1、檔案為json格式，提取某一個id的值

[{
“name”: “zhansam”,
“id”: 123
},
{
“name”: “lisi”,
“id”: 456
},
{
“name”: “wangwu”,
“id”: 789
}
]

2、

import java.io.File;
import java.io.FileNotFoundException;
import java.util.HashMap;
import java.util.HashSet;
import java.util
 
.Map;
import java.util.Scanner;
import java.util.Set;

import com.alibaba.fastjson.JSONArray;
import com.alibaba.fastjson.JSONObject;


/** 
 * @Description: json格式轉換
 * @date 2016年6月17日  下午5:03:11
 */
public class testJson {

    public static void main(String[] args) {

        //讀取硬碟中json格式的檔案
           String fullFileName = "E:/json.txt"
 
;

            File file = new File(fullFileName);
            Scanner scanner = null;
            StringBuilder buffer = new StringBuilder();
            try {
                scanner = new Scanner(file, "utf-8");
                while (scanner.hasNextLine()) {
                    buffer.append(scanner.nextLine
 
());
                }

            } catch (FileNotFoundException e) {
                e.getMessage();
            } finally {
                if (scanner != null) {
                    scanner.close();
                }
            }

            if(buffer.toString() == null || "".equals(buffer.toString())){
                System.out.println("讀取不到檔案。。。");
                return ;
            }

            System.out.println("第一步,讀取e盤下面的檔案,E: "+buffer.toString());

            // com.alibaba.fastjson.JSONObject   轉成json物件
            System.out.println("第二步,轉成json物件 JSONObject =" + JSONObject.parseArray(buffer.toString()));

            JSONArray aa =JSONObject.parseArray(buffer.toString());
            int len = aa.size();
            System.out.println("第三步,json物件屬性長度 len= "+len);

            Map<String, Object> hashMap = new HashMap<String, Object>();
            String iiiiids = "";
            Set<String> quchong = new HashSet<String>();


            //一層巢狀,第二層物件為json物件陣列  獲取所有key為id的值value
            for(int i=0 ;len > i ;i++){

                JSONObject neibuJson =new JSONObject();
                //System.out.println("neibuJson 空 "+neibuJson.parse(aa.getString(i)));

                JSONObject neibuJson2 =(JSONObject)neibuJson.parse(aa.getString(i));
                //JSONObject neibuJson3 =(JSONObject)JSONObject.parse(aa.getString(i));


                //System.out.println("第三步,每個內部物件的值 ="+neibuJson2);
                //System.out.println("neibuJson3"+neibuJson3);

                //System.out.println("第三步,json物件屬性id的值="+neibuJson.get("id"));
                //System.out.println("第三步,json物件屬性id的值="+neibuJson.getString("id"));


                Set<String> keySet = neibuJson2.keySet();

//              System.out.println("第四步,內部物件的key值"+"keySet="+keySet);
//              System.out.println("第四步,內部物件的key對應的value值"+"keySetValue-neibuJson2="+neibuJson2.get("id"));



                for (String key : keySet) {//注：hashMap中,key值唯一 
                    hashMap.put(key, neibuJson2.get(key));
                }

                //SET集合去重
                if(neibuJson2.get("id")!= null){
                    quchong.add(neibuJson2.get("id").toString());
                }


                iiiiids += neibuJson2.get("id")+ ",";

            }
            System.out.println("最後需要的結果,iiiiids= "+iiiiids);
            System.out.println("唯一 的hashMap="+hashMap);


            System.out.println("去重後Set size="+quchong.size());
            System.out.println("去重後Set 內容="+quchong);
    }

}