Added Cloud SQL MySQL Servlet connectivity sample. #1231

kurtisvg · 2018-10-12T16:55:41Z

This is the canonical sample for a new series of samples highlighting connection best practices for Cloud SQL users. It's a simple web app that allows voting between two different groups ("Tabs" vs "Spaces") and records the votes into a MySQL backend.

@saturnism PTAL

lesv

Very nice -- my comments and questions aren't required, just consider them. A few places that might benefit from a bit of explanation and I pointed you to shutdown hooks. Only the password should be passed as a param, but I'm an advocate of setting things once and moving on. You can actually grab envVars and pass them to appengine-web.xml in maven.

Consider asking Thea about password's in EnvVar's. AWS is ok w/ it, so maybe we should be, but it's often frowned on around here. That said, I tried to make it so that if we set them in appengine-web.xml that we could pass them as arguments to mvn, which then used them to set the appengine-web.xml values.

lesv · 2018-10-12T17:21:26Z

cloud-sql/mysql/servlet/README.md

+1. If you haven't already, set up a Java Development Environment (including google-cloud-sdk and 
+maven utilities) by following the [java setup guide](https://cloud.google.com/java/docs/setup).
+
+1. Create a 2nd Gen Cloud SQL Instance by following these 


Also point them at the create a project doc as well.

https://cloud.google.com/resource-manager/docs/creating-managing-projects#creating_a_project

lesv · 2018-10-12T17:26:06Z

cloud-sql/mysql/servlet/README.md

+export GOOGLE_APPLICATION_CREDENTIALS=/path/to/service/account/key.json
+export CLOUD_SQL_CONNECTION_NAME='<MY-PROJECT>:<INSTANCE-REGION>:<MY-DATABASE>'
+export DB_USER='my-db-user'
+export DB_PASS='my-db-pass'


This is often bad practice. Letting folks pass it in on the mvn / gradle command line is usually considered better.

I've added a warning to the sections with environment variables that they aren't secure with a link to KMS as a secure solution. I would prefer to avoid using mvn / gradle to configure properties because it's permanent and forces the user to rebuild rather than restart the application. We are planning on adding instructions for GKE/GCE as well, which could mean a lot of repeated steps if they have to rebuild to change instance name.

+1; Definitely do not use Maven/Gradle configuration properties for runtime environment values. Those are not idiomatic.

I might argue that, but I'm ok with it.

cloud-sql/mysql/servlet/README.md

cloud-sql/mysql/servlet/pom.xml

lesv · 2018-10-12T17:40:22Z

cloud-sql/mysql/servlet/src/main/java/com/example/cloudsql/ConnectionPoolContextListener.java

+import javax.servlet.annotation.WebListener;
+import javax.sql.DataSource;
+
+@WebListener


You might want to explain why we do this here.

cloud-sql/mysql/servlet/src/main/java/com/example/cloudsql/ConnectionPoolContextListener.java

lesv · 2018-10-12T17:45:49Z

cloud-sql/mysql/servlet/src/main/java/com/example/cloudsql/ConnectionPoolContextListener.java

+    DataSource pool = new HikariDataSource(config);
+    // [END cloud_sql_mysql_connection_pool]
+    return pool;
+  }


Might you want to create a Shutdown Hook to close any currently inactive instances and mark active ones to be closed?

Possibly in contextInitialized()?

I'm going to skip this for now as well - we want to expand the sample to additional run-times soon and I want to avoid any run-time specific options.

cloud-sql/mysql/servlet/src/main/webapp/WEB-INF/appengine-web.xml

saturnism · 2018-10-30T02:33:45Z

cloud-sql/mysql/servlet/README.md

+
+Navigate towards `http://127.0.0.1:8080` to verify your application is running correctly.
+
+## Google AppEngine-Standard


"Google AppEngine-Standard" or "Google App Engine Standard"? Want to make sure we are consistent with official naming/documentation.

saturnism · 2018-10-30T02:38:09Z

cloud-sql/mysql/servlet/src/main/java/com/example/cloudsql/ConnectionPoolContextListener.java

