Netty——网络编程（阻塞理解及代码示例）

转x33g5p2x  于2022-08-17 转载在 其他  
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一、阻塞概述

  • 阻塞模式下，相关方法都会导致线程暂停。
    （1）、ServerSocketChannel.accept 会在没有连接建立时让线程暂停；
    （2）、SocketChannel.read 会在没有数据可读时让线程暂停；
    （3）、阻塞的表现其实就是线程暂停了，暂停期间不会占用 cpu，但线程相当于闲置；
  • 单线程下，阻塞方法之间相互影响，几乎不能正常工作，需要多线程支持。
  • 但多线程下，有新的问题，体现在以下方面
    （1）、32 位 jvm 一个线程 320k，64 位 jvm 一个线程 1024k，如果连接数过多，必然导致 OOM，并且线程太多，反而会因为频繁上下文切换导致性能降低；
    （2）、可以采用线程池技术来减少线程数和线程上下文切换，但治标不治本，如果有很多连接建立，但长时间 inactive，会阻塞线程池中所有线程，因此不适合长连接，只适合短连接；

二、阻塞模式服务端代码示例（使用nio实现）

  • 服务端代码
package com.example.nettytest.nio.day3;

import lombok.extern.slf4j.Slf4j;

import java.io.IOException;
import java.net.InetSocketAddress;
import java.nio.ByteBuffer;
import java.nio.channels.*;
import java.util.ArrayList;
import java.util.Iterator;

import static com.example.nettytest.nio.day1.ByteBufferUtil.debugRead;
/**
 * @description: 阻塞模式服务端代码示例（使用nio实现）
 * @author: xz
 * @create: 2022-08-15 21:21
 */
@Slf4j
public class TestServer {
    public static void main(String[] args) throws IOException {
        nioBlockServer();
    }

    /**
     * 使用nio来理解阻塞模式(单线程服务端)
     * */
    private static void nioBlockServer() throws IOException {
        //1、创建ByteBuffer，容量16
        ByteBuffer byteBuffer = ByteBuffer.allocate(16);
        //2、创建服务器
        ServerSocketChannel ssc = ServerSocketChannel.open();
        //3、绑定监听端口
        ssc.bind(new InetSocketAddress(8080));
        //4、连接集合
        ArrayList<SocketChannel> channels = new ArrayList<>();
        while(true){
            log.info("connecting...");
            //5、accept() 建立与客户端连接, SocketChannel 用来与客户端之间通信
            SocketChannel sc = ssc.accept();//启动服务端，阻塞方法，线程停止运行
            log.info("create connected SocketChannel... {}", sc);
            //6、建立的客户端连接sc 添加到 连接集合channels中
            channels.add(sc);
            //7、遍历连接集合
            for(SocketChannel channel : channels){
                log.info("before read channel ... {}", channel);
                // 8、 接收客户端发送的数据，从channel中读取数据写入到byteBuffer中
                channel.read(byteBuffer);// 启动客户端，阻塞方法，线程停止运行
                //切换读模式
                byteBuffer.flip();
                //打印可读取内容（从byteBuffer中读取数据内容）
                debugRead(byteBuffer);
                //切换回写模式
                byteBuffer.clear();
                log.info("after read channel ... {}", channel);
            }
        }
    }
    
}

三、阻塞模式客户端代码示例（使用nio实现）

  • 客户端代码
package com.example.nettytest.nio.day3;

import java.io.IOException;
import java.net.InetSocketAddress;
import java.net.SocketAddress;
import java.nio.channels.SocketChannel;
/**
 * @description:
 * @author: xz
 * @create: 2022-08-15 21:45
 */
public class TestClient {
    public static void main(String[] args) throws IOException {
        SocketChannel sc = SocketChannel.open();
        sc.connect(new InetSocketAddress("localhost", 8080));
        SocketAddress address = sc.getLocalAddress();
        //debug模式后，点击src参数，右键选择 输入表达式sc.write(Charset.defaultCharset().encode("hello"));然后执行
        System.out.println("waiting...");

