【1】contentType預設為application/x-www-form-urlencoded的情況

① JSP例項如下

var url = "person.action";
var jsonStr = {"name":'ji',"age":20};//object型別
var jsonArrayFinal = JSON.stringify(jsonStr);//string型別

jQuery.ajax({
				type: "post",//put delete get post
				url: url,
 				//dataType : 'json',
/*
預期伺服器返回的資料型別 xml html script  json jsonp  text ;
如果不指定，則伺服器根據返回資料型別自行判斷
*/

				async:true,//預設非同步
				data : {mydata:jsonArrayFinal},
				//或{'mydata':jsonArrayFinal}
				
/*
要麼使用 \ 對json進行手動轉譯，要麼使用JSON.stringify(jsonStr) 將其轉換為字串型別；
如果不進行轉譯，使用【2】中的後臺接收方法，那麼不會報異常，但是獲取不到資料。
data : {mydata:jsonStr},//報空指標異常，傳不過去
*/
	
 				contentType:"application/x-www-form-urlencoded",//預設值
				success: function(data,textStatus){
					alert(data);
					alert("操作成功");
				},
				error: function(xhr,status,errMsg){
					alert("操作失敗!");
				}
				});
 

② 後臺接收方法：

public String getJson(){
		//引數為鍵值對方式可以直接使用getParameter方法
		String jsonStr = getRequest().getParameter("mydata");
		System.out.println(jsonStr);
		
		 ObjectMapper objectMapper = new ObjectMapper();
		 try {
			Person person1 = objectMapper.readValue(jsonStr, Person.class);
			System.out.println(person1);
			out(jsonStr);
		} catch (IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		 return null;
	}
 

result as follows :

③ F12檢視瀏覽器控制檯：

Remote Address:127.0.0.1:8080
Request URL:http://localhost:8080/JavaSE-JS/person.action
Request Method:POST
Status Code:200 OK
Response Headers//Response Headers
view source
Content-Type:text/html;charset=UTF-8
Date:Wed, 18 Jan 2017 01:31:02 GMT
Server:Apache-Coyote/1.1
Transfer-Encoding:chunked
Request Headers//Request Headers
view source
Accept:*/*
Accept-Encoding:gzip, deflate
Accept-Language:zh-CN,zh;q=0.8
Connection:keep-alive
Content-Length:51
//contentType
Content-Type:application/x-www-form-urlencoded; charset=UTF-8
Cookie:JSESSIONID=E7D60D8B9B3E1958B7077CE26E4EE75A
Host:localhost:8080
Origin:http://localhost:8080
Referer:http://localhost:8080/JavaSE-JS/testAjax1.jsp
User-Agent:Mozilla/5.0 (Windows NT 10.0; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/45.0.2454.101 Safari/537.36
X-Requested-With:XMLHttpRequest
Form Data//表單資料
view source
view URL encoded
mydata:{"name":"ji","age":20}
 

可以看到，此時請求頭，contentType為預設值，傳送資料在Form Data。

【2】contentType預設非application/x-www-form-urlencoded的情況

比如，contentType:"application/json;charset=utf-8",此時，若使用例子一中的後臺接收方法，是接收不到資料的。

① JSP例項如下：

jQuery.ajax({
				type: "post",//put delete get post
				url: url,
// 				dataType : 'json',
//預期伺服器返回的資料型別 xml html script  json jsonp  text 

			    async:true,//預設非同步
			    contentType:"application/json;charset=utf-8",
 				//data : jsonArrayFinal,
				//{"name":"ji","age":20}
				
				data : {mydata:jsonArrayFinal},
				//mydata={"name":"ji","age":20}---進行了url編碼
				//mydata=%7B%22name%22%3A%22ji%22%2C%22age%22%3A20%7D
				
 				//data : jsonStr,
				//引數：name=ji&age=20
				
 				//data : {mydata:jsonStr},
				//mydata[name]=ji&mydata[age]=20-進行了編碼-mydata%5Bname%5D=ji&mydata%5Bage%5D=20
				success: function(data,textStatus){
					alert(data);
					alert("操作成功");
				},
				error: function(xhr,status,errMsg){
					alert("操作失敗!");
				}
				});

② 後臺接收方法：

//contentType 非 application/x-www-form-urlencoded
	public String getRequestPayload() throws IOException {  
		
		HttpServletRequest req = getRequest();
        StringBuilder sb = new StringBuilder();  
        //使用getReader()方法獲取Form Data裡面資料
        try(BufferedReader reader = req.getReader();) {  
             char[]buff = new char[1024];  
             int len;  
             while((len = reader.read(buff)) != -1) {  
                      sb.append(buff,0, len);  
             }  
        }catch (IOException e) {  
                 e.printStackTrace();  
        }  
        String sb2 = URLDecoder.decode(sb.toString(),"UTF-8");
        /*
         * 解碼前：mydata=%7B%22name%22%3A%22ji%22%2C%22age%22%3A20%7D 
         * 解碼後：mydata={"name":"ji","age":20}
         */
        out(sb2); 
        System.out.println(sb2);
        return null;
	}  

第一種情況：data : jsonStr,，後臺獲取值name=ji&age=20；
第二種情況：data : {mydata:jsonStr},，後臺獲取值

進行了URL編碼：mydata%5Bname%5D=ji&mydata%5Bage%5D=20
解碼後：mydata[name]=ji&mydata[age]=20

第三種情況：data : jsonArrayFinal,，後臺獲取值{"name":"ji","age":20}；
第四種情況：data : {mydata:jsonArrayFinal},，後臺獲取值

進行了URL編碼：mydata=%7B%22name%22%3A%22ji%22%2C%22age%22%3A20%7D

解碼後：mydata={"name":"ji","age":20}

③ F12檢視瀏覽器控制檯：

Remote Address:127.0.0.1:8080
Request URL:http://localhost:8080/JavaSE-JS/person2.action
Request Method:POST
Status Code:200 OK
Response Headers
view source
Content-Type:text/html;charset=UTF-8
Date:Wed, 18 Jan 2017 01:43:03 GMT
Server:Apache-Coyote/1.1
Transfer-Encoding:chunked
Request Headers
view source
Accept:*/*
Accept-Encoding:gzip, deflate
Accept-Language:zh-CN,zh;q=0.8
Connection:keep-alive
Content-Length:22
//Content-Type:application/json;charset=UTF-8
Content-Type:application/json;charset=UTF-8
Cookie:JSESSIONID=E7D60D8B9B3E1958B7077CE26E4EE75A
Host:localhost:8080
Origin:http://localhost:8080
Referer:http://localhost:8080/JavaSE-JS/testAjax1.jsp
User-Agent:Mozilla/5.0 (Windows NT 10.0; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/45.0.2454.101 Safari/537.36
X-Requested-With:XMLHttpRequest
Request Payload//此時，資料在這裡 ！
view source
{name: "ji", age: 20}
age: 20
name: "ji"

【3】Tips

• 若使用預設contentType，則data請使用key：value形式，且如果value為json，進行轉譯；

• 若使用自定義contentType(如application/json)，則data如果使用value形式，轉譯與否看後臺接收方法；如果使用key:value形式，後臺要進行URL解碼！

• 若使用自定義contentType,第一種後臺方法是獲取不到資料的，請使用第二種後臺接收方法；

• 上面json是手動拼接，也可以可以直接獲取json如下：

var jsonStr = $('#editform').serializeArray();//JSON Object
jsonStr = JSON.stringify(queryString);//JSON string