[JAVA] Create a simple web application with Dropwizard

Create a simple web application with Dropwizard

This goal

--Create a simple web app --When you enter from the screen, it will return the input contents

Development environment

File implemented this time

  1. DropTestApplication.java
  2. DropTestConfiguration.java
  3. SampleResource.java
  4. index.html
  5. index.js
  6. config.yml
  7. pom.xml

Execution procedure

  1. Create maven project
  2. Create configuration file
  3. Create pom.xml
  4. Create config.yml
  5. Creating a core class for Dropwizard
  6. Create Configuration class
  7. Create Application class
  8. Create server-side socket
  9. Create SampleResource.java
  10. Screen creation
  11. Create index.html
  12. Create index.js
  13. Build
  14. Run

1. Create maven project

Using eclipse, right-click in the project explorer-> new-> project Maven → Maven Project → Click Next This time, check Create a simple project and click Next Enter any group Id (organization ID), artifact Id (identification ID, which will be the project name), check that the packaging is jar, and click Finish.


Depending on the settings of eclipse, the following package configuration will be completed.


2. Create configuration file

Here, specify the package to be used in maven in pom.xml, and set the application in config.yml.

2-1. Create pom.xml

Select and edit pom.xml created directly under the project. It is necessary to describe that dropwizard is used here, this time specify the necessary library and main class, and specify maven-shade assuming fat-jar at build time.


<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">


                  implementation="org.apache.maven.plugins.shade.resource.ServicesResourceTransformer" />


2-2. Create config.yml

Describe the settings used in the app. This time, create a yml file (name is arbitrary) directly under the root of the project (the same position as pom.xml), Specify the port and set the root path when starting the application. With the settings below, the app will launch on the 8090 port and the root path is set to/ api /.


# Application server setting.
    - type: http
      port: 8090

  rootPath: '/api/*'

3. Creating a core class for Dropwizard

We will create the necessary files with Dropwizard. This time, I created a package called dropTest.priv.jp.y.suzuki under src / main / java and created a core class under it.

3-1. Configuration class creation

Here, set the parameters for each environment. The yaml file information described in the previous step will be loaded into this class. For example, suppose you have made the following settings (description) in the yaml file.


~ Omitted ~

# template sentence
template: Hello!!

Then create a Configuration class as shown below


package priv.jp.y.suzuki;

import io.dropwizard.Configuration;

public class DropTestConfiguration extends Configuration {

    /**Read from the configuration file*/
    private String template;

    public String getTemplate() {
        return template;


By doing this, you can read this in the Application class etc. and use it.

3-2. Application class creation

Create an Application class that is positioned to be the main class in Java. Here, the main function, bundle settings, and resource class registration are performed. I haven't created the resource class yet, so I'll comment it out.


package dropTest.priv.jp.y.suzuki;

import io.dropwizard.Application;
import io.dropwizard.assets.AssetsBundle;
import io.dropwizard.setup.Bootstrap;
import io.dropwizard.setup.Environment;

public class DropTestApplication extends Application<DropTestConfiguration> {
  //Main settings
  public static void main(String[] args) throws Exception {
    new DropTestApplication().run(args);

  //Bundle settings
  public void initialize(Bootstrap<DropTestConfiguration> bootstrap) {
    bootstrap.addBundle(new AssetsBundle("/assets", "/", "index.html"));
    bootstrap.addBundle(new AssetsBundle("/assets/css", "/css", null, "css"));
    bootstrap.addBundle(new AssetsBundle("/assets/js", "/js", null, "js"));

  //Resource class registration
  public void run(DropTestConfiguration conf, Environment env) throws Exception {
    //Get the information read from the configuration file
    String template = conf.getTemplate();
    System.out.println(template); //Whether it could be read
    // env.jersey().register(new SampleResource());


4. Create server-side socket

Create a resource class that has the role of receiving values from the screen side. The place of creation is as follows.

