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"/>