使用 Java 读取多个对象 JSON

Question

I need to read a JSON file in Java with the following structure:

{"id_user":"10","level":"medium","text":"hello 10"}
{"id_user":"20","level":"medium","text":"hello 20"}
{"id_user":"30","level":"medium","text":"hello 30"}

Thanks!.

---

[POST-EDITED]

I have this code but only read the first JSON Object, I need read the three objects one by one.

private void loadJSONFile(){
        FileReader fileReader = new FileReader(pathFile);
        try (JsonReader jsonReader = new JsonReader(fileReader)) {
            jsonReader.beginObject();
            while (jsonReader.hasNext()) {
                String name = jsonReader.nextName();
                if (name.equals("filter_level")) {
                    System.out.println(jsonReader.nextString());
                } else if (name.equals("text")) {
                    System.out.println("text: " + jsonReader.nextString());
                } else {
                    jsonReader.skipValue();
                }
            }
            jsonReader.endObject();
            jsonReader.close();
        }
    }

thanks!

Answer 1

This is a working example based (and tested) with gson-2.8.0 . It accepts an arbitrary sequence of JSON objects on a given input stream. And, of course, it does not impose any restrictions on how you have formatted your input:

       InputStream is = /* whatever */
       Reader r = new InputStreamReader(is, "UTF-8");
       Gson gson = new GsonBuilder().create();
       JsonStreamParser p = new JsonStreamParser(r);

       while (p.hasNext()) {
          JsonElement e = p.next();
          if (e.isJsonObject()) {
              Map m = gson.fromJson(e, Map.class);
              /* do something useful with JSON object .. */
          }
          /* handle other JSON data structures */
       }

Answer 2

I know it has been almost one year for this post :) but i am actually reposing again as an answer because i had this problem same as you Yuan

I have this text.txt file - I know this is not a valid Json array - but if you look, you will see that each line of this file is a Json object in its case alone.

{"Sensor_ID":"874233","Date":"Apr 29,2016 08:49:58 Info Log1"}
{"Sensor_ID":"34234","Date":"Apr 29,2016 08:49:58 Info Log12"}
{"Sensor_ID":"56785","Date":"Apr 29,2016 08:49:58 Info Log13"}
{"Sensor_ID":"235657","Date":"Apr 29,2016 08:49:58 Info Log14"}
{"Sensor_ID":"568678","Date":"Apr 29,2016 08:49:58 Info Log15"}

Now I want to read each line of the above and parse the names "Sensor_ID" and "Date" into Json format. After long search, I have the following:

Try it and look on the console to see the result. I hope it helps.

package reading_file;

import java.io.*;
import java.util.ArrayList;

import org.json.simple.JSONObject;
import org.json.simple.parser.JSONParser;
import org.json.simple.parser.ParseException;

public class file_read {
public static void main(String [] args) {
    ArrayList<JSONObject> json=new ArrayList<JSONObject>();
    JSONObject obj;
    // The name of the file to open.
    String fileName = "C:\\Users\\aawad\\workspace\\kura_juno\\data_logger\\log\\Apr_28_2016\\test.txt ";

    // This will reference one line at a time
    String line = null;

    try {
        // FileReader reads text files in the default encoding.
        FileReader fileReader = new FileReader(fileName);

        // Always wrap FileReader in BufferedReader.
        BufferedReader bufferedReader = new BufferedReader(fileReader);

        while((line = bufferedReader.readLine()) != null) {
            obj = (JSONObject) new JSONParser().parse(line);
            json.add(obj);
            System.out.println((String)obj.get("Sensor_ID")+":"+
                               (String)obj.get("Date"));
        }
        // Always close files.
        bufferedReader.close();         
    }
    catch(FileNotFoundException ex) {
        System.out.println("Unable to open file '" + fileName + "'");                
    }
    catch(IOException ex) {
        System.out.println("Error reading file '" + fileName + "'");                  
        // Or we could just do this: 
        // ex.printStackTrace();
    } catch (ParseException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
}
}

Answer 3

I think what you mean is your Json strings are stored in a text file and you need to read them in to a Json objects. If that's the case use BufferedReader or Scanner to read the file line by line and parse each line to a Json object using json-simple

