NIO是jdk1.4之后出现的API，称作新IO（NEW IO），也叫非阻塞型IO（NON-BLOCKING IO），区别于以前的IO可以提供多路非阻塞式高伸缩性网络IO，它为所有的java基本类型提供缓存支持（不包括boolean类型），ByteBuffer，ShortBuffer，IntBuffer，LongBuffer，FloatBuffer，DoubleBuffer，CharBuffer以及MappedByteBuffer（映射到文件的字节缓冲区）。
在NIO中比较重要的三个概念是selector（选择器），channel（管道），buffer（缓冲区），它们之间的关系为selector管理channel（一个selector管理多个管道），channel与buffer交互。channel就像是IO中的stream流，数据的读取，写入都需要经过这个管道，但是跟流不一样的是：channel是双向的，可以读也可以写，而流是单向的不可复用的。输入流和输出流是分开的。在NIO中由事件触发，将管道以某一个事件（或者多个事件OP_READ,OP_WRITE,OP_ACCEPT,OP_CONNECT）注册到selector后，当管道中的中的事件准备好后，selector.select() 即可获取到准备好管道的数量，通过selector.selectedKeys()获取到所有准备好的管道，通过判断管道状态，进而获取到socketChannel进度读写链接操作....下面看一下NioServer和NioClient的小例子.....
首先编写服务端：
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.InetAddress;
import java.net.InetSocketAddress;
import java.nio.ByteBuffer;
import java.nio.channels.SelectionKey;
import java.nio.channels.Selector;
import java.nio.channels.ServerSocketChannel;
import java.nio.channels.SocketChannel;
import java.util.Iterator;
import java.util.Set;
public class NioServer {
private static final Logger LOGGER = LoggerFactory.getLogger(NioServer.class);
private final Selector selector;
public NioServer(int port) throws IOException {
this.selector = Selector.open();//根据电脑操作系统生成select选择器
ServerSocketChannel serverSocketChannel = ServerSocketChannel.open();//生成服务器socket通道
InetSocketAddress inetSocketAddress = new InetSocketAddress(InetAddress.getLocalHost(), port);
serverSocketChannel.socket().bind(inetSocketAddress);//为服务器绑定地址和监听端口
serverSocketChannel.configureBlocking(false);//将阻塞设置成false，如果不设置就会出现IllegalBlockingModeException()异常
serverSocketChannel.register(selector, SelectionKey.OP_ACCEPT);//将通道注册到选择器上，并制定监听状态....
}
public void listen() throws Exception {
System.out.println("服务端启动成功.....");
while (!Thread.interrupted()) {//采用轮询的方式...
LOGGER.info("正在扫描服务器端准备好的selector.....");
int selectCount = selector.select();
LOGGER.info("服务器准备好的选择器:" + selectCount);
if (selectCount != 0) {
Set<SelectionKey> selectionKeys = selector.selectedKeys();
Iterator<SelectionKey> keyIterator = selectionKeys.iterator();
while (keyIterator.hasNext()) {
SelectionKey selectionKey = keyIterator.next();
keyIterator.remove();//将取出来的selectedKey删除掉，避免重复处理
if (selectionKey.isAcceptable()) {
ServerSocketChannel serverSocketChannel = (ServerSocketChannel) selectionKey.channel();
SocketChannel socketChannel = serverSocketChannel.accept();
socketChannel.configureBlocking(false);
socketChannel.write(ByteBuffer.wrap(new String("收到连接请求....").getBytes()));
socketChannel.register(selector, SelectionKey.OP_READ);
LOGGER.info("服务端已发送数据....");
} else if (selectionKey.isReadable()) {
//有读取的权限
readMsg(selectionKey);
}
}
}
}
}
public void readMsg(SelectionKey selectionKey) throws Exception {
SocketChannel socketChannel = (SocketChannel) selectionKey.channel();
//创建缓冲区
ByteBuffer byteBuffer = ByteBuffer.allocate(1024);
//从管道中读取数据到buffer中
socketChannel.read(byteBuffer);//将通道中的数据写出到byteBuffer中
byte[] bytes = byteBuffer.array();
String getMsg = new String(bytes).trim();
System.out.println("服务器收到的消息是:" + getMsg);
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
System.out.println("请输入应答数据：");
byteBuffer.clear();//将缓冲区清空
byteBuffer.flip();//现在来看这句代码可以注释掉
Thread.sleep(5000);
socketChannel.write(ByteBuffer.wrap(br.readLine().getBytes()));
