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.SelectionKey;
import java.nio.channels.Selector;
import java.nio.channels.ServerSocketChannel;
import java.nio.channels.SocketChannel;
import java.nio.charset.Charset;
import java.util.Iterator;
import static com.example.nettytest.nio.day1.ByteBufferUtil.debugAll;
/**
* @description: Selector处理read事件(消息边界问题) 代码示例
* @author: xz
* @create: 2022-09-04
*/
@Slf4j
public class Test5Server {
public static void main(String[] args) {
nioSelectorReadServer();
}
/**
* 1、消息边界问题
* */
private static void nioSelectorReadServer(){
try {
// 1. 创建 selector, 管理多个 channel
Selector selector = Selector.open();
ServerSocketChannel ssc = ServerSocketChannel.open();
ssc.configureBlocking(false);
// 2. 建立 selector 和 channel 的联系(注册)
// SelectionKey 就是将来事件发生后,通过它可以知道事件和哪个channel的事件
SelectionKey sscKey = ssc.register(selector, 0, null);
// key 只关注 accept 事件
sscKey.interestOps(SelectionKey.OP_ACCEPT);
log.debug("sscKey:{}", sscKey);
ssc.bind(new InetSocketAddress(8080));
while (true) {
// 3. select 方法, 没有事件发生,线程阻塞,有事件,线程才会恢复运行
// select 在事件未处理时,它不会阻塞, 事件发生后要么处理,要么取消,不能置之不理
selector.select();
// 4. 处理事件, selectedKeys 内部包含了所有发生的事件
Iterator<SelectionKey> iter = selector.selectedKeys().iterator(); // accept, read
while (iter.hasNext()) {
SelectionKey key = iter.next();
// 处理key 时,要从 selectedKeys 集合中删除,否则下次处理就会有问题
iter.remove();
log.debug("key: {}", key);
// 5. 区分事件类型
if (key.isAcceptable()) { // 如果是 accept
ServerSocketChannel channel = (ServerSocketChannel) key.channel();
SocketChannel sc = channel.accept();
sc.configureBlocking(false);
SelectionKey scKey = sc.register(selector, 0, null);
scKey.interestOps(SelectionKey.OP_READ);
log.debug("{}", sc);
log.debug("scKey:{}", scKey);
} else if (key.isReadable()) { // 如果是 read
try {
SocketChannel channel = (SocketChannel) key.channel(); // 拿到触发事件的channel
//分配ByteBuffer容量4个字节
ByteBuffer buffer = ByteBuffer.allocate(4);
int read=channel.read(buffer); // 如果是正常断开,read 的方法的返回值是 -1
if(read == -1) {
key.cancel();
} else {
buffer.flip();
System.out.println(Charset.defaultCharset().decode(buffer));
}
} catch (IOException e) {
e.printStackTrace();
// 因为客户端断开了,因此需要将 key 取消(从 selector 的 keys 集合中真正删除 key)
key.cancel();
}
}
}
}
} catch (IOException e) {
e.printStackTrace();
}
}
}
客户端代码示例
package com.example.nettytest.nio.day3;
import java.io.IOException;
import java.net.InetSocketAddress;
import java.net.SocketAddress;
import java.nio.channels.SocketChannel;
import java.nio.charset.Charset;
/**
* @description:
* @author: xz
* @create: 2022-09-04
*/
public class Test5Client {
public static void main(String[] args) throws IOException {
SocketChannel sc = SocketChannel.open();
sc.connect(new InetSocketAddress("localhost", 8080));
SocketAddress address = sc.getLocalAddress();
//超过服务端设置的ByteBuffer容量4个字节
sc.write(Charset.defaultCharset().encode("123456789abcd\n"));
System.out.println("waiting...");
}
}
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);
}
}
启动服务端,控制台输出如下:

debug模式启动客户端【再System.out.println(“waiting…”)代码位置加断点】

然后查服务端看控制台输出如下:

