标签：trace pen flip void java7 exception and write locate
https://www.cnblogs.com/lay2017/p/12901123.html
在Java7的时候，加入了AsynchronousFileChannel，使得你可以进行异步地read或write操作。本文关于如何使用AsynchronousFileChannel。
Path path = Paths.get("data/test.xml");
AsynchronousFileChannel fileChannel = AsynchronousFileChannel.open(path, StandardOpenOption.READ);
读取数据有两种方式
通过read获取Future，read方法会立即返回
Future<Integer> operation = fileChannel.read(buffer, 0);
下面是一个完整示例
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();
示例中read直接返回了Future，通过Future不断轮询是否完成。完成以后，数据已经进入buffer。再从buffer读取数据并打印
除了通过Future主动轮询之外，还可以通过CompletionHandler接口的回调处理，示例代码如下
fileChannel.read(buffer, position, buffer, new CompletionHandler<Integer, ByteBuffer>() { @Override 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) { } });
我们看到，completed在正常回调的时候触发。failed回调在失败的时候触发
与读取数据类似，写入数据同样支持两种方式
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");
写入数据要注意file必须存在，否则会抛出NoSuchFileException。你可以这样创建文件
if(!Files.exists(path)){ Files.createFile(path); }
Path path = Paths.get("data/test-write.txt");
if(!Files.exists(path)){
Files.createFile(path);
}
AsynchronousFileChannel fileChannel = AsynchronousFileChannel.open(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();
}
});
和read类似，write正常结束会回调completed，失败回调failed。
十七、Java NIO AsynchronousFileChannel
标签：trace pen flip void java7 exception and write locate
原文地址：https://www.cnblogs.com/lay2017/p/12916545.html
