Jersey Jackson JSON Tutorial

In this Jersey REST tutorial we will learn how to integrate Jersey REST Client and Jackson to build a RESTful Web service which produces and consumes JSON Type. We use Jackson for Marshalling Java Object to JSON and vice-versa(Unmarshalling JSON back to Java Object) in a JAX-RS Web Service.

Folder Structure

1. Create a Dynamic Web Project RESTfulExample and create a package for our src files “com.javainterviewpoint“
2. Place the required jar files under WEB-INF/Lib 
   

   jersey-bundle-1.18.jar
   jaxb-api.jar
   jaxb-impl-2.0.1.jar
   asm-3.1.jar
   jackson-core-asl-1.9.2.jar
   jackson-jaxrs-1.9.2.jar
   jackson-mapper-asl-1.9.2.jar
   jackson-xc-1.9.2.jar

3. Create the Java classes MarshalExample.java, UnMarshalExample.java, CustomerService.java and Customer.java under  com.javainterviewpoint folder.
4. Place the web.xml  under the WEB-INF directory

Marshalling Java Object to JSON Using Jackson

In this Jersey Client Example we will be creating a client where we will converting a Simple Java Object into JSON, lets see how we can achieve this.

Customer.Java

package com.javainterviewpoint;

public class Customer 
{
	String name;
	int id;
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public int getId() {
		return id;
	}
	public void setId(int id) {
		this.id = id;
	}
}

Our Customer class is a simple pojo class containing getters and setters for the property name and id.

web.xml

<?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/j2ee" 
xmlns:web="http://xmlns.jcp.org/xml/ns/javaee" 
xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee%20
http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd%20
http://java.sun.com/xml/ns/j2ee%20
http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd" id="WebApp_ID" version="2.4">
  <display-name>Restful Web Application</display-name>
  <servlet>
  <servlet-name>jersey-serlvet</servlet-name>
  <servlet-class>
    com.sun.jersey.spi.container.servlet.ServletContainer
  </servlet-class>
  <init-param>
    <param-name>com.sun.jersey.api.json.POJOMappingFeature</param-name>
    <param-value>true</param-value>
  </init-param>
  <init-param>
    <param-name>com.sun.jersey.config.property.packages</param-name>
    <param-value>com.javainterviewpoint</param-value>
  </init-param>
  <load-on-startup>1</load-on-startup>
 </servlet>
 <servlet-mapping>
   <servlet-name>jersey-serlvet</servlet-name>
   <url-pattern>/rest/*</url-pattern>
 </servlet-mapping>
</web-app>

We register our jersey container “com.sun.jersey.spi.container.servlet.ServletContainer” in the servlet-class of our web.xml and we will mention the source files location as the value to the init param “com.sun.jersey.config.property.packages” so that the container will scan for annotations of the class files within that package. We have set the value of Jersey POJO mapping feature to ‘true’

Customer Service.java

package com.javainterviewpoint;

import javax.ws.rs.Consumes;
import javax.ws.rs.GET;
import javax.ws.rs.POST;
import javax.ws.rs.Path;
import javax.ws.rs.Produces;
import javax.ws.rs.QueryParam;
import javax.ws.rs.core.Response;

@Path("/createjson")
public class CustomerService
{
    @GET
    @Path("/get")
    @Produces("application/json")
    public Customer getCustomerInJSON(@QueryParam("username") String name, @QueryParam("id") int id)
    {
        Customer cust = new Customer();
        cust.setName(name);
        cust.setId(id);
        return cust;
    }
}

• Our CustomerService servers the GET request, we have added @Path(“createjson”) annotated on top of it. So whatever request which comes with the url of http://localhost:8080/RESTfulExample/rest/createjson will be served by our  CustomerService
• getCustomerInJSON() – This methods serves all the GET requests and produces the JSON response which we have mentioned using @Produces(“application/json”). It reads the input from the URL which is passed using the @QueryParam annotation and returns the Customer object in JSON format.

Jersey Client Example – MarshalExample.java

package com.javainterviewpoint;

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

public class MarshalExample 
{
    public static void main(String args[])
    {
        try
        {   
            Client client = Client.create();
            WebResource resource = client
                    .resource("http://localhost:8080/RESTfulExample/rest/createjson/get?username=javainterviewpoint&id=1");
            ClientResponse response = resource.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("<<<< Generating JSON Output >>>");
                System.out.println(output);
     
          } catch (Exception e) {
     
            e.printStackTrace();
     
          }
        
    }
}

• In our MarshalExample class, we have created a Client using the Client.create() method.
• we have passed in the url to the resource() method of the client object.
• Then we mentioned our expected format as JSON in the accept(“application/json”) method and request as GET

resource. accept("application/json").getClientResponse.class);

• Finally getting the output and displaying it back

Output

Once we have executed the MarshalExample class we will be getting the below output.

UnMarshalling JSON to Java Object to JSON Using Jackson

Lets now re-write our service to take take customer object for UnMarshalling Java Object to JSON.

Customer Service.java

package com.javainterviewpoint;

import javax.ws.rs.Consumes;
import javax.ws.rs.GET;
import javax.ws.rs.POST;
import javax.ws.rs.Path;
import javax.ws.rs.Produces;
import javax.ws.rs.QueryParam;
import javax.ws.rs.core.Response;

@Path("/createjson")
public class CustomerService
{

    @POST
    @Path("/post")
    @Consumes("application/json")
    public Response createCustomerJSON(Customer customer)
    {
        String result = "Saved Customer : " + customer;
        System.out.println(customer.getName());
        return Response.status(200).entity(customer).build();
        
    }
}

Now our CustomerService takes up the JSON input which is denoted using @Consumes annotation and we are returning the Customer object to the client.

Jersey Client Example – UnMarshalExample.java

package com.javainterviewpoint;

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

public class UnMarshalExample
{
    public static void main(String args[])
    {
        try
        {
            String input = "{\"name\": \"javainterviewpoint_POST\",\"id\": 99}";

            Client client = Client.create();

            WebResource resource = client
                    .resource("http://localhost:8080/RESTfulExample/rest/createjson/post");

            ClientResponse response = resource
                    .type("application/json").post(ClientResponse.class, input);
            
            if (response.getStatus() != 200) {
                throw new RuntimeException("Failed : HTTP error code : "
                 + response.getStatus());
             }
      
            Customer customer = response.getEntity(Customer.class);
            System.out.println("Customer Name : "+customer.getName());
            System.out.println("Customer ID   : "+customer.getId());

        } catch (Exception e)
        {
            e.printStackTrace();
        }
    }
}

• In our UnMarshalExample class, we have created a Client using the Client.create() method.
• we have passed in the url to the resource() method of the client object.
• Then we mentioned our input type as JSON in the type(“application/json”) method and request as POST

resource. type("application/json").postClientResponse.class,input);

• Finally we get the Customer object back and display the values which is set.