Java NIO 基本介绍

import java.io.FileOutputStream;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;
public class NIOFileChannel01 {
public static void main(String[] args) throws Exception{
String str = "hello,尚硅谷";
//创建一个输出流->channel
FileOutputStream fileOutputStream = new FileOutputStream("d:\\file01.txt");
//通过 fileOutputStream 获取 对应的 FileChannel
//这个 fileChannel 真实 类型是 FileChannelImpl
FileChannel fileChannel = fileOutputStream.getChannel();
//创建一个缓冲区 ByteBuffer
ByteBuffer byteBuffer = ByteBuffer.allocate(1024);
//将 str 放入 byteBuffer
byteBuffer.put(str.getBytes());//对 byteBuffer 进行 flip
byteBuffer.flip();
//将 byteBuffer 数据写入到 fileChannel
fileChannel.write(byteBuffer);
fileOutputStream.close();
}
}

import java.io.File;
import java.io.FileInputStream;
import java.nio.ByteBuffer;import java.nio.channels.FileChannel;
public class NIOFileChannel02 {
public static void main(String[] args) throws Exception {
//创建文件的输入流
File file = new File("d:\\file01.txt");
FileInputStream fileInputStream = new FileInputStream(file);
//通过 fileInputStream 获取对应的 FileChannel -> 实际类型 FileChannelImpl
FileChannel fileChannel = fileInputStream.getChannel();
//创建缓冲区
ByteBuffer byteBuffer = ByteBuffer.allocate((int) file.length());
//将 通道的数据读入到 Buffer
fileChannel.read(byteBuffer);
//将 byteBuffer 的 字节数据 转成 String
System.out.println(new String(byteBuffer.array()));
fileInputStream.close();
}
}

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;
public class NIOFileChannel03 {
public static void main(String[] args) throws Exception {
FileInputStream fileInputStream = new FileInputStream("1.txt");
FileChannel fileChannel01 = fileInputStream.getChannel();
FileOutputStream fileOutputStream = new FileOutputStream("2.txt");
FileChannel fileChannel02 = fileOutputStream.getChannel();
ByteBuffer byteBuffer = ByteBuffer.allocate(512);
while (true) { //循环读取
//这里有一个重要的操作， 一定不要忘了
/*
public final Buffer clear() {
position = 0;
limit = capacity;
mark = -1;
return this;
}
*/
byteBuffer.clear(); //清空 buffer
int read = fileChannel01.read(byteBuffer);
System.out.println("read =" + read);
if(read == -1) { //表示读完
break;
} //将 buffer 中的数据写入到 fileChannel02 -- 2.txt
byteBuffer.flip();
fileChannel02.write(byteBuffer);
} //关闭相关的流
fileInputStream.close();
fileOutputStream.close();
}
}

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.nio.channels.FileChannel;
public class NIOFileChannel04 {
public static void main(String[] args) throws Exception {
//创建相关流
FileInputStream fileInputStream = new FileInputStream("d:\\a.jpg");
FileOutputStream fileOutputStream = new FileOutputStream("d:\\a2.jpg");
//获取各个流对应的 filechannel
FileChannel sourceCh = fileInputStream.getChannel();
FileChannel destCh = fileOutputStream.getChannel();
//使用 transferForm 完成拷贝
destCh.transferFrom(sourceCh,0,sourceCh.size());
//关闭相关通道和流
sourceCh.close();
destCh.close();
fileInputStream.close();
fileOutputStream.close();
}
}

public class NIOByteBufferPutGet {
public static void main(String[] args) {
//创建一个 Buffer
ByteBuffer buffer = ByteBuffer.allocate(64);
//类型化方式放入数据
buffer.putInt(100);
buffer.putLong(9);
buffer.putChar(‘尚‘);
buffer.putShort((short) 4);
//取出
buffer.flip();
System.out.println();
System.out.println(buffer.getInt());
System.out.println(buffer.getLong());
System.out.println(buffer.getChar());
System.out.println(buffer.getShort());
}

