Cara membaca file json ke java dengan perpustakaan JSON sederhana

Saya ingin membaca JSONfile ini dengan java menggunakan json simple library.

JSONFile saya terlihat seperti ini:

[  
    {  
        "name":"John",
        "city":"Berlin",
        "cars":[  
            "audi",
            "bmw"
        ],
        "job":"Teacher"
    },
    {  
        "name":"Mark",
        "city":"Oslo",
        "cars":[  
            "VW",
            "Toyata"
        ],
        "job":"Doctor"
    }
]

Ini adalah kode java yang saya tulis untuk membaca file ini:

package javaapplication1;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;
import java.util.Iterator;
import org.json.simple.JSONArray;
import org.json.simple.JSONObject;
import org.json.simple.parser.JSONParser;
import org.json.simple.parser.ParseException;

public class JavaApplication1 {
    public static void main(String[] args) {

        JSONParser parser = new JSONParser();

        try {     
            Object obj = parser.parse(new FileReader("c:\\file.json"));

            JSONObject jsonObject =  (JSONObject) obj;

            String name = (String) jsonObject.get("name");
            System.out.println(name);

            String city = (String) jsonObject.get("city");
            System.out.println(city);

            String job = (String) jsonObject.get("job");
            System.out.println(job);

            // loop array
            JSONArray cars = (JSONArray) jsonObject.get("cars");
            Iterator<String> iterator = cars.iterator();
            while (iterator.hasNext()) {
             System.out.println(iterator.next());
            }
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } catch (ParseException e) {
            e.printStackTrace();
        }
    }
}

Tapi saya mendapatkan pengecualian berikut:

Pengecualian di utas "main" java.lang.ClassCastException: org.json.simple.JSONArray tidak dapat ditransmisikan ke org.json.simple.JSONObject di javaapplication1.JavaApplication1.main (JavaApplication1.java:24)

Bisakah seseorang memberi tahu saya apa yang saya lakukan salah? Seluruh file adalah array dan ada objek dan array lain (mobil) di seluruh array file. Tapi saya tidak tahu bagaimana saya bisa mengurai seluruh array menjadi array java. Saya berharap seseorang dapat membantu saya dengan baris kode yang saya lewatkan dalam kode saya.

Terima kasih

Seluruh file adalah array dan ada objek dan array lain (misalnya mobil) di seluruh array file.

Seperti yang Anda katakan, lapisan terluar dari blob JSON Anda adalah sebuah array. Oleh karena itu, parser Anda akan mengembalikan file JSONArray. Anda kemudian bisa mendapatkan JSONObjects dari array ...

  JSONArray a = (JSONArray) parser.parse(new FileReader("c:\\exer4-courses.json"));

  for (Object o : a)
  {
    JSONObject person = (JSONObject) o;

    String name = (String) person.get("name");
    System.out.println(name);

    String city = (String) person.get("city");
    System.out.println(city);

    String job = (String) person.get("job");
    System.out.println(job);

    JSONArray cars = (JSONArray) person.get("cars");

    for (Object c : cars)
    {
      System.out.println(c+"");
    }
  }

Untuk referensi, lihat "Contoh 1" di halaman contoh pendekodean json-simple .

Anda dapat menggunakan perpustakaan jackson dan cukup menggunakan 3 baris ini untuk mengonversi file json Anda ke Objek Java.

ObjectMapper mapper = new ObjectMapper();
InputStream is = Test.class.getResourceAsStream("/test.json");
testObj = mapper.readValue(is, Test.class);

Tambahkan Jackson databind:

<dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-databind</artifactId>
    <version>2.9.0.pr2</version>
</dependency>

Buat kelas DTO dengan bidang terkait dan baca file JSON:

ObjectMapper objectMapper = new ObjectMapper();
ExampleClass example = objectMapper.readValue(new File("example.json"), ExampleClass.class);

Membaca dari JsonFile

public static ArrayList<Employee> readFromJsonFile(String fileName){
        ArrayList<Employee> result = new ArrayList<Employee>();

        try{
            String text = new String(Files.readAllBytes(Paths.get(fileName)), StandardCharsets.UTF_8);

            JSONObject obj = new JSONObject(text);
            JSONArray arr = obj.getJSONArray("employees");

            for(int i = 0; i < arr.length(); i++){
                String name = arr.getJSONObject(i).getString("name");
                short salary = Short.parseShort(arr.getJSONObject(i).getString("salary"));
                String position = arr.getJSONObject(i).getString("position");
                byte years_in_company = Byte.parseByte(arr.getJSONObject(i).getString("years_in_company")); 
                if (position.compareToIgnoreCase("manager") == 0){
                    result.add(new Manager(name, salary, position, years_in_company));
                }
                else{
                    result.add(new OrdinaryEmployee(name, salary, position, years_in_company));
                }
            }           
        }
        catch(Exception ex){
            System.out.println(ex.toString());
        }
        return result;
    }

Anda dapat menggunakan Gson untuk ini.
GSONadalah pustaka Java yang dapat digunakan untuk mengubah Objek Java menjadi JSONrepresentasi mereka . Ini juga dapat digunakan untuk mengonversi JSONstring menjadi objek Java yang setara.

