Spring REST Hello World JSON Example

1) Using

@ResponseBody

Annotation

This technique is simple and easy. You have to include only jackson dependencies into classpath of your application and spring will register

Jackson2JsonMessageConverter

class automatically into context. Whenever you ask for a resource from REST API and provide http header “

accept: application/json

“, you will get back the json representation of resource.

Runtime JSON dependency

<!-- Jackson JSON Processor -->
<dependency>
<groupId>com.fasterxml.jackson.core</groupId>
<artifactId>jackson-databind</artifactId>
<version>2.4.1</version>
</dependency>

@ResponseBody Support

Here @RestController = @Controller + @ResponseBody

@RestController
public class EmployeeRESTController
{
@RequestMapping(value = "/employees")
public EmployeeListVO getAllEmployees()
{
EmployeeListVO employees = new EmployeeListVO();

EmployeeVO empOne = new EmployeeVO(1,"Lokesh","Gupta","howtodoinjava@gmail.com");
EmployeeVO empTwo = new EmployeeVO(2,"Amit","Singhal","asinghal@yahoo.com");
EmployeeVO empThree = new EmployeeVO(3,"Kirti","Mishra","kmishra@gmail.com");

employees.getEmployees().add(empOne);
employees.getEmployees().add(empTwo);
employees.getEmployees().add(empThree);

return employees;
}

@RequestMapping(value = "/employees/{id}")
public ResponseEntity<EmployeeVO> getEmployeeById (@PathVariable("id") int id)
{
if (id <= 3) {
EmployeeVO employee = new EmployeeVO(1,"Lokesh","Gupta","howtodoinjava@gmail.com");
return new ResponseEntity<EmployeeVO>(employee, HttpStatus.OK);
}
return new ResponseEntity(HttpStatus.NOT_FOUND);
}
}

2) Using

MappingJackson2JsonView

Support

The

MappingJackson2JsonView

class also depends on the presence of the Jackson JSON processor library in classpath, so you don’t need to add anything extra. Complete

pom.xml

looks like this:

pom.xml

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd"> <modelVersion>4.0.0</modelVersion>
<groupId>com.howtodoinjava.demo</groupId>
<artifactId>springrestexample</artifactId>
<packaging>war</packaging>
<version>0.0.1-SNAPSHOT</version>
<name>springrestexample Maven Webapp</name>
<url>http://maven.apache.org</url>
<dependencies>
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>4.12</version>
<scope>test</scope>
</dependency>

<!-- Spring MVC support -->

<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-webmvc</artifactId>
<version>4.1.4.RELEASE</version>
</dependency>

<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-web</artifactId>
<version>4.1.4.RELEASE</version>
</dependency>

<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-core</artifactId>
<version>4.1.4.RELEASE</version>
</dependency>

<!-- Jackson JSON Processor -->
<dependency>
<groupId>com.fasterxml.jackson.core</groupId>
<artifactId>jackson-databind</artifactId>
<version>2.4.1</version>
</dependency>

</dependencies>
<build>
<finalName>springrestexample</finalName>
</build>
</project>

2) Adding

MappingJackson2JsonView

view

When you are using

MappingJackson2JsonView

class, you will need to return a view name of type

MappingJackson2JsonView

. So you will need to change two places.

a) Controller change

You will need to return

viewName

from controller method. In our case, view name is “

jsonTemplate

“.

“`

package com.howtodoinjava.demo.controller;

import org.springframework.http.HttpStatus;

import org.springframework.http.MediaType;

import org.springframework.http.ResponseEntity;

import org.springframework.stereotype.Controller;

import org.springframework.ui.Model;

import org.springframework.web.bind.annotation.PathVariable;

import org.springframework.web.bind.annotation.RequestMapping;

import com.howtodoinjava.demo.model.EmployeeListVO;

import com.howtodoinjava.demo.model.EmployeeVO;

@Controller

public class EmployeeRESTController

{

private EmployeeListVO getEmployeesCollection()
{
EmployeeListVO employees = new EmployeeListVO();

EmployeeVO empOne = new EmployeeVO(1,"Lokesh","Gupta","howtodoinjava@gmail.com");
EmployeeVO empTwo = new EmployeeVO(2,"Amit","Singhal","asinghal@yahoo.com");
EmployeeVO empThree = new EmployeeVO(3,"Kirti","Mishra","kmishra@gmail.com");

employees.getEmployees().add(empOne);
employees.getEmployees().add(empTwo);
employees.getEmployees().add(empThree);

return employees;
}

@RequestMapping(value = "/employees")
public String getAllEmployeesJSON(Model model)
{
model.addAttribute("employees", getEmployeesCollection());
return "jsonTemplate";
}

}

““

b) Configuration Change

You will need to configure viewName “

jsonTemplate

” as bean of type

MappingJackson2JsonView

. And you will need to configure view resolver of type

BeanNameViewResolver

. This way viewName “

jsonTemplate

” will be matched with

MappingJackson2JsonView

and parsed JSON response will be returned to client.

RESTConfiguration.java

@Configuration
public class RESTConfiguration
{
@Bean
public View jsonTemplate() {
MappingJackson2JsonView view = new MappingJackson2JsonView();
view.setPrettyPrint(true);
return view;
}

@Bean
public ViewResolver viewResolver() {
return new BeanNameViewResolver();
}
}

Equivalent XML configuration to above java configuration is as below.

spring-servlet.xml

<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:context="http://www.springframework.org/schema/context"
xmlns:mvc="http://www.springframework.org/schema/mvc"
xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd http://www.springframework.org/schema/mvc http://www.springframework.org/schema/mvc/spring-mvc.xsd"> 
<context:component-scan base-package="com.howtodoinjava.demo" />
<mvc:annotation-driven />

<!-- JSON Support -->
<bean name="viewResolver" class="org.springframework.web.servlet.view.BeanNameViewResolver"/>
<bean name="jsonTemplate" class="org.springframework.web.servlet.view.json.MappingJackson2JsonView"/>

</beans>

3) Test Changes

Now when you hit the URL : http://localhost:8080/springrestexample/employees , you will get this result.

Project Structure