如何在Java项目中实现一个文件上传和下载功能？针对这个问题，这篇文章详细介绍了相对应的分析和解答，希望可以帮助更多想解决这个问题的小伙伴找到更简单易行的方法。
项目结构如下：
主要的是FileUploadController，doupload.jsp,up.jsp,springmvc.xml
1.先编写up.jsp
<form action="doupload.jsp" enctype="multipart/form-data" method="post"> <p>上传者：<input type="text" name="user"></p> <p>选择文件：<input type="file" name="nfile"></p> <p>选择文件：<input type="file" name="nfile1"></p> <p><input type="submit" value="提交"></p> </form>
以上便是up.jsp的核心代码；
2.编写doupload.jsp
<%
request.setCharacterEncoding("utf-8");
String uploadFileName = ""; //上传的文件名
String fieldName = ""; //表单字段元素的name属性值
//请求信息中的内容是否是multipart类型
boolean isMultipart = ServletFileUpload.isMultipartContent(request);
//上传文件的存储路径（服务器文件系统上的绝对文件路径）
String uploadFilePath = request.getSession().getServletContext().getRealPath("upload/" );
if (isMultipart) {
FileItemFactory factory = new DiskFileItemFactory();
ServletFileUpload upload = new ServletFileUpload(factory);
try {
//解析form表单中所有文件
List<FileItem> items = upload.parseRequest(request);
Iterator<FileItem> iter = items.iterator();
while (iter.hasNext()) { //依次处理每个文件
FileItem item = (FileItem) iter.next();
if (item.isFormField()){ //普通表单字段
fieldName = item.getFieldName(); //表单字段的name属性值
if (fieldName.equals("user")){
//输出表单字段的值
out.print(item.getString("UTF-8")+"上传了文件。<br/>");
}
}else{ //文件表单字段
String fileName = item.getName();
if (fileName != null && !fileName.equals("")) {
File fullFile = new File(item.getName());
File saveFile = new File(uploadFilePath, fullFile.getName());
item.write(saveFile);
uploadFileName = fullFile.getName();
out.print("上传成功后的文件名是："+uploadFileName);
out.print("\t\t下载链接:"+"<a href='download.action?name="+uploadFileName+"'>"+uploadFileName+"</a>");
out.print("<br/>");
}
}
}
} catch (Exception e) {
e.printStackTrace();
}
}
%>该页面主要是内容是，通过解析request，并设置上传路径，创建一个迭代器，先进行判空，再通过循环来实现多个文件的上传，再输出文件信息的同时打印文件下载路径。
效果图：
3.编写FilterController实现文件下载的功能（相对上传比较简单）：
@Controller
public class FileUploadController {
@RequestMapping(value="/download")
public ResponseEntity<byte[]> download(HttpServletRequest request,HttpServletResponse response,@RequestParam("name") String filename)throws Exception {
//下载显示的文件名，解决中文名称乱码问题
filename=new String(filename.getBytes("iso-8859-1"),"UTF-8");
//下载文件路径
String path = request.getServletContext().getRealPath("/upload/");
File file = new File(path + File.separator + filename);
HttpHeaders headers = new HttpHeaders();
//下载显示的文件名，解决中文名称乱码问题
String downloadFielName = new String(filename.getBytes("iso-8859-1"),"UTF-8");
//通知浏览器以attachment（下载方式）打开图片
headers.setContentDispositionFormData("Content-Disposition", downloadFielName);
//application/octet-stream ： 二进制流数据（最常见的文件下载）。
headers.setContentType(MediaType.APPLICATION_OCTET_STREAM);
return new ResponseEntity<byte[]>(FileUtils.readFileToByteArray(file),
headers, HttpStatus.CREATED);
}
}4.实现上传文件的功能还需要在springmvc中配置bean：
<bean id="multipartResolver" class="org.springframework.web.multipart.commons.CommonsMultipartResolver"> <!-- 上传文件大小上限，单位为字节（10MB） --> <property name="maxUploadSize"> <value>10485760</value> </property> <!-- 请求的编码格式，必须和jSP的pageEncoding属性一致，以便正确读取表单的内容，默认为ISO-8859-1 --> <property name="defaultEncoding"> <value>UTF-8</value> </property> </bean>
完整代码如下：
up.jsp
<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%> <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> <html> <head> <title>File控件</title> </head> <body> <form action="doupload.jsp" enctype="multipart/form-data" method="post"> <p>上传者：<input type="text" name="user"></p> <p>选择文件：<input type="file" name="nfile"></p> <p>选择文件：<input type="file" name="nfile1"></p> <p><input type="submit" value="提交"></p> </form> </body> </html>
doupload.jsp
<%@ page language="java" pageEncoding="UTF-8"%>
<%@page import="java.io.*,java.util.*"%>
<%@page import="org.apache.commons.fileupload.*"%>
<%@page import="org.apache.commons.fileupload.disk.DiskFileItemFactory" %>
<%@page import="org.apache.commons.fileupload.servlet.ServletFileUpload"%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<title>上传处理页面</title>
</head>
<body>
<%
request.setCharacterEncoding("utf-8");
String uploadFileName = ""; //上传的文件名
String fieldName = ""; //表单字段元素的name属性值
//请求信息中的内容是否是multipart类型
boolean isMultipart = ServletFileUpload.isMultipartContent(request);
//上传文件的存储路径（服务器文件系统上的绝对文件路径）
String uploadFilePath = request.getSession().getServletContext().getRealPath("upload/" );
if (isMultipart) {
FileItemFactory factory = new DiskFileItemFactory();
ServletFileUpload upload = new ServletFileUpload(factory);
try {
//解析form表单中所有文件
List<FileItem> items = upload.parseRequest(request);
Iterator<FileItem> iter = items.iterator();
while (iter.hasNext()) { //依次处理每个文件
FileItem item = (FileItem) iter.next();
if (item.isFormField()){ //普通表单字段
fieldName = item.getFieldName(); //表单字段的name属性值
if (fieldName.equals("user")){
