Passing JSON Map into Spring MVC Controller

Question

I'm trying to send a JSON representation of a Map into my controller as a POST parameter.

@RequestMapping(value = "/search.do", method = RequestMethod.GET, consumes = { "application/json" })
public @ResponseBody Results search(@RequestParam("filters") HashMap<String,String> filters, HttpServletRequest request) {
       //do stuff
}

I found that @RequestParam would just throw a 500 error, so I tried using @ModelAttribute instead.

@RequestMapping(value = "/search.do", method = RequestMethod.GET, consumes = { "application/json" })
public @ResponseBody Results search(@ModelAttribute("filters") HashMap<String,String> filters, HttpServletRequest request) {
       //do stuff
}

This would correctly respond to requests, but I realized that the Map was empty. With later experimentation, I found that any object (not just HashMap) would be instantiated, but no fields would be filled in. I do have Jackson on my classpath, and my controllers will respond with JSON. However, it would appear that my current configuration is not allowing Spring to read JSON in via a GET/POST parameter.

How does one pass JSON representations of objects from a client-side AJAX request to a Spring controller as a request parameter and get a Java object out?

EDIT Adding my relevant Spring configuration

  <bean class="org.springframework.web.servlet.view.ContentNegotiatingViewResolver">
    <property name="mediaTypes">
      <map>
        <entry key="html" value="text/html" />
        <entry key="json" value="application/json" />
      </map>
    </property>
    <property name="viewResolvers">
      <list>
        <bean class="org.springframework.web.servlet.view.UrlBasedViewResolver">
          <property name="viewClass" value="org.springframework.web.servlet.view.JstlView" />
          <property name="prefix" value="/WEB-INF/jsp/" />
          <property name="suffix" value=".jsp" />
        </bean>
      </list>
    </property>
    <property name="defaultViews">
      <list>
        <bean class="org.springframework.web.servlet.view.json.MappingJacksonJsonView">
          <property name="prefixJson" value="true" />
        </bean>
      </list>
    </property>
  </bean>
  <bean class="org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter">
    <property name="messageConverters">
      <list>
        <bean class="org.springframework.http.converter.json.MappingJacksonHttpMessageConverter"/>
      </list>
    </property>
  </bean>

On the suggestion of a commenter, I tried @RequestBody. This will work, so long as the JSON strings are quoted with double quotes.

@RequestMapping(value = "/search.do", method = RequestMethod.POST, consumes = { "application/json" })
public @ResponseBody Results<T> search(@RequestBody HashMap<String,String> filters, HttpServletRequest request) {
      //do stuff
}

This does solve my immediate issue, but I'm still curious as to how ou might pass in multiple JSON objects via an AJAX call.

Answer 1

This does solve my immediate issue, but I'm still curious as to how ou might pass in multiple JSON objects via an AJAX call.

The best way to do this is to have a wrapper object that contains the two (or multiple) objects you want to pass. You then construct your JSON object as an array of the two objects i.e.

[
  {
    "name" : "object1",
    "prop1" : "foo",
    "prop2" : "bar"
  },
  {
    "name" : "object2",
    "prop1" : "hello",
    "prop2" : "world"
  }
]

Then in your controller method you recieve the request body as a single object and extract the two contained objects. i.e:

@RequestMapping(value="/handlePost", method = RequestMethod.POST, 
                consumes = {      "application/json" })
public void doPost(@RequestBody WrapperObject wrapperObj) { 
     Object obj1 = wrapperObj.getObj1;
     Object obj2 = wrapperObj.getObj2;

     //Do what you want with the objects...


}

The wrapper object would look something like...

public class WrapperObject {    
private Object obj1;
private Object obj2;

public Object getObj1() {
    return obj1;
}
public void setObj1(Object obj1) {
    this.obj1 = obj1;
}
public Object getObj2() {
    return obj2;
}
public void setObj2(Object obj2) {
    this.obj2 = obj2;
}   

}