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前言：已经初始化了NioEventLoopGroup 的boosGroup 和 workerGroup ，那么ServerBootstrap的作用是干嘛的呢 ，本文在Spring架构篇–2.7.1 远程通信基础–Netty原理–NioEventLoopGroup 之后继续进行探究

1 首先回顾下 nettt 的使用demo：

public class DiscardServer {private int port;public DiscardServer(int port) {this.port = port;}public static void main(String[] args) {new DiscardServer(8080).run();}private void run() {NioEventLoopGroup boss = new NioEventLoopGroup();NioEventLoopGroup worker = new NioEventLoopGroup();try {ServerBootstrap server = new ServerBootstrap();server.group(boss,worker).channel(NioServerSocketChannel.class).childHandler(new ChannelInitializer<SocketChannel>() {@Overrideprotected void initChannel(SocketChannel ch) throws Exception {ch.pipeline().addLast(new DiscardServerHandler());}}).option(ChannelOption.SO_BACKLOG,128).childOption(ChannelOption.SO_KEEPALIVE,true);ChannelFuture f = server.bind(this.port).sync();System.out.println("8080服务已启动");f.channel().closeFuture().sync();} catch (InterruptedException e) {e.printStackTrace();} finally {boss.shutdownGracefully();worker.shutdownGracefully();}}
}

可以看到ServerBootstrap 的对象做了一系列的配置后最终 通过 bind(this.port).sync() 进行启动；

2 ServerBootstrap 类：

2.1 new ServerBootstrap() 工作内容：

public class ServerBootstrap extends AbstractBootstrap<ServerBootstrap, ServerChannel>private static final InternalLogger logger = InternalLoggerFactory.getInstance(ServerBootstrap.class);
private final Map<ChannelOption<?>, Object> childOptions = new LinkedHashMap();
private final Map<AttributeKey<?>, Object> childAttrs = new ConcurrentHashMap();
// ServerBootstrap 对象赋值给 config
private final ServerBootstrapConfig config = new ServerBootstrapConfig(this);
private volatile EventLoopGroup childGroup;
private volatile ChannelHandler childHandler;public ServerBootstrap() {
}

AbstractBootstrap 类

public abstract class AbstractBootstrap<B extends AbstractBootstrap<B, C>, C extends Channel> implements Cloneable {static final Map.Entry<ChannelOption<?>, Object>[] EMPTY_OPTION_ARRAY = new Map.Entry[0];static final Map.Entry<AttributeKey<?>, Object>[] EMPTY_ATTRIBUTE_ARRAY = new Map.Entry[0];volatile EventLoopGroup group;private volatile ChannelFactory<? extends C> channelFactory;private volatile SocketAddress localAddress;private final Map<ChannelOption<?>, Object> options = new LinkedHashMap();private final Map<AttributeKey<?>, Object> attrs = new ConcurrentHashMap();private volatile ChannelHandler handler;AbstractBootstrap() {}}

• 可以看到ServerBootstrap 继承了AbstractBootstrap类，当new ServerBootstrap() 时，对ServerBootstrap和AbstractBootstrap类都通过无参的构造方法，完成了这两个类的对象实例化；
• 可以看到ServerBootstrap和AbstractBootstrap这两个类的属性非常相似，实际上 ServerBootstrap 用来放NioEventLoopGroup 工作线程的数据；AbstractBootstrap 用来放 boss 线程的数据；
• 可以看到这里只是进行了初始化，里面的属性都还没有进行赋值，两个对象的属性值都是默认值；

2.2 ServerBootstrap ，AbstractBootstrap 的属性赋值：

2.2.1 server.group(boss,worker)：完成对父类和子类 NioEventLoopGroup对象进行赋值
ServerBootstrap 类的 group 方法：

public ServerBootstrap group(EventLoopGroup parentGroup, EventLoopGroup childGroup) {
// 父类AbstractBootstrap  的EventLoopGroup  赋值super.group(parentGroup);if (this.childGroup != null) {throw new IllegalStateException("childGroup set already");} else {
// 子类的EventLoopGroup   volatile EventLoopGroup group 赋值;this.childGroup = (EventLoopGroup)ObjectUtil.checkNotNull(childGroup, "childGroup");return this;}
}

super.group(parentGroup); 父类对象的赋值：
AbstractBootstrap 的group 方法：

static final Map.Entry<ChannelOption<?>, Object>[] EMPTY_OPTION_ARRAY = new Map.Entry[0];
static final Map.Entry<AttributeKey<?>, Object>[] EMPTY_ATTRIBUTE_ARRAY = new Map.Entry[0];
volatile EventLoopGroup group;
private volatile ChannelFactory<? extends C> channelFactory;
private volatile SocketAddress localAddress;
private final Map<ChannelOption<?>, Object> options = new LinkedHashMap();
private final Map<AttributeKey<?>, Object> attrs = new ConcurrentHashMap();
private volatile ChannelHandler handler;AbstractBootstrap() {
}
// 父类的EventLoopGroup  赋值
AbstractBootstrap(AbstractBootstrap<B, C> bootstrap) {this.group = bootstrap.group;this.channelFactory = bootstrap.channelFactory;this.handler = bootstrap.handler;this.localAddress = bootstrap.localAddress;synchronized(bootstrap.options) {this.options.putAll(bootstrap.options);}this.attrs.putAll(bootstrap.attrs);
}
// 父类group  AbstractBootstrap  类 对象的赋值 volatile EventLoopGroup group;
public B group(EventLoopGroup group) {ObjectUtil.checkNotNull(group, "group");if (this.group != null) {throw new IllegalStateException("group set already");} else {this.group = group;return this.self();}
}

