Monday, September 27, 2010

How to Create an Executable WAR

Have you ever wondered how Hudson let you run a WAR file as if you run an executable JAR file? The answer is simple, i.e. embed a web container inside a WAR file and create a META-INF/MANIFEST.MF that has Main-Class attribute. For Hudson, it embeds Winstone. In this example, I'm gonna use Jetty instead.

pom.xml
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
  <modelVersion>4.0.0</modelVersion>
  <groupId>org.fredy</groupId>
  <artifactId>exec-war</artifactId>
  <version>0.1</version>
  <packaging>war</packaging>
  <name>exec-war</name>
  <dependencies>
    <dependency>
      <groupId>org.mortbay.jetty</groupId>
      <artifactId>jetty</artifactId>
      <version>6.1.25</version>
    </dependency>
  </dependencies>
  <build>
    <plugins>
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-compiler-plugin</artifactId>
        <configuration>
          <source>1.6</source>
          <target>1.6</target>
        </configuration>
      </plugin>
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-assembly-plugin</artifactId>
        <configuration>
          <archive>
            <manifest>
              <mainClass>myproject.Main</mainClass>
            </manifest>
          </archive>
          <descriptorRefs>
            <descriptorRef>jar-with-dependencies</descriptorRef>
          </descriptorRefs>
        </configuration>
        <executions>
          <execution>
            <id>jar-with-dependencies</id>
            <phase>package</phase>
            <goals>
              <goal>single</goal>
            </goals>
          </execution>
        </executions>
      </plugin>
    </plugins>
  </build>
</project>

web.xml
<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.5" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">
  <display-name>exec-war</display-name>
  <session-config>
    <session-timeout>30</session-timeout>
  </session-config>
  <servlet>
    <servlet-name>MyServlet</servlet-name>
    <servlet-class>myproject.servlet.MyServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>MyServlet</servlet-name>
    <url-pattern>/MyServlet</url-pattern>
  </servlet-mapping>
</web-app>

MyServlet.java
package myproject.servlet;
import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class MyServlet extends HttpServlet {

    protected void doGet(HttpServletRequest req, HttpServletResponse resp) 
            throws ServletException, IOException {
        process(req, resp);
    }

    protected void doPost(HttpServletRequest req, HttpServletResponse resp)
            throws ServletException, IOException {
        process(req, resp);
    }

    private void process(HttpServletRequest req, HttpServletResponse resp) 
            throws ServletException, IOException {
        resp.setContentType("text/html");
        PrintWriter pw = resp.getWriter();
        try {
            pw.print("<html><body><h1>Hello World</h1></body></html>");
        } finally {
            pw.close();
        }
    }
}

Main.class
package myproject;

import java.net.URL;

import org.mortbay.jetty.Connector;
import org.mortbay.jetty.Server;
import org.mortbay.jetty.nio.SelectChannelConnector;
import org.mortbay.jetty.webapp.WebAppContext;

public class Main {
    
    public static void main(String[] args) throws Exception {
        Server server = new Server();
        
        Connector connector = new SelectChannelConnector();
        connector.setPort(8888);
        connector.setHost("127.0.0.1");
        server.addConnector(connector);
        
        URL warUrl = Main.class.getClassLoader().getResource("WEB-INF");
        System.out.println(warUrl);
        String warUrlString = warUrl.toExternalForm();
        server.setHandler(new WebAppContext(warUrlString, "/exec-war"));
        server.setStopAtShutdown(true);
        
        server.start();
    }
}

1. Package a WAR file
mvn package
2. Rename the package name from JAR to WAR. The JAR still has WAR structure. The file has a JAR extension because of the maven-assembly-plugin. So, it's basically a JAR file with a WAR structure inside.
3. Run it.
java -jar exec-war.war
4. Or deploy it in a web container, such as Tomcat.

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