Lihatlah Konversi JSON ke Java ini

Gunakan perpustakaan google-simple.

<dependency>
    <groupId>com.googlecode.json-simple</groupId>
    <artifactId>json-simple</artifactId>
    <version>1.1.1</version>
</dependency>

Temukan kode contoh di bawah ini:

public static void main(String[] args) {
    try {
        JSONParser parser = new JSONParser();
        //Use JSONObject for simple JSON and JSONArray for array of JSON.
        JSONObject data = (JSONObject) parser.parse(
              new FileReader("/resources/config.json"));//path to the JSON file.

        String json = data.toJSONString();
    } catch (IOException | ParseException e) {
        e.printStackTrace();
    }
}

Gunakan JSONObject untuk JSON sederhana seperti {"id":"1","name":"ankur"}dan JSONArray untuk array seperti JSON [{"id":"1","name":"ankur"},{"id":"2","name":"mahajan"}].

import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;

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

public class Delete_01 {
    public static void main(String[] args) throws FileNotFoundException,
            IOException, ParseException {

        JSONParser parser = new JSONParser();
        JSONArray jsonArray = (JSONArray) parser.parse(new FileReader(
                "delete_01.json"));

        for (Object o : jsonArray) {
            JSONObject person = (JSONObject) o;

            String strName = (String) person.get("name");
            System.out.println("Name::::" + strName);

            String strCity = (String) person.get("city");
            System.out.println("City::::" + strCity);

            JSONArray arrays = (JSONArray) person.get("cars");
            for (Object object : arrays) {
                System.out.println("cars::::" + object);
            }
            String strJob = (String) person.get("job");
            System.out.println("Job::::" + strJob);
            System.out.println();

        }

    }
}

Mungkin bisa membantu orang lain yang menghadapi masalah yang sama. Anda dapat memuat file sebagai string dan kemudian dapat mengonversi string ke jsonobject untuk mengakses nilai.

import java.util.Scanner;
import org.json.JSONObject;
String myJson = new Scanner(new File(filename)).useDelimiter("\\Z").next();
JSONObject myJsonobject = new JSONObject(myJson);

Semoga contoh ini juga membantu

Saya telah melakukan pengkodean java dengan cara yang sama untuk contoh array json di bawah ini sebagai berikut:

berikut adalah format data json: disimpan sebagai "EMPJSONDATA.json"

[{"EMPNO": 275172, "EMP_NAME": "Rehan", "DOB": "29-02-1992", "DOJ": "10-06-2013", "ROLE": "JAVA DEVELOPER"},

{"EMPNO": 275173, "EMP_NAME": "GK", "DOB": "10-02-1992", "DOJ": "11-07-2013", "ROLE": "WINDOWS ADMINISTRATOR"},

{"EMPNO": 275174, "EMP_NAME": "Abiram", "DOB": "10-04-1992", "DOJ": "12-08-2013", "ROLE": "PROJECT ANALYST"}

{"EMPNO": 275174, "EMP_NAME": "Mohamed Mushi", "DOB": "10-04-1992", "DOJ": "12-08-2013", "ROLE": "PROJECT ANALYST"}]

public class Jsonminiproject {

public static void main(String[] args) {

      JSONParser parser = new JSONParser();

    try {
        JSONArray a = (JSONArray) parser.parse(new FileReader("F:/JSON DATA/EMPJSONDATA.json"));
        for (Object o : a)
        {
            JSONObject employee = (JSONObject) o;

            Long no = (Long) employee.get("EMPNO");
            System.out.println("Employee Number : " + no);

            String st = (String) employee.get("EMP_NAME");
            System.out.println("Employee Name : " + st);

            String dob = (String) employee.get("DOB");
            System.out.println("Employee DOB : " + dob);

            String doj = (String) employee.get("DOJ");
            System.out.println("Employee DOJ : " + doj);

            String role = (String) employee.get("ROLE");
            System.out.println("Employee Role : " + role);

            System.out.println("\n");

        }


    } catch (FileNotFoundException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } catch (ParseException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }




}

}

package com.json;

import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;
import java.util.Iterator;

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

public class ReadJSONFile {

    public static void main(String[] args) {

        JSONParser parser = new JSONParser();

        try {
            Object obj = parser.parse(new FileReader("C:/My Workspace/JSON Test/file.json"));

            JSONArray array = (JSONArray) obj;
            JSONObject jsonObject = (JSONObject) array.get(0);

            String name = (String) jsonObject.get("name");
            System.out.println(name);

            String city = (String) jsonObject.get("city");
            System.out.println(city);

            String job = (String) jsonObject.get("job");
            System.out.println(job);

            // loop array
            JSONArray cars = (JSONArray) jsonObject.get("cars");
            Iterator<String> iterator = cars.iterator();
            while (iterator.hasNext()) {
                System.out.println(iterator.next());
            }
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } catch (ParseException e) {
            e.printStackTrace();
        }
    }

