类继承的另一种境界，模板式继承
public abstract class AbstractBootstrap<B extends AbstractBootstrap<B, C>, C extends Channel> implements Cloneable
public final class ServerBootstrap extends AbstractBootstrap<ServerBootstrap, ServerChannel>
public abstract class AbstractBootstrap<B extends AbstractBootstrap<B, C>, C extends Channel> implements Cloneable
public final class ServerBootstrap extends AbstractBootstrap<ServerBootstrap, ServerChannel>
