1. 字节流

 @Test
  public void test4() throws IOException {
      File src = new File("2.png");
      File dest = new File("2_copy.png");
      FileInputStream fis = new FileInputStream(src);
      FileOutputStream fos = new FileOutputStream(dest);
      byte[] bytes = new byte[1024];
      int len;
      while((len=fis.read(bytes))!=-1){
        fos.write(bytes,0,len);
      }
      fis.close();
      fos.close();
  }