/>
</map>
</property>
</bean>
</beans>When the accounts property of the foo bean is prepared for injection, the generics information about the element type of the strongly-typed Map is available by reflection. Thus Spring’s type conversion infrastructure recognizes the various value elements as being of type Float, and the string values 9.99, 2.75, and 3.99 are converted into an actual Float type.
当foo bean的accounts属性准备注入时，强类型Map的元素类型的泛型信息可以通过反射来获得。 因此，Spring的类型转换基础设施将各种值元素识别为“Float”类型，并且字符串值“9.99,2.75”和“3.99”被转换为实际的“Float”类型。
Spring treats empty arguments for properties and the like as empty Strings. The following XML-based configuration metadata snippet sets the email property to the empty String value ("").
Spring将空参数的属性等作为空的字符串处理。 以下基于XML的配置元数据片段将email属性设置为空的“String”值（“”）。
<bean class="ExampleBean">
<property name="email" value=""/>
</bean>以上配置等同于以下Java代码：
exampleBean.setEmail("")<null/>元素用来处理null值。 例如：
<bean class="ExampleBean">
<property name="email">
<null/>
</property>
</bean>以上配置等同于以下Java代码：
exampleBean.setEmail(null)The p-namespace enables you to use the bean element’s attributes, instead of nested <property/> elements, to describe your property values and/or collaborating beans.
Spring supports extensible configuration formats with namespaces, which are based on an XML Schema definition. The beans configuration format discussed in this chapter is defined in an XML Schema document. However, the p-namespace is not defined in an XSD file and exists only in the core of Spring.
The following example shows two XML snippets that resolve to the same result: The first uses standard XML format and the second uses the p-namespace.
p-namespace(命名空间p)使您能够使用bean元素的属性，而不是嵌套的<property/>元素来描述属性值和/或协作bean。
Spring支持基于XML的可扩展配置格式带命名空间 模式定义。 本章讨论的beans配置格式在XML Schema文档中定义。 但是，p命名空间不是在XSD文件中定义的，只存在于Spring的核心。
以下示例显示解析为相同结果的两个XML片段：第一个使用标准XML格式，第二个使用p命名空间。
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:p="http://www.springframework.org/schema/p"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans.xsd">
<bean name="classic" class="com.example.ExampleBean">
<property name="email" value="[email protected]"/>
</bean>
<bean name="p-namespace" class="com.example.ExampleBean"
p:email="[email protected]"/>
</beans>The example shows an attribute in the p-namespace called email in the bean definition. This tells Spring to include a property declaration. As previously mentioned, the p-namespace does not have a schema definition, so you can set the name of the attribute to the property name.
This next example includes two more bean definitions that both have a reference to another bean:
该示例显示了bean定义中名为email的p-namespace(p命名空间)中的属性。 这告诉Spring包含一个属性声明。 如前所述，p命名空间没有模式定义，因此你可以设置属性的名字作为bean的property的名字。
下一个示例包括两个具有对另一个bean的引用的bean定义：
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:p="http://www.springframework.org/schema/p"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans.xsd">
<bean name="john-classic" class="com.example.Person">
<property name="name" value="John Doe"/>
<property name="spouse" ref="jane"/>
</bean>
<bean name="john-modern"
class="com.example.Person"
p:name="John Doe"
p:spouse-ref="jane"/>
<bean name="jane" class="com.example.Person">
<property name="name" value="Jane Doe"/>
</bean>
</beans>As you can see, this example includes not only a property value using the p-namespace, but also uses a special format to declare property references. Whereas the first bean definition uses <property name="spouse" ref="jane"/> to create a reference from bean john to bean jane, the second bean definition uses p:spouse-ref="jane" as an attribute to do the exact same thing. In this case spouse is the property name, whereas the -ref part indicates that this is not a straight value but rather a reference to another bean.
