Tutorial

REST is an architectural style which is based on web-standards and the HTTP protocol. REST was first described by Roy Fielding in 2000.

In a REST based architecture everything is a resource. A resource is accessed via a common interface based on the HTTP standard methods. In an REST architecture you typically have a REST server which provides access to the resources and a REST client which accesses and modify the REST resources. Every resource should support the HTTP common operations. Resources are identified by global ID's (which are typically URIs).

REST allows that resources have different representations, e.g. text, xml, json etc. The rest client can ask for specific representation via the HTTP protocol (Content Negotiation).

The HTTP standards methods which are typical used in REST are PUT, GET, POST, DELETE.

A RESTFul webservices is based on the HTTP methods and the concept of REST. It typically defines the base URI for the services, the MIME-types its supports (XML, Text, JSON, user-defined,..) and the set of operations (POST, GET, PUT, DELETE) which are supported. JAX-RS supports the creation of XML and JSON via JAXB.

Java defines standard REST support via JAX-RS (The Java API for RESTful Web Services) in JSR 311.JAX-RS uses annotations to define the REST relevance of classes.

Via your "web.xml" you will register a servlet provided by Jersey and also define the path under which your REST web application will be available. The base URL of this servlet is:

				
http://your_domain:port/display-name/url-pattern/path_from_rest_class
			

This servlet which analyze the incoming HTTP request and select the correct class and method to respond to this request. This selection is based on annotation in the class and methods.

The most important annotations in JAX-RS are the following.

The complete path to a resource is therefore based on the base URL and the @PATh annotation in your class.

				
http://your_domain:port/display-name/url-pattern/path_from_rest_class
			

Jersey is the reference implementation for this specification. Jersey contains basically a REST server and a REST client. The core client is mainly available for testing and provides a library to communicate with the server.

A REST web application consists out of data classes (resources) and services. These two types are typically maintained in different packages as the Jersey servlet will be instructed via the "web.xml"to scan certain packages for data classes.

Download Jersey from Jersey Homepage . As of the time of writing the file is called ""A zip of Jersey containing the Jersey jars, core dependencies (it does not provide dependencies for third party jars beyond the those for JSON support) and JavaDoc." Download this zip; it contains the jar files required for the REST functionality.

This tutorial is using Tomcat as servlet container and Eclipse WTP as a development environment. Please see Eclipse WTP and Apache Tomcat for instructions on how to install and use Eclipse WTP and Apache Tomcat.

Alternative you could also use the Google App Engine for running the server part of the following REST examples. If you use the Google App Engine you don't have to setup Tomcat. If you are using GAE/J you have to create App Engine projects instead of "Dynamic Web Project".

Create a new "Dynamic Web Project" "de.vogella.jersey.first". See Eclipse WTP development for how to create a new dynamic web project.

Copy all jars from your Jersey download into the folder "WEB-INF/lib".

Create the following class.

				
package de.vogella.jersey.first;

import javax.ws.rs.GET;
import javax.ws.rs.Path;
import javax.ws.rs.Produces;
import javax.ws.rs.core.MediaType;

// POJO, no interface no extends

// The class registers its methods for the HTTP GET request using the @GET annotation. 
// Using the @Produces annotation, it defines that it can deliver several MIME types,
// text, XML and HTML. 

// The browser requests per default the HTML MIME type.

//Sets the path to base URL + /hello
@Path("/hello")
public class Hello {

	// This method is called if TEXT_PLAIN is request
	@GET
	@Produces(MediaType.TEXT_PLAIN)
	public String sayPlainTextHello() {
		return "Hello Jersey";
	}

	// This method is called if XML is request
	@GET
	@Produces(MediaType.TEXT_XML)
	public String sayXMLHello() {
		return "<?xml version=\"1.0\"?>" + "<hello> Hello Jersey" + "</hello>";
	}

	// This method is called if HTML is request
	@GET
	@Produces(MediaType.TEXT_HTML)
	public String sayHtmlHello() {
		return "<html> " + "<title>" + "Hello Jersey" + "</title>"
				+ "<body><h1>" + "Hello Jersey" + "</body></h1>" + "</html> ";
	}

}
			

This class register itself as a get resource via the @GET annotation. Via the @Produces annotation it defines that it delivers two MIME types, "text" and "HTML" code. It also defines via the "Path" annotation that its service should be available under the URL "hello".

