1 package com.io;
2
3 import java.io.File;
4 import java.io.FileNotFoundException;
5 import java.io.IOException;
6 import java.io.RandomAccessFile;
7
8 import org.junit.Test;
9
10 /*
11 * RandomAccessFile:支持随机访问
12 * 1、即可充当一个输入流，又可充当一个输出流
13 * 2、支持从任意位置读写
14 */
15 public class RandomAccessFileTest {
16
17
18
19 @Test
20 public void testRandomAccessFile(){
21 /*
22 * 创建RandomAccessFile对象有两个参数，
23 * 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
24 *
25 * r: 以只读方式打开
26 * rw：打开以便读取和写入
27 * rwd:打开以便读取和写入；同步文件内容的更新
28 * rws:打开以便读取和写入；同步文件内容和元数据的更新
29
30 */
31 RandomAccessFile raf_read = null;
32 RandomAccessFile raf_write = null;
33 try {
34 raf_read = new RandomAccessFile(new File("random.txt"), "r");
35 raf_write = new RandomAccessFile(new File("random_new.txt"), "rw");
36
37 byte[] b = new byte[20];
38 int len;
39 while((len = raf_read.read(b)) != -1){
40 raf_write.write(b, 0, len);
41 };
42 } catch (FileNotFoundException e) {
43 // TODO Auto-generated catch block
44 e.printStackTrace();
45 } catch (IOException e) {
46 // TODO Auto-generated catch block
47 e.printStackTrace();
48 }finally{
49 try {
50 raf_write.close();
51 } catch (IOException e) {
52 e.printStackTrace();
53 }
54
55 try {
56 raf_read.close();
57 } catch (IOException e) {
58 e.printStackTrace();
59 }
60 }
61 }
62
63
64 @Test
65 public void 覆盖(){
66 RandomAccessFile raf = null;
67 try {
68 raf = new RandomAccessFile(new File("random.txt"), "rw");
69 raf.seek(3);//把指针移到第3个字节
70 raf.write("xy".getBytes());
71 } catch (IOException e) {
72 e.printStackTrace();
73 }finally{
74 try {
75 raf.close();
76 } catch (IOException e) {
77 // TODO Auto-generated catch block
78 e.printStackTrace();
79 }
80 }
81 }
82
83 //单行插入字符
84 @Test
85 public void 插入字符串(){
86 RandomAccessFile raf = null;
87 try {
88 raf = new RandomAccessFile(new File("random.txt"), "rw");
89 raf.seek(3);//把指针移到第3个字节
90 String str = raf.readLine();
91 System.out.println(raf.getFilePointer());//指针位置
92 raf.seek(3);
93 raf.write("xy".getBytes());
94 raf.write(str.getBytes());
95 } catch (IOException e) {
96 e.printStackTrace();
97 }finally{
98 try {
99 raf.close();
100 } catch (IOException e) {
101 // TODO Auto-generated catch block
102 e.printStackTrace();
103 }
104 }
105 }
106
107
108
109 //多行插入字符
110 @Test
111 public void 多行插入字符串(){
112 RandomAccessFile raf = null;
113 try {
114 raf = new RandomAccessFile(new File("random_lines.txt"), "rw");
115 raf.seek(3);//把指针移到第3个字节
116 byte [] b = new byte[20];
117 int len;
118 StringBuffer sbr = new StringBuffer();
119 while((len = raf.read(b)) != -1){
120 sbr.append(new String(b,0,len));
121 }
122 System.out.println(raf.getFilePointer());
123 raf.seek(3);
124 raf.write("xy".getBytes());
125 } catch (IOException e) {
126 e.printStackTrace();
127 }finally{
128 try {
129 raf.close();
130 } catch (IOException e) {
131 e.printStackTrace();
132 }
133 }
134 }
135 }