}

Contoh Json

{
    "per_page": 3,
    "total": 12,
    "data": [{
            "last_name": "Bluth",
            "id": 1,
            "avatar": "https://s3.amazonaws.com/uifaces/faces/twitter/calebogden/128.jpg",
            "first_name": "George"
        },
        {
            "last_name": "Weaver",
            "id": 2,
            //"avatar": "https://s3.amazonaws.com/uifaces/faces/twitter/josephstein/128.jpg",
            "first_name": "Janet"
        },
        {
            "last_name": "Wong",
            "id": 3,
            //"avatar": "https://s3.amazonaws.com/uifaces/faces/twitter/olegpogodaev/128.jpg",
            "first_name": "Emma"
        }
    ],
    "page": 1,
    "total_pages": 4
}

Pernyataan If Pertama akan mengonversi data tunggal dari tubuh Kedua pernyataan if akan membedakan objek JsonArray

public static String getvalueJpath(JSONObject responseJson, String Jpath ) {
        Object obj = responseJson;
        for(String s : Jpath.split("/"))
            if (s.isEmpty())
                if(!(s.contains("[") || s.contains("]")))
                    obj = ((JSONObject) obj).get(s);
                else
                    if(s.contains("[") || s.contains("]"))
                        obj = ((JSONArray)((JSONObject)obj).get(s.split("\\[")[0])).get(Integer.parseInt(s.split("//[")[1].replaceAll("]", "")));

        return obj.toString();
    }
}

Solusi menggunakan perpustakaan Jackson. Mengurutkan masalah ini dengan memverifikasi json di JSONLint.com dan kemudian menggunakan Jackson. Di bawah ini adalah kode yang sama.

 Main Class:-

String jsonStr = "[{\r\n" + "       \"name\": \"John\",\r\n" + "        \"city\": \"Berlin\",\r\n"
                + "         \"cars\": [\r\n" + "            \"FIAT\",\r\n" + "          \"Toyata\"\r\n"
                + "     ],\r\n" + "     \"job\": \"Teacher\"\r\n" + "   },\r\n" + " {\r\n"
                + "     \"name\": \"Mark\",\r\n" + "        \"city\": \"Oslo\",\r\n" + "        \"cars\": [\r\n"
                + "         \"VW\",\r\n" + "            \"Toyata\"\r\n" + "     ],\r\n"
                + "     \"job\": \"Doctor\"\r\n" + "    }\r\n" + "]";

        ObjectMapper mapper = new ObjectMapper();

        MyPojo jsonObj[] = mapper.readValue(jsonStr, MyPojo[].class);

        for (MyPojo itr : jsonObj) {

            System.out.println("Val of getName is: " + itr.getName());
            System.out.println("Val of getCity is: " + itr.getCity());
            System.out.println("Val of getJob is: " + itr.getJob());
            System.out.println("Val of getCars is: " + itr.getCars() + "\n");

        }

POJO:

public class MyPojo {

private List<String> cars = new ArrayList<String>();

private String name;

private String job;

private String city;

public List<String> getCars() {
    return cars;
}

public void setCars(List<String> cars) {
    this.cars = cars;
}

public String getName() {
    return name;
}

public void setName(String name) {
    this.name = name;
}

public String getJob() {
    return job;
}

public void setJob(String job) {
    this.job = job;
}

public String getCity() {
    return city;
}

public void setCity(String city) {
    this.city = city;
} }

  RESULT:-
         Val of getName is: John
         Val of getCity is: Berlin
         Val of getJob is: Teacher
         Val of getCars is: [FIAT, Toyata]

          Val of getName is: Mark
          Val of getCity is: Oslo
          Val of getJob is: Doctor
          Val of getCars is: [VW, Toyata]

file json Anda terlihat seperti ini

import java.io.*;
import java.util.*;
import org.json.simple.*;
import org.json.simple.parser.*;
public class JSONReadFromTheFileTest {
   public static void main(String[] args) {
      JSONParser parser = new JSONParser();
      try {
         Object obj = parser.parse(new FileReader("/Users/User/Desktop/course.json"));
         JSONObject jsonObject = (JSONObject)obj;
         String name = (String)jsonObject.get("Name");
         String course = (String)jsonObject.get("Course");
         JSONArray subjects = (JSONArray)jsonObject.get("Subjects");
         System.out.println("Name: " + name);
         System.out.println("Course: " + course);
         System.out.println("Subjects:");
         Iterator iterator = subjects.iterator();
         while (iterator.hasNext()) {
            System.out.println(iterator.next());
         }
      } catch(Exception e) {
         e.printStackTrace();
      }
   }
}

hasilnya adalah

Name: Raja
Course: MCA
Subjects:
subject1: MIS
subject2: DBMS
subject3: UML

mengambilnya dari sini

Anda dapat menggunakan readAllBytes.

return String(Files.readAllBytes(Paths.get(filePath)),StandardCharsets.UTF_8);