JDK7的NIO2特性或许是我最期待的，我一直想基于它写一个高性能的Java Http Server.现在这个想法终于可以实施了。
本人基于目前最新的JDK7 b76开发了一个HTTP Server性能确实不错。
在windows平台上NIO2采用AccpetEx来异步接受连接，并且读写全都关联到IOCP完成端口。不仅如此，为了方便开发者使用，连IOCP工作线程都封装好了，你只要提供线程池就OK。
但是要注意，IOCP工作线程的线程池必须是 Fix的，因为你发出的读写请求都关联到相应的线程上，如果线程死了，那读写完成情况是不知道的。
作为一个Http Server，传送文件是必不可少的功能，那一般文件的传送都是要把程序里的buffer拷贝到内核的buffer，由内核发送出去的。windows平台上为这种情况提供了很好的解决方案，使用TransmitFile接口
BOOL TransmitFile(
SOCKET hSocket,
HANDLE hFile,
DWORD nNumberOfBytesToWrite,
DWORD nNumberOfBytesPerSend,
LPOVERLAPPED lpOverlapped,
LPTRANSMIT_FILE_BUFFERS lpTransmitBuffers,
DWORD dwFlags
);
你只要把文件句柄发送给内核就行了，内核帮你搞定其余的，真正做到Zero-Copy.
但是很不幸，NIO2里AsynchronousSocketChannel没有提供这样的支持。而为HTTP Server的性能考量，本人只好自己增加这个支持。
要无缝支持，这个必须得表现的跟 Read /Write一样，有完成的通知，通知传送多少数据，等等。
仔细读完sun的IOCP实现以后发现这部分工作他们封装得很好，基本只要往他们的框架里加东西就好了。
为了能访问他们的框架代码，我定义自己的TransmitFile支持类在sun.nio.ch包里，以获得最大的权限。
package sun.nio.ch;
import java.io.IOException;
import java.lang.reflect.Field;
import java.nio.channels.AsynchronousCloseException;
import java.nio.channels.AsynchronousSocketChannel;
import java.nio.channels.ClosedChannelException;
import java.nio.channels.CompletionHandler;
import java.nio.channels.NotYetConnectedException;
import java.nio.channels.WritePendingException;
import java.util.concurrent.Future;
/**
* @author Yvon
*
*/
public class WindowsTransmitFileSupport {
//Sun's NIO2 channel implementation class
private WindowsAsynchronousSocketChannelImpl channel;
//nio2 framework core data structure
PendingIoCache ioCache;
//some field retrieve from sun channel implementation class
private Object writeLock;
private Field writingF;
private Field writeShutdownF;
private Field writeKilledF; // f
WindowsTransmitFileSupport()
{
//dummy one for JNI code
}
/**
*
*/
public WindowsTransmitFileSupport(
AsynchronousSocketChannel
channel) {
this.channel = (WindowsAsynchronousSocketChannelImpl)channel;
try {
// Initialize the fields
Field f = WindowsAsynchronousSocketChannelImpl.class
.getDeclaredField("ioCache");
f.setAccessible(true);
ioCache = (PendingIoCache) f.get(channel);
f = AsynchronousSocketChannelImpl.class
.getDeclaredField("writeLock");
f.setAccessible(true);
writeLock = f.get(channel);
writingF = AsynchronousSocketChannelImpl.class
.getDeclaredField("writing");
writingF.setAccessible(true);
writeShutdownF = AsynchronousSocketChannelImpl.class
.getDeclaredField("writeShutdown");
writeShutdownF.setAccessible(true);
writeKilledF = AsynchronousSocketChannelImpl.class
.getDeclaredField("writeKilled");
writeKilledF.setAccessible(true);
} catch (NoSuchFieldException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (SecurityException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IllegalArgumentException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IllegalAccessException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
/**
* Implements the task to initiate a write and the handler to consume the
* result when the send file completes.
