RESTful WS using Jersey: Attach client request to a resource

In this tutorial, we will create a restful web service that attach a client request to a specific resource. We use an example in which resource is information about users (id and name). If the server receives a request as:

• http://domain-name:port/rest/users: it will return a list of users
• http://domain-name:port/rest/users/<uid>: it will return the id and name of the requested user.

1. We continue with the same Java project of the previous tutorial. (you can also create a new Java project for this tutorial)
2. Create a new Java package. Name it: my.third.rest.
3. Create a new Java class under this package. Name it User. This class handles information of a user, including ID and name. Source code as following
   
   

   package my.third.rest;
    
   public class User {
   	private String id;
   	private String name;
    
   	public User(String id, String name){
   		this.id = id;
   		this.name = name;
   	}
    
   	public void setName(String name){
   		this.name = name;
   	}
    
   	public String getID(){
   		return this.id;
   	}
    
   	public String getName(){
   		return this.name;
   	}
   }

4. Create another Java class in the same package. Name it RestResource with the source code as following:
   
   

   package my.third.rest;
    
   import java.util.HashMap;
   import java.util.Map;
   import java.util.Map.Entry;
    
   import javax.ws.rs.GET;
   import javax.ws.rs.Path;
   import javax.ws.rs.PathParam;
   import javax.ws.rs.Produces;
   import javax.ws.rs.core.MediaType;
    
   @Path("users") //attach client request to resource: .../users
   public class RestResource {
    
   	Map<String,User> listUsers;  
    
   	//initialize some resources
   	public RestResource(){
   		listUsers = new HashMap<String,User>();
   		listUsers.put("1",new User("1", "John"));
   		listUsers.put("2",new User("2", "Peter"));
   	}
    
   	//return list of users
   	@GET
   	@Produces(MediaType.TEXT_PLAIN)
   	public String listOfUsersInText(){
   		String list="";
   		for (Entry<String,User> u:listUsers.entrySet()){
   			list += u.getValue().getName() + "\n";
   		}
   		return list;
   	}
    
   	//return user information corresponding to the requested uid.
   	@GET
   	@Path("{uid}") //attach client request to resource: .../users/<uid>
   	@Produces(MediaType.TEXT_PLAIN)
   	public String getUID(@PathParam("uid") String uid){ //@PathParam is used to inject values from the URL into a method parameter
                                                               // in this way you inject the id of the user into the method to get the correct user
    
   		if (!listUsers.containsKey(uid))
   			return "User not exist!";
    
   		return listUsers.get(uid).getID()+":"+listUsers.get(uid).getName();
   	}	
   }

5. Open the file web.xml in the WebContent→WEB-INF folder. Add my.third.rest into the <param-value> tag to declare a new package that manipulate a rest resource:
   
   

   <?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_3_0.xsd" 
   id="WebApp_ID" version="3.0">
     <display-name>rest</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>my.first.rest;my.third.rest</param-value>
       </init-param>
     </servlet>
     <servlet-mapping>
       <servlet-name>Jersey REST Service</servlet-name>
       <url-pattern>/*</url-pattern>
     </servlet-mapping>
   </web-app> 

6. Restart your Tomcat server.
7. Open your web browser (or use curl command) to check:
   • http://localhost:8080/rest/users
   • http://localhost:8080/rest/users/1
   • http://localhost:8080/rest/users/2