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   源码介绍

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实现了内部存储和外部存储的写入和读取

public class MainActivity extends AppCompatActivity implements View.OnClickListener { private static final String TAG ="MainActivity" ; private  static final int REQUEST_EXTERNAL_STORAGE = 1;
    String fileName = "test.txt"; @Override  public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) { super.onRequestPermissionsResult(requestCode, permissions, grantResults); if(requestCode == 1){ for(int i=0;i<permissions.length;i  ){ if(permissions[i].equals("android.permission.WRITE_EXTERNAL_STORAGE")&&grantResults[i]== PackageManager.PERMISSION_GRANTED){
                    Toast.makeText(this,"获得权限",Toast.LENGTH_SHORT).show();
                }else{
                    Toast.makeText(this,"权限被拒绝",Toast.LENGTH_SHORT).show();
                }
            }
        }
    } @Override  protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Button btn_innerwrite = findViewById(R.id.btn_innerwrite);
        btn_innerwrite.setOnClickListener(this);
        Button btn_innerread = findViewById(R.id.btn_innerread);
        btn_innerread.setOnClickListener(this);
        Button btn_outerwrite = findViewById(R.id.btn_outerwrite);
        btn_outerwrite.setOnClickListener(this);
        Button btn_outerread = findViewById(R.id.btn_outerread);
        btn_outerread.setOnClickListener(this);
    } @Override  public void onClick(View v) { switch (v.getId()){ case R.id.btn_innerwrite:
                innerwrite(); break; case R.id.btn_innerread:
                innerread(); break; case R.id.btn_outerwrite:
                outerwrite(); break; case R.id.btn_outerread:
               outerread(); break; default: break;
        }
    } private void outerread() { //检查外部设备状态  String envior = Environment.getExternalStorageState(); //如果是加载状态，那么开始写入  if(envior.equals(Environment.MEDIA_MOUNTED)){
            ActivityCompat.requestPermissions(this,new String[]{"android.permission.WRITE_EXTERNAL_STORAGE"},1);
            File sd_path = Environment.getExternalStorageDirectory();
            sd_path = new File(sd_path,"/txtfile");//创建路径  sd_path.mkdirs();
            File file = new File(sd_path,fileName);
            String str = "";
            FileInputStream fis = null; try {
                fis = new FileInputStream(file);
                BufferedReader buff = new BufferedReader(new InputStreamReader(fis));
                str=buff.readLine(); //fis.write(str.getBytes());  fis.close();
                Toast.makeText(this,"read scucess!" str,Toast.LENGTH_SHORT).show();
                Log.i(TAG,"read scucess!" str);
            } catch (FileNotFoundException e) {
                e.printStackTrace();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    } private void outerwrite() { //检查外部设备状态  String envior = Environment.getExternalStorageState(); //如果是加载状态，那么开始写入  if(envior.equals(Environment.MEDIA_MOUNTED)){
            ActivityCompat.requestPermissions(this,new String[]{"android.permission.WRITE_EXTERNAL_STORAGE"},1);
            File sd_path = Environment.getExternalStorageDirectory();
            sd_path = new File(sd_path,"/txtfile");//创建路径  sd_path.mkdirs();
            File file = new File(sd_path,fileName);
            String str = "outer write testing!";
            FileOutputStream fos = null; try {
                fos = new FileOutputStream(file);
                fos.write(str.getBytes());
                fos.close();
                Toast.makeText(this,"write scucess!" sd_path.getAbsolutePath(),Toast.LENGTH_SHORT).show();
                Log.i(TAG,"write scucess!" sd_path.getAbsolutePath());
            } catch (FileNotFoundException e) {
                e.printStackTrace();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    } private void innerread() { //String strr = "";  FileInputStream fis = null; try {
            fis = openFileInput(fileName); byte[] buffer = new byte[fis.available()];
            fis.read(buffer);
            String strr = new String(buffer);
            Toast.makeText(this,"read scucess!" strr,Toast.LENGTH_SHORT).show();
            fis.close();
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
    } private void innerwrite() {
        String str = "innerwrite test!";
        FileOutputStream fos = null; try {
            fos = openFileOutput(fileName,MODE_PRIVATE);
            fos.write(str.getBytes());
            Toast.makeText(this,"write scucess!" getFilesDir().getAbsolutePath(),Toast.LENGTH_SHORT).show();
            Log.i(TAG,"file address:" getFilesDir().getAbsolutePath());
            fos.close();
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}