socketChannel.register(selector, SelectionKey.OP_READ);//设置通道监控的状态
LOGGER.info("服务器已发送应答请求.....");
}
public static void main(String[] args) throws Exception {
NioServer nioServer = new NioServer(8080);
nioServer.listen();
}
}
服务端的代码需要先写...然后再写客户端的代码
客户端代码：import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.net.InetAddress;
import java.net.InetSocketAddress;
import java.nio.ByteBuffer;
import java.nio.channels.SelectionKey;
import java.nio.channels.Selector;
import java.nio.channels.SocketChannel;
import java.util.Iterator;
public class NioClient {
private static final Logger LOGGER = LoggerFactory.getLogger(NioClient.class);
private final Selector selector;
public NioClient(int port) throws Exception {
this.selector = Selector.open();//根据操作系统创建选择器
SocketChannel socketChannel = SocketChannel.open();//创建socketChannel通道
socketChannel.connect(new InetSocketAddress(InetAddress.getLocalHost(), port));//连接到指定的服务器
socketChannel.configureBlocking(false);//设置阻塞参数为false，不设置在register时会报IllegalBlockingModeException()异常
socketChannel.register(selector, SelectionKey.OP_READ);
}
public void listen() throws Exception {
System.out.println("正在建立连接.....");
while (true) {
LOGGER.info("正在扫描客户端准备好的selector.....");
int selectCount = selector.select();
// LOGGER.info("准备好的通道:"+selectCount);
if (selectCount != 0) {
Iterator<SelectionKey> iterator = selector.selectedKeys().iterator();
while (iterator.hasNext()) {
// LOGGER.info("begin doing......");
SelectionKey selectionKey = iterator.next();
iterator.remove();
if (selectionKey.isConnectable()) {
SocketChannel socketChannel = (SocketChannel) selectionKey.channel();
socketChannel.finishConnect();
socketChannel.configureBlocking(false);
LOGGER.info("客户端准备发送数据....");
socketChannel.write(ByteBuffer.wrap(new String("这是客户端发送的你好数据....").getBytes()));
// socketChannel.register(selector, SelectionKey.OP_READ);
} else if (selectionKey.isReadable()) {
readServerMsg(selectionKey);
}
}
}
}
}
public void readServerMsg(SelectionKey selectionKey) throws Exception {
while (selectionKey.isReadable()) {
int selectedCount = selector.select();
if (selectedCount != 0) {
SocketChannel socketChannel = (SocketChannel) selectionKey.channel();
socketChannel.configureBlocking(false);
ByteBuffer byteBuffer = ByteBuffer.allocate(1024);
socketChannel.read(byteBuffer);
byte[] msgByte = byteBuffer.array();
String msg = new String(msgByte).trim();
if(!"".equals(msg)){//这个判断的主要原因是在客户端发送数据之后，会立刻从通道中读取数据，而此时客户端还未相应数据，所以用这个判断限制......有更好解决办法的同学可以留言互相讨论下
System.out.println("客户端收取的信息:" + msg);
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
System.out.println("请输入客户端应答信息：");
byteBuffer.clear();
byteBuffer.flip();
Thread.sleep(2000);
socketChannel.write(ByteBuffer.wrap(br.readLine().getBytes()));
socketChannel.register(selector, SelectionKey.OP_READ | SelectionKey.OP_WRITE);//设置通道需要监听的状态
}else{
continue;
}
}
}
}
public static void main(String[] args) throws Exception{
NioClient nioClient = new NioClient(8080);
nioClient.listen();
}
}
根据测试这个代码有一点点小问题：
一：在客户端中如果没有 !"".equals(msg)的判断，每次客户端发送消息之后都会立刻都回一个空的字符串显示...这个问题还未整明白
二：客户端中通道监听的状态必须要为socketChannel.register(selector, SelectionKey.OP_READ | SelectionKey.OP_WRITE);//设置通道需要监听的状态
如果只设置OP_READ的话，通道会一直阻塞，不会轮询selector.....
以上两个问题，希望有人可以帮我解答，谢谢。
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