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OSFileIO.java
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package com.zs.system.io;
import org.junit.Test;
import java.io.BufferedOutputStream;
import java.io.File;
import java.io.FileOutputStream;
import java.io.RandomAccessFile;
import java.nio.ByteBuffer;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;
public class OSFileIO {
static byte[] data = "123456789\n".getBytes();
static String path = "/root/testfileio/out.txt";
public static void main(String[] args) throws Exception {
switch ( args[0]) {
case "0" :
testBasicFileIO();
break;
case "1":
testBufferedFileIO();
break;
case "2" :
testRandomAccessFileWrite();
case "3":
// whatByteBuffer();
default:
}
}
//最基本的file写
public static void testBasicFileIO() throws Exception {
File file = new File(path);
FileOutputStream out = new FileOutputStream(file);
while(true){
Thread.sleep(10);
out.write(data);
}
}
//测试buffer文件IO
// jvm 8kB syscall write(8KBbyte[])
public static void testBufferedFileIO() throws Exception {
File file = new File(path);
BufferedOutputStream out = new BufferedOutputStream(new FileOutputStream(file));
while(true){
Thread.sleep(10);
out.write(data);
}
}
//测试文件NIO
public static void testRandomAccessFileWrite() throws Exception {
RandomAccessFile raf = new RandomAccessFile(path, "rw");
raf.write("hello mashibing\n".getBytes());
raf.write("hello seanzhou\n".getBytes());
System.out.println("write------------");
System.in.read();
raf.seek(4);
raf.write("ooxx".getBytes());
System.out.println("seek---------");
System.in.read();
FileChannel rafchannel = raf.getChannel();
//mmap 堆外 和文件映射的 byte not objtect
MappedByteBuffer map = rafchannel.map(FileChannel.MapMode.READ_WRITE, 0, 4096);
map.put("@@@".getBytes()); //不是系统调用 但是数据会到达 内核的pagecache
//曾经我们是需要out.write() 这样的系统调用，才能让程序的data 进入内核的pagecache
//曾经必须有用户态内核态切换
//mmap的内存映射，依然是内核的pagecache体系所约束的！！！
//换言之，丢数据
//你可以去github上找一些 其他C程序员写的jni扩展库，使用linux内核的Direct IO
//直接IO是忽略linux的pagecache
//是把pagecache 交给了程序自己开辟一个字节数组当作pagecache，动用代码逻辑来维护一致性/dirty。。。一系列复杂问题
System.out.println("map--put--------");
System.in.read();
// map.force(); // flush
raf.seek(0);
ByteBuffer buffer = ByteBuffer.allocate(8192);
// ByteBuffer buffer = ByteBuffer.allocateDirect(1024);
int read = rafchannel.read(buffer); //buffer.put()
System.out.println(buffer);
buffer.flip();
System.out.println(buffer);
for (int i = 0; i < buffer.limit(); i++) {
Thread.sleep(200);
System.out.print(((char)buffer.get(i)));
}
}
@Test
public void whatByteBuffer(){
// ByteBuffer buffer = ByteBuffer.allocate(1024);
ByteBuffer buffer = ByteBuffer.allocateDirect(1024);
System.out.println("postition: " + buffer.position());
System.out.println("limit: " + buffer.limit());
System.out.println("capacity: " + buffer.capacity());
System.out.println("mark: " + buffer);
buffer.put("123".getBytes());
System.out.println("-------------put:123......");
System.out.println("mark: " + buffer);
buffer.flip(); //读写交替
System.out.println("-------------flip......");
System.out.println("mark: " + buffer);
buffer.get();
System.out.println("-------------get......");
System.out.println("mark: " + buffer);
buffer.compact();
System.out.println("-------------compact......");
System.out.println("mark: " + buffer);
buffer.clear();
System.out.println("-------------clear......");
System.out.println("mark: " + buffer);
}
}