+        pool.unwrap(HikariDataSource.class).close();
+      } catch (SQLException e) {
+        // Handle exception
+        System.out.println("Any error occurred while the application was shutting down: " + e);


Please use logger, JUL if we don't already use anything. Always log exceptions in its own argument (so that the stacktrace will show).

saturnism · 2018-10-30T02:39:10Z

cloud-sql/mysql/servlet/src/main/java/com/example/cloudsql/ConnectionPoolContextListener.java

+  private static final String DB_PASS = System.getenv("DB_PASS");
+  private static final String DB_NAME = System.getenv("DB_NAME");
+
+  private DataSource mysqlConnectionPool() {


method name should indicate the action, e.g. createConnectionPool

saturnism · 2018-10-30T02:41:07Z

cloud-sql/mysql/servlet/src/main/java/com/example/cloudsql/IndexServlet.java

+
+      // PreparedStatements can also be executed multiple times with different arguments. This can
+      // improve efficiency, and project a query from being vulnerable to an SQL injection.
+      PreparedStatement voteCtStmt = conn.prepareStatement(


I'd encourage verbose variable names; Ct is unclear. I believe it means voteCount?

saturnism · 2018-10-30T02:45:04Z

cloud-sql/mysql/servlet/src/main/webapp/index.jsp

+<div class="section">
+    <div class="center">
+        <h4>
+            <% if(voteDiff != 0) { %>


would encourage using standard taglibs, <c:if ...> In fact, when using tags, we don't need so much <%= ... %> scripts.

Could you provide more context on this? When should I use a taglib over the <= ... %>? Is <%= ... &> unsafe or inefficient?

Is the advised taglib to use the JSTL core library?

JSTL core library works. The taglibs are idiomatic in the JSP world, and you don't need to use request.getAttribute() to get the variables, since taglibs will be able to get the data directly from the attribute. It'll be cleaner, less code, and safer since it'll escape tags so you don't end up w/ script injections.

Just for example (and probably don't work as is since it's been a while since I had to write JSP :):

<c:choose> <c:when test="${tabVoteCt == spaceVoteCt}"> TABS and SPACES are tied </c:when> <c:when test="${tabVoteCt > spaceVoteCt}"> TABS won </c:when> <c:when test="${tabVoteCt < spaceVoteCt}"> SPACES won </c:when> </c:choose>

To iterate through the list:

<c:forEach items="${recentVotes}" var="vote"> <li class="collection-item avatar"> <c:choose> ... </c:choose> </li> </c:forEach>

Thanks for the background - I've made the adjustments.

saturnism · 2018-10-30T02:55:09Z

cloud-sql/mysql/servlet/src/main/java/com/example/cloudsql/ConnectionPoolContextListener.java

+      );
+      createTableStatement.execute();
+    } catch (SQLException e) {
+      throw new Error(


do not throw Error. Also, don't use e.toString() or any of its string form when propagating exceptions.

It's actually better to simply propagate the SQLException upwards and declare the throw for this method.

What is the preferred way to stop the application if this context fails to initialize correctly?

I wouldn't use Error. Instead, throw a new RuntimeException w/ the cause. throw new RuntimeException("oops", e);

saturnism · 2018-10-30T03:00:49Z

cloud-sql/mysql/servlet/src/main/java/com/example/cloudsql/ConnectionPoolContextListener.java

+    try (Connection conn = pool.getConnection()) {
+      PreparedStatement createTableStatement = conn.prepareStatement(
+          "CREATE TABLE IF NOT EXISTS votes ( "
+              + "vote_id SERIAL NOT NULL, time_cast timestamp NOT NULL, canidate CHAR(6) NOT NULL, "


what does canidate mean?

canidate is the subject of the vote (e.g. tabs or spaces).

is it candidate?