The browser will always request the html MIME type. To see the text version you can use tool like curl .

You need to register Jersey as the servlet dispatcher for REST requests. Open the file "web.xml" and modify the file to the following.

				
<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" id="WebApp_ID" version="2.5">
  <display-name>de.vogella.jersey.first</display-name>
  <servlet>
    <servlet-name>Jersey REST Service</servlet-name>
    <servlet-class>com.sun.jersey.spi.container.servlet.ServletContainer</servlet-class>
    <init-param>
      <param-name>com.sun.jersey.config.property.packages</param-name>
      <param-value>de.vogella.jersey.first</param-value>
    </init-param>
    <load-on-startup>1</load-on-startup>
  </servlet>
  <servlet-mapping>
    <servlet-name>Jersey REST Service</servlet-name>
    <url-pattern>/rest/*</url-pattern>
  </servlet-mapping>
</web-app>
			

The parameter "com.sun.jersey.config.property.package" defines in which package jersey will look for the web service classes. This property must point to your resources classes. The URL pattern defines part of the base URL your application will be placed.

Run you web application in Eclipse. See Eclipse WTP for details on how to run dynamic web applications.

Test your REST service under: "http://localhost:8080/de.vogella.jersey.first/rest/hello". This name is derived from the "display-name" defined in the "web.xml" file, augmented with the servlet-mapping url-pattern and the "hello" @Path annotation from your class file. You should get the message "Hello Jersey".

The browser requests the HTML representation of your resource. In the next chapter we are going to write a client which will read the XML representation.

Jersey contains a REST client library which can be used for testing or to build a real client in Java. Alternative you could use Apache HttpClient to create a client.

Create a new Java "de.vogella.jersey.first.client" and add the jersey jars to the project and the project build path. Create the following test class.

				
package de.vogella.jersey.first.client;

import java.net.URI;

import javax.ws.rs.core.MediaType;
import javax.ws.rs.core.UriBuilder;

import com.sun.jersey.api.client.Client;
import com.sun.jersey.api.client.ClientResponse;
import com.sun.jersey.api.client.WebResource;
import com.sun.jersey.api.client.config.ClientConfig;
import com.sun.jersey.api.client.config.DefaultClientConfig;

public class Test {
	public static void main(String[] args) {
		ClientConfig config = new DefaultClientConfig();
		Client client = Client.create(config);
		WebResource service = client.resource(getBaseURI());
		// Fluent interfaces
		System.out.println(service.path("rest").path("hello").accept(
				MediaType.TEXT_PLAIN).get(ClientResponse.class).toString());
		// Get plain text
		System.out.println(service.path("rest").path("hello").accept(
				MediaType.TEXT_PLAIN).get(String.class));
		// Get XML
		System.out.println(service.path("rest").path("hello").accept(
				MediaType.TEXT_XML).get(String.class));
		// The HTML
		System.out.println(service.path("rest").path("hello").accept(
				MediaType.TEXT_HTML).get(String.class));

	}

	private static URI getBaseURI() {
		return UriBuilder.fromUri(
				"http://localhost:8080/de.vogella.jersey.first").build();
	}

}

			

Create a new "Dynamic Web Project" "de.vogella.jersey.jaxb" and copy all jersey jars into the folder "WEB-INF/lib".

