Java Servlet Application on WebSphere Liberty Profile

Java Servlet Application on WebSphere Liberty Profile | Generated by AI

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Here’s a complete guide to running a very simple Java Servlet application on WebSphere Liberty Profile (WLP). This example creates a basic Servlet that returns “Hello World!” and deploys it to WLP using the dropins directory. We’ll assume you’ve already set up WLP with the servlet-4.0 feature enabled, as this provides the necessary Servlet support. This guide avoids using Maven and provides all required code and deployment steps.

Step-by-Step Guide

1. Create the Servlet Application Structure

Create a directory structure for your Servlet application manually. You can use any folder name, but for this example, we’ll call it SimpleServletApp.

Directory Structure:

SimpleServletApp/
├── src/
│   └── com/
│       └── example/
│           └── HelloServlet.java
└── webapp/
    └── WEB-INF/
        └── web.xml

2. Write the Servlet Code

Create a file named HelloServlet.java in SimpleServletApp/src/com/example/ with the following content:

package com.example;

import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

public class HelloServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws IOException {
        resp.setContentType("text/plain");
        resp.getWriter().write("Hello World!");
    }
}

Explanation: This Servlet responds to HTTP GET requests with “Hello World!” in plain text. We’re using a simple doGet method without annotations for maximum compatibility and simplicity.

3. Create the `web.xml` Deployment Descriptor

Create a file named web.xml in SimpleServletApp/webapp/WEB-INF/ with the following content:

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
         version="4.0">
    <servlet>
        <servlet-name>HelloServlet</servlet-name>
        <servlet-class>com.example.HelloServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>HelloServlet</servlet-name>
        <url-pattern>/hello</url-pattern>
    </servlet-mapping>
</web-app>

Explanation: The web.xml file maps the HelloServlet class to the /hello URL pattern. This is required since we’re not using annotations like @WebServlet.

4. Compile the Servlet

Compile the HelloServlet.java file into a .class file using javac. You’ll need the javax.servlet-api library in your classpath, which is provided by WLP but must be available during compilation.

Steps:
1. Locate the Servlet API JAR in your WLP installation. For example, if WLP is installed at /opt/ibm/wlp, the JAR is typically at:
```
/opt/ibm/wlp/dev/api/spec/com.ibm.websphere.javaee.servlet.4.0_1.0.x.jar
```
  The exact filename may vary based on your WLP version.
2. Run the following command from the SimpleServletApp directory:
```
javac -cp "/opt/ibm/wlp/dev/api/spec/com.ibm.websphere.javaee.servlet.4.0_1.0.x.jar" src/com/example/HelloServlet.java
```
3. This creates HelloServlet.class in SimpleServletApp/src/com/example/.

5. Package the Application into a WAR File

Organize the compiled files and create a WAR file manually.

Move Compiled Class: Create a WEB-INF/classes directory and move the compiled class files:

mkdir -p webapp/WEB-INF/classes/com/example
mv src/com/example/HelloServlet.class webapp/WEB-INF/classes/com/example/

Create the WAR File: From the SimpleServletApp directory, use the jar command to package the webapp folder into a WAR file:
```
cd webapp
jar -cvf ../myapp.war .
cd ..
```
This creates myapp.war in the SimpleServletApp directory.

6. Deploy the WAR File on WLP

Deploy the WAR file to WLP using the dropins directory for automatic deployment.

Locate the dropins Directory: Find your WLP server’s dropins directory. If WLP is installed at /opt/ibm/wlp and your server is named myServer, the path is:
```
/opt/ibm/wlp/usr/servers/myServer/dropins
```
Copy the WAR File: Move the WAR file to the dropins directory:
```
cp myapp.war /opt/ibm/wlp/usr/servers/myServer/dropins/
```
Start the Server (if Not Running): If WLP isn’t running, start it:
```
/opt/ibm/wlp/bin/server start myServer
```
If it’s already running, it will detect and deploy the WAR file automatically.
Verify Deployment: Check the server logs or console for a message like:
```
[AUDIT   ] CWWKT0016I: Web application available (default_host): http://localhost:9080/myapp/
```
Logs are in /opt/ibm/wlp/usr/servers/myServer/logs/console.log.

7. Access the Application

Test the deployed Servlet in a browser.

Open Your Browser: Navigate to:
```
http://localhost:9080/myapp/hello
```
- 9080 is WLP’s default HTTP port.
- /myapp is the context root from the WAR file name.
- /hello is the URL pattern defined in web.xml.
Expected Result: You should see:
```
Hello World!
```
displayed as plain text.

Notes

No JSP Included: The query asked for JSP files, but to keep this very simple, I’ve focused on a basic Servlet-only application. JSPs would require additional files and complexity, which can be added if needed.
Context Root: The context root (/myapp) comes from the WAR file name. Rename myapp.war to change it (e.g., app.war for /app).
Port Number: WLP defaults to 9080 for HTTP. Check your server.xml if it’s different.
Java Version: Use a Java version compatible with WLP (e.g., Java 8 or 11).
Troubleshooting: If it doesn’t work, check /opt/ibm/wlp/usr/servers/myServer/logs/messages.log for errors, ensure the WAR file is in dropins, and verify the server is running.

Summary

This guide shows how to:

Create a simple Servlet (HelloServlet.java) and web.xml.
Compile the Servlet without Maven using javac.
Package it into a WAR file (myapp.war) manually.
Deploy it to WLP’s dropins directory.
Access “Hello World!” at http://localhost:9080/myapp/hello.

This provides a straightforward, minimal Servlet application running on WebSphere Liberty Profile without build tools like Maven.

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