netty源码分析一
前段时间比较忙,没有时间去学习啦,现在稍微好一点啦,看着自己年初定下的目标,还有很多没有完成的呀。从下阶段起学习netty框架啦,之前也了解netty框架,但是没有深入理解,现在好好学习一下。
学习netty框架之前,要了解java nio基本知识java nio常见的API有
channel
channel可以理解为通道,其中包括TCP/UDP还有文件
- FileChannel
- DatagramChannel
- SocketChannel
- ServerSocketChannel
buffer
buffer可以理解为一块缓存或者是一块内存,其中包括
- ByteBuffer
- CharBuffer
- DoubleBuffer
- FloatBuffer
- IntBuffer
- LongBuffer
- ShortBuffer
selector
Selector允许单线程处理多个 Channel。如果你的应用打开了多个连接(通道),但每个连接的流量都很低,使用Selector就会很方便
这是在一个单线程中使用一个Selector处理3个Channel的图示:
要使用Selector,得向Selector注册Channel,然后调用它的select()方法。这个方法会一直阻塞到某个注册的通道有事件就绪。一旦这个方法返回,线程就可以处理这些事件,事件的例子有如新连接进来,数据接收等。
java nio是一个网络编程基础,其中tomcat jetty服务器也使用java nio思想和技术,有时间可以看看里面的源码对比一下。
netty和mina都是java网络编程的框架 而且这两个框架出自于同一个作者。今天就netty4.1.9源码分析一下:
今天首先分析Bootstrap和ServerBootstrap这个两个启动类。这两个类分别客户端启动和服务器启动。他们都继承AbstractBootstrap这个抽象类
这个类里几个主要方法:
public B group(EventLoopGroup group)
{
if (group == null) {
throw new NullPointerException("group");
}
if (this.group != null) {
throw new IllegalStateException("group set already");
}
this.group = group;
return this;
}
public B channel(Class<? extends C> channelClass)
{
if (channelClass == null) {
throw new NullPointerException("channelClass");
}
return channelFactory(new ReflectiveChannelFactory(channelClass));
}
@Deprecated
public B channelFactory(ChannelFactory<? extends C> channelFactory)
{
if (channelFactory == null) {
throw new NullPointerException("channelFactory");
}
if (this.channelFactory != null) {
throw new IllegalStateException("channelFactory set already");
}
this.channelFactory = channelFactory;
return this;
}
public B channelFactory(io.netty.channel.ChannelFactory<? extends C> channelFactory)
{
return channelFactory(channelFactory);
}
今天不会详细见客户端和服务器详细的启动流程,今天让大家看看客户端启动时一个非常重要的方法是connect和服务器启动一个非常重要的方法是bind
public ChannelFuture connect(SocketAddress remoteAddress, SocketAddress localAddress)
{
if (remoteAddress == null) {
throw new NullPointerException("remoteAddress");
}
validate();
return doResolveAndConnect(remoteAddress, localAddress);
}
public ChannelFuture bind(SocketAddress localAddress)
{
validate();
if (localAddress == null) {
throw new NullPointerException("localAddress");
}
return doBind(localAddress);
}
他们俩的方法代码非常像都有一个校验方法,分别是连接服务器方法和监听客户端请求。详细的连接和监听先看看下次分析。
private ChannelFuture doResolveAndConnect(final SocketAddress remoteAddress, final SocketAddress localAddress)
{
ChannelFuture regFuture = initAndRegister();
final Channel channel = regFuture.channel();
if (regFuture.isDone()) {
if (!regFuture.isSuccess()) {
return regFuture;
}
return doResolveAndConnect0(channel, remoteAddress, localAddress, channel.newPromise());
}
final AbstractBootstrap.PendingRegistrationPromise promise = new AbstractBootstrap.PendingRegistrationPromise(channel);
regFuture.addListener(new ChannelFutureListener()
{
public void operationComplete(ChannelFuture future)
throws Exception
{
Throwable cause = future.cause();
if (cause != null)
{
promise.setFailure(cause);
}
else
{
promise.registered();
Bootstrap.this.doResolveAndConnect0(channel, remoteAddress, localAddress, promise);
}
}
});
return promise;
}
private ChannelFuture doBind(final SocketAddress localAddress) {
final ChannelFuture regFuture = initAndRegister();
final Channel channel = regFuture.channel();
if (regFuture.cause() != null) {
return regFuture;
}
if (regFuture.isDone())
{
ChannelPromise promise = channel.newPromise();
doBind0(regFuture, channel, localAddress, promise);
return promise;
}
final PendingRegistrationPromise promise = new PendingRegistrationPromise(channel);
regFuture.addListener(new ChannelFutureListener()
{
public void operationComplete(ChannelFuture future) throws Exception {
Throwable cause = future.cause();
if (cause != null)
{
promise.setFailure(cause);
}
else
{
promise.registered();
AbstractBootstrap.doBind0(regFuture, channel, localAddress, promise);
}
}
});
return promise;
}
理解其中一个,理解另一个就比较轻松了。