Detailed code explanation of jquery ajax passing arrays to the background and how to receive arrays in the background

The array in JS is weakly typed and can contain any type (object, basic type). However, if the array contains an object type, only objects will be displayed when passed to the background. String --[object Object], the reasons are as follows:

When receiving in the background, you can only use request to receive. The request.getParameterValues() method returns a String[], so , it should be that the toString() method of the object is called during the foreground transmission, so what if you still want to pass the object? But it can be implemented using JSON strings, and the JSON strings are parsed into JAVA objects in the background.
Perhaps, you want to say what to do if it is a composite object, such as the following:

public class Person { 
private String username; 
private String password; 
private Address addr; 
}

The Person object has an addr attribute of Address type. It doesn’t matter. The attribute values ​​ultimately used by any object are basicData type, you only need to use the corresponding packaging type parseInt or parseXXX to parse.
Implementation:
OK, this is the principle. Let’s first look at how to write JS:

var as = []; 
var temp = []; 
for ( var int = 0; int < 5; int++) { 
temp.push(&#39;{"k":&#39;); 
temp.push(int); 
temp.push(&#39;,"v":&#39;); 
temp.push(int); 
temp.push(&#39;}&#39;); 
as.push(temp.join("")); 
} 
//Jquery中的方法，具体参考Jquery API 
$.post( "servlet/AjaxServlet?m=putWarningRule",{"aa":as} );

The final string is the following style, (for example only)

{"k":0,"v":0}

Background reception, no framework is discussed, only HttpServletRequest is required

String[] jsonArr = request.getParameterValues("aa[]");

One thing to note is that when passing parameters in js, the parameter name is "aa", but when receiving it in the background, it is "aa[]". Jquery should have done the conversion here, so the best way is Just change it to "aa[]" in JS. The reason why "[]" is not written here is to illustrate the problem. You can use the following method to print all parameters in the request

Enumeration<String> names = request.getParameterNames(); 
while (names.hasMoreElements()) { 
String string = (String) names.nextElement(); 
System.out.println(string); 
}

OK. At this point, the reception has been completed. The only thing left is how to convert a JSON string into a POJO.

/** 
* 将对象转换为JSON格式的字符串 
* @param obj 
* @return 返回JSON字符串 
*/ 
public 
static
 String toJSONAsString(Object obj){ 
try { 
return JSONMapper.toJSON(obj).render(false); 
} catch (Mapper
Exception
 e) { 
e.printStackTrace(); 
} 
return null; 
} 
@SuppressWarnings("unchecked") 
public static <T> T jsonToObject(String jsonStr, Class<T> targetClass) throws TokenStreamException, RecognitionException, MapperException{ 
JSONValue jv = new JSONParser(new StringReader(jsonStr)).nextValue(); 
return (T) JSONMapper.toJava(jv,targetClass); 
} 
//test 
public static void main(String[] args) throws Exception { 
Person p = new Person(); 
p.setK("a"); 
p.setV("v"); 
String json = toJSONAsString(p); 
Person np = jsonToObject(json,Person.class); 
System.out.println(np.getK()+"=="+np.getV()); 
}

After the request gets the value, traverse the array and convert one by one

Person p = JSONUtils.jsonToObject(jsonArr[0], Person.class);

The Person class is as follows:

public class Person { 
private String k; 
private String v; 
public String getK() { 
return k; 
} 
public void setK(String k) { 
this.k = k; 
} 
public String getV() { 
return v; 
} 
public void setV(String v) { 
this.v = v; 
} 
}

Sometimes there will be problems, the background reception less than this value.

Solution:

Set the tradional attribute of jQuery.ajax

$.ajax({
  url: "/xxx",
  type: "GET",
  data: {
    "boxIds": boxIds,
    "boxType": 0,
    "time": new Date().getTime()
  },
  traditional: true,//这里设置为true
  success: function(data) {
    //do sth...
  }
});

Request parameters2

This time parameters Without "[]", the array can be successfully received in the background.

The above is the detailed content of Detailed code explanation of jquery ajax passing arrays to the background and how to receive arrays in the background. For more information, please follow other related articles on the PHP Chinese website!