在 Android Studio 中创建、写入、编辑 JSON 文件

Question

I would like to create a JSON file in the internal storage of the phone, to store data. I want to be able to add objects ("configX") to the file and then read the data.

It should look something like this:

{

  "config1": {

    "component1": "url",
    "component2": "url",
    "component3": "url"

  },

  "config2": {

    "component1": "url",
    "component2": "url",
    "component3": "url"

  }

}

I can create a JSON file like this:

public void saveToJson(){
    JSONObject json = new JSONObject();
    try {
        json.put("component1", "url");
        json.put("component2", "url");

        String jsonString = json.toString();
        
        FileOutputStream fos = this.openFileOutput("jsonfile", Context.MODE_PRIVATE);
        fos.write(jsonString.getBytes());
        fos.close();

        Log.d("JSON" , json.toString());

    } catch (IOException | JSONException e) {
        e.printStackTrace();
    }
}

But how to put the components in the config object? And how to retrieve the data?

EDIT 1:

https://stackoverflow.com/a/62474912/11652860

Thanks for the very detailed answer, I'm doing something wrong. I have an Activity where I put and save data to the json file:

public class Data {

        private Map<String, Map<String, String>> map;

        public Data() {

        }

        public Data(Map<String, Map<String, String>> map) {
            this.map = map;
        }

        public Map<String, Map<String, String>> getMap() {
            return map;
        }

        public void setMap(Map<String, Map<String, String>> map) {
            this.map = map;
        }

    }

Map<String, String> config1 = new HashMap<>();
config1.put("component1", "url1");
config1.put("component2", "url1");
config1.put("component3", "url1");

Map<String, Map<String, String>> map = new HashMap<>();
map.put("config1", config1);

Data data = new Data(map);

Gson gson = new Gson();
String json = gson.toJson(data);

FileOutputStream fos = null;
 try {
fos = webViewActivity.this.openFileOutput("jsonfile", Context.MODE_PRIVATE);
} catch (FileNotFoundException e) {
 e.printStackTrace();
}
 try {
 fos.write(json.getBytes());
} catch (IOException e) {
  e.printStackTrace();
}
 try {
 fos.close();
} catch (IOException e) {
 e.printStackTrace();
}

And a fragment where I load the data:

public class Data {

        private Map<String, Map<String, String>> map;

        public Data() {

        }

        public Data(Map<String, Map<String, String>> map) {
            this.map = map;
        }

        public Map<String, Map<String, String>> getMap() {
            return map;
        }

        public void setMap(Map<String, Map<String, String>> map) {
            this.map = map;
        }

    }

 public void load(){
        FileInputStream fis = null;

        try {

            fis = getContext().openFileInput("jsonfile.txt");
            InputStreamReader isr = new InputStreamReader(fis);
            BufferedReader br = new BufferedReader(isr);

            StringBuilder sb = new StringBuilder();
            String text;

            while ((text = br.readLine()) != null){
                sb.append(text).append("\n");

                Gson gson = new Gson();

                String json = gson.toJson(text);
                Data data = gson.fromJson(json, Data.class);

                String url = data.getMap().get("config1").get("component1");

                frameTV.setText(url);

            }


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

The saving and loading parts must be wrong, but they worked for getting text out a text file

EDIT 2:

I found the problem, I wasn't loading and saving properly:

SAVING:

String filename = "jsonfile.txt";

FileOutputStream outputStream;

try {
   outputStream = openFileOutput(filename, Context.MODE_PRIVATE);
   outputStream.write(json.getBytes());
   outputStream.close();
} catch (Exception e) {
   e.printStackTrace();
}

LOADING:

FileInputStream fis = getContext().openFileInput("jsonfile.txt");
InputStreamReader isr = new InputStreamReader(fis);
BufferedReader bufferedReader = new BufferedReader(isr);
StringBuilder sb = new StringBuilder();
String line;
while ((line = bufferedReader.readLine()) != null) {
    sb.append(line);
}

String json = sb.toString();

Gson gson = new Gson();
Data data = gson.fromJson(json, Data.class);
String priceURL = data.getMap().get("config1").get("url1");

EDIT 3:

My problem now is that I need to create the file once and then check if the file exists, if it does I need to check if config1 exists if it doesn't I need to put config in the file.

