Web services - Part5

How to create and consume RESTful webservices

In this blog I will explain how to create and consume RESTful web service with JAX-RS using Jersey.

Java API for RESTful Web Services (JAX-RS) is a Java programming language API that provides support in creating web services according to the Representational State Transfer (REST) architectural pattern. (http://en.wikipedia.org/wiki/Java_API_for_RESTful_Web_Services )

In order to simplify development of RESTful Web services and their clients in Java, a standard and portable JAX-RS API has been designed. Jersey RESTful Web Services framework is open source, production quality, framework for developing RESTful Web Services in Java that provides support for JAX-RS APIs and serves as a JAX-RS (JSR 311 & JSR 339) Reference Implementation (https://jersey.java.net/).

I have used Eclipse Indigo, JDK 1.7, Jersey1.19 (you can download ‘Jersey 1.19 ZIP bundle’ zip from https://jersey.java.net/download.html ), Apache Tomcat 5.5

Let’s see step by step to create Restful webservice

SETP1: Create new Dynamic Web Project

STEP2: Add downloaded jersey JARs to project lib folder. Also, you need to add dependent jars persistence-api-1.0.jar and jersey-container-servlet-core-2.17.jar.

STEP3: Create a RESTful Web Service Resource ( Java class )

package com.kmingle.webservices.restful;

import javax.ws.rs.GET;

import javax.ws.rs.Produces;

import javax.ws.rs.core.MediaType;

import javax.ws.rs.Path;

@Path("/restfulExample")

public class RestfulServiceProvider {

       @GET

       @Produces(MediaType.TEXT_PLAIN)

       public String sayHello(){

              return "RESTful Hello World!";

       }

}

Here, @Path("/restfulExample") annotation before class definition tells that restfulExample  REST service can be reached in the URL .../ restfulExample. @GET annotation before method definition means that in URL .../ restfulExample, all GET requests are going to be handled by sayHello() method. You can also pass parameters in a GET request in REST services using  URI path parameter  with annotation @Path("/{parameter}") before method definition.

The @Produces annotation used in the sayHello() method specify the MIME media types or representations a resource can produce and send back to the client. If no methods in a resource are able to produce the MIME type in a client request, the Jersey runtime sends back an HTTP “406 Not Acceptable” error.

STEP4:  Do Servlet mapping in web.xml as mentioned below -

xml version="1.0" encoding="UTF-8"?>

<web-app id="WebApp_ID" version="2.4" xmlns="http://java.sun.com/xml/ns/j2ee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd">

       <display-name>RestfulWebServiceExample</display-name>

       <welcome-file-list>

              <welcome-file>index.html</welcome-file>

              <welcome-file>index.htm</welcome-file>

              <welcome-file>index.jsp</welcome-file>

              <welcome-file>default.html</welcome-file>

              <welcome-file>default.htm</welcome-file>

              <welcome-file>default.jsp</welcome-file>

       </welcome-file-list>

      

   <servlet>

    <servlet-name>RESTful_Web_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>com.kmingle.webservices.restful</param-value>

    </init-param>

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

  </servlet>

  <servlet-mapping>

    <servlet-name>RESTful_Web_Service</servlet-name>

    <url-pattern>/restful/*</url-pattern>

  </servlet-mapping>

      

</web-app>

STEP5: Your web service is ready to run start the server and run web service in browser

URL should be (http://localhost:8080/) + ( url-pattern in web.xml) + (@Path annotation value in resource class)

RESTful webservice client( Consumer ) :

To consume this RESTful webservice we need to create a client. Let’s have a look how to create a Java Jersey client.

STEP1:  Create new Java Project

STEP2: Add jersey jars to lib folder, for that add “Web App Libraries” with RestfulWebserviceExample Project

STEP3: Create client class

package com.kmingle.webservices.restful;

import javax.ws.rs.core.MediaType;

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

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

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

public class RestfulWebserviceClient {

      

       public static void main(String args[]){

              try {

                      

                     Client client = Client.create();

                     WebResource webResource = client.resource("http://localhost:8080/RestfulWebServiceExample/restful/restfulExample");

                     ClientResponse response = webResource.accept(MediaType.TEXT_PLAIN).get(ClientResponse.class);

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

                            throw new RuntimeException("HTTP error code :" + response.getStatus());

                     }

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

                     System.out.println("Webservice Response");

                     System.out.println(output);

              } catch (Exception e) {

                     e.printStackTrace();

              }     

             

       }

}

Output:

Webservice Response

RESTful Hello World!

My next blog will be on webservice security……

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