RESTDoc Servlet Example

This is an example of creating a self-describing REST API using REST Docs and Java servlets.

Prerequisites

• Basic Java knowledge, including an installed version of the JVM and Maven.
• Basic Git knowledge, including an installed version of Git.
• A Java web application. If you don't have one follow the first step to create an example. Otherwise skip that step.

Handling RESTDoc Requests

In the example servlet below, the doOptions() handler fetches a predefined JSON file that documents the API endpoint. Appending "/describe" to the end of any REST API endpoint will also serve the RESTDoc for that particular interface.

:::java
package servlet;

import java.io.IOException;

import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import com.google.gson.stream.JsonWriter;

@WebServlet(
        name = "HelloServlet", 
        urlPatterns = {"/hello", "/hello/describe"}
    )
public class HelloServlet extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp)
            throws ServletException, IOException {
    	try {
			if(req.getServletPath().toLowerCase().endsWith("describe")){
				doOption(req, resp);
			}
			else{
				processGet(req, resp);
			}
		}
		catch (IOException e) {
			e.printStackTrace();
		}
    }

    public void processGet(HttpServletRequest req, HttpServletResponse resp) throws IOException{
		resp.setContentType("text/json");
    	PrintWriter out;
		out = resp.getWriter();
		JsonWriter writer = new JsonWriter(out);
    	writer.setIndent("    ");
    	writer.beginObject();
    	writer.name("message").value("process GET request for endpoint");
    	writer.name("path").value(req.getRequestURI());
    	writer.endObject();
	}

	public void doOption(HttpServletRequest req, HttpServletResponse resp) throws IOException{
		ServletOutputStream output = resp.getOutputStream();
		InputStream input = getServletContext().getResourceAsStream("restdocs/api.hello.json");
		byte[] buffer = new byte[1024];
	    int bytesRead;
	    while ((bytesRead = input.read(buffer)) != -1)
	    {
	        output.write(buffer, 0, bytesRead);
	    }
	}    
}

Run your Application

To generate the start scripts simply run:

:::term
$ mvn package

And then simply run the script:

:::term
$ sh target/bin/webapp

That's it. Your application should start up on port 8080. You can see the JSP at http://localhost:8080 and the servlet at http://localhost:8080/hello and http://localhost:8080/hello/describe

Deploy your Application to Heroku

Create a Procfile

You declare how you want your application executed in Procfile in the project root. Create this file with a single line:

:::term
web: sh target/bin/webapp

Optionally Choose a JDK

By default, OpenJDK 1.6 is installed with your app. However, you can choose to use a newer JDK by specifying java.runtime.version=1.7 in the system.properties file.

Here's what a system.properties file looks like:

:::term
java.runtime.version=1.7

You can specify 1.6, 1.7, or 1.8 (1.8 is in beta) for Java 6, 7, or 8 (with lambdas), respectively.

Deploy to Heroku

Commit your changes to Git:

:::term
$ git add .
$ git commit -m "Ready to deploy"

Create the app on the Cedar stack:

:::term
$ heroku create --stack cedar
Creating high-lightning-129... done, stack is cedar
http://high-lightning-129.herokuapp.com/ | git@heroku.com:high-lightning-129.git
Git remote heroku added

Deploy your code:

:::term
Counting objects: 227, done.
Delta compression using up to 4 threads.
Compressing objects: 100% (117/117), done.
Writing objects: 100% (227/227), 101.06 KiB, done.
Total 227 (delta 99), reused 220 (delta 98)

-----> Heroku receiving push
-----> Java app detected
-----> Installing Maven 3.0.3..... done
-----> Installing settings.xml..... done
-----> executing .maven/bin/mvn -B -Duser.home=/tmp/build_1jems2so86ck4 -s .m2/settings.xml -DskipTests=true clean install
       [INFO] Scanning for projects...
       [INFO]                                                                         
       [INFO] ------------------------------------------------------------------------
       [INFO] Building petclinic 0.1.0.BUILD-SNAPSHOT
       [INFO] ------------------------------------------------------------------------
       ...
       [INFO] ------------------------------------------------------------------------
       [INFO] BUILD SUCCESS
       [INFO] ------------------------------------------------------------------------
       [INFO] Total time: 36.612s
       [INFO] Finished at: Tue Aug 30 04:03:02 UTC 2011
       [INFO] Final Memory: 19M/287M
       [INFO] ------------------------------------------------------------------------
-----> Discovering process types
       Procfile declares types -> web
-----> Compiled slug size is 62.7MB
-----> Launching... done, v5
       http://pure-window-800.herokuapp.com deployed to Heroku

Congratulations! Your web app should now be up and running on Heroku. Open it in your browser with:

:::term  
$ heroku open