Spring MVC 4: "application/json" Content Type is not being set correctly

Question

I have a controller mapped with the following annotation:

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

I return a valid JSON string however, the content-type when I view the response on Chrome Dev Tools in browser is not application/json but just plain text/html. Why is the content type not being set?

My 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> 

My 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> 

Using WildFly 8.1 as my app server.

Answer 1

First thing to understand is that the RequestMapping#produces() element in

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

serves only to restrict the mapping for your request handlers. It does nothing else.

Then, given that your method has a return type of String and is annotated with @ResponseBody, the return value will be handled by StringHttpMessageConverter which sets the Content-type header to text/plain. If you want to return a JSON string yourself and set the header to application/json, use a return type of ResponseEntity (get rid of @ResponseBody) and add appropriate headers to it.

@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); } 

---

Note that you should probably have

<mvc:annotation-driven />  

in your servlet context configuration to set up your MVC configuration with the most suitable defaults.

Answer 2

As other people have commented, because the return type of your method is String Spring won't feel need to do anything with the result.

If you change your signature so that the return type is something that needs marshalling, that should help:

@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; }