Channel与Buffer

Buffer简析

写模式

读模式

都读完：

读完了，想变成写模式，调用clear()函数
position到最开始的位置，limit到capacity位置

只读取一部分数据：

但是我又想回到写模式，这时候就调用compact()函数

Channel简析

代码演示几种拷贝文件的方法

import java.io.*;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;
interface FileCopyRunner{
    void copyFile(File source, File target);
}
public class FileCopyDemo {
    private static final int ROUNDS = 5;
    private static void benchmark(FileCopyRunner test,File source, File target){
        long elapsed = 0L;
        for (int i =0; i < ROUNDS; i++){
            long startTime = System.currentTimeMillis();
            test.copyFile(source,target);
            elapsed += System.currentTimeMillis() - startTime;
            target.delete();
        }
        System.out.println(test + ": " + elapsed / ROUNDS);
    }
    private static void close(Closeable closeable){
        if (closeable != null){
            try {
                closeable.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
    public static void main(String[] args) {
        FileCopyRunner noBufferStreamCopy = new FileCopyRunner() {
            @Override
            public void copyFile(File source, File target) {
                InputStream fin = null;
                OutputStream fout = null;
                try {
                    fin = new FileInputStream(source);
                    fout = new FileOutputStream(target);
                    int result;
                    while ((result = fin.read()) != -1){
                        fout.write(result);
                    }
                } catch (FileNotFoundException e) {
                    e.printStackTrace();
                } catch (IOException e) {
                    e.printStackTrace();
                }finally {
                    close(fin);
                    close(fout);
                }
            }
            @Override
            public String toString() {
                return "noBufferStreamCopy";
            }
        };
        FileCopyRunner bufferedStreamCopy = new FileCopyRunner() {
            @Override
            public void copyFile(File source, File target) {
                InputStream fin = null;
                OutputStream fout = null;
                try {
                    fin = new BufferedInputStream(new FileInputStream(source));
                    fout = new BufferedOutputStream(new FileOutputStream(target));
                    byte[] buffer = new byte[1024];
                    int result;
                    while ((result = fin.read(buffer)) != -1){
                        fout.write(buffer,0, result);
                    }
                } catch (FileNotFoundException e) {
                    e.printStackTrace();
                } catch (IOException e) {
                    e.printStackTrace();
                }finally {
                    close(fin);
                    close(fout);
                }
            }
            @Override
            public String toString() {
                return "bufferedStreamCopy";
            }
        };
        FileCopyRunner nioBufferCopy = new FileCopyRunner() {
            @Override
            public void copyFile(File source, File target) {
                FileChannel fin = null;
                FileChannel fout = null;
                try {
                    fin = new FileInputStream(source).getChannel();
                    fout = new FileOutputStream(target).getChannel();
                    ByteBuffer buffer = ByteBuffer.allocate(1024);
                    while ((fin.read(buffer)) != -1){
                        buffer.flip();
                        while (buffer.hasRemaining()){
                            fout.write(buffer);
                        }
                        buffer.clear();
                    }
                } catch (FileNotFoundException e) {
                    e.printStackTrace();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            @Override
            public String toString() {
                return "nioBufferCopy";
            }
        };
        FileCopyRunner nioTransferCopy = new FileCopyRunner() {
            @Override
            public void copyFile(File source, File target) {
                FileChannel fin = null;
                FileChannel fout = null;
                try {
                    fin = new FileInputStream(source).getChannel();
                    fout = new FileOutputStream(target).getChannel();
                    long transferred = 0L;
                    long size = fin.size();
                    while (transferred != fin.size()){
                      transferred += fin.transferTo(0, size, fout);
                    }
                } catch (FileNotFoundException e) {
                    e.printStackTrace();
                } catch (IOException e) {
                    e.printStackTrace();
                }finally {
                    close(fin);
                    close(fout);
                }
            }
            @Override
            public String toString() {
                return "nioTransferCopy";
            }
        };
    }
}