IO流 檔案注意四點

1、快取小，快取就是每次給流分配陣列大小，快取可以看做是一輛一輛卡車運輸貨物。byte[1024] = 1kb;
2、每次快取讀多少，寫入到磁碟就多少，不要有空的寫入。
3、快取完了之後需要強制flush到磁碟
4、一定要關閉流：關閉流可以在try裡面，也可以在finally裡面關閉

package javacore;

import java.io.*;

/**
 * @author lixw
 * @date created in 22:10 2018/12/17
 */
public class FileReader {
    public static
 
 void main(String[] args) {
        //readText();
//        writeTxt();

        long start = System.currentTimeMillis();
        String source = "F:\\BaiduNetdiskDownload\\video\\01課程回顧__rec.avi";
        String target = "F:\\BaiduNetdiskDownload\\video\\01課程回顧__rec_copy.avi";
        try(InputStream is =
 
 new FileInputStream(source);
             OutputStream os = new FileOutputStream(target)) {
            System.out.println(is.available()/1024/1024);
            //8G -> 6G
            //1.快取要小(相對磁碟)
            byte[] buff = new byte[1024 * 512];
            int len = 0;
            while ((len = is.read
 
(buff)) != -1){
                //2.讀多少 寫多少
                os.write(buff,0,len);
            }
            //3.flush到磁碟
            os.flush();
        } catch (IOException e) {
            e.printStackTrace();
        }

        System.out.println(System.currentTimeMillis() - start);
    }

    private static void writeTxt() {
        //字元流
        String target = "C:\\Users\\li\\Desktop\\ArrayTest.java";
        BufferedWriter writer = null;
        FileWriter fw = null;
        try {
            fw = new FileWriter(target);
            writer = new BufferedWriter(fw);
            writer.append("222");
            //記憶體中重新整理到磁碟
            writer.flush();
        } catch (IOException e) {
            e.printStackTrace();
        }finally {
            if (fw!=null){
                try {
                    fw.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if (writer!=null){
                try {
                    writer.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }

    private static void readText() {
        InputStream is = null;
        String filePath = "D:\\eclipse x64\\mymaven\\src\\main\\java\\javacore\\ArrayTest.java";
        //包裝類
        BufferedReader reader = null;
        java.io.FileReader fileReader = null;
        try {
            fileReader = new java.io.FileReader(filePath);
            reader = new BufferedReader(fileReader);
            String s = reader.readLine();
            while (s != null){
                System.out.println(s);
                s = reader.readLine();
            }
        } catch (IOException e) {
            e.printStackTrace();
        }finally {
            //！！！使用之後關閉流
            //關閉之前先判空
            if (fileReader!=null){
                try {
                    fileReader.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if (reader !=null){
                try {
                    reader.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }
}