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netty入门02
本文来源:http://blog.csdn.net/zxhoo/article/details/17419229
感谢博主。本文仅供参考学习。
目录(?)[-]
- bootstrap包
- Bootstrap继承结构
- Bootstrap例子
- Builder模式
- AbstractBootstrap
- 设置各个Part
- ChannelFactory
- Bootstrapconnect
- AbstractBootstrapinitAndRegister
- Bootstrapinit方法
- 继续BootstrapdoConnect
Netty4的代码比我想象的要复杂的多,不
Netty4的代码比我想象的要复杂的多,不过Netty4很好的将这种复杂性隐藏了起来,暴露出来的,是一个相对容易使用的接口。Bootstrap就是Netty试图隐藏这种复杂性的一个例子。
bootstrap包
Bootstrap继承结构
AbstractBootstrap是抽象类,有两个具体的实现,Bootstrap和ServerBootstrap:Bootstrap例子
Netty4自带的例子里有一个EchoClient,看看它是如何使用Bootstrap启动一个客户端程序的:- public class EchoClient {
- private final String host;
- private final int port;
- private final int firstMessageSize;
- public EchoClient(String host, int port, int firstMessageSize) {
- this.host = host;
- this.port = port;
- this.firstMessageSize = firstMessageSize;
- }
- public void run() throws Exception {
- // Configure the client.
- EventLoopGroup group = new NioEventLoopGroup();
- try {
- Bootstrap b = new Bootstrap();
- b.group(group)
- .channel(NioSocketChannel.class)
- .option(ChannelOption.TCP_NODELAY, true)
- .handler(new ChannelInitializer<SocketChannel>() {
- @Override
- public void initChannel(SocketChannel ch) throws Exception {
- ch.pipeline().addLast(
- //new LoggingHandler(LogLevel.INFO),
- new EchoClientHandler(firstMessageSize));
- }
- });
- // Start the client.
- ChannelFuture f = b.connect(host, port).sync();
- // Wait until the connection is closed.
- f.channel().closeFuture().sync();
- } finally {
- // Shut down the event loop to terminate all threads.
- group.shutdownGracefully();
- }
- }
- public static void main(String[] args) throws Exception {
- // ...
- }
- }
Builder模式?
看上面的例子,Bootstrap的使用很像Builder模式,Bootstrap就是Builder,EventLoopGroup、Channel和Handler等是各种Part。稍有不同的是,准备好各种Part后,并不是直接build出一个Product来,而是直接通过connect()方法使用这个Product。
AbstractBootstrap
为了弄清楚Bootstrap如何工作,我们先从AbstractBootstrap入手:
- public abstract class AbstractBootstrap<B extends AbstractBootstrap<B, C>, C extends Channel> implements Cloneable {
- private volatile EventLoopGroup group;
- private volatile ChannelFactory<? extends C> channelFactory;
- private volatile SocketAddress localAddress;
- private final Map<ChannelOption<?>, Object> options = new LinkedHashMap<ChannelOption<?>, Object>();
- private final Map<AttributeKey<?>, Object> attrs = new LinkedHashMap<AttributeKey<?>, Object>();
- private volatile ChannelHandler handler;
- // ...
- }
可以看到,AbstractBootstrap这个抽象Builder一共需要有6个Part,如下图所示:
设置各个Part
AbstractBootstrap有一组方法用来设置各个Part,例如下面这些:
- public B group(EventLoopGroup group)
- public B channel(Class<? extends C> channelClass)
- public B channelFactory(ChannelFactory<? extends C> channelFactory)
- public B localAddress(SocketAddress localAddress)
- public <T> B option(ChannelOption<T> option, T value)
- public <T> B attr(AttributeKey<T> key, T value)
- public B handler(ChannelHandler handler)
还有一组对应方法获得各个Part,如下:
- final SocketAddress localAddress()
- final ChannelFactory<? extends C> channelFactory()
- final ChannelHandler handler()
- public final EventLoopGroup group()
- final Map<ChannelOption<?>, Object> options()
- final Map<AttributeKey<?>, Object> attrs()
ChannelFactory
AbstractBootstrap通过ChannelFactory创建Channel实例,channel(channelClass)方法看起来好像是设置了一个Channel,但实际上只是设置了默认的ChannelFactory实现:
- public B channel(Class<? extends C> channelClass) {
- if (channelClass == null) {
- throw new NullPointerException("channelClass");
- }
- return channelFactory(new BootstrapChannelFactory<C>(channelClass));
- }
默认的ChannelFactory实现使用反射创建Channel实例:
- private static final class BootstrapChannelFactory<T extends Channel> implements ChannelFactory<T> {
- private final Class<? extends T> clazz;
- BootstrapChannelFactory(Class<? extends T> clazz) {
- this.clazz = clazz;
- }
- @Override
- public T newChannel() {
- try {
- return clazz.newInstance();
- } catch (Throwable t) {
- throw new ChannelException("Unable to create Channel from class " + clazz, t);
- }
- }
- }
Bootstrap.connect()
再来看Bootstrap类的connect()方法:
- public ChannelFuture connect(SocketAddress remoteAddress, SocketAddress localAddress) {
- if (remoteAddress == null) {
- throw new NullPointerException("remoteAddress");
- }
- validate();
- return doConnect(remoteAddress, localAddress);
- }
connect()方法调用validate()方法看各个Part是否准备就绪,然后调用doConnect()方法:
- private ChannelFuture doConnect(final SocketAddress remoteAddress, final SocketAddress localAddress) {
- final ChannelFuture regFuture = initAndRegister();
- final Channel channel = regFuture.channel();
- if (regFuture.cause() != null) {
- return regFuture;
- }
- final ChannelPromise promise = channel.newPromise();
- if (regFuture.isDone()) {
- doConnect0(regFuture, channel, remoteAddress, localAddress, promise);
- } else {
- regFuture.addListener(new ChannelFutureListener() {
- @Override
- public void operationComplete(ChannelFuture future) throws Exception {
- doConnect0(regFuture, channel, remoteAddress, localAddress, promise);
- }
- });
- }
- return promise;
- }
doConnect()方法首先调用了initAndRegister()方法,然后又调用了doConnect0()方法,方法调用示意图如下:
AbstractBootstrap.initAndRegister()
- final ChannelFuture initAndRegister() {
- final Channel channel = channelFactory().newChannel();
- try {
- init(channel);
- } catch (Throwable t) {
- channel.unsafe().closeForcibly();
- return channel.newFailedFuture(t);
- }
- ChannelPromise regPromise = channel.newPromise();
- group().register(channel, regPromise);
- // ...
- }
而Channel在实例化的时候已经自动关联了Pipeline,这点从AbstractChannel的构造函数可以看出:
- protected AbstractChannel(Channel parent) {
- this.parent = parent;
- unsafe = newUnsafe();
- pipeline = new DefaultChannelPipeline(this);
- }
Bootstrap.init()方法
- void init(Channel channel) throws Exception {
- ChannelPipeline p = channel.pipeline();
- p.addLast(handler());
- // ...
- }
继续Bootstrap.doConnect()
initAndRegister()方法结束之后,doConnect()方法紧接着调用了doConnect0()方法,doConnect0()方法继而调用了Channel.connect()方法,这样Channel就接通服务器,可以收发消息了!
netty入门02