Java(1):java中list集合存JSONObject对象，遍历list取json值_list

本次需求：

需求1：需要生成1000-5000个json值(其中1个值是随机数)，并放入list中

其中1个json值如下：

{"keyId":"1404623066687889410“,"metadata":"ZIV5JyLgOK"}

ZIV5JyLgOK是随机数生成

需求2：需要把list转换成字符串

需求3：需要遍历生成json list取到对应的值，其他算法调用。

解决方法：

1、随机数生成的方法

方法说明：从a-z,以及0-1中生成随机数，输入长度就可以得到长度几的随机数

import java.util.Random;
    public static String getRandomString(int length) {
        String str = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
        Random random = new Random();
        StringBuffer sb = new StringBuffer();
        for (int i = 0; i < length; i++) {
            int number = random.nextInt(62);
            sb.append(str.charAt(number));
        }
        return sb.toString();
    }

2、生成1000个json值，并放入jsonlist中

//生成随机数，metadata赋值随机数

String metadata=getRandomString(10);

//object_json putjson值

//jsonList添加json

import org.json.JSONObject;     //--->需要引入json-20210307.jar
import java.util.Random;
import java.util.List;
import java.util.ArrayList;
 
 
 
        JSONObject object_json = new JSONObject();
        List<JSONObject> jsonList = new ArrayList<JSONObject>();
        for (int i=0;i<1000;i++){
            String metadata=getRandomString(10);
            //System.out.println(metadata);
 
            object_json.put("keyId", "1404623066687889410");
            object_json.put("metadata", metadata);
            //list添加json
            //objar_list.add(object_json);
            jsonList.add(object_json);
        }
 
        System.out.println(jsonList);    //打印list
        System.out.println(jsonList.size());  //打印list长度

3、把list转换成字符串，其他地方需要应用

        String aaa=jsonList.toString();

4、获取字段的数据类型

        System.out.println(getType(aaa));
 
    private static String getType(Object a) {
        return a.getClass().toString();
    }

5、遍历Jsonlist

        for(JSONObject json : jsonList) {
            String metadata = json.getString("metadata");
            String keyId = json.getString("keyId");
        }

全部代码：

//import java.util.*;
import org.json.JSONObject;
//import org.json.JSONArray;
//import org.json.JSONException;
import java.util.Random;
import java.util.List;
import java.util.ArrayList;
 
 
public class Test2 {
    public static void main(String[] args) throws Exception {
        //String aaa=getRandomString(10);
        //System.out.println(aaa);
        JSONObject object_json = new JSONObject();
        //List objar_list=new ArrayList();
        List<JSONObject> jsonList = new ArrayList<JSONObject>();
        for (int i=0;i<1000;i++){
            String metadata=getRandomString(10);
            //System.out.println(metadata);
 
            object_json.put("keyId", "1404623066687889410");
            object_json.put("metadata", metadata);
            //list添加json
            //objar_list.add(object_json);
            jsonList.add(object_json);
        }
        //System.out.println(objar_list);
        System.out.println(jsonList);
        System.out.println(jsonList.size());
 
 
        String aaa=jsonList.toString();
        System.out.println(getType(aaa));
        System.out.println("String: " + aaa);
 
        for(JSONObject json : jsonList) {
            String metadata = json.getString("metadata");
            String keyId = json.getString("keyId");
        }
    }
 
    public static String getRandomString(int length) {
        String str = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
        Random random = new Random();
        StringBuffer sb = new StringBuffer();
        for (int i = 0; i < length; i++) {
            int number = random.nextInt(62);
            sb.append(str.charAt(number));
        }
        return sb.toString();
    }
 
    private static String getType(Object a) {
        return a.getClass().toString();
    }
}

执行结果：

C:\Java\jdk1.8.0_211\jre\lib\rt.jar;C:\java_project2021\json-20210307.jar;C:\java_project2021\javatest\out\production\javatest Test2
1000
class java.lang.String
String: [{"metadata":"hiQCVqSFPM","keyId":"1404623066687889410"}, {"metadata":"hiQCVqSFPM","keyId":"1404623066687889410"}, {"metadata":"hiQCVqSFPM","keyId":"1404623066687889410"}, {"metadata":"hiQCVqSFPM","keyId":"1404623066687889410"}, {"metadata":"hiQCVqSFPM","keyId":"1404623066687889410"}, {"metadata":"hiQCVqSFPM","keyId":"1404623066687889410"}, {"metadata":"hiQCVqSFPM","keyId":"1404623066687889410"}, {"metadata":"hiQCVqSFPM","keyId":"1404623066687889410"}, {"metadata":"hiQCVqSFPM","keyId":"1404623066687889410"}, {"metadata":"hiQCVqSFPM","keyId":"1404623066687889410"}, {"metadata":"hiQCVqSFPM","keyId":"1404623066687889410"}, {"metadata":"hiQCVqSFPM","keyId":"1404623066687889410"}, {"metadata":"hiQCVqSFPM","keyId":"1404623066687889410"}, {"metadata":"hiQCVqSFPM","keyId":"1404623066687889410"}, {"metadata":"hiQCVqSFPM","keyId":"1404623066687889410"}, {"metadata":"hiQCVqSFPM","keyId":"1404623066687889410"}, {"metadata":"hiQCVqSFPM","keyId":"1404623066687889410"}, {"metadata":"hiQCVqSFPM","keyId":"1404623066687889410"}, {"metadata":"hiQCVqSFPM","keyId":"1404623066687889410"}, {"metadata":"hiQCVqSFPM","keyId":"1404623066687889410"}, {"metadata":"hiQCVqSFPM","keyId":"1404623066687889410"}, {"metadata":"hiQCVqSFPM","keyId":"1404623066687889410"}, {"metadata":"hiQCVqSFPM","keyId":"1404623066687889410"}, {"metadata":"hiQCVqSFPM","keyId":"1404623066687889410"}, {"metadata":"hiQCVqSFPM","keyId":"1404623066687889410"}, {"metadata":"hiQCVqSFPM","keyId":"1404623066687889410"},  {"metadata":"hiQCVqSFPM","keyId":"1404623066687889410"}]

Process finished with exit code 0