public class ReadOnlyBuffer {
public static void main(String[] args) {
//创建一个 buffer
ByteBuffer buffer = ByteBuffer.allocate(64);
for(int i = 0; i < 64; i++) {
buffer.put((byte)i);
} //
读取
buffer.flip();//得到一个只读的 Buffer
ByteBuffer readOnlyBuffer = buffer.asReadOnlyBuffer();
System.out.println(readOnlyBuffer.getClass());
//读取
while (readOnlyBuffer.hasRemaining()) {
System.out.println(readOnlyBuffer.get());
} r
eadOnlyBuffer.put((byte)100); //ReadOnlyBufferException
}
}

import java.io.RandomAccessFile;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;
/*
说明
1. MappedByteBuffer 可让文件直接在内存(堆外内存)修改, 操作系统不需要拷贝一次
*/
public class MappedByteBufferTest {
public static void main(String[] args) throws Exception {
RandomAccessFile randomAccessFile = new RandomAccessFile("1.txt", "rw");
//获取对应的通道
FileChannel channel = randomAccessFile.getChannel();
/**
* 参数 1: FileChannel.MapMode.READ_WRITE 使用的读写模式
* 参数 2： 0 ： 可以直接修改的起始位置
* 参数 3: 5: 是映射到内存的大小(不是索引位置) ,即将 1.txt 的多少个字节映射到内存
* 可以直接修改的范围就是 0-5
* 实际类型 DirectByteBuffer
*/
MappedByteBuffer mappedByteBuffer = channel.map(FileChannel.MapMode.READ_WRITE, 0, 5);
mappedByteBuffer.put(0, (byte) ‘H‘);
mappedByteBuffer.put(3, (byte) ‘9‘);
mappedByteBuffer.put(5, (byte) ‘Y‘);//IndexOutOfBoundsException
randomAccessFile.close();
System.out.println("修改成功~~");
}
}

import java.net.InetSocketAddress;
import java.nio.ByteBuffer;
import java.nio.channels.ServerSocketChannel;
import java.nio.channels.SocketChannel;
import java.util.Arrays;
/**
* Scattering： 将数据写入到 buffer 时， 可以采用 buffer 数组， 依次写入 [分散]
* Gathering: 从 buffer 读取数据时， 可以采用 buffer 数组， 依次读
*/
public class ScatteringAndGatheringTest {
public static void main(String[] args) throws Exception {
//使用 ServerSocketChannel 和 SocketChannel 网络
ServerSocketChannel serverSocketChannel = ServerSocketChannel.open();
InetSocketAddress inetSocketAddress = new InetSocketAddress(7000);
//绑定端口到 socket ， 并启动
serverSocketChannel.socket().bind(inetSocketAddress);
//创建 buffer 数组
ByteBuffer[] byteBuffers = new ByteBuffer[2];
byteBuffers[0] = ByteBuffer.allocate(5);
byteBuffers[1] = ByteBuffer.allocate(3);
//等客户端连接(telnet)
SocketChannel socketChannel = serverSocketChannel.accept();
int messageLength = 8; //假定从客户端接收 8 个字节
//循环的读取
while (true) {
int byteRead = 0;
while (byteRead < messageLength ) {
long l = socketChannel.read(byteBuffers);
byteRead += l; //累计读取的字节数
System.out.println("byteRead=" + byteRead);
//使用流打印, 看看当前的这个 buffer 的 position 和 limit
Arrays.asList(byteBuffers).stream().map(buffer -> "postion=" + buffer.position() + ", limit=" +
buffer.limit()).forEach(System.out::println);
} //将所有的 buffer 进行 flip
Arrays.asList(byteBuffers).forEach(buffer -> buffer.flip());//将数据读出显示到客户端
long byteWirte = 0;
while (byteWirte < messageLength) {
long l = socketChannel.write(byteBuffers); //
byteWirte += l;
} //
将所有的 buffer 进行 clear
Arrays.asList(byteBuffers).forEach(buffer-> {
buffer.clear();
});
System.out.println("byteRead:=" + byteRead + " byteWrite=" + byteWirte + ", messagelength" +
messageLength);
}
}
}