使用RandomAccessFile实现数据的插入效果

@Test
public void test3()   {
    RandomAccessFile raf1 = null;
    try {
        raf1 = new RandomAccessFile("hello.txt", "rw");
        raf1.seek(3);//指针调到角标为3的位置
        //保存指针3后面的所有数据到StringBuilder中
        StringBuilder builder = new StringBuilder((int)new File("hello.txt").length());

        byte[] bytes = new byte[20];
        int len;
        while ((len=raf1.read(bytes))!=-1){
            builder.append(new String(bytes,0,len));
        }
        //调回指针，写入"xyz"
        raf1.seek(3);
        raf1.write("xyz".getBytes());

        //将StringBuilder中的数据写入到文件中
        raf1.write(builder.toString().getBytes());
    } catch (IOException e) {
        e.printStackTrace();
    } finally {
        if (raf1!=null){
            try {
                raf1.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }

}