Spring MVC 4:"application/json"内容类型未正确设置

Question

我有一个使用以下注释映射的控制器:

@RequestMapping(value = "/json", method = RequestMethod.GET, produces = "application/json")
@ResponseBody
public String bar() {
    return "{\"test\": \"jsonResponseExample\"}";
}

我返回一个有效的JSON字符串,但是当我在浏览器中查看Chrome Dev Tools上的响应时,内容类型application/json不仅仅是简单的text/html.为什么没有设置内容类型？

我的web.xml:

<?xml version="1.0" encoding="UTF-8"?>
<web-app metadata-complete="true" version="3.0"
    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_3_0.xsd">

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

    <servlet>
        <servlet-name>dispatcher</servlet-name>
        <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
        <load-on-startup>1</load-on-startup>
    </servlet>

    <!-- static assets -->
    <servlet-mapping>
        <servlet-name>default</servlet-name>
        <url-pattern>*.js</url-pattern>
    </servlet-mapping>
    <servlet-mapping>
        <servlet-name>default</servlet-name>
        <url-pattern>*.css</url-pattern>
    </servlet-mapping>

    <servlet-mapping>
        <servlet-name>dispatcher</servlet-name>
        <url-pattern>/</url-pattern>
    </servlet-mapping>

    <context-param>
        <param-name>contextConfigLocation</param-name>
        <param-value>/WEB-INF/dispatcher-servlet.xml</param-value>
    </context-param>

    <listener>
        <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
    </listener>
</web-app>

我的dispatcher-servlet.xml:

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:context="http://www.springframework.org/schema/context"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:p="http://www.springframework.org/schema/p"
    xsi:schemaLocation="
    http://www.springframework.org/schema/beans     
    http://www.springframework.org/schema/beans/spring-beans-4.1.xsd
    http://www.springframework.org/schema/context 
    http://www.springframework.org/schema/context/spring-context-4.1.xsd">


    <context:annotation-config />

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

    <bean id="viewResolver"
        class="org.springframework.web.servlet.view.InternalResourceViewResolver">
        <property name="prefix" value="/WEB-INF/jsp/" />
        <property name="suffix" value=".jsp" />
    </bean>
</beans>

使用WildFly 8.1作为我的应用服务器.

Answer 1

首先要明白的是RequestMapping#produces()元素

@RequestMapping(value = "/json", method = RequestMethod.GET, produces = "application/json")

仅用于限制请求处理程序的映射.它没有别的.

然后,假设您的方法具有返回类型String并且带有注释@ResponseBody,则返回值将由标头StringHttpMessageConverter设置来处理.如果您想自己返回一个JSON字符串并将标头设置为,请使用返回类型(删除)并为其添加适当的标头.Content-typetext/plainapplication/jsonResponseEntity@ResponseBody

@RequestMapping(value = "/json", method = RequestMethod.GET, produces = "application/json")
public ResponseEntity<String> bar() {
    final HttpHeaders httpHeaders= new HttpHeaders();
    httpHeaders.setContentType(MediaType.APPLICATION_JSON);
    return new ResponseEntity<String>("{\"test\": \"jsonResponseExample\"}", httpHeaders, HttpStatus.OK);
}

请注意,你应该有

<mvc:annotation-driven /> 

在您的servlet上下文配置中,使用最合适的默认值设置MVC配置.

Answer 2

@ResponseBody在控制器的返回类型上使用杰克逊库和注释。

如果您希望返回表示为 JSon 的 POJO，则此方法有效。如果您想返回 String 而不是 POJO 作为 JSon，请参阅 Sotirious 答案。

Answer 3

正如其他人评论的那样，因为您的方法的返回类型是StringSpring，所以不需要对结果执行任何操作。

如果您更改签名以使返回类型需要编组，这应该会有所帮助：

@RequestMapping(value = "/json", method = RequestMethod.GET, produces = "application/json")
@ResponseBody
public Map<String, Object> bar() {
    HashMap<String, Object> map = new HashMap<String, Object>();
    map.put("test", "jsonRestExample");
    return map;
}