Parsing JSON file in java

Question

I am new to JSON and Java ,using following code ,I am trying to read JSON data from text file but its not showing result for multiple value data

Anyone Please help me ,Let me know where I am wrong

    JSONParser parser = new JSONParser();              
    try {  
     Object obj = parser.parse(new FileReader("C:/Users/Desktop/file.json"));  
     JSONObject jsonObject = (JSONObject) obj;  
     String K1= (String) jsonObject.get("V1");  
     String K2= (String) jsonObject.get("V2"); 



     System.out.println(V1);
      System.out.println(V2);

       JSONArray K3= (JSONArray) jsonObject.get("K3");

       for (Object c : K3)
       {
         System.out.println(c+"");

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

 }  
}
}


File.json
{"K1":"V1" ,"K2":"V2" ,"K3" : "V3.1 ,V3.2"}

CURRENT Output : V1 V2

Expected output V1 V2 V3.1 V3.2

any pls tell me where I am wrong

Answer 1

Either you do manual parsing or you deserialize. I don't see both. For now, you can do manual parsing. Should be some like

JSONParser parser=new JSONParser();
String s = "[0,{\"1\":{\"2\":{\"3\":{\"4\":[5,{\"6\":7}]}}}}]";
Object obj = parser.parse(s);

Answer 2

Use below example to read data from text file.

http://www.mkyong.com/java/how-to-read-file-from-java-bufferedreader-example/

Instead of hard coded value for "JSON_DATA" variable in your code, use the value in "sCurrentLine" in above code segment.

Answer 3

Some lines should go inside while loop because when the loop is finished sCurrentLine is null. So there is nothing to be parsed and then NullPointerException would be thrown. Also each line should has this pattern: {"Key":"Value"}

public class Address {
  public static void main(String[] args) throws JSONException {
    BufferedReader br = null;

    try {

        String sCurrentLine;

        br = new BufferedReader(new FileReader("C:/Users/Desktop/101.txt"));

        while ((sCurrentLine = br.readLine()) != null) {
            System.out.println(sCurrentLine);
            final JSONObject obj = new JSONObject(sCurrentLine);
            final JSONArray geodata = obj.getJSONArray("geodata");
            final int n = geodata.length();
            for (int i = 0; i < n; ++i) {
              final JSONObject person = geodata.getJSONObject(i);
              System.out.println(person.getInt("id"));
              System.out.println(person.getString("name"));
              System.out.println(person.getString("gender"));
              System.out.println(person.getDouble("latitude"));
              System.out.println(person.getDouble("longitude"));
            }
        }     

     } catch (IOException e) {
         e.printStackTrace();
     } finally {
       try {
         if (br != null)br.close();
        } catch (IOException ex) {
         ex.printStackTrace();
        }
     }
}
}

Answer 4

I find it better to parse JSON data in the object oriented way. And that means binding the data to Java Beans which can be very handy to do your work. First off let me say this will require a JAR namely gson.jar

1. Define the GeoData class to represent geo data only

   public class GeoData {

           private String id;
           private String name;
           private String latitude;
           private String longitude;
           public String getId() {
               return id;
           }
           public void setId(String id) {
               this.id = id;
           }
           public String getName() {
               return name;
           }
           public void setName(String name) {
               this.name = name;
           }
           public String getLatitude() {
               return latitude;
           }
           public void setLatitude(String latitude) {
               this.latitude = latitude;
           }
           public String getLongitude() {
               return longitude;
           }
           public void setLongitude(String longitude) {
               this.longitude = longitude;
           }
   
       }
   

Next build a wrapper, which holds a list of GeoData. To match your input. Please note that your input file has geodata key, with list of GeoData(the sample you provided)

public class GeoDataHolder {

    GeoData[] geodata;

    public GeoData[] getGeodata() {
        return geodata;
    }

    public void setGeodata(GeoData[] geodata) {
        this.geodata = geodata;
    }
}

Lastly here is an example of parsing the file:

public static void main(String[] args) throws FileNotFoundException {
        //read the file
        JsonReader reader = new JsonReader(new BufferedReader(new InputStreamReader(new FileInputStream(new File("F:\\workspace\\Parser\\geodata.xml")))));
        Gson gson = new Gson();
        GeoDataHolder response = gson.fromJson(reader, GeoDataHolder.class);
        //geodataholder is the root element
        System.out.println("size: " + response.getGeodata().length);

        for(int i=0;i<response.getGeodata().length;i++){
            System.out.println("size: " + response.getGeodata()[i].getName());
        }
    }