万恶的javaeye，编辑器能不能优化下，每次修改样式都变形了。
FileInputStream 属于数据源
BufferedInputStream 属于FileInputStream的一个装饰
BufferedInputStream 有个内部缓冲区当read时会先把缓冲区填满，然后下次读取是直接从缓冲区读取。当读取的位置大于缓冲区时会再一次加载缓冲区。
read()和read(byte[] buf, int off, int len)处理方式一样，区别在于后者一次返回多个数据，但是同样都是先放入缓冲区，然后再读取。
private void fill() throws IOException {
byte abyte0[] = getBufIfOpen();
if (markpos < 0)
pos = 0;
else if (pos >= abyte0.length)
if (markpos > 0) {
int i = pos - markpos;
System.arraycopy(abyte0, markpos, abyte0, 0, i);
pos = i;
markpos = 0;
} else if (abyte0.length >= marklimit) {
markpos = -1;
pos = 0;
} else {
int j = pos * 2;
if (j > marklimit)
j = marklimit;
byte abyte1[] = new byte[j];
System.arraycopy(abyte0, 0, abyte1, 0, pos);
abyte0 = abyte1;
}
count = pos;
int k = getInIfOpen().read(abyte0, pos, abyte0.length - pos);
if (k > 0)
count = k + pos;
}
public synchronized int read() throws IOException {
if (pos >= count) {
fill();
if (pos >= count)
return -1;
}
return getBufIfOpen()[pos++] & 255;
}
至于性能问题，我们都知道文件的物理读取性能肯定要大于内存读取，FileInputStream.read()相当于一次物理读取，而BufferedInputStream .read()大部分相当于一次内存读取。
同理FileOutputStream和BufferedOutputStream原理也是一样，也是有个缓冲区，每次write相当于写入缓冲区，当缓冲区慢了后在物理写入文件。
private void flushBuffer()
throws IOException
{
if(count > 0)
{
out.write(buf, 0, count);
count = 0;
}
}
public synchronized void write(int i)
throws IOException
{
if(count >= buf.length)
flushBuffer();
buf[count++] = (byte)i;
}
测试
public static void bufferTest() throws IOException{
BufferedInputStream is = new BufferedInputStream(new FileInputStream("d:/A.exe"));
BufferedOutputStream out = new BufferedOutputStream(new FileOutputStream("d:/B.exe"));
byte[] buffer = new byte[100];
System.out.println("buffer start "+new Date());
int size = 0 ;
while((size=is.read(buffer, 0, buffer.length))!=-1){
out.write(buffer);
}
is.close();
out.close();
System.out.println("buffer end "+new Date());
}
public static void ioTest()throws IOException{
FileInputStream is = new FileInputStream("d:/A.exe");
FileOutputStream out = new FileOutputStream("d:/C.exe");
byte[] buffer = new byte[100];
System.out.println("io start "+new Date());
int size = 0 ;
while((size=is.read(buffer, 0, buffer.length))!=-1){
out.write(buffer);
}
is.close();
out.close();
System.out.println("io end "+new Date());
}
文件大概有1G,用buffer大概用了20秒，用原始方式等了1分钟还没完，直接强制终止。