Java IO流->处理流->“随机访问” 的方式:RandomAccessFile

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

import org.junit.Test;

public class TestRandomAccessFile {
//进行文件的读写
@Test
public void test1() {
RandomAccessFile raf1 = null;
RandomAccessFile raf2 = null;
try {
raf1 = new RandomAccessFile(new File("hello.txt"), "r");
raf2 = new RandomAccessFile("hello1.txt", "rw");

byte[] b = new byte[20];
int len;
while((len = raf1.read(b)) != -1) {
raf2.write(b, 0, len);
}
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} finally {
if(raf2 != null) {
try {
raf2.close();
} catch (IOException e) {
e.printStackTrace();
}
}
if(raf1 != null) {
try {
raf1.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}

//实际上实现的是覆盖操作
@Test
public void test2() {
RandomAccessFile raf = null;
try {
raf = new RandomAccessFile("hello.txt", "rw");

//先定位到要插入的地方
raf.seek(4);
raf.write("xy".getBytes());
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} finally {
if(raf != null) {
try {
raf.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}

//插入操作：通过进行复制操作，再进行覆盖操作，test4()更好的实现了插入操作
@Test
public void test3() {
RandomAccessFile raf = null;
try {
raf = new RandomAccessFile("hello.txt", "rw");
raf.seek(4);
String str = raf.readLine();

raf.seek(4);
raf.write("xy".getBytes());
raf.write(str.getBytes());
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} finally {
if(raf != null) {
try {
raf.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}

//插入操作：相较于test3()，更通用
@Test
public void test4() {
RandomAccessFile raf = null;
try {
raf = new RandomAccessFile("hello.txt", "rw");
raf.seek(4);

byte[] b = new byte[20];
int len;
StringBuffer sb = new StringBuffer();
while((len = raf.read(b)) != -1) {
sb.append(new String(b, 0, len));
}
raf.seek(4);
raf.write("xy".getBytes());
raf.write(sb.toString().getBytes());
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} finally {
if(raf != null) {
try {
raf.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
}