再处理read事件代码中,代码修如下:
try {
SocketChannel channel = (SocketChannel) key.channel(); // 拿到触发事件的channel
// 获取 selectionKey 上关联的附件
ByteBuffer buffer = (ByteBuffer) key.attachment();
int read=channel.read(buffer); // 如果是正常断开,read 的方法的返回值是 -1
if(read == -1) {
key.cancel();
} else {
//按 \n 分隔的数据,处理消息边界
split(buffer);
// 需要扩容
if (buffer.position() == buffer.limit()) {
ByteBuffer newBuffer = ByteBuffer.allocate(buffer.capacity() * 2);
buffer.flip();
newBuffer.put(buffer); // 0123456789abcdef3333\n
key.attach(newBuffer);
}
}
} catch (IOException e) {
e.printStackTrace();
// 因为客户端断开了,因此需要将 key 取消(从 selector 的 keys 集合中真正删除 key)
key.cancel();
}
/**
* 将错乱的数据恢复成原始的按 \n 分隔的数据方法
* */
public static void split(ByteBuffer sourceByteBuffer){
//flip 切换到读模式
sourceByteBuffer.flip();
for(int i = 0; i < sourceByteBuffer.limit(); i++){
if(sourceByteBuffer.get(i) =='\n'){//找到一条完整消息
//换行符索引+1-起始位置
int length =i + 1- sourceByteBuffer.position();
// 把此条完整消息存入新的 ByteBuffer
ByteBuffer targetByteBuffer = ByteBuffer.allocate(length);
for(int j=0;j<length;j++){
targetByteBuffer.put(sourceByteBuffer.get());
}
//打印byteBuffer中所有内容
debugAll(targetByteBuffer);
}
}
//compact 把未读完的部分向前压缩,然后切换至写模式
sourceByteBuffer.compact();
}
修改后的完整代码示例
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.SelectionKey;
import java.nio.channels.Selector;
import java.nio.channels.ServerSocketChannel;
import java.nio.channels.SocketChannel;
import java.nio.charset.Charset;
import java.util.Iterator;
import static com.example.nettytest.nio.day1.ByteBufferUtil.debugAll;
/**
* @description: Selector处理read事件(消息边界问题) 代码示例
* @author: xz
* @create: 2022-09-04
*/
@Slf4j
public class Test5Server {
public static void main(String[] args) {
nioSelectorReadServer();
}
/**
* 2、处理消息边界
* */
private static void nioSelectorReadServer(){
try {
// 1. 创建 selector, 管理多个 channel
Selector selector = Selector.open();
ServerSocketChannel ssc = ServerSocketChannel.open();
ssc.configureBlocking(false);
// 2. 建立 selector 和 channel 的联系(注册)
// SelectionKey 就是将来事件发生后,通过它可以知道事件和哪个channel的事件
SelectionKey sscKey = ssc.register(selector, 0, null);
// key 只关注 accept 事件
sscKey.interestOps(SelectionKey.OP_ACCEPT);
log.debug("sscKey:{}", sscKey);
ssc.bind(new InetSocketAddress(8080));
while (true) {
// 3. select 方法, 没有事件发生,线程阻塞,有事件,线程才会恢复运行
// select 在事件未处理时,它不会阻塞, 事件发生后要么处理,要么取消,不能置之不理
selector.select();
// 4. 处理事件, selectedKeys 内部包含了所有发生的事件
Iterator<SelectionKey> iter = selector.selectedKeys().iterator(); // accept, read
while (iter.hasNext()) {
SelectionKey key = iter.next();
// 处理key 时,要从 selectedKeys 集合中删除,否则下次处理就会有问题
iter.remove();
log.debug("key: {}", key);
// 5. 区分事件类型
if (key.isAcceptable()) { // 如果是 accept
ServerSocketChannel channel = (ServerSocketChannel) key.channel();
SocketChannel sc = channel.accept();
sc.configureBlocking(false);
ByteBuffer buffer = ByteBuffer.allocate(4);
// 将一个 byteBuffer 作为附件关联到 selectionKey 上
SelectionKey scKey = sc.register(selector, 0, buffer);// attachment
scKey.interestOps(SelectionKey.OP_READ);
log.debug("{}", sc);
log.debug("scKey:{}", scKey);
} else if (key.isReadable()) { // 如果是 read
try {
SocketChannel channel = (SocketChannel) key.channel(); // 拿到触发事件的channel
// 获取 selectionKey 上关联的附件
ByteBuffer buffer = (ByteBuffer) key.attachment();
int read=channel.read(buffer); // 如果是正常断开,read 的方法的返回值是 -1
if(read == -1) {
key.cancel();
} else {
//按 \n 分隔的数据,处理消息边界
split(buffer);
// 需要扩容
if (buffer.position() == buffer.limit()) {
ByteBuffer newBuffer = ByteBuffer.allocate(buffer.capacity() * 2);
buffer.flip();
newBuffer.put(buffer); // 0123456789abcdef3333\n
key.attach(newBuffer);
}
}
} catch (IOException e) {
e.printStackTrace();
// 因为客户端断开了,因此需要将 key 取消(从 selector 的 keys 集合中真正删除 key)
key.cancel();
}
}
}
}
} catch (IOException e) {
e.printStackTrace();
}
}
/**
* 将错乱的数据恢复成原始的按 \n 分隔的数据方法
* */
public static void split(ByteBuffer sourceByteBuffer){
//flip 切换到读模式
sourceByteBuffer.flip();
for(int i = 0; i < sourceByteBuffer.limit(); i++){
if(sourceByteBuffer.get(i) =='\n'){//找到一条完整消息
//换行符索引+1-起始位置
int length =i + 1- sourceByteBuffer.position();
// 把此条完整消息存入新的 ByteBuffer
ByteBuffer targetByteBuffer = ByteBuffer.allocate(length);
for(int j=0;j<length;j++){
targetByteBuffer.put(sourceByteBuffer.get());
}
//打印byteBuffer中所有内容
debugAll(targetByteBuffer);
}
}
//compact 把未读完的部分向前压缩,然后切换至写模式
sourceByteBuffer.compact();
}
}


