public abstract class Selector implements Closeable {protected Selector() { }// 创建Selector对象public static Selector open() throws IOException {return SelectorProvider.provider().openSelector();}// 检测Selector是否打开public abstract boolean isOpen();// 返回创建该Selector的Providerpublic abstract SelectorProvider provider();// 返回Key集合，key集合不能被直接修改，只有在被cancel和channel被撤销的时候key才被移除。并且不是线程安全的集合。public abstract Set<SelectionKey> keys();// 返回selected-key集合，key可以直接移除，但是不可以直接增加。并且不是线程安全的集合。public abstract Set<SelectionKey> selectedKeys();// 选择channel有IO事件的key。// 该方法是非阻塞的selection操作，如果自上次selection操作之后无channel具有IO事件，该方法会立刻返回零。// 执行该方法会立刻清除之前执行的wakeup影响。public abstract int selectNow() throws IOException;// 阻塞操作，只有在以下的状态变化时：//（1）至少有一个IO的channel（2）调用selector.wakeup方法（3）当前线程被interrupt（4）timeout时间到(毫秒)public abstract int select(long timeout)throws IOException;// 阻塞操作，返回条件与select(long timeout)类似public abstract int select() throws IOException;// 唤醒当前select阻塞的操作：如果另一个线程当前阻塞在select或select(long)方法。// 如果当前没有select阻塞，则下次执行select或select(long)则直接返回，除非selectNow同时执行；//之后select和select(long)方法会正常阻塞；// 如果在select操作之间多次调用wakeup与调用一次效果是一样的public abstract Selector wakeup();// 关闭Selector。// 调用close方法，如果当前阻塞在selection操作，就像调用wakeup方法一样会立刻中断操作// 与该selector关联的未cancelled的key将失效，它们的channel将撤销，与Selector相关的其他资源将释放。// 如果Selector已经关闭，执行这个方法将没有影响。// selector关闭之后，如果执行与selector相关的操作会报ClosedSelectorExceptionpublic abstract void close() throws IOException;}

package java.nio.channels.spi;import java.io.IOException;
import java.nio.channels.SelectionKey;
import java.nio.channels.Selector;
import java.util.HashSet;
import java.util.Set;
import sun.nio.ch.Interruptible;
import java.util.concurrent.atomic.AtomicBoolean;// Selector的基本实现。
public abstract class AbstractSelectorextends Selector
{private AtomicBoolean selectorOpen = new AtomicBoolean(true); // 是否打开// The provider that created this selectorprivate final SelectorProvider provider;protected AbstractSelector(SelectorProvider provider) {this.provider = provider;}// 三大key集合之一cancelledKeysprivate final Set<SelectionKey> cancelledKeys = new HashSet<SelectionKey>();void cancel(SelectionKey k) {                       // package-privatesynchronized (cancelledKeys) {cancelledKeys.add(k);}}public final void close() throws IOException {boolean open = selectorOpen.getAndSet(false);if (!open)return;implCloseSelector();// 只有在Selector未关闭的情况下调用，并且只能被调用一次。}// 关闭Selector// 这个方法被close方法调用去执行Selector的关闭操作，只有在Selector未关闭的情况下调用，并且只能被调用一次。具体参考上面close实现protected abstract void implCloseSelector() throws IOException;public final boolean isOpen() {return selectorOpen.get();}public final SelectorProvider provider() {return provider;}protected final Set<SelectionKey> cancelledKeys() {return cancelledKeys;}// 为Selector注册Channel，这个方法被AbstractSelectableChannel.register方法调用protected abstract SelectionKey register(AbstractSelectableChannel ch,int ops, Object att);protected final void deregister(AbstractSelectionKey key) {((AbstractSelectableChannel)key.channel()).removeKey(key);}// -- Interruption machinery --private Interruptible interruptor = null;// 支持异步关闭和中断的begin和end方法protected final void begin() {if (interruptor == null) {interruptor = new Interruptible() {public void interrupt(Thread ignore) {AbstractSelector.this.wakeup();}};}AbstractInterruptibleChannel.blockedOn(interruptor);Thread me = Thread.currentThread();if (me.isInterrupted())interruptor.interrupt(me);}protected final void end() {AbstractInterruptibleChannel.blockedOn(null);}}　　

package sun.nio.ch;import java.io.IOException;
import java.nio.channels.*;
import java.nio.channels.spi.*;
import java.net.SocketException;
import java.util.*;
import sun.misc.*;// Selector的基本实现
abstract class SelectorImplextends AbstractSelector
{// 已经准备IO的keysprotected Set<SelectionKey> selectedKeys;// 注册到该Selector的所有keyprotected HashSet<SelectionKey> keys;// Public views of the key setsprivate Set<SelectionKey> publicKeys;             // 不可变private Set<SelectionKey> publicSelectedKeys;     // 可删除，不可增加protected SelectorImpl(SelectorProvider sp) {super(sp);keys = new HashSet<SelectionKey>();selectedKeys = new HashSet<SelectionKey>();if (Util.atBugLevel("1.4")) {publicKeys = keys;publicSelectedKeys = selectedKeys;} else {publicKeys = Collections.unmodifiableSet(keys);publicSelectedKeys = Util.ungrowableSet(selectedKeys);}}public Set<SelectionKey> keys() {if (!isOpen() && !Util.atBugLevel("1.4"))throw new ClosedSelectorException();return publicKeys;}public Set<SelectionKey> selectedKeys() {if (!isOpen() && !Util.atBugLevel("1.4"))throw new ClosedSelectorException();return publicSelectedKeys;}// 对于Windows系统，需要WindowsSelectorImpl实现doSelect方法protected abstract int doSelect(long timeout) throws IOException; private int lockAndDoSelect(long timeout) throws IOException {synchronized (this) {if (!isOpen())throw new ClosedSelectorException();synchronized (publicKeys) {synchronized (publicSelectedKeys) {return doSelect(timeout);}}}}// select方法的实现public int select(long timeout)throws IOException{if (timeout < 0)throw new IllegalArgumentException("Negative timeout");return lockAndDoSelect((timeout == 0) ? -1 : timeout);}public int select() throws IOException {return select(0);}public int selectNow() throws IOException {return lockAndDoSelect(0);}public void implCloseSelector() throws IOException {wakeup();synchronized (this) {synchronized (publicKeys) {synchronized (publicSelectedKeys) {implClose();}}}}// 需要WindowsSelectorImpl实现protected abstract void implClose() throws IOException;void putEventOps(SelectionKeyImpl sk, int ops) { }protected final SelectionKey register(AbstractSelectableChannel ch,int ops,Object attachment){if (!(ch instanceof SelChImpl))throw new IllegalSelectorException();SelectionKeyImpl k = new SelectionKeyImpl((SelChImpl)ch, this);k.attach(attachment);synchronized (publicKeys) {implRegister(k);}k.interestOps(ops);return k;}protected abstract void implRegister(SelectionKeyImpl ski);void processDeregisterQueue() throws IOException {// Precondition: Synchronized on this, keys, and selectedKeysSet cks = cancelledKeys();synchronized (cks) {if (!cks.isEmpty()) {Iterator i = cks.iterator();while (i.hasNext()) {SelectionKeyImpl ski = (SelectionKeyImpl)i.next();try {implDereg(ski);} catch (SocketException se) {IOException ioe = new IOException("Error deregistering key");ioe.initCause(se);throw ioe;} finally {i.remove();}}}}}protected abstract void implDereg(SelectionKeyImpl ski) throws IOException;abstract public Selector wakeup(); // 定义唤醒方法}