一.非阻塞
1.非阻塞:線程執行方法時,如果操作沒有就緒,就立即返回,不會一直等待操作就緒
2.java.nio提供非阻塞通信的類:
1)ServerSocketChannel:代替Server
2)SocketChannel:代替Socket
3)Selector:監控就緒事件
4)SelectionKey:註冊事件的句柄
3.服務器端程序使用多線程處理阻塞IO,雖然可以響應多用戶,但是存在侷限性
1)JVM會給每個線程分配獨立的資源,線程越多,系統開銷越大
2)容易造成死鎖
3)需要頻繁轉讓CPU使用
4.完成多個任務可以使用多線程分別處理,也可以讓單個線程以輪詢的工作方式處理就緒的任務
二.創建非阻塞服務器端程序
對於服務區端造成阻塞的原因有:
1)客戶端的連接
2)接收客戶端的數據
3)響應客戶端的數據
所以,可以在主線程中分別監控這些任務,當有任何一個就緒就執行
public class nio_demo2 {
private Selector selector = null;
private ServerSocketChannel serverSocketChannel = null;
private int port = 6666;
private Charset charset = Charset.forName("UTF-8");
public nio_demo2() throws IOException {
selector = Selector.open();
serverSocketChannel = ServerSocketChannel.open();
serverSocketChannel.socket().setReuseAddress(true);
serverSocketChannel.configureBlocking(false);
serverSocketChannel.socket().bind(new InetSocketAddress(port));
System.out.println("server start...");
}
public void service() throws IOException {
serverSocketChannel.register(selector, SelectionKey.OP_ACCEPT);
//select():監控註冊的channel,當有需要處理的IO時,將對應的selectionKey加入到selected-key集合
while(selector.select()>0){
Set readyKey = selector.selectedKeys();
Iterator it = readyKey.iterator();
while(it.hasNext()){
SelectionKey key = null;
try{
key = (SelectionKey)it.next();
it.remove();
if(key.isAcceptable()){
ServerSocketChannel ssc = (ServerSocketChannel)key.channel();
SocketChannel socketChannel = ssc.accept();
System.out.println("client connection" +
socketChannel.socket().getInetAddress()+":"
+socketChannel.socket().getPort());
//設置爲非阻塞
socketChannel.configureBlocking(false);
ByteBuffer buffer = ByteBuffer.allocate(1024);
//向selecctor註冊讀就緒事件和寫就緒時件,同時關聯buffer
socketChannel.register(selector,
SelectionKey.OP_READ|SelectionKey.OP_WRITE,buffer);
}
if(key.isReadable()){
receive(key);
}
if(key.isWritable()){
send(key);
}
}catch (IOException e){
e.printStackTrace();
try{
if(key!=null){
key.cancel();
key.channel().close();
}
}catch(Exception ex){
ex.printStackTrace();
}
}
}
}
}
//發送,處理寫就緒事件
public void send(SelectionKey key) throws IOException {
//獲得關聯的附件
ByteBuffer buffer = (ByteBuffer)key.attachment();
SocketChannel socketChannel = (SocketChannel)key.channel();
buffer.flip();
String data = decode(buffer);
if(data.indexOf("\n")==-1){
return;
}
String outputData = data.substring(0,data.indexOf("\n")+1);
System.out.println(outputData);
ByteBuffer outputBuffer = encode("echo:"+outputData);
//發送一行數據
while(outputBuffer.hasRemaining()){
socketChannel.write(outputBuffer);
}
//刪除已處理數據(讀寫操作同一個ByteBuffer)
ByteBuffer temp = encode(outputData);
buffer.position(temp.limit());
buffer.compact();
if(outputData.equals("end\n")){
key.cancel();
socketChannel.close();
System.out.println("close coonnection");
}
}
//接收,處理讀就緒事件
public void receive(SelectionKey key) throws IOException {
//獲取關聯的buffer
ByteBuffer buffer = (ByteBuffer)key.attachment();
//獲取關聯的channel
SocketChannel socketChannel = (SocketChannel)key.channel();
ByteBuffer readBuffer = ByteBuffer.allocate(32);
socketChannel.read(readBuffer);
//flip:將極限設置爲位置,將位置設置爲0
readBuffer.flip();
buffer.limit(buffer.capacity());
buffer.put(readBuffer);
}
//解碼
public String decode(ByteBuffer buffer){
CharBuffer charBuffer = charset.decode(buffer);
return charBuffer.toString();
}
//編碼
public ByteBuffer encode(String str){
return charset.encode(str);
}
public static void main(String[] args) throws IOException {
nio_demo2 server = new nio_demo2();
server.service();
}
}