    }
}

四、工具类代码示例

  • 工具类，打印输入、输出数据使用
package com.example.nettytest.nio.day1;
   
   import io.netty.util.internal.StringUtil;
   
   import java.nio.ByteBuffer;
   
   import static io.netty.util.internal.MathUtil.isOutOfBounds;
   import static io.netty.util.internal.StringUtil.NEWLINE;
   
   public class ByteBufferUtil {
       private static final char[] BYTE2CHAR = new char[256];
       private static final char[] HEXDUMP_TABLE = new char[256 * 4];
       private static final String[] HEXPADDING = new String[16];
       private static final String[] HEXDUMP_ROWPREFIXES = new String[65536 >>> 4];
       private static final String[] BYTE2HEX = new String[256];
       private static final String[] BYTEPADDING = new String[16];
   
       static {
           final char[] DIGITS = "0123456789abcdef".toCharArray();
           for (int i = 0; i < 256; i++) {
               HEXDUMP_TABLE[i << 1] = DIGITS[i >>> 4 & 0x0F];
               HEXDUMP_TABLE[(i << 1) + 1] = DIGITS[i & 0x0F];
           }
   
           int i;
   
           // Generate the lookup table for hex dump paddings
           for (i = 0; i < HEXPADDING.length; i++) {
               int padding = HEXPADDING.length - i;
               StringBuilder buf = new StringBuilder(padding * 3);
               for (int j = 0; j < padding; j++) {
                   buf.append("   ");
               }
               HEXPADDING[i] = buf.toString();
           }
   
           // Generate the lookup table for the start-offset header in each row (up to 64KiB).
           for (i = 0; i < HEXDUMP_ROWPREFIXES.length; i++) {
               StringBuilder buf = new StringBuilder(12);
               buf.append(NEWLINE);
               buf.append(Long.toHexString(i << 4 & 0xFFFFFFFFL | 0x100000000L));
               buf.setCharAt(buf.length() - 9, '|');
               buf.append('|');
               HEXDUMP_ROWPREFIXES[i] = buf.toString();
           }
   
           // Generate the lookup table for byte-to-hex-dump conversion
           for (i = 0; i < BYTE2HEX.length; i++) {
               BYTE2HEX[i] = ' ' + StringUtil.byteToHexStringPadded(i);
           }
   
           // Generate the lookup table for byte dump paddings
           for (i = 0; i < BYTEPADDING.length; i++) {
               int padding = BYTEPADDING.length - i;
               StringBuilder buf = new StringBuilder(padding);
               for (int j = 0; j < padding; j++) {
                   buf.append(' ');
               }
               BYTEPADDING[i] = buf.toString();
           }
   
           // Generate the lookup table for byte-to-char conversion
           for (i = 0; i < BYTE2CHAR.length; i++) {
               if (i <= 0x1f || i >= 0x7f) {
                   BYTE2CHAR[i] = '.';
               } else {
                   BYTE2CHAR[i] = (char) i;
               }
           }
       }
   
       /**
        * 打印所有内容
        * @param buffer
        */
       public static void debugAll(ByteBuffer buffer) {
           int oldlimit = buffer.limit();
           buffer.limit(buffer.capacity());
           StringBuilder origin = new StringBuilder(256);
           appendPrettyHexDump(origin, buffer, 0, buffer.capacity());
           System.out.println("+--------+-------------------- all ------------------------+----------------+");
           System.out.printf("position: [%d], limit: [%d]\n", buffer.position(), oldlimit);
           System.out.println(origin);
           buffer.limit(oldlimit);
       }
   
       /**
        * 打印可读取内容
        * @param buffer
        */
       public static void debugRead(ByteBuffer buffer) {
           StringBuilder builder = new StringBuilder(256);
           appendPrettyHexDump(builder, buffer, buffer.position(), buffer.limit() - buffer.position());
           System.out.println("+--------+-------------------- read -----------------------+----------------+");
           System.out.printf("position: [%d], limit: [%d]\n", buffer.position(), buffer.limit());
           System.out.println(builder);
       }
   
       public static void main(String[] args) {
           ByteBuffer buffer = ByteBuffer.allocate(10);
           buffer.put(new byte[]{97, 98, 99, 100});
           debugAll(buffer);
       }
   
       private static void appendPrettyHexDump(StringBuilder dump, ByteBuffer buf, int offset, int length) {
           if (isOutOfBounds(offset, length, buf.capacity())) {
               throw new IndexOutOfBoundsException(
                       "expected: " + "0 <= offset(" + offset + ") <= offset + length(" + length
                               + ") <= " + "buf.capacity(" + buf.capacity() + ')');
           }
           if (length == 0) {
               return;
           }
           dump.append(
                   "         +-------------------------------------------------+" +
                           NEWLINE + "         |  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |" +
                           NEWLINE + "+--------+-------------------------------------------------+----------------+");
   
           final int startIndex = offset;
           final int fullRows = length >>> 4;
           final int remainder = length & 0xF;
   
