编辑“︁Java异步IO（Java Asynchronous I O）”︁（章节）

== 核心机制 ==  

=== 1. 回调机制（CompletionHandler） ===  
异步IO操作完成后，系统会自动调用注册的`CompletionHandler`，处理成功或失败的结果。  

<syntaxhighlight lang="java">  
import java.nio.ByteBuffer;  
import java.nio.channels.AsynchronousFileChannel;  
import java.nio.file.Path;  
import java.nio.file.StandardOpenOption;  
import java.util.concurrent.Future;  

public class AsyncIOExample {  
    public static void main(String[] args) throws Exception {  
        Path path = Path.of("test.txt");  
        AsynchronousFileChannel fileChannel = AsynchronousFileChannel.open(  
            path, StandardOpenOption.READ);  

        ByteBuffer buffer = ByteBuffer.allocate(1024);  
        long position = 0;  

        fileChannel.read(buffer, position, buffer, new CompletionHandler<Integer, ByteBuffer>() {  
            @Override  
            public void completed(Integer result, ByteBuffer attachment) {  
                System.out.println("Read " + result + " bytes");  
                attachment.flip();  
                byte[] data = new byte[attachment.limit()];  
                attachment.get(data);  
                System.out.println(new String(data));  
            }  

            @Override  
            public void failed(Throwable exc, ByteBuffer attachment) {  
                System.err.println("Error: " + exc.getMessage());  
            }  
        });  

        System.out.println("继续执行其他任务...");  
        Thread.sleep(1000); // 等待异步操作完成  
    }  
}  
</syntaxhighlight>  

'''输出示例'''：  
<pre>  
继续执行其他任务...  
Read 45 bytes  
Hello, this is a test file for Java AIO.  
</pre>  

=== 2. Future机制 ===  
异步操作返回一个`Future`对象，可通过`Future.get()`阻塞等待结果，或轮询检查状态。  

<syntaxhighlight lang="java">  
Future<Integer> future = fileChannel.read(buffer, position);  
// 非阻塞检查  
if (future.isDone()) {  
    int bytesRead = future.get();  
    System.out.println("Read " + bytesRead + " bytes");  
}  
</syntaxhighlight>