Embedding Tomcat Into Java Applications
Pages: 1, 2
You should begin your examination of the
source with the
main() method. This method first creates an instance of the
EmbeddedTomcat class. It then sets the path of the Tomcat installation that will be hosting our Tomcat instance. This path is equivalent to the
environment variable. The next action performed by the
main() method is to invoke the
startTomcat() method. This is the method that implements the container-construction steps described earlier. The steps performed by this method are listed below.
main()method begins by setting the system property to the value of the path attribute:
// Set the home directory System.setProperty("catalina.home", getPath());
Make sure you use the value of
<CATALINA_HOME>as the directory value passed to the
The next step performed by this method is to create an instance of the
Embeddedobject and set the debug level and current logger.
// Create an embedded server embedded = new Embedded(); embedded.setDebug(5); // print all log statments to standard error embedded.setLogger(new SystemOutLogger());
The debug level should be
0, when deploying a production Web application. Setting the debug level to
0reduces the amount of logging performed by Tomcat, which will improve performance significantly.
After the application has an instance of the
Embeddedobject, it creates an instance of an
org.apache.catalina.Engineand sets the name of the default host. The
Engineobject represents the entire Catalina servlet container.
// Create an engine engine = embedded.createEngine(); engine.setDefaultHost("localhost");
Enginehas been instantiated, we create an
localhost, with a path pointing to the
<CATALINA_HOME>/webapps/directory, and add it the
Hostobject defines the virtual hosts that are contained in each instance of a Catalina Engine.
// Create a default virtual host host = embedded.createHost("localhost", getPath() + "/webapps"); engine.addChild(host);
The next step performed by the
startTomcat()method is to create an
org.apache.catalina.Contextobject, which represents the
ROOTWeb application packaged with Tomcat, and add it the to the previously created
ROOTWeb application is the only application that will be installed by default.
// Create the ROOT context Context context = embedded.createContext("", getPath() + "/webapps/ROOT"); host.addChild(context);
The next step adds the
Enginecontaining the created
// Install the assembled container hierarchy embedded.addEngine(engine);
After the engine is added to the
startTomcat()method creates an
org.apache.catalina.Connectorobject and associates it with the previously created
<Connector>element defines the class that does the actual handling of requests and responses to and from a calling client application. In the following snippet, an HTTP connector that listens to port 8080 is created and added to the
// Assemble and install a default HTTP connector Connector connector = embedded.createConnector(null, 8080, false); embedded.addConnector(connector);
The final step performed by the
startTomcat()method starts the Tomcat container.
startTomcat() returns, the main method calls the
method, which installs the previously deployed
onjava application to the
Embedded object. The URL used in this example can point to any Webapp directory that follows the specification for Java Servlet 2.2 and later.
URL url = new URL("file:D:/jakarta-tomcat-4.0.1" + "/webapps/onjava"); tomcat.registerWAR("/onjava", url);
The main application is then put to sleep to allow the embedded server time to service requests. When the application awakes, the embedded server is stopped and the application exits.
To test this application, you must complete the following steps:
- Compile the
- Make sure all other instances of Tomcat are shut down.
- Add the following jar files, all of which can be found in the Tomcat installation, to your application classpath.
- Make sure that your classpath includes the directory containing the compiled
- Execute the following command:
If everything went according to plan, you should see some log statements in the console window:
HttpProcessor Starting background thread HttpProcessor Background thread has been started HttpProcessor Starting background thread HttpProcessor Background thread has been started HttpProcessor Starting background thread HttpProcessor Background thread has been started HttpProcessor Starting background thread HttpProcessor Background thread has been started HttpProcessor Starting background thread HttpProcessor Background thread has been started
Once you see the previous text, you will be able to access the
/onjava Web applications using the following URLs:
onjavaapplication that we are using throughout this article is the Web application from my previous Tomcat articles.
Up next: in the next Tomcat article, we will continue our embedded discussions by debugging a Web application that is running in our embedded container.
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