java中讲讲BufferedInputStream的用法

BufferedInputStream的用法
马克-to-win：BufferedInputStream 顾名思义就是它有一个内部的buffer（缓存），它的read方法表面上看，虽然是只读了一个字节，但它是开始时猛然从硬盘读入一大堆字节到自己的缓存，当你read时，它是从缓存读进一个字节到内存。而前面讲的FileInputStream字节流，read时，都是真正每个字节都从硬盘到内存，是很慢的。为什么？请研究硬盘的结构！下面的两个例子，一个是FileInputStream的read生读进来的，另一个是BufferedInputStream的只能read，你比较一下读的时间，差距蛮大的！马克- to-win：马克 java社区：防盗版实名手机尾号： 73203。

例：2.3.1

import java.io.*;
public class TestMark_to_win {
    public static void main(String args[]) throws FileNotFoundException,
            IOException {
        FileInputStream fis = new FileInputStream("c:/2.txt");
        long t = System.currentTimeMillis();
        int c;
        while ((c = fis.read()) != -1) {}
        fis.close();
        t = System.currentTimeMillis() - t;
        System.out.println("遍历文件用了如下时间:" + t);
    }
}
结果是：

遍历文件用了如下时间:453

例：2.3.2

import java.io.*;
public class TestMark_to_win {
    public static void main(String args[]) throws FileNotFoundException,
            IOException {
        FileInputStream fis = new FileInputStream("i:\\2.txt");
        BufferedInputStream bis = new BufferedInputStream(fis);
        long t = System.currentTimeMillis();
        int c;
        /*even though the next read() also read one byte, but because
BufferedInputStream has an internal buffer,when first time to read,
it will read in a whole buffer of byte from hard disk, then digest
these bytes one by one in memory */
        while ((c = bis.read()) != -1) {}
        fis.close();
        t = System.currentTimeMillis() - t;
        System.out.println("遍历文件用了如下时间:" + t);
    }
}
结果是：
遍历文件用了如下时间:16


下面的例子讲述BufferedInputStream的read(byte b[], int off, int len)的用法。即真正的批量读入。正好前面讲到BufferedOutputStream时，还欠大家一个例子。

例：2.3.3 

import java.io.*;
public class TestMark_to_win {
    public static void main(String[] args) {
        String source = "c:\\2.txt";
        String dest = "c:\\2_copy.txt";
        try {
            FileInputStream fis = new FileInputStream(source);
            BufferedInputStream bis = new BufferedInputStream(fis);
            FileOutputStream fos = new FileOutputStream(dest);
            BufferedOutputStream bos = new BufferedOutputStream(fos);
            int readcount;
            byte[] readbyte = new byte[256];
            /* public synchronized int read(byte b[], int off, int len) Reads
bytes from this byte-input stream into the specified byte array,
starting at the given offset.
@param b destination buffer.
@param off offset at which to start storing bytes.
@param len maximum number of bytes to read.
@return the number of bytes read, or <code>-1</code> if the end
of the stream has been reached.
@exception IOException if an I/O error occurs.*/
            while ((readcount = bis.read(readbyte, 0, readbyte.length)) != -1) {
                bos.write(readbyte, 0, readcount);
            }
            bis.close();
            bos.close();
            System.out.println("复制完毕！");
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

结果是：

复制完毕！