JSP与Servlet文件上传和下载

下载较为简单先写下载

pom.xml的配置

    <dependencies>
        <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>javax.servlet-api</artifactId>
            <version>4.0.1</version>
        </dependency>
        <dependency>
            <groupId>javax.servlet.jsp</groupId>
            <artifactId>javax.servlet.jsp-api</artifactId>
            <version>2.3.3</version>
        </dependency>
    </dependencies>

导入jsp和servlet的依赖

Servlet内容：

package com.wen.servlet;


import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.PrintWriter;
import java.net.URLEncoder;

public class DownLoadServlet extends HttpServlet {
    //由于get或者post只是请求实现的不同的方式，可以相互调用，业务逻辑都一样;
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        String realPath = "D:\\upload\\2.jpg";
        System.out.println("文件下载路径"+realPath);
        String filename = realPath.substring(realPath.lastIndexOf("\\")+1);
        /*
        * 获取最后一个\分割的位置，+1就是文件名
        * */
        resp.setHeader("Content-Disposition","attachment;filename="+ URLEncoder.encode(filename,"utf-8"));
        FileInputStream in = new FileInputStream(realPath);
        int len = 0;
        byte[] buffer = new byte[1024];
        ServletOutputStream out = resp.getOutputStream();
        while ((len = in.read(buffer))!=-1){
            out.write(buffer,0,len);
        }
        out.close();
        in.close();
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    }
}

在web.xml中对上面的servlet访问路径配置

    <servlet>
        <servlet-name>downLoadServlet</servlet-name>
        <servlet-class>com.wen.servlet.DownLoadServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>downLoadServlet</servlet-name>
        <url-pattern>/down</url-pattern>
    </servlet-mapping>

tomact：

访问：

文件上传

Servlet的代码

package com.wen.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.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.util.List;
import java.util.UUID;

public class FileUploadServlet extends HttpServlet {
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //判断上传的文件是普通表单还是带文件的表单
        if (!ServletFileUpload.isMultipartContent(req)) {
            return;//终止方法运行，说明这是一个普通的表单，直按返回
        }
        //创建上传文件的保存路径，建议在WEB-INF路径下，安全，用户无法直接访问上传的文件;
        String uploadPath = this.getServletContext().getRealPath("/WEB-INF/upload");
        File uploadFile = new File(uploadPath);
        if (!uploadFile.exists()) {
            uploadFile.mkdir(); //创建这个目录
        }
        //级存，临时文件
        //临时路径，假如文件超过了预期的大小，我们就把他放到一个临时文件中，过几天白动鹏除，或者提醒用户转存为永久
        String tmpPath = this.getServletContext().getRealPath("/WEB-INF/tmp");
        File file = new File(tmpPath);
        if (!file.exists()) {
            file.mkdir(); //创建这个临时日录
        }
        //1.创建DiskFileItemFactory对象，处理文件上传路径或者大小限制的;
        DiskFileItemFactory factory = getDiskFileItemFactory(file);
        //2.获取ServletFileUpload
        ServletFileUpload upload = getServletFileUpload(factory);
        //3.处理上传的文件
        String msg = null;
        try {
            msg = uploadParseRequest(upload,req,uploadPath);
        } catch (FileUploadException e) {
            e.printStackTrace();
        }
        //servlet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;
        //通过这个工厂设置一个缓冲区，当上传的文件大于这个缓冲区的时候，将他放到临时文件中;
    }


    public static ServletFileUpload getServletFileUpload(DiskFileItemFactory factory) {
        //2.获取ServletFiLeUpload
        ServletFileUpload upload = new ServletFileUpload(factory);
//处理上传的文件，一般都需要通过流来获取，我们可以使川request.getInputStream()。原生态的文件上传流获取，十分麻烦
        //通过ServletFiLelpLoad对象的构造方法或setFiLe工temFactory()方法设置servletFiLeupLoad对象的fiLeItemFactory属性。
//监听文件上传进度;
        upload.setProgressListener(new ProgressListener() {
            @Override
            //pContentLength :文件大小  //pBytesRead: 经读取到的文件人小
            public void update(long pBytesRead, long pContentLength, int pItems) {
                System.out.println("总大小:" + pContentLength + "已上传:" + pBytesRead);
            }
        });
        //处理乱码问题
        upload.setHeaderEncoding("UTF-8");
        //设置单个文件的最大值
        upload.setFileSizeMax(1024 * 1024 * 10);
        //设置总共能够上传文件的大小
        //1024 = 1kb* 1024 =.1M* 10 = 10M
        upload.setSizeMax(1024 * 1024 * 10);
        return upload;
    }


