Shoutbox V1 (POST Requests)

Shoutbox V1 (POST Requests)

September 27, 2020

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.




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

<project xmlns=""


    <!-- App Engine currently supports Java 11 -->

    <!-- Project-specific properties -->

    <!-- Java Servlets API -->

    <!-- Jetty -->

      <!-- Copy static resources like html files into the output jar file. -->

      <!-- Package everything into a single executable jar file. -->
                <transformer implementation="org.apache.maven.plugins.shade.resource.ManifestResourceTransformer">

      <!-- App Engine plugin for deploying to the live site. -->


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 is the main class that sets up the server.

package io.happycoding;

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();

    // Load static content from inside the jar file.
    URL webAppDir =

    // 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)

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

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

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

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<>();

  public void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException {
    for(String message: messages) {
    	response.getWriter().println("<li>" + message + "</li>");
    response.getWriter().println("<p><a href=\"/\">Back</a></p>");

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

    String message = request.getParameter("message");

    // Redirect to /message.
    // The request will be routed to the doGet() function above.


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

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

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

    <p>Learn more at <a href=""></a>.</p>

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:



Learn more in these tutorials:

App Engine Examples


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