Java新AIO/NIO2：AsynchronousFileChannel以CompletionHandler方式读

红太狼 2024-02-19 18:14 36阅读 0赞

## 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