But I can't check if config1 exists because I get: java.lang.NullPointerException: Attempt to invoke virtual method 'java.util.Map com.a.app.ui.app.appFragment$Data.getMap()

I check if it exists by doing:

Boolean configTest = data.getMap().containsKey("config1");
if(!configTest){}

How can I create the file and check the data without getting a NullPointerException?

Thank you for helping me !

Answer 1

Google's Gson library will be helpful in this case.

1. Add dependency for Google Gson in your radle file.

    dependencies {
      implementation 'com.google.code.gson:gson:2.8.6'
    }

2. Create a class for your data container

    public class Data {

        private Map<String, Map<String, String>> map;

        public Data() {
        }

        public Data(Map<String, Map<String, String>> map) {
            this.map = map;
        }

        public Map<String, Map<String, String>> getMap() {
            return map;
        }

        public void setMap(Map<String, Map<String, String>> map) {
            this.map = map;
        }
    }

3. Add data to your class

    Map<String, String> config1 = new HashMap<>();
    config1.put("component1", "url1");
    config1.put("component2", "url1");
    config1.put("component3", "url1");

    Map<String, String> config2 = new HashMap<>();
    config2.put("component1", "url1");
    config2.put("component2", "url1");
    config2.put("component3", "url1");

    Map<String, Map<String, String>> map = new HashMap<>();
    map.put("config1", config1);
    map.put("config2", config2);

    Data data = new Data(map);

4. Get gson from data class

Gson gson = new Gson();
String json = gson.toJson(data);

5. You can now save this json in a file in a text format.

6. Now when reading, load the content of the text file in a String say 'jsonString'.

7. Deserialize the jsonString to Java Object

Data data = gson.fromJson(json, Data.class);

8. Access configurations

String url = data.getMap().get("config1").get("component1");

9. Add new configurations

    Map<String, String> config3 = new HashMap<>();
    config3.put("component1", "url1");
    config3.put("component2", "url1");
    config3.put("component3", "url1");

    data.getMap().put("config3", config3);

10. Follow again these steps to save configs

11. Or You can manually edit the text file to add configs according to the predefined format.

    {
       "maps":{
          "config2":{
             "component1":"url1",
             "component2":"url1",
             "component3":"url1"
          },
          "config1":{
             "component1":"url1",
             "component2":"url1",
             "component3":"url1"
          }
       }
    }

Answer 2

Please consider using https://github.com/google/gson . You will be working with class instance rather than with JSONObject. Much more convenient.

Just to give you the idea of what you can do:

public class TestClass {
    private final Map<String, String> config1;
    private final Map<String, String> config2;

    public TestClass(Map<String, String> config1, Map<String, String> config2) {
        this.config1 = config1;
        this.config2 = config2;
    }
}

        Gson gson = new GsonBuilder().setPrettyPrinting().create();

        Map<String, String> config1 = new HashMap<String, String>();
        config1.put("hello1.1", "world1.1");
        config1.put("hello1.2", "world1.2");

        Map<String, String> config2 = new HashMap<String, String>();
        config2.put("hello2.1", "world2.1");
        config2.put("hello2.2", "world2.2");

        TestClass testClass = new TestClass(config1, config2);

        Log.d("zzz", gson.toJson(testClass));

The above prints:

    {
      "config1": {
        "hello1.1": "world1.1",
        "hello1.2": "world1.2"
      },
      "config2": {
        "hello2.1": "world2.1",
        "hello2.2": "world2.2"
      }
    }

You can go back and force between json string and the entity itself. To edit, you only need to work with object - natural and convenient way.

Answer 3

This is how you create multiple Objects in a single JSON object:

//Creating first Object
JSONObject config1 = new JSONObject();
try {
    json.put("component1", "url");
    json.put("component2", "url");
    json.put("component2", "url");
    }
catch (JSONException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}

//Creating second object
JSONObject config2 = new JSONObject();
try {
    json.put("component1", "url");
    json.put("component2", "url");
    json.put("component2", "url");
    }
catch (JSONException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}

JSONObject finalJSON = new JSONObject();
try {
    //Adding both objects in one single object
    json.put("config1", config1);
    json.put("config2", config2);

    String jsonString = finalJSON.toString();

    FileOutputStream fos = this.openFileOutput("jsonfile", Context.MODE_PRIVATE);
    fos.write(jsonString.getBytes());
    fos.close();

    Log.d("JSON" , json.toString());

} catch (IOException | JSONException e) {
    e.printStackTrace();
}

This will give you the desired output. Also, if in case you want to make any object an array, you can use JSONArray for that.