//输出表单字段的值
out.print(item.getString("UTF-8")+"上传了文件。<br/>");
}
}else{ //文件表单字段
String fileName = item.getName();
if (fileName != null && !fileName.equals("")) {
File fullFile = new File(item.getName());
File saveFile = new File(uploadFilePath, fullFile.getName());
item.write(saveFile);
uploadFileName = fullFile.getName();
out.print("上传成功后的文件名是："+uploadFileName);
out.print("\t\t下载链接:"+"<a href='download.action?name="+uploadFileName+"'>"+uploadFileName+"</a>");
out.print("<br/>");
}
}
}
} catch (Exception e) {
e.printStackTrace();
}
}
%>
</body>
</html>FileUploadController.java
package ssm.me.controller;
import java.io.File;
import java.net.URLDecoder;
import java.util.Iterator;
import java.util.List;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.apache.commons.fileupload.FileItem;
import org.apache.commons.fileupload.FileItemFactory;
import org.apache.commons.fileupload.disk.DiskFileItemFactory;
import org.apache.commons.fileupload.servlet.ServletFileUpload;
import org.apache.commons.io.FileUtils;
import org.junit.runners.Parameterized.Parameter;
import org.springframework.http.HttpHeaders;
import org.springframework.http.HttpStatus;
import org.springframework.http.MediaType;
import org.springframework.http.ResponseEntity;
import org.springframework.stereotype.Controller;
import org.springframework.ui.Model;
import org.springframework.web.bind.annotation.ModelAttribute;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.multipart.MultipartFile;
@Controller
public class FileUploadController {
@RequestMapping(value="/download")
public ResponseEntity<byte[]> download(HttpServletRequest request,HttpServletResponse response,@RequestParam("name") String filename)throws Exception {
//下载显示的文件名，解决中文名称乱码问题
filename=new String(filename.getBytes("iso-8859-1"),"UTF-8");
//下载文件路径
String path = request.getServletContext().getRealPath("/upload/");
File file = new File(path + File.separator + filename);
HttpHeaders headers = new HttpHeaders();
//下载显示的文件名，解决中文名称乱码问题
String downloadFielName = new String(filename.getBytes("iso-8859-1"),"UTF-8");
//通知浏览器以attachment（下载方式）打开图片
headers.setContentDispositionFormData("Content-Disposition", downloadFielName);
//application/octet-stream ： 二进制流数据（最常见的文件下载）。
headers.setContentType(MediaType.APPLICATION_OCTET_STREAM);
return new ResponseEntity<byte[]>(FileUtils.readFileToByteArray(file),
headers, HttpStatus.CREATED);
}
}SpringMVC.xml（仅供参考，有的地方不可以照搬）
<?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:mvc="http://www.springframework.org/schema/mvc" xmlns:context="http://www.springframework.org/schema/context" xmlns:aop="http://www.springframework.org/schema/aop" xmlns:tx="http://www.springframework.org/schema/tx" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-4.2.xsd http://www.springframework.org/schema/mvc http://www.springframework.org/schema/mvc/spring-mvc-4.2.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-4.2.xsd http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx.xsd"> <!-- 一个用于自动配置注解的注解配置 --> <mvc:annotation-driven></mvc:annotation-driven> <!-- 扫描该包下面所有的Controller --> <context:component-scan base-package="ssm.me.controller"></context:component-scan> <!-- 视图解析器 --> <bean class="org.springframework.web.servlet.view.InternalResourceViewResolver"></bean> <bean id="multipartResolver" class="org.springframework.web.multipart.commons.CommonsMultipartResolver"> <!-- 上传文件大小上限，单位为字节（10MB） --> <property name="maxUploadSize"> <value>10485760</value> </property> <!-- 请求的编码格式，必须和jSP的pageEncoding属性一致，以便正确读取表单的内容，默认为ISO-8859-1 --> <property name="defaultEncoding"> <value>UTF-8</value> </property> </bean> </beans>
web.xml（仅供参考，有的地方不可以照搬）
<?xml version="1.0" encoding="UTF-8"?> <web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" id="WebApp_ID" version="3.0"> <display-name>Student</display-name> <welcome-file-list> <welcome-file>index.html</welcome-file> <welcome-file>index.htm</welcome-file> <welcome-file>index.jsp</welcome-file> <welcome-file>default.html</welcome-file> <welcome-file>default.htm</welcome-file> <welcome-file>default.jsp</welcome-file> </welcome-file-list> <servlet> <servlet-name>springmvc</servlet-name> <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class> <!-- 初始化参数 --> <init-param> <param-name>contextConfigLocation</param-name> <param-value>classpath:springmvc.xml</param-value> </init-param> <load-on-startup>1</load-on-startup> </servlet> <servlet-mapping> <servlet-name>springmvc</servlet-name> <url-pattern>*.action</url-pattern> </servlet-mapping> <context-param> <param-name>contextConfigLocation</param-name> <param-value>classpath:spring/applicationContext-*.xml</param-value> </context-param> <listener> <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class> </listener> </web-app>
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