*/
private class SendFileTask<V, A> implements Runnable, Iocp.ResultHandler {
private final PendingFuture<V, A> result;
private final long file;//file is windows file HANDLE
SendFileTask(long file, PendingFuture<V, A> result) {
this.result = result;
this.file = file;
}
@Override
// @SuppressWarnings("unchecked")
public void run() {
long overlapped = 0L;
boolean pending = false;
boolean shutdown = false;
try {
channel.begin();
// get an OVERLAPPED structure (from the cache or allocate)
overlapped = ioCache.add(result);
int n = transmitFile0(channel.handle, file, overlapped);
if (n == IOStatus.UNAVAILABLE) {
// I/O is pending
pending = true;
return;
}
if (n == IOStatus.EOF) {
// special case for shutdown output
shutdown = true;
throw new ClosedChannelException();
}
// write completed immediately
throw new InternalError("Write completed immediately");
} catch (Throwable x) {
// write failed. Enable writing before releasing waiters.
channel.enableWriting();
if (!shutdown && (x instanceof ClosedChannelException))
x = new AsynchronousCloseException();
if (!(x instanceof IOException))
x = new IOException(x);
result.setFailure(x);
} finally {
// release resources if I/O not pending
if (!pending) {
if (overlapped != 0L)
ioCache.remove(overlapped);
}
channel.end();
}
// invoke completion handler
Invoker.invoke(result);
}
/**
* Executed when the I/O has completed
*/
@Override
@SuppressWarnings("unchecked")
public void completed(int bytesTransferred, boolean canInvokeDirect) {
// release waiters if not already released by timeout
synchronized (result) {
if (result.isDone())
return;
channel.enableWriting();
result.setResult((V) Integer.valueOf(bytesTransferred));
}
if (canInvokeDirect) {
Invoker.invokeUnchecked(result);
} else {
Invoker.invoke(result);
}
}
@Override
public void failed(int error, IOException x) {
// return direct buffer to cache if substituted
// release waiters if not already released by timeout
if (!channel.isOpen())
x = new AsynchronousCloseException();
synchronized (result) {
if (result.isDone())
return;
channel.enableWriting();
result.setFailure(x);
}
Invoker.invoke(result);
}
}
public <V extends Number, A> Future<V> sendFile(long file, A att,
CompletionHandler<V, ? super A> handler) {
boolean closed = false;
if (channel.isOpen()) {
if (channel.remoteAddress == null)
throw new NotYetConnectedException();
// check and update state
synchronized (writeLock) {
try{
if (writeKilledF.getBoolean(channel))
throw new IllegalStateException(
"Writing not allowed due to timeout or cancellation");
if (writingF.getBoolean(channel))
throw new WritePendingException();
if (writeShutdownF.getBoolean(channel)) {
closed = true;
} else {
writingF.setBoolean(channel, true);
}
}catch(Exception e)
{
IllegalStateException ise=new IllegalStateException(" catch exception when write");
ise.initCause(e);
throw ise;
}
}
} else {
closed = true;
}
// channel is closed or shutdown for write
if (closed) {
Throwable e = new ClosedChannelException();
if (handler == null)
return CompletedFuture.withFailure(e);
Invoker.invoke(channel, handler, att, null, e);
return null;
}
return implSendFile(file,att,handler);
}
<V extends Number, A> Future<V> implSendFile(long file, A attachment,
CompletionHandler<V, ? super A> handler) {
// setup task
PendingFuture<V, A> result = new PendingFuture<V, A>(channel, handler,
attachment);
SendFileTask<V,A> sendTask=new SendFileTask<V,A>(file,result);
result.setContext(sendTask);
// initiate I/O (can only be done from thread in thread pool)
// initiate I/O
if (Iocp.supportsThreadAgnosticIo()) {
sendTask.run();
} else {
Invoker.invokeOnThreadInThreadPool(channel, sendTask);
}
return result;
}
private native int transmitFile0(long handle, long file,
long overlapped);
}
这个操作跟默认实现的里的write操作是很像的，只是最后调用的本地方法不一样。。
接下来，我们怎么使用呢，这个类是定义在sun的包里的，直接用的话，会报IllegalAccessError,因为我们的类加载器跟初始化加载器是不一样的。
解决办法一个是通过启动参数-Xbootclasspath，让我们的包被初始加载器加载。我个人不喜欢这种办法，所以就采用JNI来定义我们的windows TransmitFile支持类。
这样我们的工作算是完成了，注意，发送文件的时候传得是文件句柄，这样做的好处是你可以更好的控制，一般是在发送前，打开文件句柄，完成后在回调通知方法里关闭文件句柄。
有兴趣的同学可以看看我的HTTP server项目:
http://code.google.com/p/jabhttpd/
目前基本功能实现得差不多，做了些简单的测试，性能比较满意。这个服务器不打算支持servlet api，基本是专门给做基于长连接模式通信的定做的。