Springmvc of the @responsebody, @RequestBody use need to pay attention to the place

Springmvc I think it's better than struts2. One of the reasons is that you can use annotations to parse JSON data quickly and easily. However, even so, there is a need to pay attention to the place.

1, the return place sets @responsebody, the request object parameter @requestbody, the individual parameter does not add @requestbody;

@RequestMapping (value= "/validation")    String Validation (string username)throws  exception{
username ;  }

2, if you want to return an object, then return directly, spring will automatically convert to JSON data.

@RequestMapping (value= "/validation")    User validation (String username)throws  exception{
User U = New User (username);        return u;} 

3, if the transmission is a set of data, can be encapsulated with objects, using @requestbody will help us to convert the JSON to the corresponding object.

@RequestMapping (value= "/validation") public String validation (@RequestBody user user)  Throws exception{
return "Index";}

Attention:

1, the situation of a single parameter

a), return a single variable SPRINGMVC will not help us to convert, will only return the original value.

b), single parameter do not use @requestbody, can use @requestparam.

error Condition: GET: 400 parameter illegal or post: appears Username=a,key and value are passed to the parameter

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

c), single parameter do not add ' contentType ' : ' Application/json '. contentType: ' Application/json ', this sentence is removed, this sentence is described in the request Package content format, you should use the default application/x-www-form-urlencoded to properly be parsed by the server.

error Condition: 400 error occurred using @requestparam, with @requestbody Key and value passed to the parameter

2, if it is @RequestBody the whole object, then you will add ' contentType ': ' Application/json '. If not added, there may be 406Not acceptable

  $ (' #username '). blur (function () {var postdata = ' {"username": "' + $ (' #username '). Val () + '", "Password": "' + $ (' # Password '). val () + '} ';                $.ajax ({                    URL: "Validation",                    Type: "Post",                    cache:false,
ContentType: ' Application/json ', Data:postdata, DataType: ' JSON '

As mentioned above, as to the specific reasons for these situations, there is a time to study spring's source code at a breakpoint.

Springmvc of the @responsebody, @RequestBody use need to pay attention to the place