7-RandomAccessFile 随机流

 package com.io;

 import java.io.File;
 import java.io.FileNotFoundException;
 import java.io.IOException;
 import java.io.RandomAccessFile;

 import org.junit.Test;

 /*
  *  RandomAccessFile:支持随机访问
  *    1、即可充当一个输入流，又可充当一个输出流
  *    2、支持从任意位置读写
  */
 public class RandomAccessFileTest {

     @Test
     public void testRandomAccessFile(){
         /*
          * 创建RandomAccessFile对象有两个参数，
          * 一个是file对象，一个是此RandomAccessFile对象对文件读写的权限，有以下四种
          *
          * r: 以只读方式打开
          * rw：打开以便读取和写入
          * rwd:打开以便读取和写入；同步文件内容的更新
          * rws:打开以便读取和写入；同步文件内容和元数据的更新

          */
         RandomAccessFile raf_read = null;
         RandomAccessFile raf_write = null;
         try {
             raf_read = new RandomAccessFile(new File("random.txt"), "r");
             raf_write = new RandomAccessFile(new File("random_new.txt"), "rw");

             byte[] b = new byte[20];
             int len;
             while((len = raf_read.read(b)) != -1){
                 raf_write.write(b, 0, len);
             };
         } catch (FileNotFoundException e) {
             // TODO Auto-generated catch block
             e.printStackTrace();
         } catch (IOException e) {
             // TODO Auto-generated catch block
             e.printStackTrace();
         }finally{
             try {
                 raf_write.close();
             } catch (IOException e) {
                 e.printStackTrace();
             }

             try {
                 raf_read.close();
             } catch (IOException e) {
                 e.printStackTrace();
             }
         }
     }

     @Test
     public void 覆盖(){
         RandomAccessFile raf = null;
         try {
             raf = new RandomAccessFile(new File("random.txt"), "rw");
             raf.seek(3);//把指针移到第3个字节
             raf.write("xy".getBytes());
         }  catch (IOException e) {
             e.printStackTrace();
         }finally{
         try {
             raf.close();
         } catch (IOException e) {
             // TODO Auto-generated catch block
             e.printStackTrace();
         }
         }
     }

     //单行插入字符
     @Test
     public void 插入字符串(){
         RandomAccessFile raf = null;
         try {
             raf = new RandomAccessFile(new File("random.txt"), "rw");
             raf.seek(3);//把指针移到第3个字节
             String str = raf.readLine();
             System.out.println(raf.getFilePointer());//指针位置
             raf.seek(3);
             raf.write("xy".getBytes());
             raf.write(str.getBytes());
         }  catch (IOException e) {
             e.printStackTrace();
         }finally{
         try {
             raf.close();
         } catch (IOException e) {
             // TODO Auto-generated catch block
             e.printStackTrace();
         }
         }
     }

     //多行插入字符
         @Test
         public void 多行插入字符串(){
             RandomAccessFile raf = null;
             try {
                 raf = new RandomAccessFile(new File("random_lines.txt"), "rw");
                 raf.seek(3);//把指针移到第3个字节
                  byte [] b = new byte[20];
                  int len;
                  StringBuffer sbr = new StringBuffer();
                  while((len = raf.read(b)) != -1){
                      sbr.append(new String(b,0,len));
                  }
                  System.out.println(raf.getFilePointer());
                  raf.seek(3);
                  raf.write("xy".getBytes());
             }  catch (IOException e) {
                 e.printStackTrace();
             }finally{
             try {
                 raf.close();
             } catch (IOException e) {
                 e.printStackTrace();
             }
             }
         }
 }