JsonReader is use to Read One Json Object. Use Scanner or BufferedReader to Read File Line By Line as String and then Parse it to a Json Object.Here is an Example

import org.json.simple.JSONObject;
import org.json.simple.parser.JSONParser;
import org.json.simple.parser.ParseException;

import java.io.File;
import java.io.FileNotFoundException;
import java.util.ArrayList;
import java.util.Scanner;

public class JSONExample{
public static void main(String x[]){
    String FileName="C:\\Users\\Prasad\\Desktop\\JSONExample.txt";
    try {
        ArrayList<JSONObject> jsons=ReadJSON(new File(FileName),"UTF-8");
    } catch (FileNotFoundException e) {
        e.printStackTrace();
    } catch (ParseException e) {
        e.printStackTrace();
    }
}
public static synchronized ArrayList<JSONObject> ReadJSON(File MyFile,String Encoding) throws FileNotFoundException, ParseException {
    Scanner scn=new Scanner(MyFile,Encoding);
    ArrayList<JSONObject> json=new ArrayList<JSONObject>();
//Reading and Parsing Strings to Json
    while(scn.hasNext()){
        JSONObject obj= (JSONObject) new JSONParser().parse(scn.nextLine());
        json.add(obj);
    }
//Here Printing Json Objects
    for(JSONObject obj : json){
        System.out.println((String)obj.get("id_user")+" : "+(String)obj.get("level")+" : "+(String)obj.get("text"));
    }
    return json;
}

}

Answer 4

include following maven dependency:

   <dependency>
        <groupId>com.googlecode.json-simple</groupId>
        <artifactId>json-simple</artifactId>
        <version>1.1</version>
    </dependency>

then write your code as below:

public class HistoricalData {
    private static final String PATH = "<PATH>";
    public static void main(String[] args) throws FileNotFoundException,

 ParseException {

    Scanner scanner = new Scanner(new File(PATH + "/Sample.txt"));
    List<JSONObject> jsonArray = new ArrayList<JSONObject>();
    while (scanner.hasNext()) {
        JSONObject obj = (JSONObject) new JSONParser().parse(scanner.nextLine());
        jsonArray.add(obj);
    }
}
}

Answer 5

keep the data inside [ ] like [{"id_user":"10","level":"medium","text":"hello 10"} {"id_user":"20","level":"medium","text":"hello 20"} {"id_user":"30","level":"medium","text":"hello 30"}]

inside the file so that it becomes a list then you can use JSONArray . the way I wrote is as follows

public class JSONReadFromFile {

@SuppressWarnings("unchecked")
public static void main(String[] args) {
    JSONParser parser = new JSONParser();

    try {

        Object obj = parser.parse(new FileReader("\\D:\\JSON\\file3.txt"));
        JSONArray jsonArray = (JSONArray) obj;
        int length = jsonArray.size();

        LinkedList author = new LinkedList();


        for (int i =0; i< length; i++) {
            JSONObject jsonObject = (JSONObject) jsonArray.get(i);
            Set s = jsonObject.entrySet();
            Iterator iter = s.iterator();

            HashMap hm = new HashMap();

            while(iter.hasNext()){
                Map.Entry me = (Map.Entry) iter.next();
                hm.put(me.getKey(), me.getValue());
            }
            author.add(hm);             
            }            
        for(int i=0;i<author.size();i++){
       HashMap hm = (HashMap) author.get(i);
       Set s = hm.entrySet();
       Iterator iter = s.iterator();
       while(iter.hasNext()){
           Map.Entry me = (Map.Entry) iter.next();
          System.out.println(me.getKey() + "---" + me.getValue());
          }   

    } catch (Exception e) {
        e.printStackTrace();
    }
}

}

The output I get is

text---hello 10 id_user---10 level---medium text---hello 20 id_user---20 level---medium text---hello 30 id_user---30 level---medium

Answer 6

I know two option for read JSON.

JSON Simple its good for small JSON results. But GSON is very usefull for big json results. Because you can set Object form in GSON.

