blocks|key|410275|text|因为在这样做之前，您无法检测到新的事件重复。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|410276|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

Because until you do it you can't detect new event repetitions.

blocks|key|3247602|text|因为Selector从不这样做，它只会添加到set中，所以如果您不这样做，那么下次Selector返回时，您将自己重新处理该事件。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3247603|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

Because the Selector never does that, it only adds to the set, so if you don't do it you will reprocess the event yourself next time the Selector returns.

blocks|key|3461078|text|因为从选定的集合中删除关键点，当它被处理时，它将等待下一个选择事件。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3461079|选定集包含就绪通道的关键点。|3461080|+selector.select();+//This+may+block+for+a+long+time.+Upon+returning,+the+elected+set+contains+keys+of+the+ready+channels.|code-block|syntax|javascript|3461081|在选定的键集上获取迭代器，并执行Business+Information|3461082|Iterator+it+=+selector.selectedKeys().iterator(++);|3461083|最后从选定的集合中删除关键点；它已被处理|3461084|+it.remove(++);|3461085|可以直接从该集合中删除密钥，但不能添加密钥。尝试添加到选定的关键点集会引发java.lang.UnsupportedOperationException。|3461086|entityMap^0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|V|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|W|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|X|8|@]|9|@]|A|$]]|$1|K|3|L|5|F|7|Y|8|@]|9|@]|A|$G|H]]|$1|M|3|N|5|6|7|Z|8|@]|9|@]|A|$]]|$1|O|3|P|5|F|7|10|8|@]|9|@]|A|$G|H]]|$1|Q|3|R|5|6|7|11|8|@]|9|@]|A|$]]|$1|S|3|-4|5|6|7|12|8|@]|9|@]|A|$]]]|T|$]]

Because removing key from selected set, as it's been Handled, it will wait for next selection event.

selected set contains keys of the ready channels.

<pre><code> selector.select(); //This may block for a long time. Upon returning, the elected set contains keys of the ready channels.
</code></pre>

Get an iterator over the set of selected keys and Perform the Business Information

<pre><code>Iterator it = selector.selectedKeys().iterator( );
</code></pre>

Finally Remove key from selected set; it's been handled

<pre><code> it.remove( );
</code></pre>

Keys can be directly removed from this set, but not added. Attempting to add to the selected key set throws java.lang.UnsupportedOperationException.

blocks|key|3461130|text|如果你不调用remove方法，你会发现它也工作得很好。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3461131|import+java.io.IOException;
import+java.io.InputStream;
import+java.io.OutputStream;
import+java.net.InetSocketAddress;
import+java.net.ServerSocket;
import+java.net.Socket;
import+java.nio.ByteBuffer;
import+java.nio.channels.SelectionKey;
import+java.nio.channels.Selector;
import+java.nio.channels.ServerSocketChannel;
import+java.nio.channels.SocketChannel;
import+java.util.ArrayList;
import+java.util.Collection;
import+java.util.Iterator;
import+java.util.concurrent.Callable;
import+java.util.concurrent.ExecutorService;
import+java.util.concurrent.Executors;
@SuppressWarnings({+"unchecked"+})
public+class+NioServer+{
++++ServerSocketChannel+serverChannel;
++++ServerSocket+serverSocket;
++++public+final+int+port;
++++private+Selector+selector;
++++ByteBuffer+buffer+=+ByteBuffer.allocate(1024);
++++NioServer(final+int+port)+{
++++++++this.port+=+port;
++++}
++++void+init()+throws+Exception+{
++++++++//+创建+ServerSocketChannel、ServerSocket
++++++++serverChannel+=+ServerSocketChannel.open();
++++++++serverSocket+=+serverChannel.socket();
++++++++serverSocket.bind(new+InetSocketAddress(port));
++++++++//+设置通道为非阻塞模式
++++++++serverChannel.configureBlocking(false);
++++++++//+开启通道选择器，并注册+ServerSocketChannel
++++++++selector+=+Selector.open();
++++++++serverChannel.register(selector,+SelectionKey.OP_ACCEPT);
++++}

