利用commons工具包实现文件上传

利用commons工具包实现文件上传

一、首先导入commons-io/和commons-fileupload/两个包

二、编写servlet

import org.apache.commons.fileupload.FileItem;
import org.apache.commons.fileupload.FileUploadException;
import org.apache.commons.fileupload.ProgressListener;
import org.apache.commons.fileupload.disk.DiskFileItemFactory;
import org.apache.commons.fileupload.servlet.ServletFileUpload;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.*;
import java.util.List;
import java.util.UUID;

public class FileServlet extends HttpServlet {

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        if (!ServletFileUpload.isMultipartContent(req)) { //判断文件是带文件表单还是普通表单
            return;    //终止运行，说明这一定是一个不带文件的
        }
        //为保证服务器安全，上传文件应该放在外界无法直接访问你得目录下，比如放在WEB-INF目录下
        String uploadPath = this.getServletContext().getRealPath("/WEB-INF/upload");
        File uploadFile = new File(uploadPath);
        if (!uploadFile.exists()) {
            uploadFile.mkdir();
        }

        // 缓存
        String tempPath = this.getServletContext().getRealPath("/WEB-INF/temp");
        File file = new File(tempPath);
        if (!file.exists()) {
            file.mkdir();
        }
        String msg = null;
        try {
            //1.创建 DiskFileItemFactory
            DiskFileItemFactory factory = getDiskFileItemFactory(file);
            //2.获取ServletFileUpload
            ServletFileUpload upload = getServletFileUpload(factory);
            // 3.处理上传文件
            msg = uploadParseRequest(upload, req, uploadPath);
        } catch (FileUploadException e) {
            e.printStackTrace();
        }
        // 请求转发消息
        req.setAttribute("msg", msg);
        req.getRequestDispatcher("info.jsp").forward(req, resp);
    }

    public static DiskFileItemFactory getDiskFileItemFactory(File file) {
        DiskFileItemFactory factory = new DiskFileItemFactory();
        factory.setSizeThreshold(1024 * 1024);    // 缓存区大小为1M
        factory.setRepository(file);            // 临时目录的保存目录，需要一个file
        return factory;
    }

    public static ServletFileUpload getServletFileUpload(DiskFileItemFactory factory) {
        ServletFileUpload upload = new ServletFileUpload(factory);
        upload.setProgressListener(new ProgressListener() {
            @Override
            public void update(long pBytesRead, long pContenLength, int pItems) {
                System.out.println("总大小：" + pContenLength + "已上传：" + pBytesRead);
            }
        });
        upload.setHeaderEncoding("UTF-8");
        upload.setFileSizeMax(1024 * 1024 * 10);
        upload.setSizeMax(1024 * 1024 * 10);
        return upload;
    }

    public static String uploadParseRequest(ServletFileUpload upload, HttpServletRequest req, String uploadPath) throws FileUploadException, IOException {
        String message = null;
        List<FileItem> fileItems = upload.parseRequest(req); // 把前端请求解析，封装成一个FileItem对象
        for (FileItem fileItem : fileItems) {
            if (fileItem.isFormField()) {     // 普通表单
                String name = fileItem.getName();
                String value = fileItem.getString("utf-8");
                System.out.println(name + ":" + value);
            } else {  //判断是文件表单
                String uploadFileName = fileItem.getName(); // ===== 处理文件 =============
                if (uploadFileName.trim().equals("") || uploadFileName == null) {
                    continue;
                }
                String fileName = uploadFileName.substring(uploadFileName.lastIndexOf("/") + 1);
                String fileExtName = uploadFileName.substring(uploadFileName.lastIndexOf(".") + 1);
                // UUID.randomUUID() 随机生成一个唯一识别的通用码
                // 网络中传输东西，都需要序列化
                // POJO, 实体类， 如果想要生成在多个电脑上运行， 传输-->需要把对象都序列化
                // JNI java native Interface
                // implements Serializable :标记接口 ，JVM --> Java栈 本地方法栈 native --> c++
                String uuidPath = UUID.randomUUID().toString();// 可以 使用UUID(唯一识别的通用码),保证文件唯一
                String realPath = uploadPath + "/" + uuidPath; // ========= 存放地址 ========
                File realPathFile = new File(realPath);
                if (!realPathFile.exists()) {
                    realPathFile.mkdir();
                }
                InputStream is = fileItem.getInputStream(); // ========= 文件传输 ========
                FileOutputStream fos = new FileOutputStream(realPath + "/" + fileName);
                byte[] buffer = new byte[1024];
                int len = 0;
                while ((len = is.read(buffer)) != -1) {
                    fos.write(buffer, 0, len);
                }
                fos.close();
                is.close();
                message = "文件上传成功";
                fileItem.delete();  //上传成功，清除临时文件
            }
        }
        return message;
    }
}

三、在web.xml注册servlet

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd"
         version="3.1">
    <servlet>
        <servlet-name>FileServlet</servlet-name>
        <servlet-class>code.dwx.servlet.FileServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>FileServlet</servlet-name>
        <url-pattern>/upload.do</url-pattern>
    </servlet-mapping>

</web-app>

四、编写index.jsp和info.jsp

index.jsp

<%--
  Created by IntelliJ IDEA.
  User: yuyuq
  Date: 2020/11/20
  Time: 20:14
  To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>upload page</title>
</head>
<body>
<h1>UpLoad</h1>
<form action="${pageContext.request.contextPath}/upload.do" method="post" enctype="multipart/form-data">
    上传用户：<input type="text" name="username"> <br>
    <p><input type="file" name="file1"></p>
    <p><input type="file" name="file2"></p>
    <p><input type="submit">|<input type="reset"></p>
</form>
</body>
</html>

info.jsp

<%@ page language="java" contentType="text/html;charset=UTF-8" %>
<!DOCTYPE html>
<html>
<head>
    <title>Insert title here</title>
</head>
<body>
    
${msg}
    
</body>
</html>

五、页面优化

可以利用Layui框架：https://www.layui.com/里面的示例代码

六、文件上传注意事项

• 为保证服务器安全，上传文件应该放在外界无法直接访问的目录下，比如放于WEB-INF目录下
• 为防止文件覆盖的现象发生，要为上传文件产生一个唯一的文件名
• 要限制上传文件的最大值
• 可以限制上传文件的类型，在收到上传文件时，判断后缀名是否合法