Firs one json.jar

Usage :

String st = ""; // your json object to string
JSONObject newJson = null;
    try {
        newJson = new JSONObject(st);
        newJson.getJSONObject("key");
    } catch (JSONException e1) {
        // TODO Auto-generated catch block
        e1.printStackTrace();
    }

Second One gson.jar

Usage:

int one = gson.fromJson("1", int.class);
Integer one = gson.fromJson("1", Integer.class);
Long one = gson.fromJson("1", Long.class);
Boolean false = gson.fromJson("false", Boolean.class);
String str = gson.fromJson("\"abc\"", String.class);
String anotherStr = gson.fromJson("[\"abc\"]", String.class);

Answer 7

The proper way to work through this JSON file is:

"users": [
  {
    "id_user": "10",
    "level": "medium",
    "text": "hello 10"
  },
  {
    "id_user": "20",
    "level": "medium",
    "text": "hello 20"
  },
  {
    "id_user": "30",
    "level": "medium",
    "text": "hello 30"
  }
]

Try using XStream if you are using a standalone application. It parses JSON into objects in a blink of an eye.

Answer 8

I used below code and its working fine.

public static void main(String[] args)
        throws IOException, JSchException, SftpException, InterruptedException, ParseException
{
    JSONParser parser = new JSONParser();
    Object obj = parser.parse(new FileReader("c:\\netapp1.txt"));
    Map<Object, Object> shareList = new HashMap<Object, Object>();
    JSONObject jsonObject = (JSONObject) obj;
    JSONArray array = (JSONArray) jsonObject.get("dataLevels"); // it should be any array name

    Iterator<Object> iterator = array.iterator();
    while (iterator.hasNext())
    {
        Object it = iterator.next();
        JSONObject data = (JSONObject) it;
        shareList.put(data.get("name"), data.get("type"));
    }
    Iterator it = shareList.entrySet().iterator();
    while (it.hasNext())
    {
        Map.Entry value = (Map.Entry) it.next();
        System.out.println("Name: " + value.getKey() + " and type: " + value.getValue());
    }
}

JSON: {

"version": 1,

"dataLevels": 

[

{

  "name": "test1",

  "externId": "test1",

  "type": "test1"

},

{

  "name": "test2",

  "externId": "test2",

  "type": "test2"

},

{

  "name": "test3",

  "externId": "test3",

  "type": "test3"

}

]

}

Answer 9

Using gson to read multiple objects from stream. With gson-2.8.2, I had to call this: reader.setLenient(true);

JsonReader reader = new JsonReader(new InputStreamReader(is, "UTF-8"));
reader.setLenient(true);
while ((is.available() > 0))
{
    reader.beginObject();
    while (reader.hasNext()) {
        System.out.println("message: "+reader.nextName()+"="+reader.nextString());
    }
    System.out.println("=== End message ===");
    reader.endObject();

This was suggested explicitly by the stack trace, when I did it, the code worked perfectly:

com.google.gson.stream.MalformedJsonException: Use JsonReader.setLenient(true) to accept malformed JSON at line 2 column 3481 path $
    at com.google.gson.stream.JsonReader.syntaxError(JsonReader.java:1568)
    at com.google.gson.stream.JsonReader.checkLenient(JsonReader.java:1409)
    at com.google.gson.stream.JsonReader.doPeek(JsonReader.java:542)
    at com.google.gson.stream.JsonReader.beginObject(JsonReader.java:379)

...

Answer 10

My data format is :

"array": [
  {
    "id": "1",
    "name": "peter",
    "text": "hie peter"
  },
  {
    "id": "5",
    "name": "rina",
    "text": "hey rina"
  },
  {
    "id": "12",
    "name": "parx",
    "text": "hey bro"
  }
]

I tried this one and it works :

Object obj = parser.parse(new FileReader("/home/hp2/json.json"));

  JSONObject jsonObject = (JSONObject) obj;
  JSONArray array = (JSONArray) jsonObject.get("array"); // it should be any array name

     Iterator<Object> iterator = array.iterator();
        while (iterator.hasNext()) {
            System.out.println("if iterator have next element " + iterator.next());
        }