文件上传、下载

2020-08-02

字数统计: 1.3k字 | 阅读时长: 7分

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文件上传、下载

1、input标签的type设置为file

2、form的method设置为post，如果使用get请求会将文件名传给服务端，而不是文件本身。

3、form表单的enctype设置为multipart/form-data。表示以二进制的形式传输数据。

一、IO流读取、写入文件数据流底层实现

package com.huan.filter;

import javax.servlet.*;
import javax.servlet.annotation.WebFilter;
import java.io.IOException;

@WebFilter("/upload")
public class UploadFilter implements Filter {
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {

    }

    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        servletRequest.setCharacterEncoding("UTF-8");
        filterChain.doFilter(servletRequest,servletResponse);
    }

    @Override
    public void destroy() {

    }
}

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>Title</title>
</head>
<body>
    <form action="/upload" method="post" enctype="multipart/form-data">
        <input type="file" name="upload"/><br/>
        <input type="submit" value="提交"/>
    </form>

</body>
</html>

package com.huan.servlet;

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 java.io.*;

@WebServlet("/upload")
public class UploadServlet extends HttpServlet {
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        req.setCharacterEncoding("UTF-8");
        //1、通过输入流获取客户端传来的数据流
        InputStream inputStream = req.getInputStream();   /*获取前台文件输入流，为字节流*/
        /*IO字节流读取，读取结果为一连串数字*/
        /*int temp = 0;
        while ((temp = inputStream.read())!=-1){
            System.out.println(temp);
        }*/
        /*IO字符流读取*/
        Reader reader = new InputStreamReader(inputStream);   /*字节流转换为字符流，按字符读取*/
        BufferedReader bufferedReader = new BufferedReader(reader);  /*缓冲字符流，加快读取速度，按行读取*/
        //2、通过输出流将数据流输出到本地硬盘，保存
        /*获取文件夹的绝对路径*/
        String path = req.getServletContext().getRealPath("file/copy.txt");  /*将web工程里面的file文件夹传进来即可获取该文件夹绝对路径*/
        OutputStream outputStream = new FileOutputStream(path);
        Writer writer = new OutputStreamWriter(outputStream);
        BufferedWriter bufferedWriter = new BufferedWriter(writer);

        String str = "";
        while ((str = bufferedReader.readLine())!=null){
            bufferedWriter.write(str);
            System.out.println(str);
        }
        bufferedWriter.close();
        writer.close();
        outputStream.close();
        bufferedReader.close();
        reader.close();
        inputStream.close();
    }
}

二、使用Apache提供的FileUpload进行文件上传

注：通过BufferReader按字符整行读取输入数据流会出现：

1、无法读取换行符，导致读取文本文件无法换行；

2、读取图片二进制流内部结构会破坏，图片无法显示

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>Title</title>
</head>
<body>
    <form action="/upload" method="post" enctype="multipart/form-data">
        <input type="text" name="desc"/><br/>
        <input type="file" name="upload"/><br/>
        <input type="submit" value="提交"/>
    </form>

</body>
</html>

字符流读取

package com.huan.servlet;

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

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 java.io.*;
import java.util.List;

@WebServlet("/upload")
public class UploadServlet extends HttpServlet {
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        try {
            DiskFileItemFactory fileItemFactory = new DiskFileItemFactory();
            ServletFileUpload servletFileUpload = new ServletFileUpload(fileItemFactory);
            List<FileItem> list = servletFileUpload.parseRequest(req);
            for (FileItem fileItem:list){
                if (fileItem.isFormField()){  /*通过isFormField判断前台input的type是file还是text*/
                    String name = fileItem.getName();
                    String value = fileItem.getString("UTF-8");
                    System.out.println(name+":"+value);
                }else {
                    String fileName = fileItem.getName();
                    long size = fileItem.getSize();
                    System.out.println(fileName+":"+size+"Bytes");
                    InputStream inputStream = fileItem.getInputStream();
                    Reader reader = new InputStreamReader(inputStream);
                    BufferedReader bufferedReader = new BufferedReader(reader);
                    String path = req.getServletContext().getRealPath("file/"+fileName);
                    OutputStream outputStream = new FileOutputStream(path);
                    Writer writer = new OutputStreamWriter(outputStream);
                    BufferedWriter bufferedWriter = new BufferedWriter(writer);

                    String temp = null;
                    while ((temp = bufferedReader.readLine())!=null){
                        bufferedWriter.write(temp);
                    }
                    bufferedWriter.close();
                    writer.close();
                    outputStream.close();
                    bufferedReader.close();
                    reader.close();
                    inputStream.close();
                    System.out.println("文件上传成功");
                }
            }
        } catch (FileUploadException e) {
            e.printStackTrace();
        }
    }
}

字节流读取

package com.huan.servlet;

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

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 java.io.*;
import java.util.List;

@WebServlet("/upload")
public class UploadServlet extends HttpServlet {
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        try {
            DiskFileItemFactory fileItemFactory = new DiskFileItemFactory();
            ServletFileUpload servletFileUpload = new ServletFileUpload(fileItemFactory);
            List<FileItem> list = servletFileUpload.parseRequest(req);
            for (FileItem fileItem:list){
                if (fileItem.isFormField()){  /*通过isFormField判断前台input的type是file还是text*/
                    String name = fileItem.getName();
                    String value = fileItem.getString("UTF-8");
                    System.out.println(name+":"+value);
                }else {
                    String fileName = fileItem.getName();
                    long size = fileItem.getSize();
                    System.out.println(fileName+":"+size+"Bytes");
                    InputStream inputStream = fileItem.getInputStream();
                    String path = req.getServletContext().getRealPath("file/"+fileName);
                    OutputStream outputStream = new FileOutputStream(path);
                    int temp = 0;
                    while ((temp = inputStream.read())!=-1){
                        outputStream.write(temp);
                    }
                    outputStream.close();
                    inputStream.close();
                    System.out.println("文件上传成功");
                }
            }
        } catch (FileUploadException e) {
            e.printStackTrace();
        }
    }
}

三、文件下载

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>Title</title>
</head>
<body>
    <a href="/download?type=jpg">下载图片</a>
    <a href="/download?type=txt">下载文本</a>
</body>
</html>

package com.huan.servlet;

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 java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;

@WebServlet("/download")
public class DownloadServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

        String type = req.getParameter("type");

        String fileName = "";
        switch (type){
            case "jpg":
                fileName = "1.jpg";
                break;
            case "txt":
                fileName = "1.txt";
                break;
        }

        //设置响应方式，固定格式，让浏览器调用自身的下载工具
        resp.setContentType("application/x-msdownload");

        //设置下载之后的文件名
        resp.setHeader("Content-Disposition","attachment;fileName="+fileName);
        //获取输出流
        OutputStream outputStream = resp.getOutputStream();
        //获取需要下载的资源路径
        String path = req.getServletContext().getRealPath("file/"+fileName);
        InputStream inputStream = new FileInputStream(path);
        int temp = 0;
        while ((temp = inputStream.read())!=-1){
            outputStream.write(temp);
        }
        outputStream.close();
        inputStream.close();
    }
}