android实现文件读写功能

public static String _getJsonString(String fileName)
   throws IOException {
  if ((fileName == null) || fileName.isEmpty()) {
   return "";
  }
  String retString = "";
  FileInputStream fis = null;
  String state = Environment.getExternalStorageState();
  if (state.equals(Environment.MEDIA_MOUNTED)) {
   File file = new File(Environment.getExternalStorageDirectory()
     + "/" + fileName + ".json");
   if (file.exists()) {
    fis = new FileInputStream(file);
    byte[] buffer = new byte[fis.available()];
    fis.read(buffer);
    fis.close();
 
    retString = new String(buffer);
   } else {
 
   }
  }
  return retString;
 }

public static void saveSettingFile(String fileName, String content) {
  FileOutputStream fos = null;
  String state = Environment.getExternalStorageState();
  if (state.equals(Environment.MEDIA_MOUNTED)) {
   File file = new File(Environment.getExternalStorageDirectory()
     + "/" + fileName + ".json");
   try {
    fos = new FileOutputStream(file);
    byte[] buffer = content.getBytes();
    fos.write(buffer);
    fos.close();
   } catch (FileNotFoundException e) {
    e.printStackTrace();
   } catch (IOException e) {
    e.printStackTrace();
   }
  }
 }

public static void saveServerInfo(String fileName, String content) {
  FileOutputStream fos = null;
  String state = Environment.getExternalStorageState();
  if (state.equals(Environment.MEDIA_MOUNTED)) {
   File file = new File(Environment.getExternalStorageDirectory()
     + "/" + fileName + ".json");
   try {
    fos = new FileOutputStream(file);
    byte[] buffer = content.getBytes();
    fos.write(buffer);
    fos.close();
   } catch (FileNotFoundException e) {
    e.printStackTrace();
   } catch (IOException e) {
    e.printStackTrace();
   }
  }
 }
 
 public static ServerInfo getServerInfo(String fileName)
   throws IOException {
  ServerInfo serverInfo = new ServerInfo();
  if ((fileName == null) || fileName.isEmpty()) {
   serverInfo = null;
   return serverInfo;
  }
  FileInputStream fis = null;
  String state = Environment.getExternalStorageState();
  if (state.equals(Environment.MEDIA_MOUNTED)) {
   File file = new File(Environment.getExternalStorageDirectory()
     + "/" + fileName + ".json");
   if (file.exists()) {
    fis = new FileInputStream(file);
    byte[] buffer = new byte[fis.available()];
    fis.read(buffer);
    fis.close();
 
    Gson gson = new Gson();
    serverInfo = gson.fromJson(new String(buffer),
      ServerInfo.class);
   } else {
    serverInfo = null;
   }
  }
  return serverInfo;
 }

public void onSetIPAndPort(View view) {
  ServerInfo serverInfo = new ServerInfo();
  try {
   serverInfo = JsonFileWriteAndRead.getServerInfo("videochat");
  } catch (IOException e) {
   e.printStackTrace();
  }
 
  //写入ip和端口
  String ip = ipSet.getText().toString();
  String port = portSet.getText().toString();
  serverInfo.setIpString(ip);
  serverInfo.setPortString(port);
  Gson gson = new Gson();
  if (ip.isEmpty() || port.isEmpty()) {
   Toast.makeText(this, "地址或端口为空", Toast.LENGTH_SHORT).show();
  } else {
   JsonFileWriteAndRead.saveServerInfo("videochat", gson.toJson(serverInfo));
   Toast.makeText(this, "地址和端口已经写入文件", Toast.LENGTH_SHORT).show();
  }
 }