REST Service

Jars Required:

1.        asm-all-3.3.1.jar

2.        commons-codec.jar

3.        commons-httpclient.jar

4.        commons-logging.jar

5.        jersey-bundle-1.14.jar

6.        json-simple.jar

 

Tools Required:

1.        Eclipse

2.        Any webserver/application server

3.     JDK 1.7

References:

http://rest.elkstein.org/

Restful service:

REST (Representational state Transfer) is an architectural style which is based on WEB standards and the HTTP protocol.

It relies on a

a.        Stateless

b.        client-server

c.        Cacheable communications protocol.

As a programming approach REST is light weight alternative to web service (SOAP) and RPC.

Features:

1.        Data which is retrieved from the server is known as resource.

2.        Resources identified over the network by URI.

3.        Bounded by standard protocol HTTP.

4.        It’s a stateless and simple

5.        Request response represented in JSON/XML/TEXT etc.

 

REST sample:

Server side implementation:

Class: WebServices.java

Using annotation @Path (“/WebServices”) in below code we are just saying this is class needs to looked up for the request http://localhost:8080/Restwebservice/webservice. Annotation @Get used for querying the resource. A method level annotation @Path (“hello”) used to identify the resource and URI for this http://localhost:8080/Restwebservice/webservice/hello. Annotation @Produces("application/json") used for specifying the response type. 

import java.util.ArrayList;

import java.util.HashMap;

import java.util.List;

import java.util.Map; 

import javax.ws.rs.GET;

import javax.ws.rs.Path;

import javax.ws.rs.PathParam;

import javax.ws.rs.Produces;

import javax.ws.rs.QueryParam; 

@Path("/webservice")

public class WebServices { 

        private static Map<String, Employee> employees = new HashMap<String, Employee>();

        @GET

        @Path("/hello")

        @Produces("application/json")

        public List<Heloo> hello() { 

                Map hellomap = new HashMap();

                Heloo h = new Heloo();

                h.setLname("Savadi");

                h.setName("Prashant");

                hellomap.put("1", h);

                Heloo h1 = new Heloo();

                h1.setLname("Savadi");

                h1.setName("Sushant");

                hellomap.put("2", h1);

                return new ArrayList<Heloo>(hellomap.values());

        }

        @GET

        @Path("/message")

        @Produces("text/plain")

        public String showMsg(@QueryParam("message") String message) {

                return message;

        }

        @GET

        @Path("/employees")

        @Produces("application/xml")

        public List<Employee> listEmployees() {

                return new ArrayList<Employee>(employees.values());

        }

        @GET

        @Path("/employee/{employeeid}")

        @Produces("application/xml")

        public Employee getEmployee(@PathParam("employeeid") String employeeId) {

                return employees.get(employeeId);

        }

        @GET

        @Path("/json/employees/")

        @Produces("application/json")

        public Map listEmployeesJSON() {

                return  employees;

        }

        @GET

        @Path("/json/employee/{employeeid}")

        @Produces("application/json")

        public Employee getEmployeeJSON(@PathParam("employeeid") String employeeId) {

                return employees.get(employeeId);

        } 

}

Class: Heloo.java

This is model class used for returning the data.

import javax.xml.bind.annotation.XmlElement;

import javax.xml.bind.annotation.XmlRootElement;

@XmlRootElement(name = "heloo")

public class Heloo {

        private String name;

        private String lname;

        @XmlElement

        public String getName() {

                return name;

        }

        public void setName(String name) {

                this.name = name;

        }

        @XmlElement

        public String getLname() {

                return lname;

        }    

        public void setLname(String lname) {

                this.lname = lname;

        }

}

WEB.xml file entry for servlet registration:

REST is implemented by jersey API. Need jersey servlet entry in the server wheel.

<servlet>

  <servlet-name>jersey-serlvet</servlet-name>

  <servlet-class>

         com.sun.jersey.spi.container.servlet.ServletContainer

        </servlet-class>

  <load-on-startup>1</load-on-startup>

 </servlet>

 <servlet-mapping>

  <servlet-name>jersey-serlvet</servlet-name>

  <url-pattern>/*</url-pattern>

 </servlet-mapping>

 
Client:
 
Using below client we can access the resources from server (cleint/server architecture) using URI :http://localhost:9084/Rest/webservice/hello.