++++void+go()+throws+Exception+{
++++++++while+(true)+{
++++++++++++int+num+=+selector.select();
++++++++++++if+(num+<=+0)
++++++++++++++++continue;
++++++++++++Iterator<SelectionKey>+keyIter+=+selector.selectedKeys().iterator();
++++++++++++System.out.println(selector.selectedKeys().size());+//等于线程数量
++++++++++++while+(keyIter.hasNext())+{
++++++++++++++++final+SelectionKey+key+=+keyIter.next();
++++++++++++++++System.out.println("所有的key"%2Bkey);
++++++++++++++++//+接收一个Socket连接
++++++++++++++++//+key.isAcceptable（）如果为true，说明channnel支持accept（）,也就是说明是一个ServerSocketChannel
++++++++++++++++if+(key.isAcceptable())+{
++++++++++++++++++++System.out.println("可以连接的key:"%2Bkey);
++++++++++++++++++++SocketChannel+clientChannel+=+serverChannel.accept();
++++++++++++++++++++if+(clientChannel+!=+null)+{
++++++++++++++++++++++++clientChannel.configureBlocking(false);
++++++++++++++++++++++++clientChannel.register(selector,+SelectionKey.OP_READ+%7C+SelectionKey.OP_WRITE);
++++++++++++++++++++}
++++++++++++++++}
++++++++++++++++//+如果isReadable()为true,说明是一个SocketChannel
++++++++++++++++if+(key.isReadable())+{
++++++++++++++++++++String+requestContent+=+read(key);
++++++++++++++++++++//+业务处理
++++++++++++++++++++//+responseContent=doSomthing(requestContent);
++++++++++++++++++++write(key,+"ok"+/*+responseContent+*/);
++++++++++++++++}
//++++++++++keyIter.remove();
++++++++++++}
++++++++}
++++}

++++//+从通道读取数据
++++String+read(SelectionKey+key)+throws+Exception+{
++++++++SocketChannel+socketChannel+=+(SocketChannel)+key.channel();
++++++++buffer.clear();//+这一步必须有
++++++++int+len+=+0;
++++++++StringBuffer+str+=+new+StringBuffer();
++++++++while+((len+=+socketChannel.read(buffer))+>+0)+{
++++++++++++byte[]+bs+=+buffer.array();
++++++++++++String+block+=+new+String(bs,+0,+len);
++++++++++++System.out.println("Server+read:+"+%2B+block);
++++++++++++str.append(block);

++++++++}
++++++++buffer.clear();
++++++++return+str.toString();
++++}

++++//+写数据到通道

++++void+write(SelectionKey+key,+String+str)+throws+Exception+{
++++++++SocketChannel+socketChannel+=+(SocketChannel)+key.channel();
++++++++buffer.clear();
++++++++buffer.put(str.getBytes());
++++++++buffer.flip();//+这一步必须有
++++++++socketChannel.write(buffer);

++++}

++++public+static+void+main(String[]+args)+throws+Exception+{
++++++++final+int+port+=+10000;
++++++++NioServer+server+=+new+NioServer(port);
++++++++server.init();
++++++++///+========================================================
++++++++//+接下来模拟3个Client并发访问服务器
++++++++int+poolsize+=+1;
++++++++ExecutorService+pool+=+Executors.newFixedThreadPool(poolsize);
++++++++Collection<Callable>+tasks+=+new+ArrayList<Callable>(10);
++++++++final+String+clientname+=+"clientThread";
++++++++for+(int+i+=+0;+i+<+poolsize;+i%2B%2B)+{
++++++++++++final+int+n+=+i;
++++++++++++//+若每一个Client都保持使用BIO方式发送数据到Server，并读取数据。
++++++++++++tasks.add(new+Callable()+{
++++++++++++++++@Override
++++++++++++++++public+Object+call()+throws+Exception+{
++++++++++++++++++++Socket+socket+=+new+Socket("127.0.0.1",+port);
++++++++++++++++++++final+InputStream+input+=+socket.getInputStream();
++++++++++++++++++++final+OutputStream+out+=+socket.getOutputStream();
++++++++++++++++++++final+String+clientname_n+=+clientname+%2B+"_"+%2B+n;
++++++++++++++++++++//+BIO读取数据线程
++++++++++++++++++++new+Thread(clientname_n+%2B+"_read")+{
++++++++++++++++++++++++@Override
++++++++++++++++++++++++public+void+run()+{
++++++++++++++++++++++++++++byte[]+bs+=+new+byte[1024];
++++++++++++++++++++++++++++while+(true)+{
++++++++++++++++++++++++++++++++try+{

