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

Brad Maxwell

> The `ejb-throws-exception` quickstart demonstrates how to throw and handle exceptions across JARs in an EAR.

## 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 WildFly Application Server. 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.

This example consists of the following Maven projects, each with a shared parent.

Project | Description
--- | ---
`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`. If the `name` is not null or an empty String, it returns `Hello <name>`. If the `name` is null or an empty String, it throws a custom `GreeterException` exception back to the client.
`web` | This project contains the JSF pages and the CDI managed bean. The CDI Managed Bean, `GreeterBean`, is bound to the JSF page, `index.xhtml`. It invokes the `GreeterEJB` and displays the response back from the EJB. The `GreeterBean` catches the custom `GreeterException` exception thrown by `GreeterEJB` and displays the exception message in the response text on the JSF page.
`ear` | This project builds the EAR artifact and pulls in the ejb, web, and client artifacts.
`ejb-api` | This project builds the ejb-api library artifact which is used by the ejb, web, as well as remote client artifacts. This 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, using the following workflow.

1. A JSF page asks for a 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 that the field is 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 WildFly Application Server 12 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 to Build and Deploy the Quickstarts to make sure you are configured correctly for testing the quickstarts.

## Use of WILDFLY_HOME

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

## Start the WildFly Standalone Server

1. Open a terminal and navigate to the root of the WildFly directory.

2. Start the WildFly server with the default profile by typing the following command.

       $ WILDFLY_HOME/bin/standalone.sh

   Note | For Windows, use the `WILDFLY_HOME\bin\standalone.bat` script.

## Build and Deploy the Quickstart

1. Make sure you start the WildFly server as described above.

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

3. Type the following command to build the artifacts.

       $ mvn clean install wildfly:deploy

This deploys the `ejb-throws-exception/ear/target/ejb-throws-exception.ear` to the running instance of the server.

You should see a message in the server log indicating that the archive deployed successfully.

## 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 Quickstart

When you are finished testing the quickstart, follow these steps to undeploy the archive.

1. Make sure you start the WildFly server as described above.

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

3. 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 in Red Hat JBoss Developer Studio or from Eclipse using JBoss tools. For general information about how to import a quickstart, add a WildFly 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