spring4.0之三：@RestController

spring4.0重要的一个新的改进是@RestController注解，它继承自@Controller注解。4.0之前的版本，Spring MVC的组件都使用@Controller来标识当前类是一个控制器servlet。

使用这个特性，我们可以开发REST服务的时候不需要使用@Controller而专门的@RestController。

当你实现一个RESTful web services的时候，response将一直通过response body发送。为了简化开发，Spring 4.0提供了一个专门版本的controller。下面我们来看看@RestController实现的定义：

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Controller
@ResponseBody
public @interface RestController {

    /**
     * The value may indicate a suggestion for a logical component name,
     * to be turned into a Spring bean in case of an autodetected component.
     * @return the suggested component name, if any
     * @since 4.0.1
     */
    String value() default "";

}

官方文档解释：

A convenience annotation that is itself annotated with @Controller and @ResponseBody. Types that carry this annotation are treated as controllers where @RequestMapping methods assume @ResponseBody semantics by default.
注解本身使用@Controller和@ResponseBody注解。使用了这个注解的类会被看作一个controller-使用@RequestMapping的方法有一个默认的@ResponseBody注解。
@ResponseBody – As of version 4.0 this annotation can also be added on the type level in which case is inherited and does not need to be added on the method level.
@ResponseBody也可以加到类一级，通过继承方法一级不需要添加。  

示例：

UserDetails.java

package javabeat.net.rest;  

import javax.xml.bind.annotation.XmlAttribute;
import javax.xml.bind.annotation.XmlRootElement;
@XmlRootElement
public class UserDetails {
    private String userName;
    private String emailId;  

    @XmlAttribute
    public String getUserName() {
        return userName;
    }
    public void setUserName(String userName) {
        this.userName = userName;
    }  

    @XmlAttribute
    public String getEmailId() {
        return emailId;
    }
    public void setEmailId(String emailId) {
        this.emailId = emailId;
    }
}  

SpringRestControllerDemo.java

package javabeat.net.rest;  

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.http.HttpStatus;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.ResponseStatus;
import org.springframework.web.bind.annotation.RestController;  

@RestController
public class SpringRestControllerDemo {
    @Autowired UserDetails userDetails;
    @RequestMapping(value="/springcontent",
            method=RequestMethod.GET,produces={"application/xml", "application/json"})
    @ResponseStatus(HttpStatus.OK)
    public UserDetails getUser() {
        UserDetails userDetails = new UserDetails();
        userDetails.setUserName("Krishna");
        userDetails.setEmailId("krishna@gmail.com");
        return userDetails;
    }  

    @RequestMapping(value="/springcontent.htm", method=RequestMethod.GET)
    @ResponseStatus(HttpStatus.OK)
    public String getUserHtml() {
        //Test HTML view
        return "example";
    }
}  

dispatcher-servlet.xml

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

http://www.springframework.org/schema/beans/spring-beans-4.0.xsd
http://www.springframework.org/schema/mvc
http://www.springframework.org/schema/mvc/spring-mvc.xsd
http://www.springframework.org/schema/context
http://www.springframework.org/schema/context/spring-context-4.0.xsd">
    <context:component-scan base-package="com.infosys.rest" />
    <bean id="userDetails" class="javabeat.net.rest.UserDetails"/>
    <mvc:annotation-driven content-negotiation-manager="contentManager"/>
    <bean id="contentManager"
                class="org.springframework.web.accept.ContentNegotiationManagerFactoryBean">
                <property name="favorPathExtension" value="true"/>
                <property name="ignoreAcceptHeader" value="true" />
                <property name="defaultContentType" value="text/html" />
                <property name="useJaf" value="false"/>
                <property name="mediaTypes">
                    <map>
                        <entry key="json" value="application/json" />
                        <entry key="html" value="text/html" />
                        <entry key="xml" value="application/xml" />
                    </map>
                </property>
        </bean>
    <bean id="jspViewResolver"
        class="org.springframework.web.servlet.view.InternalResourceViewResolver">
        <property name="prefix" value="/WEB-INF/jsp/" />
        <property name="suffix" value=".jsp" />
    </bean>  

</beans>