Examples / Google Cloud Examples / Shoutbox V1 (POST Requests)

Shoutbox V1 (POST Requests)

example java google-cloud app-engine post

This project uses POST requests to create a shoutbox where users can post short messages.

View the code for this project here.

Download the code as a .zip from DownGit here.

input

shoutbox

pom.xml

pom.xml is a Maven POM file that defines the project.

<project xmlns="http://maven.apache.org/POM/4.0.0"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0</modelVersion>

  <groupId>io.happycoding</groupId>
  <artifactId>shoutbox-v1</artifactId>
  <version>1</version>

  <properties>
    <!-- App Engine currently supports Java 11 -->
    <maven.compiler.source>11</maven.compiler.source>
    <maven.compiler.target>11</maven.compiler.target>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    <jetty.version>9.4.31.v20200723</jetty.version>

    <!-- Project-specific properties -->
    <exec.mainClass>io.happycoding.ServerMain</exec.mainClass>
    <googleCloudProjectId>YOUR_PROJECT_ID_HERE</googleCloudProjectId>
  </properties>

  <dependencies>
    <!-- Java Servlets API -->
    <dependency>
      <groupId>javax.servlet</groupId>
      <artifactId>javax.servlet-api</artifactId>
      <version>4.0.1</version>
    </dependency>

    <!-- Jetty -->
    <dependency>
      <groupId>org.eclipse.jetty</groupId>
      <artifactId>jetty-server</artifactId>
      <version>${jetty.version}</version>
    </dependency>
    <dependency>
      <groupId>org.eclipse.jetty</groupId>
      <artifactId>jetty-annotations</artifactId>
      <version>${jetty.version}</version>
    </dependency>
  </dependencies>

  <build>
    <plugins>
      <!-- Copy static resources like html files into the output jar file. -->
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-resources-plugin</artifactId>
        <version>2.7</version>
        <executions>
          <execution>
            <id>copy-web-resources</id>
            <phase>compile</phase>
            <goals><goal>copy-resources</goal></goals>
            <configuration>
              <outputDirectory>
                ${project.build.directory}/classes/META-INF/resources
              </outputDirectory>
              <resources>
                <resource><directory>./src/main/webapp</directory></resource>
              </resources>
            </configuration>
          </execution>
        </executions>
      </plugin>

      <!-- Package everything into a single executable jar file. -->
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-shade-plugin</artifactId>
        <version>3.2.4</version>
        <executions>
          <execution>
            <phase>package</phase>
            <goals><goal>shade</goal></goals>
            <configuration>
              <createDependencyReducedPom>false</createDependencyReducedPom>
              <transformers>
                <transformer implementation="org.apache.maven.plugins.shade.resource.ManifestResourceTransformer">
                  <mainClass>${exec.mainClass}</mainClass>
                </transformer>
              </transformers>
            </configuration>
          </execution>
        </executions>
      </plugin>

      <!-- App Engine plugin for deploying to the live site. -->
      <plugin>
        <groupId>com.google.cloud.tools</groupId>
        <artifactId>appengine-maven-plugin</artifactId>
        <version>2.2.0</version>
        <configuration>
          <projectId>${googleCloudProjectId}</projectId>
          <version>1</version>
        </configuration>
      </plugin>
    </plugins>
  </build>
</project>

app.yaml

app.yaml is a config file that sets up App Engine. This hello world project only uses a single property that sets the runtime to Java 11.

runtime: java11

ServerMain.java

ServerMain.java is the main class that sets up the server.

package io.happycoding;

import java.net.URL;
import org.eclipse.jetty.annotations.AnnotationConfiguration;
import org.eclipse.jetty.server.Handler;
import org.eclipse.jetty.server.handler.DefaultHandler;
import org.eclipse.jetty.server.Server;
import org.eclipse.jetty.servlet.DefaultServlet;
import org.eclipse.jetty.webapp.Configuration;
import org.eclipse.jetty.webapp.WebAppContext;
import org.eclipse.jetty.webapp.WebInfConfiguration;

/**
 * Starts up the server, including a DefaultServlet that handles static files,
 * and any servlet classes annotated with the @WebServlet annotation.
 */
public class ServerMain {

  public static void main(String[] args) throws Exception {

    // Create a server that listens on port 8080.
    Server server = new Server(8080);
    WebAppContext webAppContext = new WebAppContext();
    server.setHandler(webAppContext);

    // Load static content from inside the jar file.
    URL webAppDir =
        ServerMain.class.getClassLoader().getResource("META-INF/resources");
    webAppContext.setResourceBase(webAppDir.toURI().toString());

    // Enable annotations so the server sees classes annotated with @WebServlet.
    webAppContext.setConfigurations(new Configuration[]{ 
      new AnnotationConfiguration(),
      new WebInfConfiguration(), 
    });

    // Look for annotations in the classes directory (dev server) and in the
    // jar file (live server)
    webAppContext.setAttribute(
        "org.eclipse.jetty.server.webapp.ContainerIncludeJarPattern", 
        ".*/target/classes/|.*\\.jar");

    // Handle static resources, e.g. html files.
    webAppContext.addServlet(DefaultServlet.class, "/");

    // Start the server! 🚀
    server.start();
    System.out.println("Server started!");

    // Keep the main thread alive while the server is running.
    server.join();
  }
}

MessageServlet.java

MessageServlet.java is a Java servlet that contains a doGet() function that loads messages from Datastore and outputs them as HTML, and a doPost() function that stores new messages in an ArrayList.

package io.happycoding.servlets;

import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

@WebServlet("/message")
public class MessageServlet extends HttpServlet {

  // In-memory data structure for a simple example.
  // This is for testing only!
  // In real life you'd want to use persistent storage like Datastore.
  private List<String> messages = new ArrayList<>();

  @Override
  public void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException {
    response.setContentType("text/html;");
    response.getWriter().println("<h1>Shoutbox</h1>");
    response.getWriter().println("<ul>");
    for(String message: messages) {
    	response.getWriter().println("<li>" + message + "</li>");
    }
    response.getWriter().println("</ul>");
    response.getWriter().println("<p><a href=\"/\">Back</a></p>");
  }

  @Override
  public void doPost(HttpServletRequest request, HttpServletResponse response)
      throws IOException {

    String message = request.getParameter("message");
    messages.add(message);
 
    // Redirect to /message.
    // The request will be routed to the doGet() function above.
    response.sendRedirect("/message");
  }
}

index.html

index.html is an HTML file that shows a form with a file input.

<!DOCTYPE html>
<html>
  <head>
    <meta charset="UTF-8">
    <title>Shoutbox v1</title>
  </head>
  <body>
    <h1>Shoutbox v1</h1>
    <p>Type a message and click submit:</p>

    <form method="POST" action="/message">
      <textarea name="message"></textarea>
      <br/>
      <button>Submit</button>
    </form>

    <p>Learn more at <a href="https://happycoding.io">HappyCoding.io</a>.</p>
  </body>
</html>

You can run this locally by executing this command:

mvn package exec:java

Then visit http://localhost:8080 in your web browser, and you should see this:

input

shoutbox

Learn more in these tutorials: