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Hello Java Sample

This sample aims to demonstrate the simplest possible Servlet-based Java webapp. Here we walk through the entire content of the application.

The Servlet

In the org.cloudfoundry.samples package under src/main/java, you will see HelloServlet.java:

package org.cloudfoundry.samples;

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 HelloServlet extends HttpServlet {

	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		response.setContentType("text/plain");
		response.setStatus(200);
		PrintWriter writer = response.getWriter();
		writer.println("Hello from " + System.getenv("VCAP_APP_HOST") + ":" + System.getenv("VCAP_APP_PORT"));
		writer.close();
	}
}

Notice that it contains only java and javax imports. In the doGet(..) method, it simply writes the Content-Type header value, sets the status to 200 (OK), and then writes a message. The content of that message includes the HOST and PORT where this application is running. Those environment variables, VCAP_APP_HOST and VCAP_APP_PORT are available anytime the application is running on Cloud Foundry.

The web.xml File

As a standard Java webapp, the configuration of HelloServlet is included within the WEB-INF/web.xml file. You will find that under src/main/webapp. It looks like this:

<?xml version="1.0" encoding="UTF-8"?>
<web-app id="WebApp_ID" version="2.4" xmlns="http://java.sun.com/xml/ns/j2ee"
		xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
		xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd">

	<display-name>Hello Java</display-name>
	
	<servlet>
		<servlet-name>HelloServlet</servlet-name>
		<servlet-class>org.cloudfoundry.samples.HelloServlet</servlet-class>
	</servlet>
	
	<servlet-mapping>
		<servlet-name>HelloServlet</servlet-name>
		<url-pattern>/</url-pattern>
	</servlet-mapping>
	
</web-app>

There you see the servlet is declared, and then a mapping is provided. In this case, the context root of the application is mapped directly to HelloServlet since it is the only servlet in the application.

The pom.xml File

Since this application is built with Maven, there is a pom.xml file directly in the root directory. That POM is as simple as it can be.

<project>
	<modelVersion>4.0.0</modelVersion>
	<groupId>org.cloudfoundry.samples</groupId>
	<artifactId>hello-java</artifactId>
	<version>1.0</version>
	<packaging>war</packaging>
	<dependencies>
		<dependency>
			<groupId>javax.servlet</groupId>
			<artifactId>servlet-api</artifactId>
			<version>2.5</version>
			<scope>provided</scope>
		</dependency>
	</dependencies>
</project>

Notice that it has the standard project metadata (groupId, artifactId, version, etc.), and it has a single dependency: the Servlet API. That dependency is marked as provided since it's available in the deployment environment itself.

Building the Application

To build the application, make sure you have Maven installed. Then, cd into the root directory and execute:

mvn clean package

That will create the hello-java-1.0.war file within the 'target' directory.

Running the Application

To run the application, make sure you have VMC installed and that you are logged in successfully for your desired target environment (e.g. http://api.cloudfoundry.com). Then, cd into the target directory and execute:

vmc push

That will ask a few questions, and in most cases you can simply accept the defaults. Here is an example of the output:

Would you like to deploy from the current directory? [Yn]: Y
Application Name: hello-java-sample
Application Deployed URL: 'hello-java-sample.cloudfoundry.com'? 
Detected a Java Web Application, is this correct? [Yn]: Y
Memory Reservation [Default:512M] (64M, 128M, 256M or 512M) 256
Creating Application: OK
Would you like to bind any services to 'hello-java-sample'? [yN]: N
Uploading Application:
  Checking for available resources: OK
  Packing application: OK
  Uploading (4K): OK   
Push Status: OK
Staging Application: OK                                                         
Starting Application: OK

Notice that it detected the app type as "Java Web Application". In this case, it's only recognizing a runtime (Java) but not a framework (e.g. Spring or Grails), since this really is just a barebones Java web application. If you were to create a Spring or Grails application, you would see that it detects both the runtime and the framework.

The result when visiting the 'Application Deployed URL' should look something like this:

Hello from 172.30.49.150:20488

That's all. Have fun!