Java NIO FileChannel读写复制文件

Love The Way You Lie 2024-02-19 18:29 71阅读 0赞

import java.io.BufferedReader;
    import java.io.FileInputStream;
    import java.io.FileOutputStream;
    import java.io.InputStream;
    import java.io.InputStreamReader;
    import java.io.RandomAccessFile;
    import java.nio.ByteBuffer;
    import java.nio.channels.FileChannel;
    
    public class FileTest {
    	public static void main(String[] args) {
    		try {
    			new FileTest();
    		} catch (Exception e) {
    			e.printStackTrace();
    		}
    	}
    
    	public FileTest() throws Exception {
    		String pathIn = "D:/code/file.txt";
    		String pathOut = "D:/code/copy.txt";
    
    		FileChannel fcIn = new RandomAccessFile(pathIn, "rw").getChannel();
    		System.out.println("源文件总长度:" + fcIn.size());
    
    		System.out.println("源文件全部内容:");
    		printer(pathIn);
    
    		FileChannel fcOut = new FileOutputStream(pathOut).getChannel();
    
    		final int capacity = 4;
    		ByteBuffer buffer = ByteBuffer.allocate(capacity);
    
    		int count = 0;
    		while (true) {
    			count = fcIn.read(buffer);
    			if (count == -1) {
    				break;
    			}
    
    			buffer.flip();
    			fcOut.write(buffer);
    			buffer.clear();
    		}
    
    		System.out.println("复制文件总长度:" + fcOut.size());
    		System.out.println("复制文件全部内容:");
    		printer(pathOut);
    	}
    
    	// 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 br = new BufferedReader(new InputStreamReader(is));
    		String s = null;
    		while (true) {
    			s = br.readLine();
    			if (s != null)
    				System.out.println(s);
    			else
    				break;
    		}
    
    		br.close();
    		is.close();
    	}
    }

运行后输出：

源文件总长度:10
    源文件全部内容:
    0123456789
    复制文件总长度:10
    复制文件全部内容:
    0123456789

上面是常规的文件复制，包含对源文件的读，以及把读出来的文件写入到目标复制文件。在Java NIO中，用FileChannel复制文件有更简单的方案，一行代码实现，如下：

import java.io.BufferedReader;
    import java.io.FileInputStream;
    import java.io.FileOutputStream;
    import java.io.InputStream;
    import java.io.InputStreamReader;
    import java.io.RandomAccessFile;
    import java.nio.channels.FileChannel;
    
    public class FileTest {
    	public static void main(String[] args) {
    		try {
    			new FileTest();
    		} catch (Exception e) {
    			e.printStackTrace();
    		}
    	}
    
    	public FileTest() throws Exception {
    		String pathIn = "D:/code/file.txt";
    		String pathOut = "D:/code/copy.txt";
    
    		FileChannel fcIn = new RandomAccessFile(pathIn, "rw").getChannel();
    		System.out.println("源文件总长度:" + fcIn.size());
    
    		System.out.println("源文件全部内容:");
    		printer(pathIn);
    
    		FileChannel fcOut = new FileOutputStream(pathOut).getChannel();
    
    		// FileChannel方式的复制，一行代码实现。
    		fcIn.transferTo(0, fcIn.size(), fcOut);
    
    		System.out.println("复制文件总长度:" + fcOut.size());
    		System.out.println("复制文件全部内容:");
    		printer(pathOut);
    	}
    
    	// 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 br = new BufferedReader(new InputStreamReader(is));
    		String s = null;
    		while (true) {
    			s = br.readLine();
    			if (s != null)
    				System.out.println(s);
    			else
    				break;
    		}
    
    		br.close();
    		is.close();
    	}
    }