Creation location: dropTest.priv.jp.y.suzuki.resource

This time, it takes a value and returns it with "" input word: "".


package dropTest.priv.jp.y.suzuki.resource;

import javax.ws.rs.Consumes;
import javax.ws.rs.POST;
import javax.ws.rs.Path;
import javax.ws.rs.PathParam;
import javax.ws.rs.Produces;
import javax.ws.rs.core.MediaType;

public class SampleResource {

	public String responseMessage(@PathParam("sentence") String sentence) {
		String message = "Input word:" + sentence;
		return message;

The above points are various annotations.

--@POST specifies that the call should be made only during POST communication. --@Consumes @Produces specifies the input / output format. This time, JSON format and TEXT format are specified. --@PathParam is specified to receive the value from the screen, and the {sentence} part is acquired with the specified type (String this time). --@Path specifies the call target during REST communication by URL

In this case, this resource class is / message and the method you want to execute is/ response / {sentence}. Therefore, it is assumed to be executed with the following URL including the root path specified in the yml file.

POST communication: / api / message / response /" input statement "

Finally, register the resource class with the Application class created so far, and you're done.


import dropTest.priv.jp.y.suzuki.resource.SampleResource;

  // ~Omission~

  //Resource class registration
  public void run(DropTestConfiguration conf, Environment env) throws Exception {
    //Get the information read from the configuration file
    String template = conf.getTemplate();
    System.out.println(template); //Whether it could be read
    env.jersey().register(new SampleResource()); //Validate what was commented out earlier


5. Screen creation

Here, html and javascript are described as screen creation. First, create a folder called ʻassets under src / main / resources. Create a ʻindex.html file and ajs folder under the created ʻassets, Create a javascript file that describes the movement of ʻindex.html under the created js folder (this time ʻindex.js`).

Package example: src/main/resources   |__ assets     |__ index.html     |__ js       |__ index.js

5-1. Create index.html

This time, I will create a simple one that displays the input field, the submit button, and the characters returned from the server. It is assumed that jQuery will be used for screen display and REST communication. Therefore, [Download] jQuery (https://code.jquery.com/jquery-3.2.1.min.js) and place it in the js file.

<!DOCTYPE html>
<meta charset="UTF-8">
  <script src="js/jquery-3.2.1.min.js"></script>
  <script src="js/index.js"></script>
<input type="text" id="inputSentence"><br>
<input type="button" id="start" value="REST communication"><br>

<div><span id="result">The response content is written here</span></div>


5-2. Create index.js

Here, when the button is pressed, REST communication is executed and the result is output. This time, we will use jQuery ajax.


/**Responds to button press*/
$(document).on('click', '#start', function() {
  var SendData = $("#inputSentence").val();
  Request("/api/message/response/" + SendData, "POST", null, resultOpen, FailAnon);
  return false;

/**for ajax*/
function Request(Uri, Method, Data, CallbackFunc, ErrorCallbackFunc) {
    url:  Uri,
    type: Method,
    data: Data,
    contentType: "application/json; charset=utf-8",
    cache: false
    return false;
  }).fail(function(XMLHttpRequest, textStatus, errorThrown) {
    return false;
  return false;

/**Called when ajax fails*/
function FailAnon() {
  $("#result").html("<b>ERROR!</b>Communication failed");
  return false;

/**Display the result*/
function resultOpen(response) {
  $("#result").html(response + "<br>");
  return false;

6. Build

Build the completed application. Build is done with Maven. Build from the project directory with the following command. If "BUILD SUCCESS" is displayed, it is successful. You should have a jar file under your target directory.

Build command: maven package

7. Run

Two files are required for execution. There are two files, a jar file created by the build and a yaml file that is a configuration file.

The execution command is as follows.

Execution command example: java -jar target / droptest-0.0.1-SNAPSHOT.jar server config.yml

At the end

When the startup is completed successfully, let's actually open the Web and check it. If you cannot connect, it is easy to understand the cause by using the output log or the developer mode such as F12.


By the way, the launched app can be stopped by the Ctrl + c command like many apps.

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