Here response us JSON format and JSON data can be handled by simple-Json API. 

import java.util.ArrayList;

import java.util.Iterator;

import java.util.List;

import org.json.simple.JSONArray;

import org.json.simple.JSONObject;

import org.json.simple.parser.JSONParser;

import com.sun.jersey.api.client.Client;

import com.sun.jersey.api.client.ClientResponse;

import com.sun.jersey.api.client.WebResource;

public class RestWebServiceClient { 

       /**

        * @param args

        */

       public static void main(String[] args) {

              RestWebServiceClient restWebServiceClient = new RestWebServiceClient();

              restWebServiceClient.sayHello();

              // restWebServiceClient.getJSONEmployees();

              /*

               * restWebServiceClient.getMessage("Welcome");

               * restWebServiceClient.getXMLEmployees();

               * restWebServiceClient.getXMLEmployee(11111);

               * restWebServiceClient.getJSONEmployees();

               * restWebServiceClient.getJSONEmployee(11111);

               */

       }

       private void sayHello() {

              try {

                     Client client = Client.create();

                     WebResource webResource = client

                                  .resource("http://localhost:9084/Rest/webservice/hello");

                     ClientResponse response = webResource.accept("application/json")

                                  .get(ClientResponse.class);

                     if (response.getStatus() != 200) {

                           throw new RuntimeException("Failed : HTTP error code : "

                                         + response.getStatus());

                     } 

                     String output = response.getEntity(String.class);

                     System.out.println("\n============getResponse============");

                     Object p = new JSONParser().parse(output);

                     JSONObject array = (JSONObject) p;

                     JSONArray jarray = (JSONArray) array.get("heloo");

                     Heloo h=null;

                     List list = new ArrayList();                   

                     Iterator it = jarray.iterator();

                     while (it.hasNext()) {

                           h= new Heloo();

                           JSONObject obj=((JSONObject) it.next());

                           System.out.println(obj.get("name"));

                           System.out.println(obj.get("lname"));

                           h.setName(obj.get("name")+"");

                           h.setLname(obj.get("lname")+"");

                           list.add(h);                   

                          

                     }

                      System.out.println(list.toString());

              } catch (Exception e) {

                     e.printStackTrace();

              }

       }

       private void getMessage(String msg) {

              try {

                     Client client = Client.create();

                     WebResource webResource = client

                                  .resource("http://localhost:8080/Restwebservice/webservice/message/"

                                                + msg);

                     ClientResponse response = webResource.accept("text/plain").get(

                                  ClientResponse.class);

                     if (response.getStatus() != 200) {

                           throw new RuntimeException("Failed : HTTP error code : "

                                         + response.getStatus());

                     }

 

                     String output = response.getEntity(String.class);

                     System.out.println("\n============getCResponse============");

                     System.out.println(output);

 

              } catch (Exception e) {

                     e.printStackTrace();

              }

       }

 

       private void getXMLEmployees() {

              try {

                     Client client = Client.create();

                     WebResource webResource = client

                                  .resource("http://localhost:8080/Restwebservice/webservice/employees");

                     ClientResponse response = webResource.accept("application/xml")

                                  .get(ClientResponse.class);

                     if (response.getStatus() != 200) {

                           throw new RuntimeException("Failed : HTTP error code : "

                                         + response.getStatus());

                     }

 

                     String output = response.getEntity(String.class);

                     System.out.println("\n============getCResponse============");

                     System.out.println(output);

 

              } catch (Exception e) {

                     e.printStackTrace();

              }

       }

 

       private void getXMLEmployee(int empid) {

              try {

                     Client client = Client.create();

                     WebResource webResource = client

                                  .resource("http://localhost:8080/Restwebservice/webservice/employee/"

                                                + empid);

                     ClientResponse response = webResource.accept("application/xml")

                                  .get(ClientResponse.class);

                     if (response.getStatus() != 200) {

                           throw new RuntimeException("Failed : HTTP error code : "

                                         + response.getStatus());

                     }

 

                     String output = response.getEntity(String.class);

                     System.out.println("\n============getCResponse============");

                     System.out.println(output);

 

              } catch (Exception e) {

                     e.printStackTrace();

              }

       }

 

       private void getJSONEmployees() {

              try {

                     Client client = Client.create();

                     WebResource webResource = client

                                  .resource("http://localhost:8080/Restwebservice/webservice/json/employees/");

                     ClientResponse response = webResource.accept("application/json")

                                  .get(ClientResponse.class);

                     if (response.getStatus() != 200) {

                           throw new RuntimeException("Failed : HTTP error code : "

                                         + response.getStatus());

                     }

 

                     String output = response.getEntity(String.class);

                     System.out.println("\n============getCResponse============");

                     System.out.println(output);

 

              } catch (Exception e) {

                     e.printStackTrace();

              }

       }

 

       private void getJSONEmployee(int empid) {

              try {

                     Client client = Client.create();

                     WebResource webResource = client

                                  .resource("http://localhost:8080/Restwebservice/webservice/json/employee/"

                                                + empid);

                     ClientResponse response = webResource.accept("application/json")

                                  .get(ClientResponse.class);

                     if (response.getStatus() != 200) {

                           throw new RuntimeException("Failed : HTTP error code : "

                                         + response.getStatus());

                     }

 

                     String output = response.getEntity(String.class);

                     System.out.println("\n============getCResponse============");

                     System.out.println(output);

 

              } catch (Exception e) {

                     e.printStackTrace();

              }

       }

}