java nio解決半包 粘包問題
NIO socket是非阻塞的通訊模式，與IO阻塞式的通訊不同點在於NIO的數據要通過channel放到一個緩存池ByteBuffer中，然後再從這個緩存池中讀出數據，由於服務端緩存池大小限制以及網速不均勻等原因，會造成服務端讀取到緩衝池中的數據不完整，就形成了斷包問題，當緩存池大小夠大的情況下又會發生一次讀取到緩存池中的數據多於一個完整的數據包，這種情況因爲無法分清數據包之間的界限，就形成了粘包問題。對於NIO的SocketChannel每次觸發OP_READ事件時，發送端不一定僅僅寫入了一次，同理，發送端如果一次發送數據包過大，那麼發送端的一次寫入也可能會被拆分成兩次OP_READ事件，所以OP_READ事件和發送端的OP_WRITE事件並不是一一對應的。
一、斷包、粘包問題的重現
package org.weir.socket.socketPackage;
import java.io.IOException;
import java.net.InetSocketAddress;
import java.nio.ByteBuffer;
import java.nio.channels.ClosedChannelException;
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 NioSocketClient extends Thread {
private SocketChannel socketChannel;
private Selector selector = null;
private int clientId;
public static void main(String args[]) throws IOException {
NioSocketClient client = new NioSocketClient();
client.initClient();
client.start();
}
public NioSocketClient() {
}
public NioSocketClient(int clientId) {
this.clientId = clientId;
}
public void initClient() throws IOException {
InetSocketAddress inetSocketAddress = new InetSocketAddress(8888);
selector = Selector.open();
socketChannel = SocketChannel.open();
socketChannel.configureBlocking(false);
socketChannel.connect(inetSocketAddress);
synchronized (selector) {
socketChannel.register(selector, SelectionKey.OP_CONNECT);
}
}
public void run() {
while (true) {
try {
int key = selector.select();
if (key > 0) {
Set<SelectionKey> keySet = selector.selectedKeys();
Iterator<SelectionKey> iter = keySet.iterator();
while (iter.hasNext()) {
SelectionKey selectionKey = null;
synchronized (iter) {
selectionKey = iter.next();
iter.remove();
}
if (selectionKey.isConnectable()) {
finishConnect(selectionKey);
}
if (selectionKey.isWritable()) {
send(selectionKey);
}
if (selectionKey.isReadable()) {
read(selectionKey);
}
}
}
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
public void finishConnect(SelectionKey key) {
System.out.println("client finish connect!");
SocketChannel socketChannel = (SocketChannel) key.channel();
try {
socketChannel.finishConnect();
synchronized (selector) {
socketChannel.register(selector, SelectionKey.OP_WRITE);
key.interestOps(SelectionKey.OP_WRITE);
}
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
public void read(SelectionKey key) throws IOException {
SocketChannel channel = (SocketChannel) key.channel();
ByteBuffer byteBuffer = ByteBuffer.allocate(1024);
int len = channel.read(byteBuffer);
if (len > 0) {
byteBuffer.flip();
byte[] byteArray = new byte[byteBuffer.limit()];
byteBuffer.get(byteArray);
System.out.println("client[" + clientId + "]" + "receive from server:");
System.out.println(new String(byteArray));
len = channel.read(byteBuffer);
byteBuffer.clear();
}
key.interestOps(SelectionKey.OP_READ);
}
public void send(SelectionKey key) {
SocketChannel channel = (SocketChannel) key.channel();
// byteBuffer.put(ss.getBytes());
for (int i = 0; i < 10; i++) {
String ss = i + "Server ,how are you? this is package message from NioSocketClient!";
ByteBuffer byteBuffer = ByteBuffer.wrap(ss.getBytes());
System.out.println("[client] send:{" + i + "}-- " + ss);
while (byteBuffer.hasRemaining()) {
try {
channel.write(byteBuffer);
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
// key.interestOps(SelectionKey.OP_READ);
try {
synchronized (selector) {
channel.register(selector, SelectionKey.OP_READ);
}
} catch (ClosedChannelException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
/**
* int到byte[]
*
* @param i
* @return
*/
public static byte[] intToBytes(int value) {
byte[] result = new byte[4];
// 由高位到低位
result[0] = (byte) ((value >> 24) & 0xFF);
result[1] = (byte) ((value >> 16) & 0xFF);
result[2] = (byte) ((value >> 8) & 0xFF);
result[3] = (byte) (value & 0xFF);
return result;
}
}
package org.weir.socket.socketPackage;
