Spring-mvc – Spring MVC: How to return image in @ResponseBody

Since I spent a lot of time on this issue, I thought I'd share my solution. Since spring 3.0.4, there is a configuration parameter that is called <mvc:resources/> (more about that on the reference documentation website) which can be used to serve static resources while still using the DispatchServlet on your site's root.

In order to use this, use a directory structure that looks like the following:

src/
 springmvc/
  web/
   MyController.java
WebContent/
  resources/
   img/
    image.jpg
  WEB-INF/
    jsp/
      index.jsp
    web.xml
    springmvc-servlet.xml

The contents of the files should look like:

src/springmvc/web/HelloWorldController.java:

package springmvc.web;

import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;

@Controller
public class HelloWorldController {

 @RequestMapping(value="/")
 public String index() {
  return "index";
 }
}

WebContent/WEB-INF/web.xml:

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.4" xmlns="http://java.sun.com/xml/ns/j2ee"
 xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
 xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee 
         http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd">

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

 <servlet-mapping>
  <servlet-name>springmvc</servlet-name>
  <url-pattern>/</url-pattern>
 </servlet-mapping>
</web-app>

WebContent/WEB-INF/springmvc-servlet.xml:

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
 xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:context="http://www.springframework.org/schema/context"
 xmlns:mvc="http://www.springframework.org/schema/mvc"
 xsi:schemaLocation="http://www.springframework.org/schema/beans
 http://www.springframework.org/schema/beans/spring-beans-2.5.xsd
 http://www.springframework.org/schema/mvc
 http://www.springframework.org/schema/mvc/spring-mvc-3.0.xsd
 http://www.springframework.org/schema/context
 http://www.springframework.org/schema/context/spring-context-3.0.xsd">

    <!-- not strictly necessary for this example, but still useful, see http://static.springsource.org/spring/docs/3.0.x/spring-framework-reference/html/mvc.html#mvc-ann-controller for more information -->
 <context:component-scan base-package="springmvc.web" />

    <!-- the mvc resources tag does the magic -->
 <mvc:resources mapping="/resources/**" location="/resources/" />

    <!-- also add the following beans to get rid of some exceptions -->
 <bean      class="org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter" />
 <bean
class="org.springframework.web.servlet.mvc.annotation.DefaultAnnotationHandlerMapping">
 </bean>

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

</beans>

WebContent/jsp/index.jsp:

<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<h1>Page with image</h1>
<!-- use c:url to get the correct absolute path -->
<img src="<c:url value="/resources/img/image.jpg" />" />

Hope this helps :-)

First, and most important - all Spring beans are managed - they "live" inside a container, called "application context".

Second, each application has an entry point to that context. Web applications have a Servlet, JSF uses a el-resolver, etc. Also, there is a place where the application context is bootstrapped and all beans - autowired. In web applications this can be a startup listener.

Autowiring happens by placing an instance of one bean into the desired field in an instance of another bean. Both classes should be beans, i.e. they should be defined to live in the application context.

What is "living" in the application context? This means that the context instantiates the objects, not you. I.e. - you never make new UserServiceImpl() - the container finds each injection point and sets an instance there.

In your controllers, you just have the following:

@Controller // Defines that this class is a spring bean
@RequestMapping("/users")
public class SomeController {

    // Tells the application context to inject an instance of UserService here
    @Autowired
    private UserService userService;

    @RequestMapping("/login")
    public void login(@RequestParam("username") String username,
           @RequestParam("password") String password) {

        // The UserServiceImpl is already injected and you can use it
        userService.login(username, password);

    }
}

A few notes:

• In your applicationContext.xml you should enable the <context:component-scan> so that classes are scanned for the @Controller, @Service, etc. annotations.
• The entry point for a Spring-MVC application is the DispatcherServlet, but it is hidden from you, and hence the direct interaction and bootstrapping of the application context happens behind the scene.
• UserServiceImpl should also be defined as bean - either using <bean id=".." class=".."> or using the @Service annotation. Since it will be the only implementor of UserService, it will be injected.
• Apart from the @Autowired annotation, Spring can use XML-configurable autowiring. In that case all fields that have a name or type that matches with an existing bean automatically get a bean injected. In fact, that was the initial idea of autowiring - to have fields injected with dependencies without any configuration. Other annotations like @Inject, @Resource can also be used.