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();
 }
 }