使用getPart接收表单文件时，注意Tomcat版本要在8之上。
前台 : form.jsp
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
<title>Title</title>
</head>
<body>
<form action="${pageContext.request.contextPath}/test" method="post" enctype="multipart/form-data">
请选择文件：<input type="file" name="file"><br>
<input type="submit" value="提交">
</form>
</body>
</html>后台：TestServlet
@WebServlet(name = "TestServlet", urlPatterns = "/test")
@MultipartConfig
public class TestServlet extends HttpServlet {
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
//获取文件,参数为前台的name
Part part = request.getPart("photo");
//判断是否选择了文件
if (part.getSize() == 0) {
request.setAttribute("msg", "请选择用户头像");
request.getRequestDispatcher("/register.jsp").forward(request, response);
return; //不再执行后续操作
}
//获取文件名，获取到文件名的格式如：a.jpg
String fileName = part.getSubmittedFileName();
/**
截取文件名的后缀名：
photo.lastIndexOf('.')的返回值为"."的位置，加1表示后缀名的起始位置。
photo.substring(photo.lastIndexOf('.')+1)，表示从后缀名的起始位置截取到结束位置。
* */
String fileType = fileName.substring(fileName.lastIndexOf('.') + 1);
//判断该文件是不是图片格式
if (!("jpg".equalsIgnoreCase(fileType) || "jpeg".equalsIgnoreCase(fileType) || "png".equalsIgnoreCase(fileType))) {
//不是图片格式,停止下一步，并将信息反馈给前台页面
request.setAttribute("msg","上传的文件必须为图片");
request.getRequestDispatcher("/form.jsp").forward(request, response);
return;
}
//是图片类型，构建一个上传图片的存储路径
String path = "E:\\upload";
File file = new File(path);
if (!file.exists()) {
file.mkdirs(); //创建文件和文件夹
}
//将part内容写到文件夹内，生成一个文件
part.write(path + "/" + fileName);
}
}String path = "E:\\testPic";设置成本地文件夹路径与Tomcat服务器脱离关联，可以防止文件丢失。但需要将该文件夹挂载到Tomcat服务器。
挂载方式：Eclipse：
1、双击集成在Eclipse中的tomcat服务器
2、点击添加额外的web资源
3、将本地存储上传文件的文件夹添加进来即可！
一定要ctrl + S
IDEA:
优化：将上传图片封装成工具类
UploadUtils.java
public class UploadUtils {
public static String upload(Part part, HttpServletRequest request, HttpServletResponse response) {
//获取文件的名称
String photo = part.getSubmittedFileName();
//重命名该文件，防止出现重名文件被覆盖的情况
photo = UUID.randomUUID() + photo;
/**
截取文件名的后缀名：
photo.lastIndexOf('.')的返回值为"."的位置，加1表示后缀名的起始位置。
photo.substring(photo.lastIndexOf('.')+1)，表示从后缀名的起始位置截取到结束位置。
* */
String fileType = photo.substring(photo.lastIndexOf('.') + 1);
//判断该文件是不是图片格式
if (!("jpg".equalsIgnoreCase(fileType) || "jpeg".equalsIgnoreCase(fileType) || "png".equalsIgnoreCase(fileType))) {
//不是图片格式，返回空字串
return "";
}
//是图片类型，构建一个上传图片的存储路径，并返回字符串的名称，用于存储到数据库
String path = "E:\\upload";
File file = new File(path);
if (!file.exists()) {
file.mkdirs(); //创建文件和文件夹
}
//将part内容写到文件夹内，生成一个文件
try {
part.write(path + "/" + photo);
} catch (IOException e) {
e.printStackTrace();
}
return photo;
}
}调用工具类：
@WebServlet(name = "TestServlet", urlPatterns = "/test")
@MultipartConfig
public class TestServlet extends HttpServlet {
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException{
//获取文件
Part part = request.getPart("photo");
//判断用户是否选择文件,如果没有选择头像，不进行后续操作
if (part.getSize() == 0) {
request.setAttribute("msg", "请选择用户头像");
request.getRequestDispatcher("/register.jsp").forward(request, response);
return;
}
String photo = UploadUtils.upload(part, request, response);
//判断photo是否为空字符串,为空字符串,说明不是图片类型，也不进行后续操作
if (photo == "") {
request.setAttribute("msg", "请选择图片类型的文件,如png,jpg,jpeg");
request.getRequestDispatcher("/register.jsp").forward(request, response);
return;
}
//不是空字符串，执行后续操作，如将路径存储到数据库等
............................................
}推荐教程：《Java教程》
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