Create your domain class.

				
package de.vogella.jersey.jaxb.model;

import javax.xml.bind.annotation.XmlRootElement;

@XmlRootElement
// JAX-RS supports an automatic mapping from JAXB annotated class to XML and JSON
// Isn't that cool?
public class Todo {
	private String summary;
	private String description;
	public String getSummary() {
		return summary;
	}
	public void setSummary(String summary) {
		this.summary = summary;
	}
	public String getDescription() {
		return description;
	}
	public void setDescription(String description) {
		this.description = description;
	}

	
}

			

Create the following resource class. This class simply return an instance of the Todo class.

				
package de.vogella.jersey.jaxb;

import javax.ws.rs.GET;
import javax.ws.rs.Path;
import javax.ws.rs.Produces;
import javax.ws.rs.core.MediaType;

import de.vogella.jersey.jaxb.model.Todo;

@Path("/todo")
public class TodoResource {
	// This method is called if XMLis request
	@GET
	@Produces( { MediaType.APPLICATION_XML, MediaType.APPLICATION_JSON })
	public Todo getXML() {
		Todo todo = new Todo();
		todo.setSummary("This is my first todo");
		todo.setDescription("This is my first todo");
		return todo;
	}
	
	// This can be used to test the integration with the browser
	@GET
	@Produces( { MediaType.TEXT_XML })
	public Todo getHTML() {
		Todo todo = new Todo();
		todo.setSummary("This is my first todo");
		todo.setDescription("This is my first todo");
		return todo;
	}

}

			

Change "web.xml" to the following.

				
<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xmlns="http://java.sun.com/xml/ns/javaee" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
	xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
	id="WebApp_ID" version="2.5">
	<display-name>de.vogella.jersey.jaxb</display-name>
	<servlet>
		<servlet-name>Jersey REST Service</servlet-name>
		<servlet-class>com.sun.jersey.spi.container.servlet.ServletContainer</servlet-class>
		<init-param>
			<param-name>com.sun.jersey.config.property.packages</param-name>
			<param-value>de.vogella.jersey.jaxb</param-value>
		</init-param>
		<load-on-startup>1</load-on-startup>
	</servlet>
	<servlet-mapping>
		<servlet-name>Jersey REST Service</servlet-name>
		<url-pattern>/rest/*</url-pattern>
	</servlet-mapping>
</web-app>
			

Run you web application in Eclipse and validate that you can access your service. Your application should be available under "http://localhost:8080/de.vogella.jersey.jaxb/rest/todo".

Create a new Java "de.vogella.jersey.jaxb.client" and add the jersey jars to the project and the project build path. Create the following test class.

				
package de.vogella.jersey.jaxb.client;


import java.net.URI;

import javax.ws.rs.core.MediaType;
import javax.ws.rs.core.UriBuilder;

import com.sun.jersey.api.client.Client;
import com.sun.jersey.api.client.WebResource;
import com.sun.jersey.api.client.config.ClientConfig;
import com.sun.jersey.api.client.config.DefaultClientConfig;

public class Test {
	public static void main(String[] args) {
		ClientConfig config = new DefaultClientConfig();
		Client client = Client.create(config);
		WebResource service = client.resource(getBaseURI());
		// Get XML
		System.out.println(service.path("rest").path("todo").accept(
				MediaType.TEXT_XML).get(String.class));
		// Get XML for application
		System.out.println(service.path("rest").path("todo").accept(
				MediaType.APPLICATION_JSON).get(String.class));
		// Get JSON for application
		System.out.println(service.path("rest").path("todo").accept(
				MediaType.APPLICATION_XML).get(String.class));
	}

	private static URI getBaseURI() {
		return UriBuilder.fromUri(
				"http://localhost:8080/de.vogella.jersey.jaxb").build();
	}

}

			

Create a new dynamic project "de.vogella.jersey.todo" and add the jersey libs. Modify "web.xml" to the following.

