Java有缓冲与无缓冲读写效率对比

最新推荐文章于 2023-01-12 00:31:37 发布

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最新推荐文章于 2023-01-12 00:31:37 发布

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分类专栏： Java Demo

本文链接：https://blog.youkuaiyun.com/darkLight2017/article/details/119786870

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将1~100000整数写入（读取）out.txt文件中，记录不同写入方式的运行时间

一、无缓冲写

public class Main {
    public static void main(String[] args) throws Exception {
        FileOutputStream fos = new FileOutputStream("D:\\out.txt");
        long start = System.currentTimeMillis();
        for (int i = 0; i < 1e6; ++i) {
            fos.write(i);
        }
        fos.close();
        long end = System.currentTimeMillis();
        System.out.println("time = " + (end - start) + "ms");
    }
}

用时：2053ms

二、有缓冲写

BufferedOutputStream提供了一个byte数组作为缓冲区，默认大小为8KB。缓冲区写满后才会真正地写入磁盘。

public class Main {
    public static void main(String[] args) throws Exception {
        BufferedOutputStream fos = new BufferedOutputStream(new FileOutputStream("D:\\out.txt"));
        long start = System.currentTimeMillis();
        for (int i = 1; i <= 1e6; ++i) {
            fos.write(i);
        }
        fos.flush();
        fos.close();
        long end = System.currentTimeMillis();
        System.out.println("time = " + (end - start) + "ms");
    }
}

用时：53ms

在创建BufferedOutputStream对象时也可以指定缓冲区大小，当指定为1时，又变为了无缓冲写。

public class Main {
    public static void main(String[] args) throws Exception {
        BufferedOutputStream fos = new BufferedOutputStream(new FileOutputStream("D:\\out.txt"), 1);
        long start = System.currentTimeMillis();
        for (int i = 1; i <= 1e6; ++i) {
            fos.write(i);
        }
        fos.flush();
        fos.close();
        long end = System.currentTimeMillis();
        System.out.println("time = " + (end - start) + "ms");
    }
}

用时：2117ms

三、无缓冲读

public class Main {
    public static void main(String[] args) throws Exception {
        FileInputStream fis = new FileInputStream("D:\\out.txt");
        int b = 0;
        long start = System.currentTimeMillis();
        while ((b = fis.read()) != -1);
        fis.close();
        long end = System.currentTimeMillis();
        System.out.println("time = " + (end - start) + "ms");
    }
}

用时：1757ms

四、有缓冲读

public class Main {
    public static void main(String[] args) throws Exception {
        BufferedInputStream fis = new BufferedInputStream(new FileInputStream("D:\\out.txt"));
        int b = 0;
        long start = System.currentTimeMillis();
        while ((b = fis.read()) != -1);
        fis.close();
        long end = System.currentTimeMillis();
        System.out.println("time = " + (end - start) + "ms");
    }
}

用时：19ms