当响应不包含头信息时，如何解析json响应

Question

I am trying to parse a json response so that i can get elements out of an object, getting the following error A JSONObject text must begin with '{' at 1 [character 2 line 1]

public static  String parseJsonResponse(String json){
    String uId ="";

    try {
         JSONObject jsonObj = new JSONObject(json);
         // String fname = jsonObj.getString("fname");
         //String lname = jsonObj.getString("lname");
         String aId = jsonObj.getString("id");
         uId = aId; 
     } catch (Exception e) {
         e.printStackTrace();
     }
    return uId;
}

Here is json response using postman you will notice there is no header

[
    {
        "id": "emplo000000000043567",
        "displayName": "Tester, user1",
           },
    {
        "id": "emplo000000000035386",
        "displayName": "Tester, User2",

    }
]

Answer 1

Like the comment above mentioned, that is a JSON array so it needs to be parsed as a JSON array and not a JSON object. Just use the JSONArray equivalent provided in the library you are using.

On another note, with the JSON response above, parsing this as a JSON array would fail since the format is incorrect. Notice the comma at the end of every last keyvalue in each object. That would cause the parser to fail when attempting to parse that as a JSON array. If that was your mistake when you were writing the snippet here then ignore this paragraph. Else if that was the actual JSON response then I guess you need to make a new question... over at the Postman forum.

Answer 2

There are several ideas for this case. Here is mine.

1. With a json simple library [link] .

You can simply change your library to a json simple library which has a parser class for a json string then use an instanceof method for detection before processing a json object.

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

public static  String parseJsonResponse(String json){
    String uId ="";

    try {
        JSONParser parser = new JSONParser();
        Object whichone = parser.parse(json);

        if(whichone instanceof JSONObject)
        {
            JSONObject jsonObj = (JSONObject)whichone;
             // String fname = jsonObj.getString("fname");
             //String lname = jsonObj.getString("lname");
            if(jsonObj.containsKey("id"))
                uId = (String)jsonObj.get("id");
       }
        else if(whichone instanceof JSONArray)
        {
            JSONArray jsonArr = (JSONArray)whichone;
            JSONObject jsonObj = null;

            for(int i = 0; i < jsonArr.size(); i++)
            {
                jsonObj = (JSONObject) jsonArr.get(i);
                if(jsonObj.containsKey("id"))
                {
                    uId = (String)jsonObj.get("id");
                    System.out.println(uId);
                }

            }
        }
        else if(whichone instanceof String)
        {
            System.out.println("1?????" + whichone.toString());
        }
        else
        {
            System.out.println("2?????" + whichone.toString());
        }

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

2. Detect the object type from a json excetpion. You can catch it whether some string is a json object or json array during exception handling.

import org.json.JSONArray;
import org.json.JSONObject;

public static  String parseJsonResponse(String json){
    String uId ="";

    try {
        JSONObject jobj =  new JSONObject(json);

        if(jobj.has("id"))
            uId = jobj.getString("id");

        System.out.println(uId);

     } catch (org.json.JSONException e) {
         //e.printStackTrace();

         JSONArray jsonArr = new JSONArray(json);
         JSONObject jsonObj = null;

         for(int i = 0; i < jsonArr.length(); i++)
            {
                jsonObj = jsonArr.getJSONObject(i);
                if(jsonObj.has("id"))
                {
                    uId = (String)jsonObj.get("id");
                    System.out.println(uId);
                }

            }
     }
    return uId;
}

3. With a java work.

You can find it whether it's a json object or array after parsing a first character. (I think it will work...)

import org.json.JSONArray;
import org.json.JSONObject;
public static  String parseJsonResponse(String json){
    String uId ="";

    boolean isJobj = json.charAt(0) == '[';

    if(!isJobj) {
        JSONObject jobj =  new JSONObject(json);

        if(jobj.has("id"))
            uId = jobj.getString("id");

        System.out.println(uId);

     } else {
         JSONArray jsonArr = new JSONArray(json);
         JSONObject jsonObj = null;

         for(int i = 0; i < jsonArr.length(); i++)
            {
                jsonObj = jsonArr.getJSONObject(i);
                if(jsonObj.has("id"))
                {
                    uId = (String)jsonObj.get("id");
                    System.out.println(uId);
                }

            }
     }
    return uId;
}

Have a good day..

Answer 3

First, Your json format is wrong. The correct json format would be:

[
    {
        "id": "emplo000000000043567",
        "displayName": "Tester, user1"
    },
    {
        "id": "emplo000000000035386",
        "displayName": "Tester, User2"
    }
]

Now,

1. Your Response is JSON Array. So first assign parsed object into JSON Array as JSONArray array = (JSONArray) obj ;
2. this JSON Array consists of two JSON Object so traverse the array, get each JSON Object and print/return key/value pair whatever you want.

A sample code is given below:(see the logic)

public static void parseJsonResponse(String json)
            throws JsonParseException, JsonMappingException, IOException, ParseException {
        String aId ="";
        JSONParser parser = new JSONParser();
        Object obj = parser.parse(json);
        JSONArray array = (JSONArray) obj;
        for(int i=0;i<array.size();i++)
        {
            JSONObject jsonObject = (JSONObject) array.get(i);
            aId = (String) jsonObject.get("id");
            System.out.println(aId);
        }

    }

Note: I have used json-simple java library here.