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 NioSocketServer extends Thread {
ServerSocketChannel serverSocketChannel = null;
Selector selector = null;
SelectionKey selectionKey = null;
public void initServer() throws IOException {
selector = Selector.open();
serverSocketChannel = ServerSocketChannel.open();
serverSocketChannel.configureBlocking(false);
serverSocketChannel.socket().bind(new InetSocketAddress(8888));
selectionKey = serverSocketChannel.register(selector, SelectionKey.OP_ACCEPT);
}
public void run() {
while (true) {
try {
int selectKey = selector.select();
if (selectKey > 0) {
Set<SelectionKey> keySet = selector.selectedKeys();
Iterator<SelectionKey> iter = keySet.iterator();
while (iter.hasNext()) {
SelectionKey selectionKey = iter.next();
iter.remove();
if (selectionKey.isAcceptable()) {
accept(selectionKey);
}
if (selectionKey.isReadable()) {
read(selectionKey);
}
if (selectionKey.isWritable()) {
// write(selectionKey);
System.out.println();
}
}
}
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
try {
serverSocketChannel.close();
} catch (IOException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
}
}
}
}
public void accept(SelectionKey key) {
try {
ServerSocketChannel serverSocketChannel = (ServerSocketChannel) key.channel();
SocketChannel socketChannel = serverSocketChannel.accept();
System.out.println("is acceptable");
socketChannel.configureBlocking(false);
socketChannel.register(selector, SelectionKey.OP_READ);
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
public void read(SelectionKey selectionKey) {
System.out.println("read事件");
try {
SocketChannel channel = (SocketChannel) selectionKey.channel();
ByteBuffer byteBuffer = ByteBuffer.allocate(100);
int len = channel.read(byteBuffer);
if (len > 0) {
byteBuffer.flip();
byte[] byteArray = new byte[byteBuffer.limit()];
byteBuffer.get(byteArray);
System.out.println("NioSocketServer receive from client:" + new String(byteArray));
}
selectionKey.interestOps(SelectionKey.OP_READ);
selectionKey.interestOps(SelectionKey.OP_READ);
} catch (IOException e) {
// TODO Auto-generated catch block
try {
serverSocketChannel.close();
selectionKey.cancel();
} catch (IOException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
}
e.printStackTrace();
}
}
public void write(SelectionKey selectionKey) {
SocketChannel socketChannel = (SocketChannel) selectionKey.channel();
String httpResponse = "HTTP/1.1 200 OK\r\n" + "Content-Length: 38\r\n" + "Content-Type: text/html\r\n" + "\r\n"
+ "<html><body>Hello World!</body></html>";
System.out.println("response from server to client");
try {
ByteBuffer byteBuffer = ByteBuffer.wrap(httpResponse.getBytes());
while (byteBuffer.hasRemaining()) {
socketChannel.write(byteBuffer);
}
selectionKey.cancel();
} catch (IOException e) {
try {
selectionKey.cancel();
serverSocketChannel.close();
} catch (IOException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
}
// TODO Auto-generated catch block
e.printStackTrace();
}
}
/**
* byte[]轉int
*
* @param bytes
* @return
*/
public static int byteArrayToInt(byte[] bytes) {
int value = 0;
// 由高位到低位
for (int i = 0; i < 4; i++) {
int shift = (4 - 1 - i) * 8;
value += (bytes[i] & 0x000000FF) << shift;// 往高位遊
}
return value;
}
public static void main(String args[]) throws IOException {
NioSocketServer server = new NioSocketServer();
server.initServer();
server.start();
}
}
由於server端的ByteBuffer大小爲100，所以會發生粘包問題，當把server端的ByteBuffer大小改爲50的情況下，運行結果如下
這種情況下就形成了斷包問題，接收到的數據都是不完整的數據
二、斷包、粘包問題的解決
解決思路是在封裝自己的包協議：包=包內容長度(4byte)+包內容
對於粘包問題先讀出包頭即包體長度n，然後再讀取長度爲n的包內容，這樣數據包之間的邊界就清楚了。
對於斷包問題先讀出包頭即包體長度n，由於此次讀取的緩存池長度小於n，這時候就需要先緩存這部分的內容，等待下次read事件來時拼接起來形成完整的數據包。
由於讀取channel數據到ByteBuffer緩存池時ByteBuffer的大小限制，client的一次write事件不一定一一對應server的read事件，所以需要一個全局變量來緩存這部分不完整的數據包。
代碼如下：
package org.weir.socket.socketPackage;
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 NioSocketServer extends Thread {