++++++++++++++++++++++++++++++++++++Thread.sleep(1000);

++++++++++++++++++++++++++++++++}+catch+(InterruptedException+e)+{
++++++++++++++++++++++++++++++++++++e.printStackTrace();
++++++++++++++++++++++++++++++++}
++++++++++++++++++++++++++++++++int+len+=+0;
++++++++++++++++++++++++++++++++try+{
++++++++++++++++++++++++++++++++++++while+((len+=+input.read(bs))+!=+-1)+{

++++++++++++++++++++++++++++++++++++++++System.out.println("Clinet+thread+"+%2B+Thread.currentThread().getName()
++++++++++++++++++++++++++++++++++++++++++++++++%2B+"+read:+"+%2B+new+String(bs,+0,+len));
++++++++++++++++++++++++++++++++++++}

++++++++++++++++++++++++++++++++}+catch+(IOException+e)+{

++++++++++++++++++++++++++++++++++++e.printStackTrace();
++++++++++++++++++++++++++++++++}
++++++++++++++++++++++++++++}
++++++++++++++++++++++++}

++++++++++++++++++++}.start();
++++++++++++++++++++//+BIO写数据线程
++++++++++++++++++++new+Thread(clientname_n+%2B+"_write")+{
++++++++++++++++++++++++@Override
++++++++++++++++++++++++public+void+run()+{
++++++++++++++++++++++++++++int+a+=+0;
++++++++++++++++++++++++++++while+(true)+{
++++++++++++++++++++++++++++++++try+{
++++++++++++++++++++++++++++++++++++Thread.sleep(100);

++++++++++++++++++++++++++++++++}+catch+(InterruptedException+e)+{
++++++++++++++++++++++++++++++++++++e.printStackTrace();
++++++++++++++++++++++++++++++++}

++++++++++++++++++++++++++++++++String+str+=+Thread.currentThread().getName()+%2B+"+hello,+"+%2B+a;
++++++++++++++++++++++++++++++++try+{
++++++++++++++++++++++++++++++++++++out.write(str.getBytes());
++++++++++++++++++++++++++++++++++++a%2B%2B;

++++++++++++++++++++++++++++++++}+catch+(IOException+e)+{
++++++++++++++++++++++++++++++++++++e.printStackTrace();
++++++++++++++++++++++++++++++++}
++++++++++++++++++++++++++++}
++++++++++++++++++++++++}

++++++++++++++++++++}.start();

++++++++++++++++++++return+null;

++++++++++++++++}

++++++++++++});

++++++++}
++++++++pool.invokeAll((Collection<?+extends+Callable<Object>>)+tasks);
++++++++server.go();