如您所见，此示例不仅包含使用 p-namespace(p命名空间)的属性值，还使用特殊格式声明属性引用。 第一个bean定义使用<property name =“spouse” ref =“jane”/>创建一个john bean 对jane bean的引用,第二个bean的定义使用了p:spouse-ref="jane"作为一个属性来做同样的事情。 在这种情况下，spouse是属性名，而-ref部分表示这不是一个直接的值，而是一个对另一个bean的引用。
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| p-namespace(p命名空间)不如标准XML格式灵活。 例如，声明属性引用的格式与以“Ref”结尾的属性冲突(声明属性的引用是以Ref结尾的，采用p命名空间将会产生冲突)，而标准XML格式不会。 我们建议您仔细选择您的方法，并将其传达给您的团队成员，以避免生成同时使用所有这三种方法的XML文档。 |
Similar to the the section called “XML shortcut with the p-namespace”, the c-namespace, newly introduced in Spring 3.1, allows usage of inlined attributes for configuring the constructor arguments rather then nested constructor-arg elements.
Let’s review the examples from the section called “Constructor-based dependency injection” with the c: namespace:
类似于 “XML shortcut with the p-namespace”这一节，在Spring 3.1中新引入的* c-namespace *允许使用内联属性来配置构造函数参数，而不是嵌套constructor-argthe section called “XML shortcut with the p-namespace”元素。
让我们回顾一下“基于构造函数的依赖注入”一节中的例子并顺带使用c：命名空间进行改造：
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:c="http://www.springframework.org/schema/c"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans.xsd">
<bean id="bar" class="x.y.Bar"/>
<bean id="baz" class="x.y.Baz"/>
<!-- traditional declaration -->
<bean id="foo" class="x.y.Foo">
<constructor-arg ref="bar"/>
<constructor-arg ref="baz"/>
<constructor-arg value="[email protected]"/>
</bean>
<!-- c-namespace declaration -->
<bean id="foo" class="x.y.Foo" c:bar-ref="bar" c:baz-ref="baz" c:email="[email protected]"/>
</beans>The c: namespace uses the same conventions as the p: one (trailing -ref for bean references) for setting the constructor arguments by their names. And just as well, it needs to be declared even though it is not defined in an XSD schema (but it exists inside the Spring core).
For the rare cases where the constructor argument names are not available (usually if the bytecode was compiled without debugging information), one can use fallback to the argument indexes:
c：命名空间使用与p：一样的约定（用于bean引用的尾部“-ref”），用于通过其名称设置构造函数参数。 同样，它需要被声明，即使它没有在XSD模式中定义（但它存在于Spring核心内部）。
对于少数情况下构造函数参数名称不可用（通常如果字节码没有调试信息编译），可以使用fallback到参数索引：
<!-- c-namespace index declaration -->
<bean id="foo" class="x.y.Foo" c:_0-ref="bar" c:_1-ref="baz"/> |
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由于XML语法，索引符号需要存在前导_，因为XML属性名称不能以数字开头（即使某些IDE允许它）. |
In practice, the constructor resolution mechanism is quite efficient in matching arguments so unless one really needs to, we recommend using the name notation through-out your configuration.
实际上，构造函数的解析机制在匹配参数方面是 相当高效的，除非一个真正需要，我们建议通过使用名称符号来进行你的配置。
You can use compound or nested property names when you set bean properties, as long as all components of the path except the final property name are not null. Consider the following bean definition.
您可以在设置bean属性时使用复合或嵌套属性名称，只要路径的所有组件（最终属性名称除外）不为null。 考虑下面的bean定义:
<bean id="foo" class="foo.Bar">
<property name="fred.bob.sammy" value="123" />
</bean>The foo bean has a fred property, which has a bob property, which has a sammy property, and that final sammy property is being set to the value 123. In order for this to work, the fred property of foo, and the bob property of fred must not be null after the bean is constructed, or a NullPointerException is thrown.
foo bean有一个fred属性，fred又有一个bob属性，bob又有一个sammy属性，最后的sammy属性被设置为值123。 为了使这个工作，foo的fred属性和fred的bob属性在构造bean之后不能是null，否则NullPointerException会被抛出。