				
<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" id="WebApp_ID" version="2.5">
  <display-name>de.vogella.jersey.todo</display-name>
  <servlet>
    <servlet-name>Jersey REST Service</servlet-name>
    <servlet-class>com.sun.jersey.spi.container.servlet.ServletContainer</servlet-class>
    <init-param>
      <param-name>com.sun.jersey.config.property.packages</param-name>
      <param-value>de.vogella.jersey.todo.resources</param-value>
    </init-param>
    <load-on-startup>1</load-on-startup>
  </servlet>
  <servlet-mapping>
    <servlet-name>Jersey REST Service</servlet-name>
    <url-pattern>/rest/*</url-pattern>
  </servlet-mapping>
</web-app>

			

Create the following data model and a Singleton which serves as the data provider for the model. We use the implementation based on an enumeration. Please see the link for details. The Todo class is annotated with a JAXB annotation. See Java and XML to learn about JAXB.

				
package de.vogella.jersey.todo.model;


import javax.xml.bind.annotation.XmlRootElement;

@XmlRootElement
public class Todo {
	private String id;
	private String summary;
	private String description;
	
	public Todo(){
		
	}
	public Todo (String id, String summary){
		this.id = id;
		this.summary = summary;
	}
	public String getId() {
		return id;
	}
	public void setId(String id) {
		this.id = id;
	}
	public String getSummary() {
		return summary;
	}
	public void setSummary(String summary) {
		this.summary = summary;
	}
	public String getDescription() {
		return description;
	}
	public void setDescription(String description) {
		this.description = description;
	}
	
	
}

			

				
package de.vogella.jersey.todo.dao;

import java.util.HashMap;
import java.util.Map;

import de.vogella.jersey.todo.model.Todo;

public enum TodoDao {
	instance;
	
	private Map<String, Todo> contentProvider = new HashMap<String, Todo>();
	
	private TodoDao() {
		
		Todo todo = new Todo("1", "Learn REST");
		todo.setDescription("Read http://www.vogella.com/articles/REST/article.html");
		contentProvider.put("1", todo);
		todo = new Todo("2", "Do something");
		todo.setDescription("Read complete http://www.vogella.com");
		contentProvider.put("2", todo);
		
	}
	public Map<String, Todo> getModel(){
		return contentProvider;
	}
	
}

			

The rest service can be used via HTML forms. The following HTML form will allow to post new data to the service. Create the following page "create_todo.html" in the folder "WEB-INF".

				
<!DOCTYPE html>
<html>
 <head>
  <title>Form to create a new resource</title>
 </head>
<body>
	<form action="../de.vogella.jersey.todo/rest/todos" method="POST">
	<label for="id">ID</label>
	<input name="id" />
	<br/>
	<label for="summary">Summary</label>
	<input name="summary" />
	<br/>
	Description:
	<TEXTAREA NAME="description" COLS=40 ROWS=6></TEXTAREA>
	<br/>
	<input type="submit" value="Submit" />
	</form>
</body>
</html>
			

Create the following classes which will be used as REST resources.

				
package de.vogella.jersey.todo.resources;

import javax.ws.rs.Consumes;
import javax.ws.rs.DELETE;
import javax.ws.rs.GET;
import javax.ws.rs.PUT;
import javax.ws.rs.Produces;
import javax.ws.rs.core.Context;
import javax.ws.rs.core.MediaType;
import javax.ws.rs.core.Request;
import javax.ws.rs.core.Response;
import javax.ws.rs.core.UriInfo;
import javax.xml.bind.JAXBElement;

import de.vogella.jersey.todo.dao.TodoDao;
import de.vogella.jersey.todo.model.Todo;

public class TodoResource {
	@Context
	UriInfo uriInfo;
	@Context
	Request request;
	String id;
	public TodoResource(UriInfo uriInfo, Request request, String id) {
		this.uriInfo = uriInfo;
		this.request = request;
		this.id = id;
	}
	
	//Application integration 		
	@GET
	@Produces({MediaType.APPLICATION_XML, MediaType.APPLICATION_JSON})
	public Todo getTodo() {
		Todo todo = TodoDao.instance.getModel().get(id);
		if(todo==null)
			throw new RuntimeException("Get: Todo with " + id +  " not found");
		return todo;
	}
	
	// For the browser
	@GET
	@Produces(MediaType.TEXT_XML)
	public Todo getTodoHTML() {
		Todo todo = TodoDao.instance.getModel().get(id);
		if(todo==null)
			throw new RuntimeException("Get: Todo with " + id +  " not found");
		return todo;
	}
	