ServerSocketChannel serverSocketChannel = null;
Selector selector = null;
SelectionKey selectionKey = null;
// 緩存一個read事件中一個不完整的包，以待下次read事件到來時拼接成完整的包
ByteBuffer cacheBuffer = ByteBuffer.allocate(100);
boolean cache = false;
public void initServer() throws IOException {
selector = Selector.open();
serverSocketChannel = ServerSocketChannel.open();
serverSocketChannel.configureBlocking(false);
serverSocketChannel.socket().bind(new InetSocketAddress(8888));
selectionKey = serverSocketChannel.register(selector, SelectionKey.OP_ACCEPT);
}
public void run() {
while (true) {
try {
int selectKey = selector.select();
if (selectKey > 0) {
Set<SelectionKey> keySet = selector.selectedKeys();
Iterator<SelectionKey> iter = keySet.iterator();
while (iter.hasNext()) {
SelectionKey selectionKey = iter.next();
iter.remove();
if (selectionKey.isAcceptable()) {
accept(selectionKey);
}
if (selectionKey.isReadable()) {
read(selectionKey);
}
if (selectionKey.isWritable()) {
// write(selectionKey);
System.out.println();
}
}
}
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
try {
serverSocketChannel.close();
} catch (IOException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
}
}
}
}
public void accept(SelectionKey key) {
try {
ServerSocketChannel serverSocketChannel = (ServerSocketChannel) key.channel();
SocketChannel socketChannel = serverSocketChannel.accept();
System.out.println("is acceptable");
socketChannel.configureBlocking(false);
socketChannel.register(selector, SelectionKey.OP_READ);
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
// 一個client的write事件不一定唯一對應server的read事件，所以需要緩存不完整的包，以便拼接成完整的包
//包協議：包=包頭(4byte)+包體，包頭內容爲包體的數據長度
public void read(SelectionKey selectionKey) {
System.out.println("read事件");
int head_length = 4;//數據包長度
byte[] headByte = new byte[4];
try {
SocketChannel channel = (SocketChannel) selectionKey.channel();
ByteBuffer byteBuffer = ByteBuffer.allocate(100);
int bodyLen = -1;
if (cache) {
cacheBuffer.flip();
byteBuffer.put(cacheBuffer);
}
channel.read(byteBuffer);// 當前read事件
byteBuffer.flip();// write mode to read mode
while (byteBuffer.remaining() > 0) {
if (bodyLen == -1) {// 還沒有讀出包頭，先讀出包頭
if (byteBuffer.remaining() >= head_length) {// 可以讀出包頭，否則緩存
byteBuffer.mark();
byteBuffer.get(headByte);
bodyLen = byteArrayToInt(headByte);
} else {
byteBuffer.reset();
cache = true;
cacheBuffer.clear();
cacheBuffer.put(byteBuffer);
break;
}
} else {// 已經讀出包頭
if (byteBuffer.remaining() >= bodyLen) {// 大於等於一個包，否則緩存
byte[] bodyByte = new byte[bodyLen];
byteBuffer.get(bodyByte, 0, bodyLen);
bodyLen = -1;
System.out.println("receive from clien content is:" + new String(bodyByte));
} else {
byteBuffer.reset();
cacheBuffer.clear();
cacheBuffer.put(byteBuffer);
cache = true;
break;
}
}
}
selectionKey.interestOps(SelectionKey.OP_READ);
} catch (IOException e) {
// TODO Auto-generated catch block
try {
serverSocketChannel.close();
selectionKey.cancel();
} catch (IOException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
}
e.printStackTrace();
}
}
public void write(SelectionKey selectionKey) {
SocketChannel socketChannel = (SocketChannel) selectionKey.channel();
String httpResponse = "HTTP/1.1 200 OK\r\n" + "Content-Length: 38\r\n" + "Content-Type: text/html\r\n" + "\r\n"
+ "<html><body>Hello World!</body></html>";
System.out.println("response from server to client");
try {
ByteBuffer byteBuffer = ByteBuffer.wrap(httpResponse.getBytes());
while (byteBuffer.hasRemaining()) {
socketChannel.write(byteBuffer);
}
selectionKey.cancel();
} catch (IOException e) {
try {
selectionKey.cancel();
serverSocketChannel.close();
} catch (IOException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
}
// TODO Auto-generated catch block
e.printStackTrace();
}
}
/**
* byte[]轉int
*
* @param bytes
* @return
*/
public static int byteArrayToInt(byte[] bytes) {
