摘要
BootStrap在netty的应用程序中负责引导服务器和客户端。netty包含了两种不同类型的引导:
- 1. 使用服务器的ServerBootStrap,用于接受客户端的连接以及为已接受的连接创建子通道。
- 2. 用于客户端的BootStrap,不接受新的连接,并且是在父通道类完成一些操作。
服务端的代码
SimpleServer.java
/**
* Created by xjl on 2021/1/9.
*/
public final class SimpleServer {
public static void main(String[] args) throws Exception {
EventLoopGroup bossGroup = new NioEventLoopGroup(1);
EventLoopGroup workerGroup = new NioEventLoopGroup();
try {
ServerBootstrap b = new ServerBootstrap();
b.group(bossGroup, workerGroup)
.channel(NioServerSocketChannel.class)
.handler(new SimpleServerHandler())
.childHandler(new SimpleServerInitializer())
.option(ChannelOption.SO_BACKLOG, 128)
.childOption(ChannelOption.SO_KEEPALIVE, true);
ChannelFuture f = b.bind(8888).sync();
f.channel().closeFuture().sync();
} finally {
bossGroup.shutdownGracefully();
workerGroup.shutdownGracefully();
}
}
}
SimpleServerHandler.java
private static class SimpleServerHandler extends ChannelInboundHandlerAdapter {
@Override
public void channelActive(ChannelHandlerContext ctx) throws Exception {
System.out.println("channelActive");
}
@Override
public void channelRegistered(ChannelHandlerContext ctx) throws Exception {
System.out.println("channelRegistered");
}
@Override
public void handlerAdded(ChannelHandlerContext ctx) throws Exception {
System.out.println("handlerAdded");
}
}
SimpleServerInitializer.java
public class SimpleServerInitializer extends ChannelInitializer<SocketChannel>{
@Override
protected void initChannel(SocketChannel ch) throws Exception {
ChannelPipeline pipeline = ch.pipeline();
pipeline.addLast("framer", new DelimiterBasedFrameDecoder(8192, Delimiters.lineDelimiter()));
pipeline.addLast("decoder", new StringDecoder());
pipeline.addLast("encoder", new StringEncoder());
pipeline.addLast("handler", new SimpleChatServerHandler());
System.out.println("SimpleChatClient:" + ch.remoteAddress()+"连接上");
}
}
ServerBootstrap类分析
//使用了链式编程方式
ServerBootstrap b = new ServerBootstrap();
b.group(bossGroup, workerGroup)
.channel(NioServerSocketChannel.class)
.handler(new SimpleServerHandler())
.childHandler(new SimpleServerInitializer())
.option(ChannelOption.SO_BACKLOG, 128)
.childOption(ChannelOption.SO_KEEPALIVE, true);
ServerBootstrap类的继承结构如下:
该类的参数,有必要列出:
private final Map<ChannelOption<?>, Object> childOptions = new LinkedHashMap<ChannelOption<?>, Object>();
private final Map<AttributeKey<?>, Object> childAttrs = new LinkedHashMap<AttributeKey<?>, Object>();
private volatile EventLoopGroup childGroup;
private volatile ChannelHandler childHandler;
其父类AbstractBootstrap的参数
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;
group(bossGroup, workerGroup)
// 即将workerGroup保存在 ServerBootstrap对象的childGroup属性上。 bossGroup保存在ServerBootstrap对象的group属性上
public ServerBootstrap group(EventLoopGroup parentGroup, EventLoopGroup childGroup) {
super.group(parentGroup);
if (childGroup == null) {
throw new NullPointerException("childGroup");
}
if (this.childGroup != null) {
throw new IllegalStateException("childGroup set already");
}
this.childGroup = childGroup;
return this;
}
channel(NioServerSocketChannel.class)
//设置父类属性channelFactory 为: BootstrapChannelFactory类的对象。其中这里BootstrapChannelFactory对象中包括一个clazz属性为:NioServerSocketChannel.class,
public B channel(Class<? extends C> channelClass) {
if (channelClass == null) {
throw new NullPointerException("channelClass");
}
return channelFactory(new BootstrapChannelFactory<C>(channelClass));
}
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 (B) this;
}
//channel该类的构造函数
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 {
