user1757703 user1757703 - 6 months ago 48
JSON Question

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

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

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.

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