Android 如何加快读取文件以使用缓冲输入/输出创建 Java 对象？

Question

我有这种方法，它从存储中获取一个 json 文件并将其转换为一堆 java 对象。如何添加缓冲输出/输入流以加快速度？还是有其他方法可以优化速度？

编辑：我不仅要使用它来读取 JSON 文件，所以我不需要 json 到 java 解析器，我实际上需要使用缓冲区来加速文件操作 :)

public static ArrayList<String> convertJSONtoArrayList(File jsonStrings) {
        FileInputStream fileInputStream = null;

        try {
            fileInputStream = new FileInputStream(jsonStrings);
        } catch (FileNotFoundException e1) {
            e1.printStackTrace();
        }

        return convertJSONtoArrayList(fileInputStream);
    }

    public static ArrayList<String> convertJSONtoArrayList(InputStream fileInputStream) {
        ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();

        ArrayList<String> arrayListString = new ArrayList<String>();

        int ctr;
        try {
            if (fileInputStream != null) {
                ctr = fileInputStream.read();
                while (ctr != -1) {
                    byteArrayOutputStream.write(ctr);
                    ctr = fileInputStream.read();
                }
            }
            fileInputStream.close();
        } catch (IOException e) {
            e.printStackTrace();
        }

        try {
            // Parse the data into jsonobject to get original data in form of
            // json.
            JSONArray jsonArray = new JSONArray(byteArrayOutputStream.toString());
            int arrayLength = jsonArray.length();
            for (int i = 0; i < arrayLength; i++) {

                JSONObject jsonObject = jsonArray.getJSONObject(i);
                arrayListString.add(jsonObject.getString(Tags.VALUE));

            }

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

        return arrayListString;
    }

我的想法来自这里：How to speed up unzipping time in Java / Android? - 答案很清楚，如果添加了 BufferedInputStream，操作速度会非常好。

Answer 1

使用相同的代码，但将 BufferedInputStream 包裹在 FileInputStream 周围。

Answer 2

public static List<String> convertJSONtoArrayList(File f) {
    final StringBuilder jsonString = new StringBuilder(500);
    try {
        final BufferedReader reader = new BufferedReader(new FileReader(f));
        String s;
        while ((s = reader.readLine()) != null) {
            jsonString.append(s);
        }
        reader.close();
    } catch (IOException e) {
        e.printStackTrace();
        return Collections.emptyList();
    }

    try {
        JSONArray jsonArray = new JSONArray(jsonString.toString());
        int arrayLength = jsonArray.length();
        final List<String> result = new ArrayList<String>(arrayLength);
        for (int i = 0; i < arrayLength; i++) {
            JSONObject jsonObject = jsonArray.getJSONObject(i);
            result.add(jsonObject.getString(Tags.VALUE));
        }
        return result;
    } catch (Exception e) {
        e.printStackTrace();
        return Collections.emptyList();
    }
}

或试试这个（应该更快）：

public static List<String> convertJSONtoArrayList(File f) {
    ByteBuffer buffer = ByteBuffer.allocate(f.length());
    try {
        ReadableByteChannel channel = Channels.newChannel(new FileInputStream(f));
        channel.read(buffer);
        channel.close();
    } catch (Exception e) {
        e.printStackTrace();
        return Collections.emptyList();
    }

    final String jsonString = new String(buffer.array());

    try {
        JSONArray jsonArray = new JSONArray(jsonString);
        int arrayLength = jsonArray.length();
        final List<String> result = new ArrayList<String>(arrayLength);
        for (int i = 0; i < arrayLength; i++) {
            JSONObject jsonObject = jsonArray.getJSONObject(i);
            result.add(jsonObject.getString(Tags.VALUE));
        }
        return result;
    } catch (Exception e) {
        e.printStackTrace();
        return Collections.emptyList();
    }
}