java see 的作用 java seek

package stream;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.RandomAccessFile;
import org.junit.jupiter.api.Test;
/*
* RandomAccessTile：随机读写访问流
* 既可以是输入流，也可以是输出流
* r|w|d|s:读|写|更新数据|元数据更新
*
* w:是对开头对文件内容进行覆盖
*
* */
public class RandomAccessFileTest {
@Test
public void test1(){
RandomAccessFile raf1 = null;
RandomAccessFile raf2 = null;
try {
//1.流对象
raf1 = new RandomAccessFile(new File("hello.txt"),"r");
raf2 = new RandomAccessFile(new File("hello2.txt"),"rw");
//2.读写
byte[] buffer = new byte[1024];
int len;
while((len = raf1.read(buffer))!=-1) {
raf2.write(buffer,0,len);
}
} catch (Exception e) {
e.printStackTrace();
}
finally {
try {
if(raf1!=null)
raf1.close();
} catch (Exception e) {
e.printStackTrace();
}
try {
if(raf2!=null)
raf2.close();
} catch (Exception e) {
e.printStackTrace();
}
}
}
/*
* seek随机访问|插入方法
*
* */
@Test
public void test2() throws IOException {
RandomAccessFile raf1 = new RandomAccessFile("hello.txt", "rw");
/*raf1.seek(3);
raf1.write("abc".getBytes());
*/
/*
* 使用StringBuilder
* */
StringBuilder sb = new StringBuilder((int)(new File("hello.txt").length()));
raf1.seek(3L);
int len;
byte[] buffer = new byte[20];
while((len = raf1.read(buffer))!=-1) {
sb.append(new String(buffer,0,len));
}
raf1.seek(3L);
raf1.write("xyz".getBytes());
raf1.write(sb.toString().getBytes());
raf1.close();
}
}