Java新AIO/NIO2：AsynchronousFileChannel以Future方式读

男娘i 2024-02-19 17:41 0阅读 0赞

假设现在有一个文件file.txt。里面有10个字符串文本：0123456789。为了完整说明BufferByte和AsynchronousFileChannel的读，故意设置ByteBuffer只有4字节。这样导致AsynchronousFileChannel一次性读取到缓冲器读不完，需要多次读写。

import java.nio.ByteBuffer;
    import java.nio.channels.AsynchronousFileChannel;
    import java.nio.file.Path;
    import java.nio.file.Paths;
    import java.nio.file.StandardOpenOption;
    import java.util.concurrent.Future;
    
    
    public class Test {
    	public static void main(String[] args) throws Exception {
    		Path path = Paths.get("D:\\code\\file.txt");
    		System.out.println(path);
    
    		AsynchronousFileChannel fileChannel = AsynchronousFileChannel.open(path, StandardOpenOption.READ);
    
    		ByteBuffer buffer = ByteBuffer.allocate(4);
    
    		long size = fileChannel.size();
    
    		int pos = 0, count = 0;
    		while (pos < size) {
    			count = read(fileChannel, buffer, pos);
    			pos = pos + count;
    		}
    	}
    
    	private static int read(AsynchronousFileChannel fileChannel, ByteBuffer buffer, int pos) throws Exception {
    		Future<Integer> operation = fileChannel.read(buffer, pos);
    		while (!operation.isDone()) {
    			//不粗暴抢占CPU。
    			Thread.sleep(1);
    		}
    
    		int count = 0;
    
    		count = operation.get();
    		System.out.println("读取数量:" + count);
    
    		buffer.flip();
    		System.out.println("数据内容:"+new String(buffer.array(), 0, count));
    		buffer.clear();
    
    		return count;
    	}
    }

输出：

D:\code\file.txt
    读取数量:4
    数据内容:0123
    读取数量:4
    数据内容:4567
    读取数量:2
    数据内容:89