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();  } }