标签：read java NPU [] bad 相关 throw conf 例子
首先是使用java原生nio类库编写的例子，开发一套nio框架不简单，所以选择了netty,该例完成后，是netty举例。
package com.smkj.netty; public class TimeServer { public static void main(String[] args) { int port = 8080; if(args!=null&&args.length!=0) { try { port = Integer.valueOf(args[0]); } catch (NumberFormatException e) { //采用默认值 } } MultiplexerTimeServer timeServer = new MultiplexerTimeServer(port); new Thread(timeServer,"NIO-MultiplexerTimeServer-001").start(); } }
package com.smkj.netty; import java.io.IOException; import java.net.InetSocketAddress; 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.Iterator; import java.util.Set; public class MultiplexerTimeServer implements Runnable { private Selector selector; private ServerSocketChannel servChannel; private volatile boolean stop; /** * 初始化多路复用器，绑定监听端口 * * @param port */ public MultiplexerTimeServer(int port) { try { selector = Selector.open(); servChannel = ServerSocketChannel.open(); servChannel.configureBlocking(false); servChannel.socket().bind(new InetSocketAddress(port), 1024); servChannel.register(selector, SelectionKey.OP_ACCEPT); System.out.println("The time server is start in port:" + port); } catch (IOException e) { e.printStackTrace(); System.exit(1); } } public void stop() { this.stop = true; } @Override public void run() { while (!stop) { try { selector.select(1000); Set<SelectionKey> selectedKeys = selector.selectedKeys(); Iterator<SelectionKey> it = selectedKeys.iterator(); SelectionKey key = null; while (it.hasNext()) { key = it.next(); it.remove(); try { handleInput(key); // 处理key } catch (Exception e) { // TODO: handle exception if (key != null) { key.cancel(); if (key.channel() != null) { key.channel().close(); } } } } } catch (Exception e) { // TODO: handle exception e.printStackTrace(); } } // 多路复用器关闭后，所有注册在上面的Channel和Pipe等资源都会被自动去注册，所以不需要重复释放资源 if (selector != null) { try { selector.close(); } catch (Exception e) { // TODO: handle exception e.printStackTrace(); } } } private void handleInput(SelectionKey key) throws IOException { if (key.isValid()) { // 处理新接入的请求消息 if (key.isAcceptable()) { // Accept the new connection ServerSocketChannel ssc = (ServerSocketChannel) key.channel(); SocketChannel sc = ssc.accept(); sc.configureBlocking(false); // Add the new connection to the selector sc.register(selector, SelectionKey.OP_READ); } if (key.isReadable()) { // Read the Data SocketChannel sc = (SocketChannel) key.channel(); ByteBuffer readBuffer = ByteBuffer.allocate(1024); int readBytes = sc.read(readBuffer); if (readBytes > 0) { readBuffer.flip(); byte[] bytes = new byte[readBuffer.remaining()]; readBuffer.get(bytes); String body = new String(bytes, "UTF-8"); System.out.println("the time server receive order:" + body); String currentTime = "QUERY TIME ORDER".equalsIgnoreCase(body) ? new java.util.Date(System.currentTimeMillis()).toString() : "Bad Order"; doWrite(sc,currentTime); }else if(readBytes<0) { //对端链路关闭 key.cancel(); sc.close(); }else { //读到0字节 忽略 ; } } } } private void doWrite(SocketChannel channel,String response) throws IOException { if(response!=null&&response.trim().length()>0) { byte[] bytes = response.getBytes(); ByteBuffer writeBuffer = ByteBuffer.allocate(bytes.length); writeBuffer.put(bytes); writeBuffer.flip(); channel.write(writeBuffer); if (!writeBuffer.hasRemaining()) System.out.println("Send response to client succeed."); } } }
package com.smkj.netty; public class TimeClient { public static void main(String[] args) { int port = 8080; if(args!=null&&args.length!=0) { try { port = Integer.valueOf(args[0]); } catch (NumberFormatException e) { //采用默认值 } } new Thread(new TimeClientHandle("127.0.0.1",port),"TimeClient-001").start(); } }
