当我们在编写使用Java语言开发的多线程应用程序时,一种常见的高并发处理方式是使用Reactor模式。Reactor模式是一种基于事件驱动和非阻塞IO操作的设计模式。其主要思想是将多个客户端请求封装成一个事件,并由事件处理器进行处理。以下是Java中多线程Reactor模式的实现攻略。
Reactor模式的简单介绍
Reactor模式包含三个核心组件:事件处理器、事件个数限制器和事件分发器。其中,事件处理器负责处理事件;事件个数限制器用于限制可以处理的事件个数;事件分发器用于将外部事件转化为内部事件并将其分发到事件处理器中。反应器模式的工作方式如下:
- 从外部读取事件。
- 将事件转化为内部事件。
- 将内部事件队列中的事件交给事件处理器处理。
- 处理完毕后,将结果返回给外部。
Reactor模式的Java实现
Java中多线程Reactor模式的实现基于Java NIO库中的Selector和SocketChannel。这里是一个Java的多线程Reactor模式的示例:
import java.io.IOException;
import java.nio.channels.SelectionKey;
import java.nio.channels.ServerSocketChannel;
import java.nio.channels.SocketChannel;
import java.util.concurrent.ExecutorService;
public class Acceptor implements Runnable {
private final ServerSocketChannel ssc;
private final Dispatcher d;
private final ExecutorService pool;
public Acceptor(ServerSocketChannel ssc, Dispatcher d, ExecutorService pool) {
this.ssc = ssc;
this.d = d;
this.pool = pool;
}
public void run() {
try {
SocketChannel sc = ssc.accept();
if (sc != null) {
d.register(sc);
}
} catch(IOException e) {
// handle exception
}
}
}
public class Dispatcher implements Runnable {
private final Selector sel;
private final ExecutorService pool;
private int n = 0;
public Dispatcher(ExecutorService pool) throws IOException {
this.sel = Selector.open();
this.pool = pool;
}
public void register(SocketChannel sc) throws IOException {
sc.register(sel, SelectionKey.OP_READ);
}
public void run() {
while (true) {
sel.select();
Set<SelectionKey> selectedKeys = sel.selectedKeys();
Iterator<SelectionKey> it = selectedKeys.iterator();
while (it.hasNext()) {
SelectionKey sk = it.next();
it.remove();
Runnable r = (Runnable)(sk.attachment());
pool.execute(r);
}
}
}
}
public class EventHandler implements Runnable {
private final SocketChannel sc;
public EventHandler(SocketChannel sc) {
this.sc = sc;
}
public void run() {
// handle event
}
}
public class Reactor implements Runnable {
private final ServerSocketChannel ssc;
private final ExecutorService pool;
private final Dispatcher d;
public Reactor(int port, ExecutorService pool) throws IOException {
this.pool = pool;
this.ssc = ServerSocketChannel.open();
this.d = new Dispatcher(pool);
ssc.bind(new InetSocketAddress(port));
ssc.configureBlocking(false);
SelectionKey sk = ssc.register(d.getSelector(), SelectionKey.OP_ACCEPT);
sk.attach(new Acceptor(ssc, d, pool));
}
public void run() {
pool.execute(d);
while (true) {
if (d.n > 0) {
d.n = 0;
// do something
}
}
}
}
这里的Acceptor类用于接受请求并将其发送到Dispatcher中。Dispatcher类使用Selector进行事件选择并且对选中的事件进行调度。EventHandler类用于处理事件。最后,Reactor类将Acceptor和Dispatcher类绑定在了一起。
示例说明
下面是两个通过Reactor模式实现的Java多线程Web服务器的示例:
示例一:基本的Java多线程Web服务器
import java.io.IOException;
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.nio.charset.StandardCharsets;
import java.util.Iterator;
public class BasicWebServer {
private static final int PORT = 8080;
private static int BUFFER_SIZE = 1024;
private Selector selector;
private ByteBuffer readBuffer = ByteBuffer.allocate(BUFFER_SIZE);
private ByteBuffer writeBuffer = ByteBuffer.allocate(BUFFER_SIZE);
public BasicWebServer() { }
public void start() throws Exception {
ServerSocketChannel ssc = ServerSocketChannel.open();
ssc.configureBlocking(false);
ssc.bind(new InetSocketAddress(PORT));
this.selector = Selector.open();
ssc.register(selector, SelectionKey.OP_ACCEPT);
while (true) {
selector.select();
Iterator<SelectionKey> keys = selector.selectedKeys().iterator();
while (keys.hasNext()) {
SelectionKey key = keys.next();
keys.remove();
if (!key.isValid()) {
continue;
}
if (key.isAcceptable()) {
accept(key);
} else if (key.isReadable()) {
read(key);
} else if (key.isWritable()) {
write(key);
}
}
}
}
private void accept(SelectionKey key) throws IOException {
ServerSocketChannel ssc = (ServerSocketChannel) key.channel();
SocketChannel sc = ssc.accept();
sc.configureBlocking(false);
sc.register(selector, SelectionKey.OP_READ);
}
