servlet-async: How to Write an Asynchronous Servlet

Author: Christian Sadilek
Level: Intermediate
Technologies: Asynchronous Servlet, CDI, EJB
Summary: The servlet-async quickstart demonstrates how to use asynchronous servlets to detach long-running tasks and free up the request processing thread.
Target Product: JBoss EAP
Source: https://github.com/jboss-developer/jboss-eap-quickstarts/

What is it?

The servlet-async quickstart is a sample project showing the use of asynchronous servlets in Red Hat JBoss Enterprise Application Platform.

It shows how to detach the execution of a long-running task from the request processing thread, so the thread is free to serve other client requests. The long-running tasks are executed using a dedicated thread pool and create the client response asynchronously.

A long-running task in this context does not refer to a computation intensive task executed on the same machine but could for example be contacting a third-party service that has limited resources or only allows for a limited number of concurrent connections. Moving the calls to this service into a separate and smaller sized thread pool ensures that less threads will be busy interacting with the long-running service and that more requests can be served that do not depend on this service.

System requirements

The application this project produces is designed to be run on Red Hat JBoss Enterprise Application Platform 6.1 or later.

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

Configure Maven

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

Use of EAP_HOME

In the following instructions, replace EAP_HOME with the actual path to your JBoss EAP 6 installation. The installation path is described in detail here: Use of EAP_HOME and JBOSS_HOME Variables.

Start the JBoss EAP Server

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

The following shows the command line to start the server:

For Linux:   EAP_HOME/bin/standalone.sh
For Windows: EAP_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.

Make sure you have started the JBoss EAP server as described above.
Open a command prompt and navigate to the root directory of this quickstart.
Type this command to build and deploy the archive:
```
mvn clean install jboss-as:deploy
```
This will deploy target/jboss-servlet-async.war to the running instance of the server.

Access the application

The application will be running at the following URL http://localhost:8080/jboss-servlet-async/.

Undeploy the Archive

Make sure you have started the JBoss EAP server as described above.
Open a command prompt and navigate to the root directory of this quickstart.
When you are finished testing, type this command to undeploy the archive:
```
mvn jboss-as: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

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