android 创建目录/文件/读写文件

1、创建目录及文件 

 private void mkdir_folder_file(){

    File folder = new File("/sdcard/test");
    if(!folder.exists()){
      folder.mkdirs();//创建目录
    }
    File test_f = new File(folder,"test.txt");
    if(!test_f.exists()){
      try {
test_f.createNewFile();//创建文件
      } catch (IOException e) {
e.printStackTrace();
      }
    }
  }

2.写文件
  public void write_file(){
    try{
      File file = new File("/sdcard/test/test.txt");
      FileOutputStream stream = new FileOutputStream(file);
      String str = "Wirte SD file test is Ok!";
      byte[] buf = str.getBytes();  
      stream.write(buf);//写文件
      stream.close();  
    }catch(Exception e){
      e.printStackTrace();
    }
  }

3、读文件
  public static String read_file() {
    StringBuilder stringBuilder = new StringBuilder();        
    try {  
      File Profile = new File("/sdcard/test/test.txt"));
      if (!Profile.exists()) {
return null;
      }
      InputStream ins = new FileInputStream(Profile);
      BufferedReader bf = new BufferedReader(new InputStreamReader(ins));
      String line;
      while ((line = bf.readLine()) != null) {
stringBuilder.append(line);
      }
    } catch (IOException e) {
      e.printStackTrace();
    }
    return stringBuilder.toString();

  }

4、权限

    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
    <uses-permission android:name="android.permission.MOUNT_UNMOUNT_FILESYSTEMS" />    
    <uses-permission android:name="android.permission.ACCESS_ALL_EXTERNAL_STORAGE"/>