一、非阻塞概述

• 非阻塞模式下，相关方法都会不会让线程暂停。
  （1）、在 ServerSocketChannel.accept 在没有连接建立时，会返回 null，继续运行；
  （2）、SocketChannel.read 在没有数据可读时，会返回 0，但线程不必阻塞，可以去执行其它 SocketChannel 的 read 或是去执行 ServerSocketChannel.accept；
  （3）、写数据时，线程只是等待数据写入 Channel 即可，无需等 Channel 通过网络把数据发送出去；
• 非阻塞模式下，即使没有连接建立和可读数据，线程仍然在不断运行，白白浪费了 cpu。
• 数据复制过程中，线程实际还是阻塞的（AIO 改进的地方）。

二、非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: 非阻塞模式服务端代码示例（使用nio实现）
 * @author: xz
 * @create: 2022-08-16 21:21
 */
@Slf4j
public class TestServer {
    public static void main(String[] args) throws IOException {
        nioNoBlockServer();
    }
    
    /**
     * 使用nio来理解非阻塞模式(单线程服务端)
     * */
    private static void nioNoBlockServer() throws IOException {
        //1、创建ByteBuffer，容量16
        ByteBuffer byteBuffer = ByteBuffer.allocate(16);
        //2、创建服务器
        ServerSocketChannel ssc = ServerSocketChannel.open();
        ssc.configureBlocking(false);//ssc设置为非阻塞模式
        //3、绑定监听端口
        ssc.bind(new InetSocketAddress(8080));
        //4、连接集合
        ArrayList<SocketChannel> channels = new ArrayList<>();
        while(true){
            //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，非阻塞方法，线程会继续运行。如果没有建立连接 sc=null
            if(sc !=null){
                log.info("create connected SocketChannel... {}", sc);
                sc.configureBlocking(false);//sc设置为非阻塞模式
                //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){
                // 8、 接收客户端发送的数据，从channel中读取数据写入到byteBuffer中
                int read = channel.read(byteBuffer);// 启动客户端，非阻塞方法，线程会继续运行，read 返回 0
                if(read>0){
                    //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、非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: 2022-08-16 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、非阻塞模式代码示例本地调试

• 先启动服务端，然后在启动2个客户端，在服务端控制台可以看到服务端接收到了2个客户端的连接，accept方法为非阻塞方法，线程会继续运行。如下图所示：

• 客户端1选择sc参数右键，点击【Evaluate Expression…】,弹出的窗口输入sc.write(Charset.defaultCharset().encode(“111111”));表示客户端1发送数据。如下图所示：

• 查看服务端，已经接收到了客户端1发送的111111数据，服务端程序已执行到完成，但是线程仍会继续运行，等待客户端发送数据。如下图所示：

• 客户端2选择sc参数右键，点击【Evaluate Expression…】,弹出的窗口输入sc.write(Charset.defaultCharset().encode(“222222”));表示客户端2发送数据。如下图所示：

• 此时，再次查看服务端，已经接收到了客户端2发送的222222数据，服务端程序已执行到完成，但是线程仍会继续运行，等待客户端发送数据。如下图所示：