package com.smkj.netty; import java.io.IOException; import java.net.InetSocketAddress; import java.nio.ByteBuffer; import java.nio.channels.SelectionKey; import java.nio.channels.Selector; import java.nio.channels.SocketChannel; import java.util.Iterator; import java.util.Set; public class TimeClientHandle implements Runnable { private String host; private int port; private Selector selector; private SocketChannel socketChannel; private volatile boolean stop; public TimeClientHandle(String host, int port) { this.host = host == null ? "127.0.0.1" : host; this.port = port; try { selector = Selector.open(); socketChannel = SocketChannel.open(); socketChannel.configureBlocking(false); } catch (IOException e) { e.printStackTrace(); System.exit(1); } } /* 022 * (non-Javadoc) 023 * 024 * @see java.lang.Runnable#run() 025 */ @Override public void run() { try { doConnect(); } catch (IOException e) { e.printStackTrace(); System.exit(1); } while (!stop) { try { selector.select(1000); Set<SelectionKey> selectedKeys = selector.selectedKeys(); Iterator<SelectionKey> it = selectedKeys.iterator(); SelectionKey key = null; while (it.hasNext()) { key = it.next(); it.remove(); try { handleInput(key); } catch (Exception e) { if (key != null) { key.cancel(); if (key.channel() != null) key.channel().close(); } } } } catch (Exception e) { e.printStackTrace(); System.exit(1); } } // 多路复用器关闭后，所有注册在上面的Channel和Pipe等资源都会被自动去注册并关闭，所以不需要重复释放资源 if (selector != null) try { selector.close(); } catch (IOException e) { e.printStackTrace(); } } private void handleInput(SelectionKey key) throws IOException { if (key.isValid()) { // 判断是否连接成功 SocketChannel sc = (SocketChannel) key.channel(); if (key.isConnectable()) { if (sc.finishConnect()) { sc.register(selector, SelectionKey.OP_READ); doWrite(sc); } else System.exit(1);// 连接失败，进程退出 } if (key.isReadable()) { ByteBuffer readBuffer = ByteBuffer.allocate(1024); int readBytes = sc.read(readBuffer); if (readBytes > 0) { readBuffer.flip(); byte[] bytes = new byte[readBuffer.remaining()]; readBuffer.get(bytes); String body = new String(bytes, "UTF-8"); System.out.println("Now is : " + body); this.stop = true; } else if (readBytes < 0) { // 对端链路关闭 key.cancel(); sc.close(); } else ; // 读到0字节，忽略 } } } private void doConnect() throws IOException { // 如果直接连接成功，则注册到多路复用器上，发送请求消息，读应答 if (socketChannel.connect(new InetSocketAddress(host, port))) { socketChannel.register(selector, SelectionKey.OP_READ); doWrite(socketChannel); } else socketChannel.register(selector, SelectionKey.OP_CONNECT); } private void doWrite(SocketChannel sc) throws IOException { byte[] req = "QUERY TIME ORDER".getBytes(); ByteBuffer writeBuffer = ByteBuffer.allocate(req.length); writeBuffer.put(req); writeBuffer.flip(); sc.write(writeBuffer); if (!writeBuffer.hasRemaining()) System.out.println("Send order 2 server succeed."); } }
可以发现服务端的最后进行了remove()操作，将SelectionKey从迭代器中删除了，博主一开始总觉得很纳闷，SelectionKey中可是记录了相关的channel信息，如果将SelectionKey删除了，那不就代表着将通道信息也抹除了吗，那后续还怎么继续获取通道，说来惭愧，这问题问的确实缺乏水准。
后来博主理了理selector的思路，要知道，一码事归一码事，channel是注册在selector中的，在后面的轮询中，是先将已准备好的channel挑选出来，即selector.select()，再通过selectedKeys()生成的一个SelectionKey迭代器进行轮询的，一次轮询会将这个迭代器中的每个SelectionKey都遍历一遍，每次访问后都remove()相应的SelectionKey，但是移除了selectedKeys中的SelectionKey不代表移除了selector中的channel信息(这点很重要)，注册过的channel信息会以SelectionKey的形式存储在selector.keys()中，也就是说每次select()后的selectedKeys迭代器中是不能还有成员的，但keys()中的成员是不会被删除的(以此来记录channel信息)。
那么为什么要删除呢，要知道，迭代器如果只需要访问的话，直接访问就好了，完全没必要remove()其中的元素啊，查询了相关资料，一致的回答是为了防止重复处理（大雾），后来又有信息说明：每次循环调用remove()是因为selector不会自己从已选择集合中移除selectionKey实例，必须在处理完通道时自己移除，这样，在下次select时，会将这个就绪通道添加到已选择通道集合中，其实到这里就已经可以理解了，selector不会自己删除selectedKeys()集合中的selectionKey，那么如果不人工remove()，将导致下次select()的时候selectedKeys()中仍有上次轮询留下来的信息，这样必然会出现错误，假设这次轮询时该通道并没有准备好，却又由于上次轮询未被remove()的原因被认为已经准备好了，这样能不出错吗？
即selector.select()会将准备好的channel以SelectionKey的形式放置于selector的selectedKeys()中供使用者迭代，使用的过程中需将selectedKeys清空，这样下次selector.select()时就不会出现错误了。
标签：read java NPU [] bad 相关 throw conf 例子
原文地址：https://www.cnblogs.com/fengwenzhee/p/10407587.html
