Cloud Storage Hello World

Cloud Storage Hello World

September 20, 2020

example java server google-cloud app-engine cloud-storage

This is a barebones example webapp that lets the user upload files to Google Cloud Storage.

View the code for this project here.

Download the code as a .zip from DownGit here.

file input

image uploaded


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 -->

    <!-- Google Cloud Storage -->

    <!-- 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 handles the file upload and outputs some HTML content.

package io.happycoding.servlets;

import javax.servlet.ServletException;
import javax.servlet.annotation.MultipartConfig;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.Part;

public class UploadServlet extends HttpServlet {

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

    // Submissions can contain other types of data
    String message = request.getParameter("message");

    // Get the file chosen by the user
    Part filePart = request.getPart("image");
    String fileName = filePart.getSubmittedFileName();
    InputStream fileInputStream = filePart.getInputStream();

    // Upload the file and get its URL
    String uploadedFileUrl = uploadToCloudStorage(fileName, fileInputStream);

    // Use the URL to output some HTML
    response.getWriter().println("<p>Your message: " + message + "</p>");
    response.getWriter().println("<p>Your image:</p>");
    response.getWriter().println("<img src=\"" + uploadedFileUrl + "\"  />");

  /** Uploads a file to Cloud Storage and returns the uploaded file's URL. */
  private static String uploadToCloudStorage(String fileName, InputStream fileInputStream) {
    String projectId = "happy-coding-gcloud";
    String bucketName = "";
    Storage storage =
    BlobId blobId = BlobId.of(bucketName, fileName);
    BlobInfo blobInfo = BlobInfo.newBuilder(blobId).build();
    Blob blob = storage.create(blobInfo, fileInputStream);
    return blob.getMediaLink();


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

<!DOCTYPE html>
    <meta charset="UTF-8">
    <title>Google Cloud Storage Hello World</title>
    <h1>Google Cloud Storage Hello World</h1>
    <p>This form lets you upload a file to Google Cloud Storage.</p>

    <form method="POST" enctype="multipart/form-data" action="/upload">

      <p>Type some text:</p>
      <textarea name="message"></textarea>

      <p>Upload an image:</p>
      <input type="file" name="image">


    <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:

file input

image uploaded

Learn more in these tutorials:

Cloud Storage Examples


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