Java新AIO/NIO2：AsynchronousFileChannel以CompletionHandler方式读

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Java新AIO/NIO2：AsynchronousFileChannel以CompletionHandler方式读

import java.io.BufferedReader;
import java.io.FileInputStream;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.nio.ByteBuffer;
import java.nio.channels.AsynchronousFileChannel;
import java.nio.channels.CompletionHandler;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.nio.file.StandardOpenOption;

public class Test {
	private AsynchronousFileChannel fileChannel;
	private MyCompletionHandler completionHandler;
	private ByteBuffer buffer;

	private final int COUNT = 3;

	public static void main(String[] args) {
		try {
			new Test();
		} catch (Exception e) {
			e.printStackTrace();
		}
	}

	public Test() throws Exception {
		Path path = Paths.get("D:\\code\\file.txt");
		System.out.println("文件路径:" + path);

		fileChannel = AsynchronousFileChannel.open(path, StandardOpenOption.READ);
		buffer = ByteBuffer.allocate(COUNT);
		completionHandler = new MyCompletionHandler();

		long size = fileChannel.size();
		System.out.println("文件长度:" + size);
		System.out.println("文件内容:");
		printer(path.toString());
		System.out.println("==========");

		int pos = 0;
		int i = 0;
		while (pos < size) {
			System.out.println("第" + (++i) + "次读");
			fileChannel.read(buffer, pos, buffer, completionHandler);

			pos = pos + COUNT;

			// 如果不中断while循环若干时间，读出的数据不准、错乱。
			Thread.sleep(5);
		}
	}

	private class MyCompletionHandler implements CompletionHandler<Integer, ByteBuffer> {
		@Override
		public void completed(Integer result, ByteBuffer buf) {
			System.out.println("读取数据长度:" + result + ",内容:" + new String(buf.array(), 0, result));
			buf.clear();
		}

		@Override
		public void failed(Throwable t, ByteBuffer attachment) {
			t.printStackTrace();
		}
	}

	// 打印path指向的文件中的内容。
	private void printer(String path) throws Exception {
		InputStream is = new FileInputStream(path);
		BufferedReader reader = new BufferedReader(new InputStreamReader(is));
		String str = null;
		while (true) {
			str = reader.readLine();
			if (str != null)
				System.out.println(str);
			else
				break;
		}

		is.close();
	}
}

输出：

文件路径:D:\code\file.txt
文件长度:10
文件内容:
0123456789
==========
第1次读
读取数据长度:3,内容:012
第2次读
读取数据长度:3,内容:345
第3次读
读取数据长度:3,内容:678
第4次读
读取数据长度:1,内容:9