++++}

}|code-block|syntax|javascript|3461132|只需打印并测试它即可。你会发现即使你不删除，使用key.isAcceptable()也可以过滤出正确的结果|3461133|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

if you dont invoke remove method you will find it also work fine。

<pre><code>import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.InetSocketAddress;
import java.net.ServerSocket;
import java.net.Socket;
import java.nio.ByteBuffer;
import java.nio.channels.SelectionKey;
import java.nio.channels.Selector;
import java.nio.channels.ServerSocketChannel;
import java.nio.channels.SocketChannel;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Iterator;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
@SuppressWarnings({ "unchecked" })
public class NioServer {
 ServerSocketChannel serverChannel;
 ServerSocket serverSocket;
 public final int port;
 private Selector selector;
 ByteBuffer buffer = ByteBuffer.allocate(1024);
 NioServer(final int port) {
 this.port = port;
 }
 void init() throws Exception {
 // 创建 ServerSocketChannel、ServerSocket
 serverChannel = ServerSocketChannel.open();
 serverSocket = serverChannel.socket();
 serverSocket.bind(new InetSocketAddress(port));
 // 设置通道为非阻塞模式
 serverChannel.configureBlocking(false);
 // 开启通道选择器，并注册 ServerSocketChannel
 selector = Selector.open();
 serverChannel.register(selector, SelectionKey.OP_ACCEPT);
 }

 void go() throws Exception {
 while (true) {
 int num = selector.select();
 if (num &lt;= 0)
 continue;
 Iterator&lt;SelectionKey&gt; keyIter = selector.selectedKeys().iterator();
 System.out.println(selector.selectedKeys().size()); //等于线程数量
 while (keyIter.hasNext()) {
 final SelectionKey key = keyIter.next();
 System.out.println("所有的key"+key);
 // 接收一个Socket连接
 // key.isAcceptable（）如果为true，说明channnel支持accept（）,也就是说明是一个ServerSocketChannel
 if (key.isAcceptable()) {
 System.out.println("可以连接的key:"+key);
 SocketChannel clientChannel = serverChannel.accept();
 if (clientChannel != null) {
 clientChannel.configureBlocking(false);
 clientChannel.register(selector, SelectionKey.OP_READ | SelectionKey.OP_WRITE);
 }
 }
 // 如果isReadable()为true,说明是一个SocketChannel
 if (key.isReadable()) {
 String requestContent = read(key);
 // 业务处理
 // responseContent=doSomthing(requestContent);
 write(key, "ok" /* responseContent */);
 }
// keyIter.remove();
 }
 }
 }

 // 从通道读取数据
 String read(SelectionKey key) throws Exception {
 SocketChannel socketChannel = (SocketChannel) key.channel();
 buffer.clear();// 这一步必须有
 int len = 0;
 StringBuffer str = new StringBuffer();
 while ((len = socketChannel.read(buffer)) &gt; 0) {
 byte[] bs = buffer.array();
 String block = new String(bs, 0, len);
 System.out.println("Server read: " + block);
 str.append(block);

 }
 buffer.clear();
 return str.toString();
 }

 // 写数据到通道

 void write(SelectionKey key, String str) throws Exception {
 SocketChannel socketChannel = (SocketChannel) key.channel();
 buffer.clear();
 buffer.put(str.getBytes());
 buffer.flip();// 这一步必须有
 socketChannel.write(buffer);

 }

 public static void main(String[] args) throws Exception {
 final int port = 10000;
 NioServer server = new NioServer(port);
 server.init();
 /// ========================================================
 // 接下来模拟3个Client并发访问服务器
 int poolsize = 1;
 ExecutorService pool = Executors.newFixedThreadPool(poolsize);
 Collection&lt;Callable&gt; tasks = new ArrayList&lt;Callable&gt;(10);
 final String clientname = "clientThread";
 for (int i = 0; i &lt; poolsize; i++) {
 final int n = i;
 // 若每一个Client都保持使用BIO方式发送数据到Server，并读取数据。
 tasks.add(new Callable() {
 @Override
 public Object call() throws Exception {
 Socket socket = new Socket("127.0.0.1", port);
 final InputStream input = socket.getInputStream();
 final OutputStream out = socket.getOutputStream();
 final String clientname_n = clientname + "_" + n;
 // BIO读取数据线程
 new Thread(clientname_n + "_read") {
 @Override
 public void run() {
 byte[] bs = new byte[1024];
 while (true) {
 try {

