随机存取文件流

 /**
     * 将文件中的最开始的位置的数据进行替代。
     * Replace the data at the beginning of the file.
     */
    @Test
    public void test1(){
     
        try(RandomAccessFile af = new RandomAccessFile(new File("hi.txt"),"rw");){
     
            af.write("我 ".getBytes());
        } catch (FileNotFoundException e) {
     
            e.printStackTrace();
        } catch (IOException e) {
     
            e.printStackTrace();
        }
    }

2、插入操作

  /**
     * 插入操作
     * insert operation
     */
    @Test
    public void test2(){
     
        try(RandomAccessFile rw = new RandomAccessFile("hi.txt","rw")) {
     
            rw.seek(10);
            StringBuffer stringBuffer = new StringBuffer((int) new File("hi.txt").length());
            byte[] buffer = new byte[10];
            int len = -1;
            while((len = rw.read(buffer)) != -1){
     
                stringBuffer.append(new String(buffer,0,len));    // 通过toString会导致中文无法解析。
            }
            //调用指针，写入“xyz”
            rw.seek(10);
            rw.write("xyz".getBytes());
            rw.write(stringBuffer.toString().getBytes());
        } catch (FileNotFoundException e) {
     
            e.printStackTrace();
        } catch (IOException e) {
     
            e.printStackTrace();
        }
    }