版权声明：转载请注明出处，谢谢 https://blog.csdn.net/Sirius_hly/article/details/81912666
一.文件上传下载的实现
1.maven依赖
该功能需要添加三个jar，分别如下:
<dependency>
<groupId>javax.servlet</groupId>
<artifactId>javax.servlet-api</artifactId>
<version>3.0.1</version>
</dependency>
<dependency>
<groupId>commons-fileupload</groupId>
<artifactId>commons-fileupload</artifactId>
<version>1.3.1</version>
</dependency>
<!--是处理IO的工具类包，对java.io进行扩展，提供了更加方便的IO操作。-->
<dependency>
<groupId>commons-io</groupId>
<artifactId>commons-io</artifactId>
<version>2.4</version>
</dependency>2.前端代码
<%@ page contentType="text/html;charset=UTF-8" language="java"%>
<html>
<head>
<title>file</title>
</head>
<body>
<form action="/fileUpload" method="post" enctype="multipart/form-data">
<a class="upload"><input class="file" type="file" name="file"></a>
<input type="submit" value="上传">
</form>
${message}
<a href="/FileDownload?fileName=${fileName}" rel="nofollow">${fileName}</a>
<%--https://www.baidu.com/s?wd=nofollow%E6%A0%87%E7%AD%BE&tn=SE_PcZhidaonwhc_ngpagmjz&rsv_dl=gh_pc_zhidao--%>
<%--nofollow不要追踪此特定链接--%>action的内容为后端接收的地址，即为后端代码中@WebServlet("/fileUpload")的地址。
3.后端接收代码
package com.hly.jsp.file;
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.File;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.List;
/**
* @author :hly
* @github :github.com/SiriusHly
* @blog :blog.csdn.net/Sirius_hly
* @date :2018/8/20
*/
@WebServlet("/fileUpload")
public class FileUpload extends HttpServlet {
//临界值，超过临界值，上传过程中会存到临时目录
private static final int BOUNDARY_MEMORY_SIDE = 1024 * 1024 * 10;
//文件最大值
private static final int MAX_MEMORY_SIDE = 1024 * 1024 * 300;
//请求值
private static final int MAX_REQUEST_MEMORY_SIDE = 1024 * 1024 * 1000;
public void doPost(HttpServletRequest request, HttpServletResponse response) throws IOException, ServletException {
//判断普通表单还是文件上传表单，enctype属性是否是"multipart/form-data"。
if (!ServletFileUpload.isMultipartContent(request)) {
System.out.println("不是多媒体上传");
PrintWriter out = response.getWriter();
out.println("不是多媒体上传");
out.flush();
return;
}
//配置上传参数
DiskFileItemFactory factory = new DiskFileItemFactory();
//设置临界值,超过部分存在临时目录
factory.setSizeThreshold(BOUNDARY_MEMORY_SIDE);
//设置临时存储目录,上传过程中超过大小存到临时目录中，也可以设置成系统临时存储目录，https://www.cnblogs.com/nbjin/p/7392541.html
File tempFile = new File("d:/FileUploadTemp");
if(!tempFile.exists())
tempFile.mkdirs();
factory.setRepository(tempFile);
ServletFileUpload upload = new ServletFileUpload(factory);
//编码
upload.setHeaderEncoding("UTF-8");
//设置文件最大上传值
upload.setFileSizeMax(MAX_MEMORY_SIDE);
//设置文件最大请求值,包括所有form
upload.setSizeMax(MAX_REQUEST_MEMORY_SIDE);
//设置相对路径
String path = getServletContext().getRealPath("/") + File.separator + "uploadFile";
File uploadDir = new File(path);
if (!uploadDir.exists()) {
uploadDir.mkdirs();
}
try {
//解析请求内容获取文件数据
List<FileItem> fileItems = upload.parseRequest(request);
if (fileItems != null && fileItems.size() > 0) {
for (FileItem item : fileItems) {
//判断是否为普通类型，否则为file类型
if (!item.isFormField()) {
//得到前端的name
String fileName = item.getName();
String filePath = path + File.separator + fileName;
File storeFile = new File(filePath);
System.out.println("上传路径为:" + filePath);
//保存文件到硬盘
item.write(storeFile);
request.setAttribute("message", "上传成功");
request.setAttribute("fileName", fileName);
// request.setAttribute();
}
}
}else{
request.setAttribute("message", "上传失败");
}
} catch (FileUploadException e) {
e.printStackTrace();
} catch (Exception e) {
e.printStackTrace();
}
getServletContext().getRequestDispatcher("/file/fileUpload.jsp").forward(request, response);
System.out.println("上传成功");
}
}
4.后端下载代码
package com.hly.jsp.file;
import javax.servlet.ServletContext;
import javax.servlet.ServletOutputStream;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.*;
/**
* @author :hly
* @github :github.com/SiriusHly
* @blog :blog.csdn.net/Sirius_hly
* @date :2018/8/22
*/
@WebServlet("/FileDownload")
public class FileDownload extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException {
String fileName = request.getParameter("fileName");
System.out.println("下载路径为:"+fileName);
//设置mime类型,getMimeType获得文档类型，这里是text/plain
response.setContentType(getServletContext().getMimeType(fileName));
System.out.println("mime类型:"+getServletContext().getMimeType(fileName));
//设置Context-Disposition
//Content-disposition：HTTP相应头的属性，允许用户下载软件到磁盘
//attachment表示以附件方式下载。如果要在页面中打开，则改为inline。
response.setHeader("Content-Disposition", "attachment;filename=" + fileName);
//输入流
String filePath = getServletContext().getRealPath("/")+ File.separator +"uploadFile"+File.separator +fileName;
InputStream in = new FileInputStream(filePath);
ServletOutputStream os = response.getOutputStream();
//缓冲区
int len =1;
byte[] b = new byte[1024];
while ((len = in.read(b))!=-1){
os.write(b,0,len);
}
in.close();
os.close();
}
public void doPost(HttpServletRequest request, HttpServletResponse response) throws IOException {
doGet(request, response);
}
}
前端代码的文件目录为:
上传的文件可以在target里面找到
5.代码分析
1.关于代码中的getName()方法
源码如下，我们可以发现他返回的是前端的name，当不是普通类型的表单，是file时，则进行保存
@Override
public String toString() {
return format("name=%s, StoreLocation=%s, size=%s bytes, isFormField=%s, FieldName=%s",
getName(), getStoreLocation(), Long.valueOf(getSize()),
Boolean.valueOf(isFormField()), getFieldName());
}