Java Servlets Examples

Here you can find the example Java Servlets from my distributed computing class. The project is built using Maven.

1. Examples

1.1. HelloWorldServlet

This small servlet accepts an incoming HTTP request and sends back a Hello World message in text/plain format.

If your application is running in GlassFish, you can access this servlet as http://localhost:8080/myServlets/HelloWorld.

1. HelloWorldServlet

1.2. RequestDataServlet

This servlet is similar to our MinHTTPServer.java example in the Java sockets example set. It accepts an incoming HTTP request and dynamically creates a text/html formatted response (i.e., a web page). This web page contains all the request's data, such as the client address, all request headers, cookies, and dynamic query parameters (such as form data).

If your application is running in GlassFish, you can access this servlet as http://localhost:8080/myServlets/RequestData.

1. RequestDataServlet

1.3. SessionDataServlet

This servlet shows how sessions can be handled with Java Servlets. It accepts an incoming connection and dynamically creates a text/html formatted response (i.e., a web page). This web page contains all the information of (and stored in) the current session. The first time you access this servlet, there is no current session, so it is created. This session initially has no information stored in it in form of attributes. However, this servlet adds some attributes to the session. The next time you access this servlet, these attributes will be printed. Hence, sessions are a way to preserve information between HTTP requests to a servlet.

If your application is running in GlassFish, you can access this servlet as http://localhost:8080/myServlets/SessionData.

1. SessionDataServlet

2. Building and Deployment

2.1. Import Project into Eclipse

If you import this project in Eclipse, it may first show you a lot of errors. (I recommend using Eclipse Mars or later.) This is a Maven project, so you should "update" it first in Eclipse by

1. Make sure that you can see the package view on the left-hand side of the Eclipse window.
2. Right-click on the project (JavaServlets) in the package view.
3. In the opening pop-up menu, left-click on Maven.
4. In the opening sub-menu, left-click on Update Project....
5. In the opening window...
6. Make sure the project (JavaServlets) is selected.
7. Make sure that Update project configuration from pom.xml is selected.
8. You can also select Clean projects.
9. Click OK.
10. Now the structure of the project in the package view should slightly change, the project will be re-compiled, and the errors should disappear.

2.2. Build Project in Eclipse

Now you can actually build the project, i.e., generate a war file that you can deploy in a servlet container. For building this war, take the following steps:

1. Make sure that you can see the package view on the left-hand side of the Eclipse window.
2. Right-click on the project (JavaServlets) in the package view.
3. In the opening pop-up menu, choose Run As.
4. In the opening sub-menu choose Run Configurations....
5. In the opening window, choose Maven Build
6. In the new window Run Configurations / Create, manage, and run configurations, choose Maven Build in the small white pane on the left side.
7. Click New launch configuration (the first symbol from the left on top of the small white pane).
8. Write a useful name for this configuration in the Name field. You can use this configuration again later.
9. In the tab Main enter the Base directory of the project, this is the folder called javaServlets containing the Eclipse/Maven project.
10. Under Goals, enter clean compile war:war. This will build a war archive.
11. Click Apply
12. Click Run
13. The build will start, you will see its status output in the console window.
14. The folder target will contain a file myServlets.war after the build. This is the deployable archive with our application.

2.3. Building under Linux without Eclipse

Under Linux, you can also simply run make_linux.sh in this project's folder to build the servlet without Eclipse, given that you have Maven installed.

2.4. Deploy

2.4.1. Deploy to GlassFish

GlassFish is a reference implementation of a Java EE 7 application server.

2.4.1.1. Install GlassFish

The following steps are for Linux, but under Windows it will be pretty much the same.

1. Go to the GlassFish website https://glassfish.java.net/.
2. Select download.
3. Download the Java EE 7 Web Profile, at the time of this writing, this is GlassFish 4.1.1
4. Unpack the downloaded archive into a folder of your liking (let's call this folder F).
5. Open a terminal console and go (cd) into folder F.
6. In the folder F (where you unpackaged the archive), go to sub-folder glassfish4/bin/, i.e., to F/glassfish4/bin/.
7. Type ./asadmin start-domain. (Under Windows, type asadmin start-domain without the leading ./.) The server will now start.
8. Under Windows, a window may pop up asking you for allowing the program internet access permission, which you should OK.
9. Open your web browser and visit its configuration page at http://localhost:4848.

2.4.1.2. Deploy war to GlassFish

1. Find the file myServlets.war in the folder target of this example project.

2. Copy it into the folder F/glassfish4/glassfish/domains/domain1.

3. In your web browser, visit http://localhost:4848.

4. Click Applications in the menu pane on the right.

5. It should list myServlets. If you click this menu point, you get a list of the installed servlets.

6. You can access the servlets as follows

7. http://localhost:8080/myServlets/HelloWorld

8. http://localhost:8080/myServlets/RequestData

9. http://localhost:8080/myServlets/SessionData

3. Stand-alone Java Servlets?

In the stand-alone JSPs example in the JavaServer Pages example set, I describe how stand-alone JavaServer Pages (JSPs) can be built with Jetty. These are JSPs which do not need to be deployed but where the whole application server is packaged into one jar archive also including the JSPs. You just need to start this jar to get the application running. Of course, you can modify this example to serve Java Servlets instead rather easily