Example of jquery ajax passing array parameters to the background

Requirements:
Transfer array parameters to the background in JS

Analysis:
Arrays in JS are weakly typed and can be of any type (object, basic type), but if What is put is the object type. When passed to the background, only the object string - [object Object] can be displayed. The reasons are as follows:
When receiving in the background, you can only use request to receive, request.getParameterValues() method What is returned is a String[], so the toString() method of the object should be called during the foreground transmission. So what if you still want to pass the object? Salad!
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 value ultimately used by any object is It is a basic data type and only needs to be parsed using the corresponding packaging type parseInt or parseXXX.

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. I use jsontools-core-1.7.jar. This jar package depends on antlr-2.7.7.jar. I download it from the code library by myself. After downloading, import classpath and write a simple tool class. There are two main methods:

/** 
* 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 (MapperException 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 request gets the value, traverse the array and convert one by one

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

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; 
} 
}

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