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ejb-throws-exception: Handle Exceptions across JARs in an EAR

Author: Brad Maxwell
Level: Intermediate
Technologies: EJB, EAR
Summary: The ejb-throws-exception quickstart demonstrates how to throw and handle Exceptions across JARs in an EAR.
Target Product: JBoss EAP
Source: https://github.com/jboss-developer/jboss-eap-quickstarts/

What is it?

The ejb-throws-exception quickstart extends the ejb-in-ear quickstart and demonstrates how to handle Exceptions across JARs in an EAR deployed to Red Hat JBoss Enterprise Application Platform. In this quickstart, an EJB in the EJB JAR throws a custom Exception. The web application in the client JAR catches the Exception and displays it in a nicely formatted message. The EAR contains: JSF WAR, an EJB JAR and a client library JAR containg classes that both the WAR and EJB JAR use.

The example is composed of three Maven projects, each with a shared parent. The projects are as follows:

  1. ejb: This project contains the EJB code and can be built independently to produce the JAR archive. The EJB has a single method sayHello which will take in a String name and return Hello <name> if the name is not null or an empty String. If the name is null or an empty String, then it will throw a custom Exception (GreeterException) back to the client.

  2. web: This project contains the JSF pages and the CDI managed bean. The CDI Managed Bean (GreeterBean) will be bound to the JSF page (index.xhtml) and will invoke the GreeterEJB and display the response back from the EJB. The GreeterBean catches the custom Exception (GreeterException) thrown by GreeterEJB and displays the Exception message in the response text on the JSF page.

  3. ear: This project builds the EAR artifact and pulls in the ejb, web, and client artifacts.

  4. ejb-api: This project builds the ejb-api library artifact which is used by the ejb, web, as well as remote client artifacts. The ejb-api directory contains the EJB interfaces, custom exceptions the EJB throws and any other transfer objects which the EJB may receive or send back to the client. The EJB interfaces, custom exceptions, and other transfer objects are split into a separate JAR which is packaged in the ear/lib. This allows all sub deployments of the EAR to see the classes of the ejb-api JAR in the classpath. This is also useful for remote clients. The ejb-api JAR can be distributed to a remote client and give the remote clients the classes that are needed to interact with the EJB.

The root pom.xml builds each of the subprojects in the above order and deploys the EAR archive to the server.

The example follows the common Hello World pattern. These are the steps that occur:

  1. A JSF page (http://localhost:8080/ejb-throws-exception/) asks for the user name.
  2. On clicking Say Hello, the value of the Name input text is sent to a managed bean named GreeterBean.
  3. On setting the name, the Greeter invokes the GreeterEJB, which was injected to the managed bean. Notice the field annotated with @EJB.
  4. The EJB responds with Hello <name> or throws an Exception if the name is empty or null.
  5. The response or exception's message from invoking the GreeterEJB is stored in a field (response) of the managed bean.
  6. The managed bean is annotated as @RequestScoped, so the same managed bean instance is used only for the request/response.

System Requirements

The application this project produces is designed to be run on Red Hat JBoss Enterprise Application Platform 7.1 or later.

All you need to build this project is Java 8.0 (Java SDK 1.8) or later and Maven 3.3.1 or later. See Configure Maven for JBoss EAP 7.1 to make sure you are configured correctly for testing the quickstarts.

Use of EAP7_HOME

In the following instructions, replace EAP7_HOME with the actual path to your JBoss EAP installation. The installation path is described in detail here: Use of EAP7_HOME and JBOSS_HOME Variables.

Start the Server

  1. Open a command prompt and navigate to the root of the JBoss EAP directory.

  2. The following shows the command line to start the server:

     For Linux:   EAP7_HOME/bin/standalone.sh
 For Windows: EAP7_HOME\bin\standalone.bat

Build and Deploy the Quickstart

  1. Make sure you have started the JBoss EAP server as described above.

  2. Open a command prompt and navigate to the root directory of this quickstart.

  3. Type this command to build and deploy the archive:

     mvn clean install wildfly:deploy

  4. This will deploy ear/target/ejb-throws-exception.ear to the running instance of the server.

Access the Application

The application will be running at the following URL http://localhost:8080/ejb-throws-exception/.

Enter a name in the input field Name and click the Say Hello button to see the response.

The Response output text will display the response from the EJB. If the Name input text box is not empty, then the Response output text will display Hello <name> If the Name input text box is empty, then the Response output text will display the message of the exception throw back from the EJB.

Undeploy the Archive

  1. Make sure you have started the JBoss EAP server as described above.

  2. Open a command prompt and navigate to the root directory of this quickstart.

  3. When you are finished testing, type this command to undeploy the archive:

     mvn wildfly:undeploy

Run the Quickstart in Red Hat JBoss Developer Studio or Eclipse

You can also start the server and deploy the quickstarts or run the Arquillian tests from Eclipse using JBoss tools. For general information about how to import a quickstart, add a JBoss EAP server, and build and deploy a quickstart, see Use JBoss Developer Studio or Eclipse to Run the Quickstarts.

For this quickstart, follow the special instructions to build Quickstarts Containing an EAR

  1. Right-click on the ejb-throws-exception-ear subproject, and choose Run As --> Run on Server.
  2. Choose the server and click Finish.
  3. This starts the server, deploys the application, and opens a browser window that accesses the running application.
  4. To undeploy the project, right-click on the ejb-throws-exception-ear project and choose Run As --> Maven build. Enter wildfly:undeploy for the Goals and click Run.

Debug the Application

If you want to debug the source code of any library in the project, run the following command to pull the source into your local repository. The IDE should then detect it.

    mvn dependency:sources