RESTful WS using Jersey: "Hello world!!!"

JAX-RS is a java specification which define APIs to implement RESTful web services. Jersey is a reference implementation of JAX-RS. It provides libraries to develop RESTful web services based on the JAX-RS specification. It uses a servlet to receive and dispatch client requests to right execution classes. In this tutorial, we will develop a simple service which returns string “Hello world!” to client using Jersey.

Prerequisites

Eclipse Java EE.
Tomcat server.
jersey library v 2.34. Scroll down to JAX-RS 2.1 / Jersey 2.26+, and download Jersey JAX-RS 2.1 RI bundle.

All needed tools are also provided in https://www-inf.telecom-sudparis.eu/~gaaloulw/Downloads.

Step 1: setting up Tomcat on Eclipse

Refer to this tutorial.

Step 2: Create your project

Open Eclipse, File→New→Dynamic Web Project.
Name the project: rest. Select Target runtime as your Apache Tomcat. Click Finish.
Download and extract the Jersey package.
Copy all jar files from lib, ext and api folders to the WebContent→WEB-INF→lib folder
Create new package in the src folder. Name it: my.first.rest.
Create new Java class inside this package. Name it: Hello.

Edit it as following:

package my.first.rest;
 
import javax.ws.rs.GET;
import javax.ws.rs.Path;
import javax.ws.rs.Produces;
import javax.ws.rs.core.MediaType;
 
@Path("hello") //set your service url path to <base_url>/hello
               // the <base_url> is based on your application name, the servlet and the URL pattern from the web.xml configuration file
public class Hello {
 
  // This method is called if TEXT_PLAIN is requested
  @GET
  @Produces(MediaType.TEXT_PLAIN) // defines which MIME type is delivered by a method annotated with @GET
  public String sayHelloInPlainText() {		  
    return "Hello world!";
  }
 
  // This method is called if HTML is requested
  @GET
  @Produces(MediaType.TEXT_HTML)
  public String sayHelloInHtml() {
    return "<html> " + "<title>" + "Hello world!" + "</title>"
        + "<body><h1>" + "Hello world!" + "</body></h1>" + "</html> ";
  }
}

Step 3: Define the servlet container

Create a file: web.xml in the WebContent→WEB-INF folder.

Insert the following code into the web.xml file:

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://xmlns.jcp.org/xml/ns/javaee" xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd" id="WebApp_ID" version="4.0">
  <display-name>rest</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>jersey-servlet</servlet-name>
        <servlet-class>org.glassfish.jersey.servlet.ServletContainer</servlet-class>
        <init-param>
             <param-name>jersey.config.server.provider.packages</param-name>
             <param-value>my.first.rest</param-value>
        </init-param>
        <load-on-startup>1</load-on-startup>
    </servlet>
 
    <servlet-mapping>
        <servlet-name>jersey-servlet</servlet-name>
        <url-pattern>/*</url-pattern>
    </servlet-mapping>
</web-app>

Note that:
1. The parameter jersey.config.server.provider.packages for <param-name> defines in which package Jersey will look for the web service classes
2. <param-value> is your package's name.
3. the URL of your service will be: http://your_domain:port/<display-name>/<url-pattern>/<path_from_rest_class>. In this example, this URL is: http://localhost:8080/rest/hello:
  - <display-name> in web.xml is rest
  - <url-pattern> in web.xml is empty (the * is a wild card, meaning any text)
  - <path_from_rest_class> is the path as defined in step 7

Step 4: Publish and check your service

Start the Tomcat server
Right click on Tomcat server→Add and Remove…. Select the rest project.
Verify the response in HTML by your browser: http://localhost:8080/rest/hello.
Verify the response in PLAINTEXT using command curl: open your terminal and type: curl http://localhost:8080/rest/hello

teaching_assistant/web_services/jersey_helloworld.txt · Last modified: 2023/09/06 07:50 by IT Courses (NNC)

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