Java实现上传图片功能与限制

<%@ page autoFlush="false" contentType="text/html;charset=utf-8" language="java" import="java.io.*,java.awt.Image,java.awt.image.*,com.sun.image.codec.jpeg.*,java.sql.*,com.jspsmart.upload.*,java.util.*,java.io.FileInputStream,java.io.FileOutputStream,java.awt.*"%>
<%@ page import="com.blog.vo.*" %>
<%
SmartUpload mySmartUpload =new SmartUpload();
long file_size_max=4000000;
String fileName2="",ext="",testvar="";
String url="uploadfile/images/"; //应保证在根目录中有此目录的存在
//初始化
mySmartUpload.initialize(pageContext);
//只允许上载此类文件
try {
mySmartUpload.setAllowedFilesList("jpg,gif,JPG,GIF");
//上载文件 
mySmartUpload.upload();
} catch (Exception e){
%>
<SCRIPT language=javascript>
alert("只允许上传.jpg和.gif类型图片文件");
window.location='face.jsp';
</script>
<%
}
try{ 
com.jspsmart.upload.File myFile = mySmartUpload.getFiles().getFile(0);
if (myFile.isMissing()){%>
<SCRIPT language=javascript>
alert("请先选择要上传的文件");
window.location='face.jsp';
</script>
<%}