           // Dump the rows which have 16 bytes.
           for (int row = 0; row < fullRows; row++) {
               int rowStartIndex = (row << 4) + startIndex;
   
               // Per-row prefix.
               appendHexDumpRowPrefix(dump, row, rowStartIndex);
   
               // Hex dump
               int rowEndIndex = rowStartIndex + 16;
               for (int j = rowStartIndex; j < rowEndIndex; j++) {
                   dump.append(BYTE2HEX[getUnsignedByte(buf, j)]);
               }
               dump.append(" |");
   
               // ASCII dump
               for (int j = rowStartIndex; j < rowEndIndex; j++) {
                   dump.append(BYTE2CHAR[getUnsignedByte(buf, j)]);
               }
               dump.append('|');
           }
   
           // Dump the last row which has less than 16 bytes.
           if (remainder != 0) {
               int rowStartIndex = (fullRows << 4) + startIndex;
               appendHexDumpRowPrefix(dump, fullRows, rowStartIndex);
   
               // Hex dump
               int rowEndIndex = rowStartIndex + remainder;
               for (int j = rowStartIndex; j < rowEndIndex; j++) {
                   dump.append(BYTE2HEX[getUnsignedByte(buf, j)]);
               }
               dump.append(HEXPADDING[remainder]);
               dump.append(" |");
   
               // Ascii dump
               for (int j = rowStartIndex; j < rowEndIndex; j++) {
                   dump.append(BYTE2CHAR[getUnsignedByte(buf, j)]);
               }
               dump.append(BYTEPADDING[remainder]);
               dump.append('|');
           }
   
           dump.append(NEWLINE +
                   "+--------+-------------------------------------------------+----------------+");
       }
   
       private static void appendHexDumpRowPrefix(StringBuilder dump, int row, int rowStartIndex) {
           if (row < HEXDUMP_ROWPREFIXES.length) {
               dump.append(HEXDUMP_ROWPREFIXES[row]);
           } else {
               dump.append(NEWLINE);
               dump.append(Long.toHexString(rowStartIndex & 0xFFFFFFFFL | 0x100000000L));
               dump.setCharAt(dump.length() - 9, '|');
               dump.append('|');
           }
       }
   
       public static short getUnsignedByte(ByteBuffer buffer, int index) {
           return (short) (buffer.get(index) & 0xFF);
       }
   }

### 五、阻塞模式代码示例本地调试

* **启动服务端，服务端accept方法为阻塞方法，线程停止运行。如下图所示：**

![](//img.saoniuhuo.com/images/202208/21251660737711943.jpg)

* **debug模式启动客户端，服务端read方法为，阻塞方法，线程停止运行。如下图所示：**
![](//img.saoniuhuo.com/images/202208/3731660737712597.jpg)

* **客户端选择sc参数右键，点击【Evaluate Expression…】,弹出的窗口输入sc.write(Charset.defaultCharset().encode(“hello”)); 表示客户端发送数据。如下图所示：**

![](//img.saoniuhuo.com/images/202208/96851660737714144.jpg)

![](//img.saoniuhuo.com/images/202208/42931660737715511.jpg)

* **此时，再看服务端，已经接收到了客户端发送的hello数据，服务端并重新进入到了accept方法，阻塞方法，线程停止运行。如下图所示：**

![](//img.saoniuhuo.com/images/202208/54421660737716977.jpg)

* **最后放过客户端debug断点，输出如下图所示：**

![](//img.saoniuhuo.com/images/202208/56191660737718495.jpg)

版权说明 : 本文为转载文章, 版权归原作者所有 版权申明

原文链接 : https://wwwxz.blog.csdn.net/article/details/126355973

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