Examples / Google Cloud Examples / Translation Web App Hello World

Translation Web App Hello World

example java google-cloud app-engine post fetch translation

This is a web app that uses Google Translate to analyze some text uploaded by the user.

View the code for this project here.

Download the code as a .zip from DownGit here.

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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>google-cloud-translation-hello-world-webapp</artifactId>
  <version>1</version>

  <properties>
    <!-- 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>happy-coding-gcloud</googleCloudProjectId>
  </properties>

  <dependencies>
    <!-- Java Servlets API -->
    <dependency>
      <groupId>javax.servlet</groupId>
      <artifactId>javax.servlet-api</artifactId>
      <version>4.0.1</version>
    </dependency>
    
    <!-- Google Cloud Translation -->
    <dependency>
      <groupId>com.google.cloud</groupId>
      <artifactId>google-cloud-translate</artifactId>
      <version>1.95.2</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>
              <filters>
                <filter>
                  <artifact>*:*</artifact>
                  <!-- The Cloud Translation library signs its jar, so exclude its signature in the output jar -->
                  <excludes>
                    <exclude>META-INF/*.SF</exclude>
                    <exclude>META-INF/*.DSA</exclude>
                    <exclude>META-INF/*.RSA</exclude>
                  </excludes>
                </filter>
              </filters>
            </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();
  }
}

TranslationServlet.java

TranslationServlet.java is a Java servlet that handles the POST request including the text entered by the user, sends the request for translation, and outputs the result.

package io.happycoding.servlets;

import com.google.cloud.translate.Translate;
import com.google.cloud.translate.TranslateOptions;
import com.google.cloud.translate.Translation;
import java.io.IOException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

@WebServlet("/translate")
public class TranslationServlet extends HttpServlet {

  @Override
  public void doPost(HttpServletRequest request, HttpServletResponse response) throws IOException {
    // Get the request parameters
    String originalText = request.getParameter("text");
    String languageCode = request.getParameter("languageCode");

    // Get the translation
    Translate translate = TranslateOptions.getDefaultInstance().getService();
    Translation translation =
        translate.translate(originalText, Translate.TranslateOption.targetLanguage(languageCode));
    String translatedText = translation.getTranslatedText();

    // Output the translation
    response.setContentType("text/html; charset=UTF-8");
    response.setCharacterEncoding("UTF-8");
    response.getWriter().println(translatedText);
  }
}

index.html

index.html is an HTML file that shows a form, and includes JavaScript that calls the fetch() function to send the user’s input to the server and show the result in the DOM.

<!DOCTYPE html>
<html>
  <head>
    <meta charset="UTF-8">
    <title>Translation</title>

    <script>
      function requestTranslation() {
        // Get the user's input from the UI
        const text = document.getElementById('text').value;
        const languageCode = document.getElementById('language').value;

        // Show a placeholder while waiting for the response
        const resultContainer = document.getElementById('result');
        resultContainer.innerText = 'Loading...';

        // Build the request params
        const params = new URLSearchParams();
        params.append('text', text);
        params.append('languageCode', languageCode);

        // Send a POST request to the server
        fetch('/translate', {
          method: 'POST',
          body: params
        })
        // Convert the response to plain text
        .then(response => response.text())
        // Show the translated text in the page
        .then((translatedMessage) => {
          resultContainer.innerText = translatedMessage;
        });
      }
    </script>

    <style>
      #text {
        width: 500px;
        height: 125px;
      }

      #language {
        display: block;
        margin-top: 25px;
        margin-bottom: 25px;
      }
    </style>

  </head>
  <body>
    <h1>Translation</h1>
    <p>Type a message and select a language, then click submit to translate it.</p>

    <textarea id="text"></textarea>

    <select id="language">
      <option value="en">English</option>
      <option value="zh">Chinese</option>
      <option value="es">Spanish</option>
      <option value="hi">Hindi</option>
      <option value="ar">Arabic</option>
    </select>

    <button onclick="requestTranslation();">Translate</button>

    <hr/>
    <div id="result"></div>
  </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:

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Learn more in these tutorials: