Spring MVC 2中的ResponseBody

Question

I am currently working on implementing REST webservices into existing system. This system is using Spring in version 2 (particularly 2.5.6.SEC02). I can't upgrade it to version 3 as it could break existing system components. We didn't make the rest of this system, don't have source codes and don't want to lose warranty, so Spring version should basically stay as it is :)

The question is, how can I implement Rest WS with automatic DTO serialization from/to JSON? I have appropriate Jackson libraries on the classpath. Spring 2 doesn't seem to know about @RequestBody and @ResponseBody yet. Are there any other annotations that can be used, or some alternative way?

Answer 1

You may need to manually parse the JSON String and write it to the response for this to work for you. I suggest using the jackson2 API.

https://github.com/FasterXML/jackson

First, accept a json String as the argument from the request, and then manually parse the String to and from a POJO using the jackson ObjectMapper.

Here's the jQuery/JavaScript:

function incrementAge(){

    var person = {name:"Hubert",age:32};

    $.ajax({

        dataType: "json",
        url: "/myapp/MyAction",
        type: "POST",
        data: {
            person: JSON.stringify(person)
        }

    })
    .done(function (response, textStatus, jqXHR) {

        alert(response.name);//Hubert
        alert(response.age);//33
        //Do stuff here
    });
}

The person pojo:

import com.fasterxml.jackson.annotation.JsonIgnoreProperties;

//Allows name or age to be null or empty, which I like to do to make things easier on the JavaScript side
@JsonIgnoreProperties(ignoreUnknown = true)
public class Person{

    private String name;
    private int age;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }
}

And here's the the controller:

import com.fasterxml.jackson.databind.ObjectMapper;

/*snip*/

@Controller
public class MyController{

    //I prefer to have a single instance of the mapper and then inject it using Spring autowiring
    private ObjectMapper mapper;

    @Autowired
    public MyController(ObjectMapper objectMapper){

        this.objectMapper = objectMapper;
    }

    @RequestMapping(value="/myapp/MyAction", method= {RequestMethod.POST})
    public void myAction(@RequestParam(value = "person") String json, 
                         HttpServletResponse response) throws IOException {

        Person pojo = objectMapper.readValue(new StringReader(json), Person.class);

        int age = pojo.getAge();
        age++;
        pojo.setAge(age);

        objectMapper.writeValue(response.getOutputStream(),pojo);
    }
}

Answer 2

You can try a DIY approach with Spring MVC controllers and JSONObject from json.org. Just use it to json-serialize your returned objects and flush it down the response, with the appropiate headers.

It has its pitfalls (I would recommend you use a simple wrapper class with a getter when you try to send a collection), but I have been happy with it for some years.