REST

In this article we will learn how to use JACKSON api in a jersey based rest web services project in java. Jersey uses Jackson to convert object to / form JSON. In this tutorial, we show you how to convert a “Track” object into JSON format, and return it back to user.

Tools used

Maven
JDK 1.8 (even 1.6 would work fine)
Eclipse/IntelliJ(you can use whichever you are comfortable with)
Tomcat Server 8

These steps are followed in this tutorial,

it’s Damn Easy !

Step 1: create a java web project in eclipse and convert it to maven project.
Step 2: add jersey jackson dependency in pom.xml and update the project.
Step 3: create an API class.
Step 4: in the web.xml add the servlet and servlet mapping.
Step 5: Just run the project, Hurray !

POM Dependencies

<properties>
    <jersey2.version>2.28</jersey2.version>
    <jaxrs.version>2.0.1</jaxrs.version>
</properties>

<dependencies>
  <!-- JAX-RS -->
      <dependency>
          <groupId>javax.ws.rs</groupId>
          <artifactId>javax.ws.rs-api</artifactId>
          <version>${jaxrs.version}</version>
      </dependency>
      <!-- Jersey 2.28 -->
      <dependency>
          <groupId>org.glassfish.jersey.containers</groupId>
          <artifactId>jersey-container-servlet</artifactId>
          <version>${jersey2.version}</version>
      </dependency>
      <dependency>
          <groupId>org.glassfish.jersey.core</groupId>
          <artifactId>jersey-server</artifactId>
          <version>${jersey2.version}</version>
      </dependency>
      <dependency>
          <groupId>org.glassfish.jersey.inject</groupId>
          <artifactId>jersey-hk2</artifactId>
          <version>2.28</version>
      </dependency>

      <!-- https://mvnrepository.com/artifact/org.glassfish.jersey.media/
        jersey-media-json-jackson -->
      <dependency>
        <groupId>org.glassfish.jersey.media</groupId>
        <artifactId>jersey-media-json-jackson</artifactId>
        <version>2.28</version>
      </dependency>
</dependencies>
  

Note: What happens when you do not add jersey-media-json-jackson jar in pom.xml ? The API when hit returns a SEVERE exception:
SEVERE: MessageBodyWriter not found for media type=application/json, type=class com.programmertoday.restjersey.model.Department, genericType=class com.programmertoday.restjersey.model.Department.
Because the resource is trying to produce an object of type json, but it does not find any convertor which converts Object into a json, hence adding the above jackson jar resolves this issue.

1. API code

package com.programmertoday.restjersey.api;

import javax.ws.rs.GET;
import javax.ws.rs.Path;

@Path("/api")
public class JerseyResource {

  @GET
  @Path("/department")
  @Produces(MediaType.APPLICATION_JSON)
    public Department getDepartment()
    {
          return new Department("IT","Information Technology");
    }
}
   

2. Model Class

package com.programmertoday.restjersey.model;

public class Department {

  private String depName;
  private String depCode;

  public Department(String a, String b) {
    this.depCode = a;
    this.depName = b;
  }

  public String getDepName() {
    return depName;
  }

  public void setDepName(String depName) {
    this.depName = depName;
  }

  public String getDepCode() {
    return depCode;
  }

  public void setDepCode(String depCode) {
    this.depCode = depCode;
  }
}
    

3. 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/javaee" 
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>RESTful_Project</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-serlvet</servlet-name>
        <servlet-class>org.glassfish.jersey.servlet.ServletContainer</servlet-class>
        <init-param>
              <param-name>jersey.config.server.provider.packages</param-name>
              <param-value>com.programmertoday.restjersey.api</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>
      

TEST the code

Add a tomcat server and run the project !!

Using any REST client OR any web browser like google chrome open the below url to hit the api.

http://localhost:8080/RESTful_Project/rest/api/department

{"depName":"Information Technology","depCode":"IT"}

Summary

In this article we learnt how to create a simple Jersey based REST API with JACKSON, which leverages us to convert the model class to JSON on the fly. There is no need to write a JSON Array explicitly for this. It’s Super simple and easy !.
Hope you liked the article !

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