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.

We continue with the same Java project of the previous tutorial. (you can also create a new Java project for this tutorial)
Create a new Java package. Name it: my.third.rest.

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;
	}
}

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();
	}	
}

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>

Restart your Tomcat server.
Open your web browser (or use curl command) to check: