手写代码，加强记忆。
InputStream in = null;
OutputStream out = null;
try{
//读文件
String path = "C://a//b//c.xls";
in = new FileInputStream(path);
//设置输出流
out = response.getOutputStream();
//写文件
int len = 0;
byte[] b = new byte[1024];
while( len != -1){
len = in.read(b);
if(len != -1){
out.write(b, 0, len);
}
}
}catch(Exception e){
} finally{
//关闭流（先开后关）
if(out != null){
try{
out.flush();
out.close();
}catch(){
}
}
if(in != null){
try{
in.close();
}catch(){
}
}
}