//并且BootstrapChannelFactory中提供 newChannel()方法,我们可以看到 clazz.newInstance(),主要是通过反射来实例化NioServerSocketChannel.class
return clazz.newInstance();
} catch (Throwable t) {
throw new ChannelException("Unable to create Channel from class " + clazz, t);
}
}
@Override
public String toString() {
return StringUtil.simpleClassName(clazz) + ".class";
}
}
handler(new SimpleServerHandler())
public B handler(ChannelHandler handler) {
if (handler == null) {
throw new NullPointerException("handler");
}
this.handler = handler;
return (B) this;
}
注意:这里的handler函数的入参类是我们自己提供的。如下,后面的博文中将会分析这个handler将会在哪里以及何时被调用,这里只需要记住这一点即可
private static class SimpleServerHandler extends ChannelInboundHandlerAdapter {
@Override
public void channelActive(ChannelHandlerContext ctx) throws Exception {
System.out.println("channelActive");
}
@Override
public void channelRegistered(ChannelHandlerContext ctx) throws Exception {
System.out.println("channelRegistered");
}
@Override
public void handlerAdded(ChannelHandlerContext ctx) throws Exception {
System.out.println("handlerAdded");
}
}
childHandler(new SimpleServerInitializer())
public ServerBootstrap childHandler(ChannelHandler childHandler) {
if (childHandler == null) {
throw new NullPointerException("childHandler");
}
this.childHandler = childHandler;
return this;
}
由最后一句可知,其实就是讲传入的childHandler赋值给ServerBootstrap的childHandler属性。该函数的主要作用是设置channelHandler来处理客户端的请求的channel的IO。 这里我们一般都用ChannelInitializer这个类的实例或则继承自这个类的实例这里我是通过新建类SimpleChatServerInitializer继承自ChannelInitializer。
public class SimpleChatServerInitializer extends ChannelInitializer<SocketChannel>{
@Override
protected void initChannel(SocketChannel ch) throws Exception {
ChannelPipeline pipeline = ch.pipeline();
pipeline.addLast("framer", new DelimiterBasedFrameDecoder(8192, Delimiters.lineDelimiter()));
pipeline.addLast("decoder", new StringDecoder());
pipeline.addLast("encoder", new StringEncoder());
pipeline.addLast("handler", new SimpleChatServerHandler());
System.out.println("SimpleChatClient:" + ch.remoteAddress()+"连接上");
}
}
我们看ChannelInitializer这个类的继承图可知ChannelInitializer其实是继承自ChannelHandler的。
可知,这个类其实就是往pipeline中添加了很多的channelHandler。
配置ServerBootstrap的option
这里调用的是父类的AbstractBootstrap的option()方法,源码如下:
public <T> B option(ChannelOption<T> option, T value) {
if (option == null) {
throw new NullPointerException("option");
}
if (value == null) {
synchronized (options) {
options.remove(option);
}
} else {
synchronized (options) {
options.put(option, value);
}
}
return (B) this;
}
其中最重要的一行代码就是:
options.put(option, value);这里用到了options这个参数,在AbstractBootstrap的定义如下:
private final Map<ChannelOption<?>, Object> options = new LinkedHashMap<ChannelOption<?>, Object>();
可知是私有变量,而且是一个Map集合。这个变量主要是设置TCP连接中的一些可选项,而且这些属性是作用于每一个连接到服务器被创建的channel。
配置ServerBootstrap的childOption
这里调用的是父类的ServerBootstrap的childOption()方法
public <T> ServerBootstrap childOption(ChannelOption<T> childOption, T value) {
if (childOption == null) {
throw new NullPointerException("childOption");
}
if (value == null) {
synchronized (childOptions) {
childOptions.remove(childOption);
}
} else {
synchronized (childOptions) {
childOptions.put(childOption, value);
}
}
return this;
}
这个函数功能与option()函数几乎一样,唯一的区别是该属性设定只作用于被acceptor(也就是boss EventLoopGroup)接收之后的channel。
BootStrap总结
主要是将我们提供的参数设置到其相应的对象属性中去了。 因为后面会用到如下的几个属性,因此最好知道下,这些属性是何时以及在那里赋值的。
- 1、group:workerGroup保存在 ServerBootstrap对象的childGroup属性上。 bossGroup保存在ServerBootstrap对象的group属性上
- 2、channelFactory:BootstrapChannelFactory类的对象(clazz属性为:NioServerSocketChannel.class)
- 3、handler:SimpleServerHandler
- 4、childHandler
- 5、option
- 6、childOption