Servlet cannot directly obtain JSON format data in request request

Servlet Can't get... Directly request In the request JSON Format data

Reuqest Of Conventional methods

request.getParameter(name)

In general

1. Form request and Form serialization
2. ajax.post( url, params, data=>{} )
3. axios.post( url, qs.stringify{ (params}).then( res=>{ })
4. …

Now? JSON Format data You can't get parameters

let params = {
    "uname":"yc", "upwd":"123321"}
$.ajax({
    
     type:"post",
       url:"amdin/login",
       contentType:'application/json;charset=UTF-8',
       data: params ,  //  data format  json String passing 
       success:function(data){
    
        	console.log(data);
       }
 });

String uname = request.getParameter("uname"); // null 

Scheme 1

jQuery Of ajax Change the request parameter type to Default encoding Key value pair K->V Serialization

contentType: "application/x-www-form-urlencoded",

Option two

With the help of tripartite Library GSON Not only can we get parameters , And it can also be encapsulated into entity classes

	/** *  Premise ：  Pass it on the front desk json Data to the backstage doPOST Interface ,request The regular program of   Can't get json data   Show  null *  Use the third-party library   On the front JSON Request parameters of data format   Encapsulated as an object  * @param <T> * @param cls * @param request * @return * @throws IOException */
	public static <T> T getJSONParamesToObject(Class<T> cls , HttpServletRequest request) throws IOException{
    
		BufferedReader reader = request.getReader();	
		Gson gson = new Gson();
		return gson.fromJson( reader, cls);
	}