Java

Java NIO-AsynchronousFileChannel

Java NIO 异步文件通道，原文地址：http://tutorials.jenkov.com/java-nio/asynchronousfilechannel.html

Java 7 NIO 中添加了 AsynchronousFileChannel。通过 AsynchronousFileChannel，我们可以异步地从文件中读写数据。本教程将会解释 AsynchronousFileChannel 的用法。

创建异步文件通道

创建异步文件通道的语法：

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Path path = Paths.get("data/test.xml");
AsynchronousFileChannel fileChannel = AsynchronousFileChannel.open(path, StandardOpenOption.READ);

读取数据

通过 AsynchronousFileChannel 读取数据有两种方式，下面我们慢慢叙来。

Reading Data Via a Future

用法如下：

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AsynchronousFileChannel fileChannel = AsynchronousFileChannel.open(path, StandardOpenOption.READ);
ByteBuffer buffer = ByteBuffer.allocate(1024);
long position = 0;
Future<Integer> operation = fileChannel.read(buffer, position);
while(!operation.isDone());
buffer.flip();
byte[] data = new byte[buffer.limit()];
buffer.get(data);
System.out.println(new String(data));
buffer.clear();

Reading Data Via a CompletionHandler

用法：

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

写入数据

和读取数据一样，写入数据也有两种形式，下面我们一一道来。

Writing Data Via a Future

用法如下：

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Path path = Paths.get("data/test-write.txt");
AsynchronousFileChannel fileChannel = AsynchronousFileChannel.open(path, StandardOpenOption.WRITE);
ByteBuffer buffer = ByteBuffer.allocate(1024);
long position = 0;
buffer.put("test data".getBytes());
buffer.flip();
Future<Integer> operation = fileChannel.write(buffer, position);
buffer.clear();
while(!operation.isDone());
System.out.println("Write Done.");

Writing Data Via a CompletionHandler

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Path path = Paths.get("data/test-write.txt");
if(!Files.exists(path)) {
    Files.createFile(path);
}
AsynchronousFileChannel fileChannel = AsynchronousFileChannel.oepn(path, StandardOpenOption.WRITE);
ByteBuffer buffer = ByteBuffer.allocate(1024);
long position = 0;
buffer.put("test data".getBytes());
buffer.flip();
fileChannel.write(buffer, position, buffer, new CompletionHandler<Integer, ByteBuffer>(){
    @Override
    public void completed(Integer result, ByteBuffer attachment){
        System.out.println("bytes written: " + result);
    } 
    @Override
    public void failed(Throwable exc, ByteBuffer attachment){
        System.out.println("Write failed");
        exc.printStackTrace();
    }
});

至此，Java NIO 教程十七篇终于看完了。。。接下来要赶紧把《Tomcat 权威指南》和《深入剖析Tomcat》看完了！