	@PUT
	@Consumes(MediaType.APPLICATION_XML)
	public Response putTodo(JAXBElement<Todo> todo) {
		Todo c = todo.getValue();
		return putAndGetResponse(c);
	}
	
	@DELETE
	public void deleteTodo() {
		Todo c = TodoDao.instance.getModel().remove(id);
		if(c==null)
			throw new RuntimeException("Delete: Todo with " + id +  " not found");
	}
	
	private Response putAndGetResponse(Todo todo) {
		Response res;
		if(TodoDao.instance.getModel().containsKey(todo.getId())) {
			res = Response.noContent().build();
		} else {
			res = Response.created(uriInfo.getAbsolutePath()).build();
		}
		TodoDao.instance.getModel().put(todo.getId(), todo);
		return res;
	}
	
	

}

			

				
package de.vogella.jersey.todo.resources;


import java.io.IOException;
import java.net.URI;
import java.util.ArrayList;
import java.util.List;

import javax.servlet.http.HttpServletResponse;
import javax.ws.rs.Consumes;
import javax.ws.rs.FormParam;
import javax.ws.rs.GET;
import javax.ws.rs.POST;
import javax.ws.rs.Path;
import javax.ws.rs.PathParam;
import javax.ws.rs.Produces;
import javax.ws.rs.core.Context;
import javax.ws.rs.core.MediaType;
import javax.ws.rs.core.Request;
import javax.ws.rs.core.Response;
import javax.ws.rs.core.UriInfo;

import de.vogella.jersey.todo.dao.TodoDao;
import de.vogella.jersey.todo.model.Todo;


// Will map the resource to the URL todos
@Path("/todos")
public class TodosResource {

	// Allows to insert contextual objects into the class, 
	// e.g. ServletContext, Request, Response, UriInfo
	@Context
	UriInfo uriInfo;
	@Context
	Request request;


	// Return the list of todos to the user in the browser
	@GET
	@Produces(MediaType.TEXT_XML)
	public List<Todo> getTodosBrowser() {
		List<Todo> todos = new ArrayList<Todo>();
		todos.addAll( TodoDao.instance.getModel().values() );
		return todos; 
	}
	
	// Return the list of todos for applications
	@GET
	@Produces({MediaType.APPLICATION_XML, MediaType.APPLICATION_JSON})
	public List<Todo> getTodos() {
		List<Todo> todos = new ArrayList<Todo>();
		todos.addAll( TodoDao.instance.getModel().values() );
		return todos; 
	}
	
	
	// retuns the number of todos
	// Use http://localhost:8080/de.vogella.jersey.todo/rest/todos/count
	// to get the total number of records
	@GET
	@Path("count")
	@Produces(MediaType.TEXT_PLAIN)
	public String getCount() {
		int count = TodoDao.instance.getModel().size();
		return String.valueOf(count);
	}
	
	@POST
	@Produces(MediaType.TEXT_HTML)
	@Consumes(MediaType.APPLICATION_FORM_URLENCODED)
	public void newTodo(
			@FormParam("id") String id,
			@FormParam("summary") String summary,
			@FormParam("description") String description,
			@Context HttpServletResponse servletResponse
	) throws IOException {
		Todo todo = new Todo(id,summary);
		if (description!=null){
			todo.setDescription(description);
		}
		TodoDao.instance.getModel().put(id, todo);
		
		servletResponse.sendRedirect("../create_todo.html");
	}
	
	
	// Defines that the next path parameter after todos is
	// treated as a parameter and passed to the TodoResources
	// Allows to type http://localhost:8080/de.vogella.jersey.todo/rest/todos/1
	// 1 will be treaded as parameter todo and passed to TodoResource
	@Path("{todo}")
	public TodoResource getTodo(
			@PathParam("todo") String id) {
		return new TodoResource(uriInfo, request, id);
	}
	
}

			

This TodosResource uses "@PathParam" annotation to use the parameter "id" to forward the request to the class "TodoResource".

