Crear un webservice RESTFUL en Spring (JSON)

Vamos a crear un webservice Restful con JSON en Spring. 

1 Crear un modulo maven para web.

2. Agregar lo siguiente en web.xml.  En el archivo web.xml se define el servlet DispatcherServlet.

<web-app id="WebApp_ID" version="2.4"

xmlns="http://java.sun.com/xml/ns/j2ee" 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">

<display-name>Spring MVC Application</display-name>

<servlet>

<servlet-name>SpringRest</servlet-name>

<servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>

<load-on-startup>1</load-on-startup>

</servlet>

<servlet-mapping>

<servlet-name>SpringRest</servlet-name>

<url-pattern>/</url-pattern>

</servlet-mapping>

</web-app>

3. Crear el archivo SpringRest-servlet.xml para la configuracion de spring mvc. En el archivo SpringRest-servlet.xml se definen  varias cosas entre ellas se carga el bean del servicio web, y se definen los beans para convertir de pojo a json y de json a pojo.

<?xml version="1.0" encoding="UTF-8"?>
<beans:beans xmlns="http://www.springframework.org/schema/mvc"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:beans="http://www.springframework.org/schema/beans"
xmlns:context="http://www.springframework.org/schema/context"
xsi:schemaLocation="http://www.springframework.org/schema/mvc http://www.springframework.org/schema/mvc/spring-mvc.xsd
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">

<!-- DispatcherServlet Context: defines this servlet's request-processing 
infrastructure -->

<!-- Enables the Spring MVC @Controller programming model -->
<annotation-driven />



<!-- Resolves views selected for rendering by @Controllers to .jsp resources 
in the /WEB-INF/views directory -->
<beans:bean
class="org.springframework.web.servlet.view.InternalResourceViewResolver">
<beans:property name="prefix" value="/" />
<beans:property name="suffix" value=".jsp" />

</beans:bean>
        <resources mapping="/**" location="/" />

<context:component-scan base-package="com.webservices" />

</beans:beans>

4. Crear el modelo employee

package com.model;

import java.io.Serializable;

import java.util.Date;

import com.fasterxml.jackson.databind.annotation.JsonSerialize;

import com.fasterxml.jackson.databind.ser.std.DateSerializer;

public class Employee implements Serializable {

private static final long serialVersionUID = -7788619177798333712L;

private int id;

private String name;

private Date createdDate;

public int getId() {

return id;

}

public void setId(int id) {

this.id = id;

}

public String getName() {

return name;

}

public void setName(String name) {

this.name = name;

}

@JsonSerialize(using = DateSerializer.class)

public Date getCreatedDate() {

return createdDate;

}

public void setCreatedDate(Date createdDate) {

this.createdDate = createdDate;

}

}

5. Crear una clase estatica para las URIs

package com.model;

public class EmpRestURIConstants {

public static final String DUMMY_EMP = "/rest/emp/dummy";

public static final String GET_EMP = "/rest/emp/{id}";

public static final String GET_ALL_EMP = "/rest/emps";

public static final String CREATE_EMP = "/rest/emp/create";

public static final String DELETE_EMP = "/rest/emp/delete/{id}";

}

6. Crear el controlador principal.

package com.webservices;

import java.util.ArrayList;

import java.util.Date;

import java.util.HashMap;

import java.util.List;

import java.util.Map;

import java.util.Set;

import org.slf4j.Logger;

import org.slf4j.LoggerFactory;

import org.springframework.stereotype.Controller;

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

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

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

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

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

import com.model.Employee;

import com.model.EmpRestURIConstants;

/**

 * Handles requests for the Employee service.

 */

@Controller

public class EmployeeController {

private static final Logger logger = LoggerFactory.getLogger(EmployeeController.class);

//Map to store employees, ideally we should use database

Map<Integer, Employee> empData = new HashMap<Integer, Employee>();

@RequestMapping(value = EmpRestURIConstants.DUMMY_EMP, method = RequestMethod.GET)

public @ResponseBody Employee getDummyEmployee() {

logger.info("Start getDummyEmployee");

Employee emp = new Employee();

emp.setId(9999);

emp.setName("Dummy");

emp.setCreatedDate(new Date());

empData.put(9999, emp);

return emp;

}

@RequestMapping(value = EmpRestURIConstants.GET_EMP, method = RequestMethod.GET)

public @ResponseBody Employee getEmployee(@PathVariable("id") int empId) {

logger.info("Start getEmployee. ID="+empId);

return empData.get(empId);

}

@RequestMapping(value = EmpRestURIConstants.GET_ALL_EMP, method = RequestMethod.GET)

public @ResponseBody List<Employee> getAllEmployees() {

logger.info("Start getAllEmployees.");

List<Employee> emps = new ArrayList<Employee>();

Set<Integer> empIdKeys = empData.keySet();

for(Integer i : empIdKeys){

emps.add(empData.get(i));

}

return emps;

}

@RequestMapping(value = EmpRestURIConstants.CREATE_EMP, method = RequestMethod.POST)

public @ResponseBody Employee createEmployee(@RequestBody Employee emp) {

logger.info("Start createEmployee.");

emp.setCreatedDate(new Date());

empData.put(emp.getId(), emp);

return emp;

}

@RequestMapping(value = EmpRestURIConstants.DELETE_EMP, method = RequestMethod.PUT)

public @ResponseBody Employee deleteEmployee(@PathVariable("id") int empId) {

logger.info("Start deleteEmployee.");

Employee emp = empData.get(empId);

empData.remove(empId);

return emp;

}

}

@ResponseBody traduce el bean a un formato especificado en la configuracion. En este caso se convierte automaticamente a una version de Json del bean. @RequestMapping es usado para mapear la url al metodo. @PathVariable es usado para mapear el path de variable.

7. Usaremos postman para probar los servicios web:

Empezamos probando el health del servicio web. 

http://localhost:8080/SpringRest/rest/emp/dummy

Para extraer un empleado en particular:

http://localhost:8080/SpringRest/rest/emp/9999/

Para crear un registro para un empleado nuevo, se utiliza el siguiente webservice con el metodo POST con el siguiente body: {"id": 1,"name": "Luis Mi"}

http://localhost:8080/SpringRest/rest/emp/create

Para extraer el empleado que acabamos de generar:

http://localhost:8080/SpringRest/rest/emp/1/