int value = 0;
// 由高位到低位
for (int i = 0; i < 4; i++) {
int shift = (4 - 1 - i) * 8;
value += (bytes[i] & 0x000000FF) << shift;// 往高位遊
}
return value;
}
public static void main(String args[]) throws IOException {
NioSocketServer server = new NioSocketServer();
server.initServer();
server.start();
}
}
package org.weir.socket.socketPackage;
import java.io.IOException;
import java.net.InetSocketAddress;
import java.nio.ByteBuffer;
import java.nio.channels.ClosedChannelException;
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 NioSocketClient extends Thread {
private SocketChannel socketChannel;
private Selector selector = null;
private int clientId;
public static void main(String args[]) throws IOException {
NioSocketClient client = new NioSocketClient();
client.initClient();
client.start();
}
public NioSocketClient() {
}
public NioSocketClient(int clientId) {
this.clientId = clientId;
}
public void initClient() throws IOException {
InetSocketAddress inetSocketAddress = new InetSocketAddress(8888);
selector = Selector.open();
socketChannel = SocketChannel.open();
socketChannel.configureBlocking(false);
socketChannel.connect(inetSocketAddress);
synchronized (selector) {
socketChannel.register(selector, SelectionKey.OP_CONNECT);
}
}
public void run() {
while (true) {
try {
int key = selector.select();
if (key > 0) {
Set<SelectionKey> keySet = selector.selectedKeys();
Iterator<SelectionKey> iter = keySet.iterator();
while (iter.hasNext()) {
SelectionKey selectionKey = null;
synchronized (iter) {
selectionKey = iter.next();
iter.remove();
}
if (selectionKey.isConnectable()) {
finishConnect(selectionKey);
}
if (selectionKey.isWritable()) {
send(selectionKey);
}
if (selectionKey.isReadable()) {
read(selectionKey);
}
}
}
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
public void finishConnect(SelectionKey key) {
System.out.println("client finish connect!");
SocketChannel socketChannel = (SocketChannel) key.channel();
try {
socketChannel.finishConnect();
synchronized (selector) {
socketChannel.register(selector, SelectionKey.OP_WRITE);
key.interestOps(SelectionKey.OP_WRITE);
}
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
public void read(SelectionKey key) throws IOException {
SocketChannel channel = (SocketChannel) key.channel();
ByteBuffer byteBuffer = ByteBuffer.allocate(1024);
int len = channel.read(byteBuffer);
if (len > 0) {
byteBuffer.flip();
byte[] byteArray = new byte[byteBuffer.limit()];
byteBuffer.get(byteArray);
System.out.println("client[" + clientId + "]" + "receive from server:");
System.out.println(new String(byteArray));
len = channel.read(byteBuffer);
byteBuffer.clear();
}
key.interestOps(SelectionKey.OP_READ);
}
public void send(SelectionKey key) {
SocketChannel channel = (SocketChannel) key.channel();
for (int i = 0; i < 10; i++) {
String ss = i + "Server ,how are you? this is package message from NioSocketClient!";
int head = (ss).getBytes().length;
ByteBuffer byteBuffer = ByteBuffer.allocate(4 + head);
byteBuffer.put(intToBytes(head));
byteBuffer.put(ss.getBytes());
byteBuffer.flip();
System.out.println("[client] send:" + i + "-- " + head + ss);
while (byteBuffer.hasRemaining()) {
try {
channel.write(byteBuffer);
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
// key.interestOps(SelectionKey.OP_READ);
try {
synchronized (selector) {
channel.register(selector, SelectionKey.OP_READ);
}
} catch (ClosedChannelException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
/**
* int到byte[]
*
* @param i
* @return
*/
public static byte[] intToBytes(int value) {
byte[] result = new byte[4];
// 由高位到低位
result[0] = (byte) ((value >> 24) & 0xFF);
result[1] = (byte) ((value >> 16) & 0xFF);
result[2] = (byte) ((value >> 8) & 0xFF);
result[3] = (byte) (value & 0xFF);
return result;
}
}
斷包、粘包問題解決了，接下來寫下關於ByteBuffer這個類的使用。