private void read(SelectionKey key) throws IOException {
SocketChannel sc = (SocketChannel) key.channel();
readBuffer.clear();
int len = sc.read(readBuffer);
if (len == -1) {
sc.close();
return;
}
readBuffer.flip();
byte[] bytes = new byte[readBuffer.remaining()];
readBuffer.get(bytes);
String request = new String(bytes, StandardCharsets.UTF_8);
if (request.contains("GET / HTTP/1.1")) {
String response = "HTTP/1.1 200 OK\r\n" +
"Content-Type: text/plain\r\n" +
"\r\n" +
"Hello, World!\r\n";
writeBuffer.clear();
writeBuffer.put(response.getBytes());
writeBuffer.flip();
sc.register(selector, SelectionKey.OP_WRITE, writeBuffer);
}
}
private void write(SelectionKey key) throws IOException {
ByteBuffer buffer = (ByteBuffer) key.attachment();
SocketChannel sc = (SocketChannel) key.channel();
sc.write(buffer);
}
public static void main(String[] args) throws Exception {
BasicWebServer basicWebServer = new BasicWebServer();
basicWebServer.start();
}
}
这个Web服务器可以接受来自浏览器的GET请求。如果请求是GET / HTTP/1.1,服务器将返回一个简单的响应,即"Hello, World!"。
示例二:使用线程池的Java多线程Web服务器
import java.io.IOException;
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.nio.charset.StandardCharsets;
import java.util.Iterator;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
public class PoolWebServer {
private static final int PORT = 8080;
private static int BUFFER_SIZE = 1024;
private static int THREAD_POOL_SIZE = 10;
private Selector selector;
private ByteBuffer readBuffer = ByteBuffer.allocate(BUFFER_SIZE);
private ByteBuffer writeBuffer = ByteBuffer.allocate(BUFFER_SIZE);
private ExecutorService pool = Executors.newFixedThreadPool(THREAD_POOL_SIZE);
public PoolWebServer() throws IOException {
ServerSocketChannel ssc = ServerSocketChannel.open();
ssc.configureBlocking(false);
ssc.bind(new InetSocketAddress(PORT));
this.selector = Selector.open();
ssc.register(selector, SelectionKey.OP_ACCEPT);
}
public void start() throws Exception {
while (true) {
selector.select();
Iterator<SelectionKey> keys = selector.selectedKeys().iterator();
while (keys.hasNext()) {
SelectionKey key = keys.next();
keys.remove();
if (!key.isValid()) {
continue;
}
if (key.isAcceptable()) {
accept(key);
} else if (key.isReadable()) {
read(key);
} else if (key.isWritable()) {
write(key);
}
}
}
}
private void accept(SelectionKey key) throws IOException {
ServerSocketChannel ssc = (ServerSocketChannel) key.channel();
SocketChannel sc = ssc.accept();
sc.configureBlocking(false);
sc.register(selector, SelectionKey.OP_READ);
}
private void read(SelectionKey key) {
pool.execute(new EventHandler(key));
}
private void write(SelectionKey key) throws IOException {
ByteBuffer buffer = (ByteBuffer) key.attachment();
SocketChannel sc = (SocketChannel) key.channel();
sc.write(buffer);
}
public static void main(String[] args) throws Exception {
PoolWebServer poolWebServer = new PoolWebServer();
poolWebServer.start();
}
private class EventHandler implements Runnable {
private final SelectionKey key;
public EventHandler(SelectionKey key) {
this.key = key;
}
@Override
public void run() {
try {
SocketChannel sc = (SocketChannel) key.channel();
readBuffer.clear();
int len = sc.read(readBuffer);
if (len == -1) {
sc.close();
return;
}
readBuffer.flip();
byte[] bytes = new byte[readBuffer.remaining()];
readBuffer.get(bytes);
String request = new String(bytes, StandardCharsets.UTF_8);
if (request.contains("GET / HTTP/1.1")) {
String response = "HTTP/1.1 200 OK\r\n" +
"Content-Type: text/plain\r\n" +
"\r\n" +
"Hello, World!\r\n";
writeBuffer.clear();
writeBuffer.put(response.getBytes());
writeBuffer.flip();
sc.register(selector, SelectionKey.OP_WRITE, writeBuffer);
}
} catch (IOException e) {
// handle error
}
}
}
}
这个Web服务器使用了一个线程池来处理客户端请求。它的流程与示例一相似。但是,当服务器接收到一个请求时,它将这个请求交给线程池中的某个线程去处理。当线程池中没有线程可用时,新的请求将被放置在队列中,直到有线程被释放出来并被分配给这个请求。这个Web服务器对多个客户端的请求进行处理,并且响应时间不会因为线程的数量导致线程之间的争用。
本站文章如无特殊说明,均为本站原创,如若转载,请注明出处:Java中多线程Reactor模式的实现 - Python技术站