将JSON写入文件

Question

我有一个名为compositionJSON的类。该类有一个名为makeJSONObject的方法，用于创建JSON对象并将内容放入其中。以下是该类的代码。

public class CompositionJso extends JSONObject {



public JSONObject makeJSONObject (String title, String desc, ArrayList<String> imgPath, ArrayList<Resources> imgView) {

    JSONObject obj = new JSONObject() ;

    try {
        obj.put("title", title);
        obj.put("desc", desc);
        obj.put("imgPath", imgPath);
        obj.put("imgViewPath", imgView);
    } catch (JSONException e) {
        e.printStackTrace();
    }

    return obj;
}

现在我创建了该类的一个实例并在另一个类中调用了该方法。之后，我希望将JSONObject写入文件并保存在设备的sd卡上。以下是代码：

 saveCompo.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            setName();
            createJSONFolder();
            CompositionJso obj = new CompositionJso();
            obj.makeJSONObject(compoTitle, compoDesc, imgPaths, imageViewPaths);
            MyCompositionsListActivity.buildList();

            try {
                Writer output = null;
                File file = new File("storage/sdcard/MyIdea/MyCompositions/" + compoTitle + ".json");
                output = new BufferedWriter(new FileWriter(file));
                output.write(obj.toString());
                output.close();
                Toast.makeText(getApplicationContext(), "Composition saved", Toast.LENGTH_LONG).show();

            } catch (Exception e) {
                Toast.makeText(getBaseContext(), e.getMessage(), Toast.LENGTH_LONG).show();
            }
            finish();
        }
    });

文件已成功保存，但如果我打开它，里面什么都没有。代码有什么问题？

- dudi

---

你需要将makeJSONObject分配给一个JSONObject变量，并在其上调用toString吗？ - Chris Handy

可以，谢谢。现在可以正常工作了！ - dudi

Answer 1

makeJSONObject 返回 JSONObject

你的代码应该是

saveCompo.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            setName();
            createJSONFolder();
            CompositionJso obj = new CompositionJso();
            JSONObject  jsonObject = obj.makeJSONObject(compoTitle, compoDesc, imgPaths, imageViewPaths);
            MyCompositionsListActivity.buildList();

            try {
                Writer output = null;
                File file = new File("storage/sdcard/MyIdea/MyCompositions/" + compoTitle + ".json");
                output = new BufferedWriter(new FileWriter(file));
                output.write(jsonObject.toString());
                output.close();
                Toast.makeText(getApplicationContext(), "Composition saved", Toast.LENGTH_LONG).show();

            } catch (Exception e) {
                Toast.makeText(getBaseContext(), e.getMessage(), Toast.LENGTH_LONG).show();
            }
            finish();
        }
    });

- Parag Chauhan

Answer 2

尝试编写一个简单的class，其中包含静态方法，用于将json对象保存到文件中并检索它： 代码：

public class RetriveandSaveJSONdatafromfile {

 public static String objectToFile(Object object) throws IOException {
    String path = Environment.getExternalStorageDirectory() + File.separator + "/AppName/App_cache" + File.separator;
    File dir = new File(path);
    if (!dir.exists()) {
        dir.mkdirs();
    }
    path += "data";
    File data = new File(path);
    if (!data.createNewFile()) {
        data.delete();
        data.createNewFile();
    }
    ObjectOutputStream objectOutputStream = new ObjectOutputStream(new FileOutputStream(data));
    objectOutputStream.writeObject(object);
    objectOutputStream.close();
    return path;
}

public static Object objectFromFile(String path) throws IOException, ClassNotFoundException {
    Object object = null;
    File data = new File(path);
    if(data.exists()) {
        ObjectInputStream objectInputStream = new ObjectInputStream(new FileInputStream(data));
        object = objectInputStream.readObject();
        objectInputStream.close();
    }
    return object;
}
} 

要将json保存在文件中，请使用RetriveandSaveJSONdatafromfile.objectToFile(jsonObj)，要从文件中获取数据，请使用

 path = Environment.getExternalStorageDirectory() + File.separator +   
 "/AppName/App_cache/data" + File.separator; 
 RetriveandSaveJSONdatafromfile.objectFromFile(path);

- Kapil Rajput

Answer 3

感谢 @Chris Handy！我创建了一个 JSONObjectVariable 并将其赋值给 makeJSONObject。这是我的最终代码：

saveCompo.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            setName();
            createJSONFolder();
            CompositionJso compositionJso = new CompositionJso();
            JSONObject obj;
            obj = compositionJso.makeJSONObject(compoTitle, compoDesc, imgPaths, imageViewPaths);
            MyCompositionsListActivity.buildList();

            try {
                Writer output;
                File file = new File("storage/sdcard/MyIdea/MyCompositions/" + compoTitle + ".json");
                output = new BufferedWriter(new FileWriter(file));
                output.write(obj.toString());
                output.close();
                Toast.makeText(getApplicationContext(), "Composition saved", Toast.LENGTH_LONG).show();


            } catch (Exception e) {
                Toast.makeText(getBaseContext(), e.getMessage(), Toast.LENGTH_LONG).show();
            }
            finish();
        }
    });

- dudi

Answer 4

在 makeJSONObject 方法中，您实例化了一个新的 JSONObject。

这段代码应该可以工作。

public void makeJSONObject (String title, String desc, ArrayList<String> imgPath, ArrayList<Resources> imgView) {

    try {
        this.put("title", title);
        this.put("desc", desc);
        this.put("imgPath", imgPath);
        this.put("imgViewPath", imgView);
    } catch (JSONException e) {
        e.printStackTrace();
    }
}

- Nicola Meneghini