deltaspike-exception-handling: An example how to use DeltaSpike exception handling

Author: Rafael Benevides Level: Intermediate Technologies: CDI, JSF, DeltaSpike Summary: Exception being handled by different handlers and purpose Prerequisites: Target Product: WFK

What is it?

This quickstart demonstrates exception handling with Java EE and CDI using the DeltaSpike library. Exception handling is based around the CDI eventing model.

The entire exception handling process starts with an event. This means your application is not tightly coupled to DeltaSpike, and allows for further extension. Exception handling in DeltaSpike aims to keep out of your way, and let you handle exceptions the way that makes the most sense to you. The eventing model allows for this delicate balance; firing an event is the main way to start handling an exception.

The quickstart can be told to throw two Exceptions: MyException and MyOtherException. And there are 4 different handlers:

• FacesExceptionHandler - Displays each exception on the page using a Faces. Only handles @FacesRequest exceptions.
• LogExceptionHandler - Logs each exception to the server console.
• MyExceptionCountHandler - Counts the the number of times MyException is thrown. This handler is also a CDI bean with a name.
• RestExceptionHandler - Produces a javax.ws.rs.core.Response which encapsulates the error, using a ResponseBuilder. Only handles @RestRequest exceptions.

Any exceptions from the REST endpoint are passed to the DeltaSpikeExceptionMapper (a JAX-RS exception mapper), which fires an exception event, which is observed by all relevant exception handlers. Of particular interest is the RestExceptionHandler which uses the ResponseBuilderProducer to create a instance of a javax.ws.rs.core.Response. The built response is then returned to the client by the RestExceptionMapper.

Any exceptions from beans invoked by JSF are passed to the DeltaSpikeExceptionHandler which fires an exception event, which is observed by all relevant exception handlers. Of particular interest is the FacesExceptionHandler which builds and registers some FacesMessages.

System requirements

All you need to build this project is Java 6.0 (Java SDK 1.6) or better, Maven 3.0 or better.

The application this project produces is designed to be run on JBoss Enterprise Application Platform 6 or JBoss AS 7.

Configure Maven

If you have not yet done so, you must Configure Maven before testing the quickstarts.

Start JBoss Enterprise Application Platform 6 or JBoss AS 7

1. Open a command line and navigate to the root of the JBoss server directory.

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

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

Build and Deploy the Quickstart

NOTE: The following build command assumes you have configured your Maven user settings. If you have not, you must include Maven setting arguments on the command line. See Build and Deploy the Quickstarts for complete instructions and additional options.

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

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

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

    mvn clean package jboss-as:deploy
   

4. This will deploy target/jboss-as-ds-exception-handling.war to the running instance of the server.

Access the application

Access the running application in a browser at the following URL: http://localhost:8080/jboss-as-ds-exception-handling

You will be presented with a form that contains two buttons. One button throws the exception MyException. The other button throws the exception MyOtherException.

When you click on a button, a message is displayed showing the exception message followed by the number of times the service was invoked. Notice that the MyException counter is only incremented when MyException is thrown. You can also view the exception messages in the server log.

Click on REST Invocation Test link. The rest response is displayed on the iframe bellow.

Undeploy the Archive

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

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

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

    mvn jboss-as:undeploy
   

Run the Quickstart in JBoss Developer Studio or Eclipse

You can also start the server and deploy the quickstarts from Eclipse using JBoss tools. For more information, see Use JBoss Developer Studio or Eclipse to Run the Quickstarts

Debug the Application

If you want to debug the source code or look at the Javadocs of any library in the project, run either of the following commands to pull them into your local repository. The IDE should then detect them.

mvn dependency:sources
mvn dependency:resolve -Dclassifier=javadoc