Sorry yes - my bad. Fixed.

saturnism · 2018-10-30T03:01:59Z

cloud-sql/mysql/servlet/src/main/java/com/example/cloudsql/IndexServlet.java

+      // If something goes wrong, the application needs to react appropriately. This might mean
+      // getting a new connection and executing the query again, or it might mean redirecting the
+      // user to a different page to let them know something went wrong.
+      throw new ServletException("Unable to successfully connect to the database. Please check the "


pls propagate e in ServletException

See https://tomcat.apache.org/tomcat-5.5-doc/servletapi/javax/servlet/ServletException.html#ServletException(java.lang.String,%20java.lang.Throwable)

IRL you'd probably log the event, maybe add to some monitor value as well before propagating.

saturnism · 2018-10-30T03:03:26Z

cloud-sql/mysql/servlet/src/main/java/com/example/cloudsql/IndexServlet.java

+      team = team.toLowerCase();
+    }
+    Timestamp now = new Timestamp(new Date().getTime());
+    if (team == null || !team.equals("tabs") && !team.equals("spaces")) {


to be clear on the operation precedence, if (team == null || ("tabs".equals(team) && !"spaces".equals(team))

saturnism · 2018-10-30T03:04:08Z

cloud-sql/mysql/servlet/src/main/java/com/example/cloudsql/IndexServlet.java

+      // If something goes wrong, handle the error in this section. This might involve retrying or
+      // adjusting parameters depending on the situation.
+      // [START_EXCLUDE]
+      System.out.println("An SQL error occurred during executions: \n" + e.toString());


same comments as above regarding exception handling.

saturnism · 2018-10-30T03:10:01Z

cloud-sql/mysql/servlet/src/main/java/com/example/cloudsql/ConnectionPoolContextListener.java

+    DataSource pool = (DataSource) event.getServletContext().getAttribute("my-pool");
+    if (pool != null) {
+      try {
+        pool.unwrap(HikariDataSource.class).close();


Since we know this is already an HikariDataSource, it should simply cast to it.

`HikariDataSource pool = (HikariDataSource) ...

saturnism · 2018-11-02T17:37:05Z

cloud-sql/mysql/servlet/src/main/java/com/example/cloudsql/IndexServlet.java

+      voteCtStmt.setString(1, "spaces");
+      ResultSet spacesResult = voteCtStmt.executeQuery();
+      spacesResult.next(); // Move to the first result
+      voteCt = spacesResult.getInt(1);


should this be spaceCt?

saturnism · 2018-11-02T17:43:34Z

cloud-sql/mysql/servlet/src/main/webapp/index.jsp

+    </ul>
+</div>
+</body>
+<footer>


footer tag should be part of the body tag. And if that's done, we should remove footer tag altogether and simply use script in the end.

<html> <head></head> <body> ... <script>...</script> </body> </html>

saturnism · 2018-11-02T19:11:23Z

cloud-sql/mysql/servlet/src/main/java/com/example/cloudsql/Vote.java

+
+public class Vote {
+
+  private String candiate;


Fix checkstyle violations.

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kurtisvg added the do not merge Indicates a pull request not ready for merge, due to either quality or timing. label Oct 12, 2018

kurtisvg requested a review from lesv October 12, 2018 16:55

googlebot added the cla: yes This human has signed the Contributor License Agreement. label Oct 12, 2018

lesv suggested changes Oct 12, 2018

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kurtisvg dismissed lesv’s stale review via 45119fb October 16, 2018 21:59

saturnism suggested changes Oct 30, 2018

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kurtisvg removed the do not merge Indicates a pull request not ready for merge, due to either quality or timing. label Nov 5, 2018

kurtisvg added 4 commits November 6, 2018 08:38

Added MySQL Servlet connectivity sample.

507f376

Fix checkstyle violations.

Partially address lesv feedback.

2aa5147

Address rest of lesv's feedback.

2437011

Address additional feedback.

8784790

saturnism approved these changes Nov 6, 2018

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lesv approved these changes Nov 6, 2018

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lesv merged commit ffdb971 into GoogleCloudPlatform:master Nov 6, 2018

This was referenced Nov 7, 2018

Add Cloud SQL Postgres connectivity sample for servlets. #1255

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Added Cloud SQL MySQL Servlet connectivity sample. #1231

Added Cloud SQL MySQL Servlet connectivity sample. #1231

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		Navigate towards `http://127.0.0.1:8080` to verify your application is running correctly.

		## Google AppEngine-Standard

Added Cloud SQL MySQL Servlet connectivity sample. #1231

Added Cloud SQL MySQL Servlet connectivity sample. #1231

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