2.2.2 channel(NioServerSocketChannel.class)：
AbstractBootstrap 类 private volatile ChannelFactory<? extends C> channelFactory; 对象赋值
调用 AbstractBootstrap 类中 channel(NioServerSocketChannel.class) 方法：

public B channel(Class<? extends C> channelClass) {
//  先使用ReflectiveChannelFactory 反射工厂类，对传入的channel 进行包装
// 调用channelFactory 对父类AbstractBootstrap 对象channel 工厂进行初始化return this.channelFactory((io.netty.channel.ChannelFactory)(new ReflectiveChannelFactory((Class)ObjectUtil.checkNotNull(channelClass, "channelClass"))));
}
// 工厂方法调用
public B channelFactory(io.netty.channel.ChannelFactory<? extends C> channelFactory) {return this.channelFactory((ChannelFactory)channelFactory);
}
// AbstractBootstrap 对象属性的初始化@Deprecated
public B channelFactory(ChannelFactory<? extends C> channelFactory) {ObjectUtil.checkNotNull(channelFactory, "channelFactory");if (this.channelFactory != null) {throw new IllegalStateException("channelFactory set already");} else {this.channelFactory = channelFactory;return this.self();}
}
// channel类反射工厂的创建
public class ReflectiveChannelFactory<T extends Channel> implements ChannelFactory<T> {private final Constructor<? extends T> constructor;public ReflectiveChannelFactory(Class<? extends T> clazz) {ObjectUtil.checkNotNull(clazz, "clazz");try {// 赋值 NioServerSocketChannel 类的构造器，使得在需要实例化channel 对象的时候// 可以通过改channel 的无参构造方法完成对象实例化this.constructor = clazz.getConstructor();} catch (NoSuchMethodException var3) {throw new IllegalArgumentException("Class " + StringUtil.simpleClassName(clazz) + " does not have a public non-arg constructor", var3);}}// 对当前的channel 通过反射调用channel 对象的无参构造方法public T newChannel() {try {return (Channel)this.constructor.newInstance();} catch (Throwable var2) {throw new ChannelException("Unable to create Channel from class " + this.constructor.getDeclaringClass(), var2);}}public String toString() {return StringUtil.simpleClassName(ReflectiveChannelFactory.class) + '(' + StringUtil.simpleClassName(this.constructor.getDeclaringClass()) + ".class)";}
}

• 通过channle 方法可以看到，完成了对父类AbstractBootstrap 对象 channel 工厂的属性初始化;
• 在真正需要NioServerSocketChannel 对象的时候，可以通过ReflectiveChannelFactory的 newChannel() 方法完成对 NioServerSocketChannel 无参的构造方法调用，从而实例化一个NioServerSocketChannel的对象出来；

2.2.3 childHandler(new ChannelInitializer() { })：
调用ServerBootstrap 类中 childHandler(ChannelHandler childHandler) 方法：

public ServerBootstrap childHandler(ChannelHandler childHandler) {this.childHandler = (ChannelHandler)ObjectUtil.checkNotNull(childHandler, "childHandler");return this;
}

对ServerBootstrap 事件处理属性private volatile ChannelHandler childHandler; 赋值；

2.2.4 option(ChannelOption.SO_BACKLOG,128)：
AbstractBootstrap 的option 方法，对父类AbstractBootstrap 对象options 顺序赋值：

// private final Map<ChannelOption<?>, Object> options = new LinkedHashMap(); 属性赋值
public <T> B option(ChannelOption<T> option, T value) {ObjectUtil.checkNotNull(option, "option");synchronized(this.options) {if (value == null) {this.options.remove(option);} else {this.options.put(option, value);}}return this.self();
}

2.2.5 childOption(ChannelOption.SO_KEEPALIVE,true)：
ServerBootstrap 类中的childOption 方法：

// private final Map<ChannelOption<?>, Object> childOptions = new LinkedHashMap(); 赋值
public <T> ServerBootstrap childOption(ChannelOption<T> childOption, T value) {ObjectUtil.checkNotNull(childOption, "childOption");synchronized(this.childOptions) {if (value == null) {this.childOptions.remove(childOption);} else {this.childOptions.put(childOption, value);}return this;}
}

• 可以看到上面的这些步骤先是对ServerBootstrap 和AbstractBootstrap 对象实例化 然后为其属性进行赋值操作；
• 将NioEventLoopGroup worker = new NioEventLoopGroup(); 的worker 对象对其ServerBootstrap 的EventLoopGroup childGroup 赋值；然后将 NioEventLoopGroup boss = new NioEventLoopGroup(); 对象对其AbstractBootstrap 的 volatile EventLoopGroup group 属性赋值；
• 对AbstractBootstrap 的channel 工厂类属性 private volatile ChannelFactory<? extends C> channelFactory; 赋值为NioServerSocketChannel 对象工厂；
• 对AbstractBootstrap 的options 属性赋值key：ChannelOption.SO_BACKLOG, value ：128;
• 对ServerBootstrap 的childOptions 属性赋值key：ChannelOption.SO_KEEPALIVE, value： true；

以上步骤都是初始化和赋值操作，没有socket 端口的绑定，以及时间监听的处理，那么这些处理就只剩在bind(this.port).sync() 进行处理，由于bind 方法嵌套较深，所有放在下一篇继续探究；