 Thread.sleep(1000);

 } catch (InterruptedException e) {
 e.printStackTrace();
 }
 int len = 0;
 try {
 while ((len = input.read(bs)) != -1) {

 System.out.println("Clinet thread " + Thread.currentThread().getName()
 + " read: " + new String(bs, 0, len));
 }

 } catch (IOException e) {

 e.printStackTrace();
 }
 }
 }

 }.start();
 // BIO写数据线程
 new Thread(clientname_n + "_write") {
 @Override
 public void run() {
 int a = 0;
 while (true) {
 try {
 Thread.sleep(100);

 } catch (InterruptedException e) {
 e.printStackTrace();
 }

 String str = Thread.currentThread().getName() + " hello, " + a;
 try {
 out.write(str.getBytes());
 a++;

 } catch (IOException e) {
 e.printStackTrace();
 }
 }
 }

 }.start();

 return null;

 }

 });

 }
 pool.invokeAll((Collection&lt;? extends Callable&lt;Object&gt;&gt;) tasks);
 server.go();

 }

}
</code></pre>

just print it and test it 。you will find even you not remove，use
key.isAcceptable() can filter corrent result

blocks|key|3247739|text|避免publicSelectedKeys+private+final+Set<SelectionKey>+publicSelectedKeys;|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|3247740|entityMap^0|L|1F|0^^$0|@$1|2|3|4|5|6|7|H|8|@$9|I|A|J|B|C]]|D|@]|E|$]]|$1|F|3|-4|5|6|7|K|8|@]|D|@]|E|$]]]|G|$]]

avoid publicSelectedKeys
<code> private final Set&lt;SelectionKey&gt; publicSelectedKeys;</code>

I found some sample code of java nio:

<pre><code> ServerSocketChannel server = ServerSocketChannel.open(); 
 Selector selector = Selector.open(); 
 server.socket().bind(new InetSocketAddress(8080)); 
 server.configureBlocking(false); 
 server.register(selector, SelectionKey.OP_ACCEPT); 

 while(true) {
 selector.select(); 
 Iterator iter = selector.selectedKeys().iterator(); 
 while (iter.hasNext()) { 
 SelectionKey key = (SelectionKey) iter.next(); 
 iter.remove(); // Why remove it? 
 process(key); 
 }
 }
</code></pre>

When he gets the selected keys, he remove the key in the loop. Why we should do this?

<hr>

UPDATE

Thanks to the answers provided by EJP and user270349, I think I understand it now, let me explain it in detail.

There are 2 tables in the selector:

<ol>
<li>registration table: when we call <code>channel.register</code>, there will be a new item(key) into it. Only if we call <code>key.cancel()</code>, it will be removed from this table.</li>
<li>ready for selection table: when we call <code>selector.select()</code>, the selector will look up the registration table, find the keys which are available, copy the references of them to this selection table. The items of this table won't be cleared by selector(that means, even if we call <code>selector.select()</code> again, it won't clear the existing items)</li>
</ol>

That's why we have to invoke <code>iter.remove()</code> when we got the key from selection table. If not, we will get the key again and again by <code>selector.selectedKeys()</code> even if it's not ready to use.

Why the key should be removed in `selector.selectedKeys().iterator()` in java nio?

服务器

我找到了一些java nio的示例代码： ServerSocketChannel server = ServerSocketChannel.open();   Selector selector = Selector.open();   server.socket().bind(new InetSocketAddres...

问为什么要在java nio的`selector.selectedKeys().iterator()`中删除密钥？
EN

社区

活动

资源

关于

腾讯云开发者

热门产品

热门推荐

更多推荐

问为什么要在java nio的`selector.selectedKeys().iterator()`中删除密钥？EN

社区

活动

资源

关于

腾讯云开发者

热门产品

热门推荐

更多推荐

问为什么要在java nio的`selector.selectedKeys().iterator()`中删除密钥？
EN