文件上传的准备:
1.在表单中必须有一个上传的控件
<input type="file" name="headImg"/>
2.get方式的请求有大小的限制,在文件上传的时候get方式不能满足要求,所有表单的提交方式必须是post
<form action="/upload" method="post">
3.表单的编码方式应该修改为multipart/form-data,以二进制的形式进行数据的传输
<form action="/upload" method="post" enctype="multipart/form-data">
注意:此时,Servlet中就不能再使用request对象.getParameter(String name)获取请求参数
因为已经改成了流,可以通过打印的字节数可以看出,因此不能getParameter
02基于Apache FileUpload组件使用基于Apache FileUpload上传组件实现文件的上传:
使用步骤:
1.将jar包导入到项目中 (注意需要倒入两个包)
commons-fileupload-1.2.2.jar commons-io-1.4.jar
2.参考commons-fileupload-1.2.2/site/using.html用户指南
3.代码:
package uploading;
import java.io.File;
import java.io.IOException;
import java.util.List;
import java.util.UUID;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.apache.commons.fileupload.FileItem;
import org.apache.commons.fileupload.FileItemFactory;
import org.apache.commons.fileupload.FileUploadException;
import org.apache.commons.fileupload.disk.DiskFileItemFactory;
import org.apache.commons.fileupload.servlet.ServletFileUpload;
import org.apache.commons.io.FilenameUtils;
@WebServlet("/upload")
public class registerRequset extends HttpServlet{
private static final long serialVersionUID = 1L;
@Override
protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
req.setCharacterEncoding("UTF-8");
//判断是否文件上传的按钮
boolean isMultipart = ServletFileUpload.isMultipartContent(req);
if (!isMultipart) {
return;
}
try {
// Create a factory for disk-based file items
FileItemFactory factory = new DiskFileItemFactory();
// Create a new file upload handler
ServletFileUpload upload = new ServletFileUpload(factory);
// Parse the request
List<FileItem>items = upload.parseRequest(req);
for (FileItem fileItem : items) {
if (fileItem.isFormField()) {
/*System.out.println("文件名"+fileItem.getFieldName());
System.out.println("文件大小"+fileItem.getSize());
System.out.println(fileItem.getSize());*/
}else {
System.out.println("文件名"+fileItem.getFieldName());
System.out.println("文件大小"+fileItem.getSize());
System.out.println(fileItem.getString());
String fileName=UUID.randomUUID().toString()+"."+FilenameUtils.getExtension(fileItem.getName());
//将文件保存到服务器上:
fileItem.write(new File("D:/",fileName));
}
}
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
测试表单;
/upload/register.jsp
<%@page import="java.util.Arrays"%>
<%@page import="java.util.List"%>
<%@ page language="java" contentType="text/html; charset=UTF-8"
pageEncoding="UTF-8"%>
<%@taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>
<!-- 用户注册 -->
<form action="/upload" method="post" enctype="multipart/form-data">
用户名:<input type="test" name="username"/><br/>
年龄:<input type="test" name="age"/><br/>
头像:<input type="file" name="headImg"/><br/>
<input type="submit" value="注册"/><br/>
</form>
</body>
</html>
Notes:
细节处理:
文件名称的处理问题:
如果A用户上传了一个文件名叫做小黄人,B用户上传了一个文件也叫做小黄人,此时后面的文件会将前面的额文件覆盖掉
解决方案:
使用UUID来生成一个随机的而且不重复字符串作为文件的名称
获取真实文件的名称,使用FilenameUtils这个工具类来获取它的后缀名
String fileName = UUID.randomUUID().toString()+"."+FilenameUtils.getExtension(fileItem.getName());