Java IO学习笔记七：多路复用从单线程到多线程

发布时间：2023-04-17 11:40:04 所属栏目：教程来源：

导读： public void readHandler(SelectionKey key) {
SocketChannel client = (SocketChannel) key.channel();
ByteBuffer buffer = (ByteBuffer) key.attachment();
buffer.clear();

public void readHandler(SelectionKey key) {
SocketChannel client = (SocketChannel) key.channel();
ByteBuffer buffer = (ByteBuffer) key.attachment();
buffer.clear();
int read;
try {
while (true) {
read = client.read(buffer);
if (read > 0) {
buffer.flip();
while (buffer.hasRemaining()) {
client.write(buffer);
}
buffer.clear();
} else if (read == 0) {
break;
} else {
client.close();
break;
}
}
} catch (IOException e) {
e.printstacktrace();
}
}
为了权责清晰一些，我们分开了两个事件处理：

Set<SelectionKey> selectionKeys = selector.selectedKeys();
Iterator<SelectionKey> iter = selectionKeys.iterator();
while (iter.hasNext()) {
SelectionKey key = iter.next();
iter.remove();
if (key.isAcceptable()) {
acceptHandler(key);
} else if (key.isReadable()) {
// 处理读数据
readHandler(key);
} else if (key.isWritable()) {
// 处理写数据
writeHandler(key);
}
}
一个负责写，一个负责读

读的事件处理, 如下代码

public void readHandler(SelectionKey key) {
System.out.println("read handler.....");
SocketChannel client = (SocketChannel) key.channel();
ByteBuffer buffer = (ByteBuffer) key.attachment();
buffer.clear();
int read = 0;
try {
while (true) {
read = client.read(buffer);
if (read > 0) {
client.register(key.selector(), SelectionKey.OP_WRITE, buffer);
} else if (read == 0) {
break;
} else {
client.close();
break;
}
}
} catch (IOException e) {
e.printstacktrace();
}
}
其中read > 0 即从客户端读取到了数据，我们才注册一个写事件：

client.register(key.selector(), SelectionKey.OP_WRITE, buffer);
其他事件不注册写事件。（PS：只要send-queue没有满，就可以注册写事件）

写事件的处理逻辑如下：

private void writeHandler(SelectionKey key) {
System.out.println("write handler...");
SocketChannel client = (SocketChannel) key.channel();
ByteBuffer buffer = (ByteBuffer) key.attachment();
buffer.flip();
while (buffer.hasRemaining()) {
try {
client.write(buffer);
} catch (IOException e) {
e.printstacktrace();
}
}
buffer.clear();
key.cancel();
try {
client.close();
} catch (IOException e) {
e.printstacktrace();
}
}

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