    public static String uploadParseRequest(ServletFileUpload upload, HttpServletRequest request, String uploadPath)
            throws FileUploadException, IOException {
        String msg = "";
        //3.把前端请求解析，封装成一个FileItem对象
        List<FileItem> fileItems = upload.parseRequest(request);
        for (FileItem fileItem : fileItems) {//判断上传的文件是普通的表单还是带文件的表单
            if (fileItem.isFormField()) {//getFieLdName指的是前端表单控件的name ;
                String name = fileItem.getFieldName();
                String value = fileItem.getString("UTF-8");//处理乱码
                System.out.println(name + ":" + value);
            } else { //判断他是上传的文件
                //处理文件
                String uploadFileName = fileItem.getName();
                System.out.println("上传的文件名:"+uploadFileName);
                //可能存在文件名不合法的情况
                if (uploadFileName.trim().equals("") || uploadFileName == null) {
                    continue;
                }
                //获得上传文件后缀名
                String fileExtName = uploadFileName.substring(uploadFileName.lastIndexOf(".") + 1);
                //获得上传文件名
                String fileName = uploadFileName.substring(uploadFileName.lastIndexOf("\\") + 1);
        /*
        如果文件后缀名fileExtName不是我们所需要的
        就直接return，不处理，告诉用户文件类型不对。*/
                System.out.println("文件信息[文件名:" + fileName + "---文件类型" + fileExtName + "]");
                String uuidPath = UUID.randomUUID().toString();
                //l存到哪?uploadPath
                //文件真实存在的路径realPath
                String realPath = uploadPath + "/" + uuidPath;
                //给每个文件创建一个对应的文件夹
                File realPathFile = new File(realPath);
                if (!realPathFile.exists()) {
                    realPathFile.mkdir();
                }

                //获得文件上传的流
                InputStream inputstream = fileItem.getInputStream();
                //创建一个文件输出流
                //realPath =真实的文件灭;
                //差了一个文件;加上输出文件的名宁+"/"+uuidFiLeName
                FileOutputStream fos = new FileOutputStream(realPath + "/" + fileName);
                //创建一个缓冲区
                byte[] buffer = new byte[1024 * 1024];
                //判断是否读取完毕
                int len = 0;
                //如果大于0说明还存在数据;
                while ((len = inputstream.read(buffer)) > 0) {
                    fos.write(buffer, 0, len);
                }
                //关闭流
                fos.close();
                inputstream.close();
                msg = "文件上传成功!";
                fileItem.delete(); //上传成功，清除临时文件
            }
        }
        return msg;
    }

}

jsp代码：

<%--
  Created by IntelliJ IDEA.
  User: wjh0
  Date: 2020/9/11
  Time: 12:26
  To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>upload</title>
</head>
<body>
<%--通过表单上传文件
get:上传文件大小有限制
post:上传文件大小没有限制
--%>
<form action="${pageContext.request.contextPath}/upload.do" enctype="multipart/form-data" method="post">
    <p>上传用户: <input type="text" name="username" ></p>
    <p><input type="file" name="file1"></p>
    <p><input type="file" name="file1"></p>
    <p><input type="submit"> | <input type="reset"></p>
</form>

</body>
</html>

在web.xml中加入上面servlet的访问路径

<servlet>
    <servlet-name>FileUploadServlet</servlet-name>
    <servlet-class>com.wen.servlet.FileUploadServlet</servlet-class>
</servlet>
    <servlet-mapping>
        <servlet-name>FileUploadServlet</servlet-name>
        <url-pattern>/upload.do</url-pattern>
    </servlet-mapping>

info.jsp的内容

<%--
  Created by IntelliJ IDEA.
  User: wjh0
  Date: 2020/9/11
  Time: 18:36
  To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>Title</title>
</head>
<body>
<p>${msg}</p>
</body>
</html>

tomcat的访问路径和访问情况不在书写，上传的servlet中将上传的过程写作3个方法在dopost中调用，
也可以书写在一起，代码量较大。