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

Question

我有一个映射有以下注释的控制器：

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

我返回了一个有效的JSON字符串，但是，当我在浏览器中的Chrome Dev
Tools上查看响应时，内容类型不是application/json唯一的text/html。为什么未设置内容类型？

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

要了解的第一件事是，RequestMapping#produces()在元素

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

仅用于限制请求处理程序的映射。 它什么也没做。

然后，假设您的方法的返回类型为，String并带有注释@ResponseBody，则将通过处理返回值并将StringHttpMessageConverter其设置Content- type为text/plain。如果您想自己返回JSON字符串并将标头设置为application/json，请使用返回类型ResponseEntity（摆脱@ResponseBody）并向其添加适当的标头。

@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，您可能应该有

<mvc:annotation-driven />

在Servlet上下文配置中使用最合适的默认设置来设置MVC配置。