REST Project to return JSON Response

Overview

In this chapter we will modify the previous chapters code to return the output in JSON format other than XML

Lets Begin

We will create Eclipse Maven project as follows-
final-mvc2-1

In our POM will add the additional dependencied of required for JSON format.


<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.test</groupId>
    <artifactId>employee-management-system</artifactId>
    <packaging>war</packaging>
    <version>0.0.1-SNAPSHOT</version>
    <name>employee-management-system Maven Webapp</name>
    <url>http://maven.apache.org</url>
    <dependencies>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>3.8.1</version>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-context</artifactId>
            <version>4.0.5.RELEASE</version>
        </dependency>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-webmvc</artifactId>
            <version>4.0.5.RELEASE</version>
        </dependency>
        <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>jstl</artifactId>
            <version>1.2</version>
        </dependency>
        <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-annotations</artifactId>
            <version>2.5.4</version>
        </dependency>
        <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-databind</artifactId>
            <version>2.5.4</version>
        </dependency>
        <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-core</artifactId>
            <version>2.5.4</version>
        </dependency>
    </dependencies>
    <build>
        <finalName>employee-management-system</finalName>
        <plugins>
            <plugin>
                <groupId>org.apache.tomcat.maven</groupId>
                <artifactId>tomcat7-maven-plugin</artifactId>
                <version>2.2</version>
            </plugin>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-war-plugin</artifactId>
                <version>2.4</version>
            </plugin>
        </plugins>
    </build>
</project>

The web.xml is as follows. It has a filter to allow all URLs.

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://java.sun.com/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
	version="2.5">

	<!-- Configure the Disptcher Servlet -->
	<servlet>
		<servlet-name>Dispatcher</servlet-name>
		<servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
		<load-on-startup>1</load-on-startup>
	</servlet>
	
	<!-- Allow URLs with all extensions -->
	<servlet-mapping>
		<servlet-name>Dispatcher</servlet-name>
		<url-pattern>/*</url-pattern>
	</servlet-mapping>
</web-app>

Define the DispatcherServlet.xml to define the configuration for ContentNegotiation parameter.

<beans xmlns="http://www.springframework.org/schema/beans"
			xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
			xmlns:p="http://www.springframework.org/schema/p"
			xmlns:mvc="http://www.springframework.org/schema/mvc"
			xmlns:context="http://www.springframework.org/schema/context"
			xsi:schemaLocation="
        http://www.springframework.org/schema/beans 
        http://www.springframework.org/schema/beans/spring-beans-3.2.xsd
        http://www.springframework.org/schema/context 
        http://www.springframework.org/schema/context/spring-context-3.2.xsd
        http://www.springframework.org/schema/mvc
        http://www.springframework.org/schema/mvc/spring-mvc-3.2.xsd">

	<context:component-scan base-package="com.javainuse.controller" />
	<context:component-scan base-package="com.javainuse.service" />
	<mvc:annotation-driven
			content-negotiation-manager="contentNegotiationManager" />

	<bean id="contentNegotiationManager"
			class="org.springframework.web.accept.ContentNegotiationManagerFactoryBean">

		<property name="favorPathExtension" value="false" />

		<property name="favorParameter" value="true" />

		<property name="parameterName" value="type" />

<!-- define the keys which will be specified in the URL to specify the return type -->
		<property name="mediaTypes">
			<map>
				<entry key="json" value="application/json"></entry>
				<entry key="xml" value="application/xml" />
			</map>
		</property>
	</bean>
</beans>

Also in the Dispatcher-context.xml we have context:component-scan base-package="com.javainuse.service" Spring scans this particular package for a class annotated with @Component. The EmployeeService class will actually fetch all the required Employee information. Usually EmployeeService should call the EmployeeDAO which will return all items from the DataBase.But here we will mock the EmployeeService class to just return the list of items as follows. We are using the Programming to Interface concept here. You can read more about this in this chapter. So we create the EmployeeService.java and EmployeeServiceMockImpl.java as follows.

  
package com.javainuse.service;

import java.util.List;

import com.javainuse.domain.Employee;

public interface EmployeeService {
	public List<Employee> getAllEmployees();

}

  
package com.javainuse.service;

import java.util.ArrayList;
import java.util.List;

import org.springframework.stereotype.Component;

import com.javainuse.domain.Employee;

@Component
public class EmployeeServiceMockImpl implements EmployeeService {

	private List<Employee> testEmployees = new ArrayList<Employee>();

	// populate the Employee List
	public EmployeeServiceMockImpl() {
		testEmployees.add(new Employee("1", "emp1", "M1", 10000));
		testEmployees.add(new Employee("2", "emp2", "M2", 20000));
		testEmployees.add(new Employee("3", "emp3", "M3", 30000));
		testEmployees.add(new Employee("4", "emp4", "M4", 40000));
		testEmployees.add(new Employee("5", "emp5", "M5", 50000));
		testEmployees.add(new Employee("6", "emp6", "M6", 60000));
	}

	// Return the Mocked Employee List
	public List<Employee> getAllEmployees() {
		return new ArrayList<Employee>(testEmployees);
	}
}

Modify the DisplayEmployeeController.java. Add the headers="Accept=application/json", to tell the MVC to return Employee info in JSON format.

package com.javainuse.controller;

import java.util.List;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.ResponseBody;

import com.javainuse.domain.Employee;
import com.javainuse.service.EmployeeService;

@Controller
public class DisplayEmployeeController {

    @Autowired
    private EmployeeService employeeService;

    @RequestMapping(value = "/viewEmployee/{id}", headers = "Accept=application/json")
    @ResponseBody
    public Employee viewAllItems(@PathVariable String id) {
        List<Employee> allEmployees = employeeService.getAllEmployees();
        return allEmployees.get(Integer.parseInt(id) - 1);
    }
}

These are the only changes required. Build this project and hit the browser with the URL http://localhost:8080/employee-management-system/viewEmployee/4

final-rest3-1

Download Source Code

Download it - Spring REST Project to return JSON Response

What Next?

In the next chapter will REST Project to return both JSON and XML Response using Spring ContentNegotiationManager.

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