Channel应用实例FileChannel

不念不忘少年蓝@ 2022-09-02 00:58 108阅读 0赞

FileChannel用于对文件数据进行读写。

**从缓冲区写入到通道**

通过FileChannel将内存中的数据写入到文件，其实现过程：首先创建ByteBuffer缓冲区，因为通道是和缓冲区交互的；将内存中数据写入到缓冲区；将缓冲区中的数据写入到通道；

package com.tech.netty.nio;
    
    import java.io.FileNotFoundException;
    import java.io.FileOutputStream;
    import java.io.IOException;
    import java.nio.ByteBuffer;
    import java.nio.channels.FileChannel;
    
    /**
     * @author lw
     * @since 2021/7/29
     **/
    public class NioFileChannel {
        public static void main(String[] args) throws IOException {
            String str="hello word";
            FileOutputStream fileOutputStream = new FileOutputStream("d://testfile.txt");
            FileChannel channel = fileOutputStream.getChannel();
            ByteBuffer byteBuffer = ByteBuffer.allocate(1024);
            byteBuffer.put(str.getBytes());
            //重置position
            byteBuffer.flip();
            channel.write(byteBuffer);
            fileOutputStream.close();
        }
    }

**从通道读取到缓冲区**

读取文件中的数据到通道，将通道中的数据读取到缓冲区，输出缓冲区数组中的数据。

package com.tech.netty.nio;
    
    import java.io.File;
    import java.io.FileInputStream;
    import java.io.IOException;
    import java.nio.ByteBuffer;
    import java.nio.channels.FileChannel;
    
    /**
     * @author lw
     * @since 2021/7/29
     **/
    public class NIOFileChannelRead {
        public static void main(String[] args) throws IOException {
            File file = new File("d://testfile.txt");
            FileInputStream fileInputStream = new FileInputStream(file);
            FileChannel channel = fileInputStream.getChannel();
            ByteBuffer byteBuffer = ByteBuffer.allocate((int) file.length());
            channel.read(byteBuffer);
            System.out.println(new String(byteBuffer.array()));
            fileInputStream.close();
        }
    }

**复制文件**

将文件中的数据从通道读取到缓冲区，再从缓冲区写入到另外一个文件的通道，实现复制

package com.tech.netty.nio;
    
    import java.io.FileInputStream;
    import java.io.FileNotFoundException;
    import java.io.FileOutputStream;
    import java.io.IOException;
    import java.nio.ByteBuffer;
    import java.nio.channels.FileChannel;
    
    /**
     * @author lw
     * @since 2021/7/29
     **/
    public class NIOFileChannelReadWrite {
        public static void main(String[] args) throws IOException {
            FileInputStream fileInputStream = new FileInputStream("1.txt");
            FileChannel channelIn = fileInputStream.getChannel();
    
            FileOutputStream fileOutputStream = new FileOutputStream("2.txt");
            FileChannel channelOut = fileOutputStream.getChannel();
    
            ByteBuffer byteBuffer = ByteBuffer.allocate(512);
    
            while(true){
                byteBuffer.clear();
                int read = channelIn.read(byteBuffer);
                System.out.println("read="+read);
                if(read==-1){
                    break;
                }
                byteBuffer.flip();
                channelOut.write(byteBuffer);
            }
            fileInputStream.close();
            fileOutputStream.close();
        }
    }

**使用通道的transferFrom拷贝文件**

使用transferFrom将一个通过的数据拷贝到另外一个通道，实现文件复制。

package com.tech.netty.nio;
    
    import java.io.FileInputStream;
    import java.io.FileOutputStream;
    import java.io.IOException;
    import java.nio.channels.FileChannel;
    
    /**
     * @author lw
     * @since 2021/7/29
     **/
    public class NioFileChannelTransferFrom {
        public static void main(String[] args) throws IOException {
            FileInputStream fileInputStream = new FileInputStream("d://a.png");
            FileOutputStream fileOutputStream = new FileOutputStream("d://b.png");
            FileChannel channelIn = fileInputStream.getChannel();
            FileChannel channelOut = fileOutputStream.getChannel();
            channelOut.transferFrom(channelIn,0,channelIn.size());
    
            channelIn.close();
            channelOut.close();
            fileInputStream.close();
            fileOutputStream.close();
    
        }
    }