写在前面
对于Java NIO已经学习了一段时间了，周末实践了下，折腾了一天，总算对NIO的理论，有了一个感性的认识。下面的实践是：服务器与客户端都采用NIO的方式来实现文件下载。对于传统的SOCKET BIO方式，服务器端会为每个连接上的客户端分配一个Worker线程来进行doWork，而NIO SERVER却没有为每个Socket链接分配线程的必要了，避免了大量的线程所需的上下文切换，借助NIO提供的Selector机制，只需要一个或者几个线程来管理成百上千的SOCKET连接。那么下面我们就来看看吧！
文件下载辅助类
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/** * 这个类的基本思路是,读取本地文件到缓冲区
* 因为通道只能操作缓冲区
*/
class DownloadFileProcesser implements Closeable{
private ByteBuffer buffer = ByteBuffer.allocate(8 * 1024);
private FileChannel fileChannel ;
public DownloadFileProcesser() {
try{
FileInputStream fis = new FileInputStream("e:/tmp/Shell学习笔记.pdf");
fileChannel = fis.getChannel();
}catch(Exception e){
e.printStackTrace();
}
}public int readFile2Buffer() throws IOException{
int count = 0;
buffer.clear();
count = fileChannel.read(buffer);
buffer.flip();
return count;
}public ByteBuffer getByteBuffer(){
return buffer;
}@Overridepublic void close() throws IOException {
fileChannel.close();
}} |
服务端代码：
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public class ServerMain {
public static void main(String[] args) throws IOException {
ServerSocketChannel serverSocketChannel = ServerSocketChannel.open();
serverSocketChannel.configureBlocking(false);
serverSocketChannel.socket().bind(new InetSocketAddress(8887));
Selector selector = Selector.open();
serverSocketChannel.register(selector, SelectionKey.OP_ACCEPT);
while (true) {
selector.select();
Iterator<SelectionKey> iterator = selector.selectedKeys().iterator();
while (iterator.hasNext()) {
SelectionKey s = iterator.next();
// 如果客户端有连接请求
if (s.isAcceptable()) {
System.out.println("客户端连接请求..");
ServerSocketChannel ssc = (ServerSocketChannel) s.channel();
SocketChannel sc = ssc.accept();
sc.configureBlocking(false);
sc.register(selector, SelectionKey.OP_READ);
}
// 如果客户端有发送数据请求
if (s.isReadable()) {
System.out.println("接受客户端发送过来的文本消息...");
//这里拿出的通道就是ACCEPT上注册的SocketChannel通道
SocketChannel sc = (SocketChannel) s.channel();
//要读取数据先要准备好BUFFER缓冲区
ByteBuffer buffer = ByteBuffer.allocate(8 * 1024);
//准备BYTE数组,形成输出
sc.read(buffer);
byte[] clientByteInfo = new byte[buffer.position()];
buffer.flip();
buffer.get(clientByteInfo);
System.out.println("服务器端收到消息：" + new String(clientByteInfo,"utf-8"));
//CLIENT下一步的动作就是读取服务器端的文件,因此需要注册写事件
SelectionKey selectionKey = sc.register(selector, SelectionKey.OP_WRITE);
//在这个selectionKey上绑定一个对象,以供写操作时取出进行处理
DownloadFileProcesser downloadFileProcesser = new DownloadFileProcesser();
selectionKey.attach(downloadFileProcesser);
}
// 如果客户端有下载文件数据请求
if (s.isWritable()) {
//这里把attachment取出进行写入操作
DownloadFileProcesser downloadFileProcesser = (DownloadFileProcesser)s.attachment();
int count = downloadFileProcesser.readFile2Buffer();
if(count <= 0){
System.out.println("客户端下载完毕...");
//关闭通道
s.channel().close();
downloadFileProcesser.close();
}else{
//需要注意的是我们这里并没有出现常见的while写的结构,这是为何?
//因为client其实不断的在read操作，从而触发了SELECTOR的不断写事件!
SocketChannel sc = (SocketChannel)s.channel();
sc.write(downloadFileProcesser.getByteBuffer());
}
}
iterator.remove();
}
}
}
} |
客户端代码：
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class Client4DownloadFile implements Runnable{
//标示
private String name;
private FileChannel fileChannel;
public Client4DownloadFile(String name , RandomAccessFile randomAccessFile){
this.name = name;
this.fileChannel = randomAccessFile.getChannel();
}
private ByteBuffer buffer = ByteBuffer.allocate(8 * 1024);
@Override
public void run() {
try {
SocketChannel sc = SocketChannel.open();
Selector selector = Selector.open();
sc.configureBlocking(false);
sc.register(selector, SelectionKey.OP_CONNECT);
sc.connect(new InetSocketAddress("127.0.0.1",8887));
while(true){
selector.select();
Iterator<SelectionKey> iterator = selector.selectedKeys().iterator();
while(iterator.hasNext()){
SelectionKey s = iterator.next();
if(s.isConnectable()){
System.out.println("客户端[" + name + "]已经连接上了服务器...");
SocketChannel sc2 = (SocketChannel)s.channel();
if(sc2.isConnectionPending() && sc2.finishConnect()){
sc2.configureBlocking(false);
String msg = "Thread-" + name + " send message!";
byte[] b = msg.getBytes("utf-8");
sc2.write(ByteBuffer.wrap(b));
System.out.println("客户端[" + name + "]给服务器端发送文本消息完毕...");
sc2.register(selector, SelectionKey.OP_READ);
}
}
if(s.isReadable()){
SocketChannel sc3 = (SocketChannel)s.channel();
buffer.clear();
int count = sc3.read(buffer);
if(count <= 0){
s.cancel();
System.out.println("Thread " + name + " 下载完毕...");
}
while(count > 0){
buffer.flip();
fileChannel.write(buffer);
count = sc3.read(buffer);
}
}
iterator.remove();
}
}
} catch (IOException e) {
e.printStackTrace();
}
}} |
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public class ClientMain {
public static void main(String[] args) throws FileNotFoundException{
for(int i = 0 ; i < 10 ; i++){
File file = new File("e:/tmp/" + i + ".pdf");
RandomAccessFile raf = new RandomAccessFile(file,"rw");
Client4DownloadFile client4DownloadFile = new Client4DownloadFile("" + i, raf);
new Thread(client4DownloadFile).start();
}
}
} |
本文转自zfz_linux_boy 51CTO博客，原文链接：http://blog.51cto.com/zhangfengzhe/1726488，如需转载请自行联系原作者