Creating a multi-module application

duration 30 minutes

You will learn how to build an application with multiple modules with Maven and Open Liberty.

What you’ll learn

A Java Platform, Enterprise Edition (Java EE) application consists of modules that work together as one entity. An enterprise archive (EAR) is a wrapper for a Java EE application, which consists of web archive (WAR) and Java archive (JAR) files. Package modules and resources into an EAR file to deploy or distribute the Java EE application to new environments.

You will learn how to establish a dependency between a web module and a Java library module. Next, use Maven to package the WAR file and the JAR file into an EAR file so that you can run and test the application on Open Liberty.

You will build a unit converter application that converts heights from centimeters into feet and inches. Enter heights in centimeters from a web page, and the application processes the input with functions in the JAR file to return the corresponding height in Imperial units.

When the application is running, you can access the unit converter at the following location:


Getting started

The fastest way to work through this guide is to clone the Git repository and use the projects that are provided inside:

git clone
cd guide-maven-multimodules

The start directory contains the starting project that you will build upon.

The finish directory contains the finished project, which is what you will build.

Access partial implementation of the application from the start folder. This folder includes a web module in the war folder, a Java library in the jar folder, and template files in the ear folder. However, the Java library and the web module are independent projects, and you will need to complete the following steps to implement the application:

  1. Add a dependency relationship between two modules.

  2. Assemble the entire application into an EAR file.

  3. Test the multi-module application.

  4. Aggregate the entire build.

Adding dependencies between WAR and JAR modules

To use the Java library in your web module, add a dependency relationship between them.

As you might notice, each module has its own pom.xml file because each module is treated as an independent project. You can rebuild, reuse, and reassemble every module on its own.

Open the pom.xml file of your WAR module. Go to the dependency section, where you can add more dependencies. Enter the following lines to add the Java library module that implements the functions that you need for the unit converter:


After you add the dependency, use any functions included in the library in the class of the web module.

In the start/war/src/main/java/io/openliberty/guides/multimodules/web/ class, add the following line to the setHeightFeet method to convert a measurement into feet:

this.feet = io.openliberty.guides.multimodules.lib.Converter.getFeet(cm);

Then, add the following line to the setHeightInches method to convert a measurement into inches:

this.inches = io.openliberty.guides.multimodules.lib.Converter.getInches(cm);

Assembling multiple modules into an EAR file

To deploy the entire application on the Open Liberty server, first package the application. Use the EAR project to assemble multiple modules into an EAR file.

Navigate to the ear folder and find a template pom.xml file. In the pom.xml file, set the basic configuration for the project and set the packaging type to ear:


Next, add the dependencies. Define the web module and the Java library module as dependencies. Specify <type>war</type> for the web module. If you don’t specify the web module, Maven looks for a JAR file.


Add the definition and configuration of the maven-ear-plugin plug-in for creating an EAR file. Define the <webModule> and <jarModule> modules to be packaged into the EAR file. To customize the context root of the application, set the appropriate contextRoot in the webModule. Otherwise, Maven automatically uses the WAR file artifactId ID as the context root for the application while generating the application.xml file.

        <!-- Set custom context root -->

To download and start an Open Liberty server, use the liberty-maven-plugin plug-in for Maven. This configuration is provided, and the executions of the plug-in follow the typical phases of a Maven life cycle.

To deploy the EAR application, create a server.xml file to configure the server. Add the following lines to the server.xml file in the start/ear/src/main/liberty/config directory:

<!-- To access this server from a remote client add a host attribute to the following
  element, e.g. host="*" -->
<httpEndpoint host="*" httpPort="${default.http.port}" httpsPort="${default.https.port}"
  id="defaultHttpEndpoint" />

<enterpriseApplication id="io.openliberty.guides.multimodules.ear"
  location="io.openliberty.guides.multimodules.ear-0.0.1-SNAPSHOT.ear" name="io.openliberty.guides.multimodules.ear" />

Building the modules

To build the three modules, run the following commands from the jar directory, war directory, and ear directory in that order. Start with the jar directory, proceed to the war directory, and end with the ear directory.

mvn clean install

These commands create a JAR file in the jar/target directory, a WAR file in the war/target directory, and an EAR file in the ear/target directory, which contains the JAR and WAR files.

Starting the application

To deploy your EAR application on an Open Liberty server, run the Maven liberty:start-server goal from the ear directory:

# Change directory if necessary
cd ../../start/ear

mvn liberty:start-server

Once the server is running, you can find the application at the following URL:


To stop the server, enter the following command:

mvn liberty:stop-server

Testing the multi-module application

To test the multi-module application, add integration tests to the EAR project.

Navigate to the start/ear/src/test/java/it/io/openliberty/guides/multimodules directory. Open the file. Helper functions for the integration test class are provided.

Add the testIndexPage test to check that you can access the landing page:

public void testIndexPage() throws Exception {
  String url = this.urlBase;
  HttpURLConnection con = testRequestHelper(url, "GET");
  assertEquals("Incorrect response code from " + url, 200, con.getResponseCode());
  assertTrue("Incorrect response from " + url,
      testBufferHelper(con).contains("Enter the height in centimeters"));

Add the testHeightsPage test to check that the application can process the input value and calculate the result correctly:

public void testHeightsPage() throws Exception {
  String url = this.urlBase + "heights.jsp?heightCm=10";
  HttpURLConnection con = testRequestHelper(url, "POST");
  assertTrue("Incorrect response from " + url,
      testBufferHelper(con).contains("3    inches"));

For a Maven EAR project, specify the testCompile goal for the maven-compiler-plugin plug-in so that the test cases are compiled and picked up for execution.


Enter the following command to run the test from the start/ear directory:

mvn verify

If the tests pass, you will see a similar output to the following:

 T E S T S
Tests run: 2, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.712 sec - in

Results :

Tests run: 2, Failures: 0, Errors: 0, Skipped: 0

Aggregating the entire build

Because you have multiple modules, aggregate the Maven projects to simplify the build process.

Create a parent pom.xml file under the start directory to link all of the child modules together. A template is provided for you.

Set pom as the <packaging> of the parent pom.xml file. Specify io.openliberty.guides as the groupId ID, which the child pom.xml files will inherit.


In the parent pom.xml file, list all of the modules that you want to aggregate for the application:


Lastly, add a parent section to each of the pom.xml files in the child modules, such as the jar, war, and ear projects:


Building the application

Use the following command to build the entire application from the start directory:

mvn clean install

You no longer need to execute multiple mvn install commands from different directories. With a single command, you can build and test the whole application and all of the modules.

Great work! You’re done!

You built and tested a multi-module unit converter application on the Open Liberty runtime with Maven.

Contribute to this guide

Is something missing or broken? Raise an issue, or send us a pull request.