處理可寫事件

什么情況下需要注冊可寫事件？

• 在服務(wù)端一次性無法把數(shù)據(jù)發(fā)送完的情況下，需要注冊可寫事件
  • 服務(wù)端一次性是否能夠把數(shù)據(jù)全部發(fā)送完成取決于服務(wù)端的緩沖區(qū)大小，該緩沖區(qū)不受程序控制

注冊可寫事件的步驟

• 判斷ByteBuffer是否仍有剩余，如果有剩余注冊可寫事件

  ByteBuffer bf = "hello client,welcome";
  SocketChannel sc = (SocketChannel) selectionKey.channel();
  sc.write(bf);
  if(bf.hasRemaining){
      selectionKey.interestOps(SelectionKey.OP_READ + SelectionKey.OP_WRITE);
      selectionKey.attachment(bf);
  }
  

• 監(jiān)聽可寫事件，判斷數(shù)據(jù)是否寫完，數(shù)據(jù)寫完需要

  if (key.isWritable()){
      // 監(jiān)聽可寫事件
      SocketChannel channel = (SocketChannel) key.channel();
      ByteBuffer byteBuffer = (ByteBuffer) key.attachment();
      channel.write(byteBuffer);
      if (!byteBuffer.hasRemaining()) {
          // 判斷數(shù)據(jù)是否寫完
          // 數(shù)據(jù)寫完，解除對buffer的引用
          key.attach(null);
          // 數(shù)據(jù)寫完，不再關(guān)注可寫事件
          key.interestOps(key.interestOps() - SelectionKey.OP_WRITE);
      }
  }
  

代碼示例

• 客戶端

  package com.ysf;
  
  import java.io.IOException;
  import java.net.InetSocketAddress;
  import java.nio.ByteBuffer;
  import java.nio.channels.SocketChannel;
  import java.nio.charset.Charset;
  
  public class Client {
  
      public static void main(String[] args) throws IOException {
          SocketChannel sc = SocketChannel.open();
          sc.connect(new InetSocketAddress("127.0.0.1",11027));
          sc.write(Charset.defaultCharset().encode("123456\n223456\nhello server\n"));
          while (true){
              ByteBuffer allocate = ByteBuffer.allocate(16);
              sc.read(allocate);
              allocate.flip();
              System.out.println(Charset.defaultCharset().decode(allocate));
          }
      }
  }
  

• 服務(wù)端文章來源地址http://www.zghlxwxcb.cn/news/detail-673294.html

  package com.ysf;
  
  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.nio.charset.Charset;
  import java.util.HashMap;
  import java.util.Iterator;
  import java.util.Map;
  
  public class WriterSelectorServer {
  
      public static void handleContent(ByteBuffer byteBuffer){
          byteBuffer.flip();
          for (int i = 0;i < byteBuffer.limit();i++){
              if (byteBuffer.get(i) == '\n'){
                  int length = i + 1 - byteBuffer.position();
                  ByteBuffer allocate = ByteBuffer.allocate(length);
                  for (int j = 0;j<length;j++){
                      allocate.put(byteBuffer.get());
                  }
                  allocate.flip();
                  System.out.println(Charset.defaultCharset().decode(allocate));
              }
          }
          byteBuffer.compact();
      }
  
      public static void main(String[] args) throws IOException {
          Selector selector = Selector.open();
  
          ServerSocketChannel ssc = ServerSocketChannel.open();
          ssc.configureBlocking(false);
          ssc.bind(new InetSocketAddress(11027));
          SelectionKey sscKey = ssc.register(selector, 0, null);
          sscKey.interestOps(SelectionKey.OP_ACCEPT);
  
          while (true){
              selector.select();
              Iterator<SelectionKey> iterator = selector.selectedKeys().iterator();
              while (iterator.hasNext()){
                  SelectionKey key = iterator.next();
                  iterator.remove();
                  if (key.isAcceptable()){
                      ServerSocketChannel serverSocketChannel = (ServerSocketChannel) key.channel();
                      SocketChannel sc = serverSocketChannel.accept();
                      sc.configureBlocking(false);
                      ByteBuffer welcome = Charset.defaultCharset().encode("welcome");
                      sc.write(welcome);
                      Map<String,ByteBuffer> attach = new HashMap<>();
                      ByteBuffer readBuffer = ByteBuffer.allocate(16);
                      attach.put("read",readBuffer);
                      SelectionKey scKey = sc.register(selector, 0, attach);
                      if (welcome.hasRemaining()){
                          attach.put("write",welcome);
                          scKey.interestOps(SelectionKey.OP_READ + SelectionKey.OP_WRITE);
                      }else {
                          scKey.interestOps(SelectionKey.OP_READ);
                      }
                  }else if (key.isReadable()){
                      SocketChannel channel = (SocketChannel) key.channel();
                      Map<String, ByteBuffer> attachment = ((Map<String,ByteBuffer>) key.attachment());
                      ByteBuffer readBuffer = attachment.get("read");
                      int read;
                      try {
                          read = channel.read(readBuffer);
                      } catch (IOException e) {
                          e.printStackTrace();
                          key.cancel();
                          continue;
                      }
                      if (read == -1){
                          key.cancel();
                      }else {
                          handleContent(readBuffer);
                          if (readBuffer.position() == readBuffer.limit()){
                              ByteBuffer newAttachment = ByteBuffer.allocate(readBuffer.capacity() * 2);
                              readBuffer.flip();
                              newAttachment.put(readBuffer);
                              attachment.put("read",newAttachment);
                          }
                      }
                  }else if (key.isWritable()){
                      SocketChannel channel = (SocketChannel) key.channel();
                      Map<String, ByteBuffer> attachment = (Map<String, ByteBuffer>) key.attachment();
                      ByteBuffer byteBuffer = attachment.get("write");
                      channel.write(byteBuffer);
                      if (!byteBuffer.hasRemaining()) {
                          attachment.remove("write");
                          key.interestOps(key.interestOps() - SelectionKey.OP_WRITE);
                      }
                  }
              }
          }
      }
  }
  
  

到了這里，關(guān)于netty（二）：NIO——處理可寫事件的文章就介紹完了。如果您還想了解更多內(nèi)容，請在右上角搜索TOY模板網(wǎng)以前的文章或繼續(xù)瀏覽下面的相關(guān)文章，希望大家以后多多支持TOY模板網(wǎng)！