Run you web application in Eclipse and test the availability of your REST service under: "http://localhost:8080/de.vogella.jersey.todo/rest/todos". You should see the XML representation of your Todo items.

To see the count of Todo items use "http://localhost:8080/de.vogella.jersey.todo/rest/todos/count" to see an exiting todo use "http://localhost:8080/de.vogella.jersey.todo/rest/todos/{id}", e.g. "http://localhost:8080/de.vogella.jersey.todo/rest/todos/1" to see the todo with ID 1. We currently have only todos with the id's 1 and 2, all other requests will result an HTTP error code.

Please note that with the browser you can only issue HTTP GET requests. The next chapter will use the jersey client libraries to issue get, post and delete.

Create a Java project "de.vogella.jersey.todo.client". Create a folder "lib", place all jersey libs there and add then to your classpath. Create the following class.

				
package de.vogella.jersey.todo.client;

import java.net.URI;

import javax.ws.rs.core.MediaType;
import javax.ws.rs.core.UriBuilder;

import com.sun.jersey.api.client.Client;
import com.sun.jersey.api.client.ClientResponse;
import com.sun.jersey.api.client.WebResource;
import com.sun.jersey.api.client.config.ClientConfig;
import com.sun.jersey.api.client.config.DefaultClientConfig;
import com.sun.jersey.api.representation.Form;

import de.vogella.jersey.todo.model.Todo;

public class Tester {
	public static void main(String[] args) {
		ClientConfig config = new DefaultClientConfig();
		Client client = Client.create(config);
		WebResource service = client.resource(getBaseURI());
		// Create one todo
		Todo todo = new Todo("3", "Blabla" );
		ClientResponse response = service.path("rest").path("todos").path(todo.getId()).accept(MediaType.APPLICATION_XML).put(ClientResponse.class, todo);
		// Return code should be 201 == created resource
		System.out.println(response.getStatus());
		// Get the Todos
		System.out.println(service.path("rest").path("todos").accept(
				MediaType.TEXT_XML).get(String.class));
		// Get XML for application
		System.out.println(service.path("rest").path("todos").accept(
				MediaType.APPLICATION_JSON).get(String.class));
		// Get JSON for application
		System.out.println(service.path("rest").path("todos").accept(
				MediaType.APPLICATION_XML).get(String.class));
		
		// Get the  Todo with id 1
		System.out.println(service.path("rest").path("todos/1").accept(
				MediaType.APPLICATION_XML).get(String.class));
		// get Todo with id 1 
		service.path("rest").path("todos/3").delete();
		// Get the all todos, id 1 should be deleted
		System.out.println(service.path("rest").path("todos").accept(
				MediaType.APPLICATION_XML).get(String.class));
		
		
		// Create a Todo
		Form form = new Form();
		form.add("id", "4");
		form.add("summary", "Demonstration of the client lib for forms");
		response = service.path("rest").path("todos").type(MediaType.APPLICATION_FORM_URLENCODED)
								   .post(ClientResponse.class, form);
		System.out.println("Form response " + response.getEntity(String.class));
		// Get the all todos, id 4 should be created
		System.out.println(service.path("rest").path("todos").accept(
				MediaType.APPLICATION_XML).get(String.class));
		
	}
	private static URI getBaseURI() {
		return UriBuilder.fromUri(
				"http://localhost:8080/de.vogella.jersey.todo").build();
	}
}

			

The above example contains a form which calls a post method of your rest service.

Usually every programming language provide somewhere libraries for creating HTTP get, post, put and delete requests. For Java the project Apache HttpClient.

Source Code of Examples

http://jersey.java.net/ Jersey Homepage

http://www.ibm.com/developerworks/library/wa-aj-tomcat/ IBM Article about Rest with Tomcat and Jersey

Eclipse RCP Training (German) Eclipse RCP Training with Lars Vogel

Android Tutorial Introduction to Android Programming

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Eclipse RCP Tutorial Create native applications in Java

JUnit Tutorial Test your application

Git Tutorial Put everything you have under distributed version control system