【文件上传和下载】是很多系统必备功能， 比如PM\OA\ERP等；系统中常见的开发模式有B/S和C/S，而前者主要是通过浏览器来访问web服务器，一般采用七层协议中的【应用层http】进行数据传输，后者主要通过编程语言开发的app作为客户端来访问服务端，一般采用七层协议中的【传输层tcp】进行数据传输。
文章主要完成简单java web涉及的文件上传和下载功能。
正文
1. java原生servlet实现：
pom.xml配置：
<dependency>
<groupId>javax</groupId>
<artifactId>javaee-api</artifactId>
<version>8.0</version>
<scope>provided</scope>
</dependency>
<dependency>
<groupId>javax</groupId>
<artifactId>javaee-web-api</artifactId>
<version>8.0</version>
<scope>provided</scope>
</dependency>
<dependency>
<groupId>javax.servlet</groupId>
<artifactId>jstl</artifactId>
<version>1.</version>
<scope>runtime</scope>
</dependency>
web.xml配置：
<welcome-file-list>
<welcome-file>/WEB-INF/view/jsp/upload/upload.jsp</welcome-file>
</welcome-file-list>
<!-- 声明Servlet对象 -->
<servlet>
<!-- 指定Servlet对象的名称 -->
<servlet-name>UploadServlet</servlet-name>
<!-- 指定Servlet对象的完整位置，包含包名和类名 -->
<servlet-class>pers.chaffee.servlet.UploadServlet</servlet-class>
</servlet>
<!-- 映射Servlet -->
<servlet-mapping>
<!--<servlet-name>与上面<Servlet>标签的<servlet-name>元素相对应，不可以随便起名 -->
<servlet-name>UploadServlet</servlet-name>
<!-- 用于映射访问URL -->
<url-pattern>/UploadFileServlet</url-pattern>
</servlet-mapping>
servlet实现：
@WebServlet("/UploadServlet")
public class UploadServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) {
//根据文件扩展名设置文件MIME类型
resp.setContentType(getServletContext().getMimeType("hello.txt"));
//设置下载消息响应,提示文件保存attachment
resp.setHeader("Content-Disposition", "attachment;filename=" + "hello");
/*
* 设置缓冲区
* is.read(b)当文件读完时返回-1
*/
try {
//输入流为项目文件，输出流指向浏览器
InputStream is = new FileInputStream("E:\\hello.txt");
// 提供了将二进制数据写入响应的流
ServletOutputStream os = resp.getOutputStream();
int len = -1;
byte[] b = new byte[1024];
while ((len = is.read(b)) != -1) {
os.write(b, 0, len);
}
//关闭流
is.close();
os.close();
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) {
// 文件上传到本地磁盘工厂类
DiskFileItemFactory factory = new DiskFileItemFactory();
//设置内存缓冲区的大小
factory.setSizeThreshold(20480);
//设置临时文件目录,供上传文件过大时临时存储
factory.setRepository(new File("F:\\f"));
//文件上传操作核心类
ServletFileUpload upload = new ServletFileUpload(factory);
//设置限制单个上传文件的大小
upload.setFileSizeMax(50480);
//设置限制总上传文件大小
upload.setSizeMax(80480);
// 这个路径相对当前应用的目录
try {
List<FileItem> formItems = upload.parseRequest(req);
if (formItems != null && formItems.size() > 0) {
// 迭代表单数据
for (FileItem item : formItems) {
// 处理不在表单中的字段
if (!item.isFormField()) {
File storeFile = new File("F:\\fromweb_" + item.getName());
// 保存文件到硬盘
item.write(storeFile);
}
}
}
} catch (FileUploadException e) {
e.printStackTrace();
} catch (Exception e) {
e.printStackTrace();
}
}
}
upload.jsp:
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
<title>Title</title>
</head>
<body>
<h1>文件上传实例</h1>
<!--请求编码类型必须为"multipart/form-data"-->
<form method="post" action="/UploadFileServlet" enctype="multipart/form-data">
选择一个文件:
<input type="file" name="uploadFile"/>
<input type="file" name="uploadFile2"/>
<br/><br/>
<input type="submit" value="上传"/>
</form>
<a href="/UploadFileServlet" rel="nofollow">下载</a>
</body>
</html>
2. java web主流框架【ssm】实现：
pom.xml配置
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-core</artifactId>
<version>${spring.version}</version>
</dependency>
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-webmvc</artifactId>
<version>${spring.version}</version>
</dependency>
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-web</artifactId>
<version>${spring.version}</version>
</dependency>
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-context</artifactId>
<version>${spring.version}</version>
</dependency>
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-context-support</artifactId>
<version>${spring.version}</version>
</dependency>
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-aop</artifactId>
<version>${spring.version}</version>
</dependency>
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-aspects</artifactId>
<version>${spring.version}</version>
</dependency>
web.xml配置
<context-param>
<param-name>contextConfigLocation</param-name>
<!--<param-value>classpath*:applicationContext-*.xml</param-value>-->
<param-value>classpath*:*.xml</param-value>
</context-param>
<listener>
<listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
</listener>
<listener>
<listener-class>org.springframework.web.util.IntrospectorCleanupListener</listener-class>
</listener>
<servlet>
<servlet-name>dispatcherServlet</servlet-name>
<servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
<init-param>
<param-name>contextConfigLocation</param-name>
<param-value>classpath:spring-mvc.xml</param-value>
</init-param>
<load-on-startup>1</load-on-startup>
</servlet>
<servlet-mapping>
<servlet-name>dispatcherServlet</servlet-name>
<url-pattern>/service/*</url-pattern>
</servlet-mapping>
spring-mvc.xml:
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:p="http://www.springframework.org/schema/p"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:context="http://www.springframework.org/schema/context"
xmlns:mvc="http://www.springframework.org/schema/mvc"
xsi:schemaLocation="
http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans-3.2.xsd
http://www.springframework.org/schema/context
http://www.springframework.org/schema/context/spring-context-3.2.xsd
http://www.springframework.org/schema/mvc
http://www.springframework.org/schema/mvc/spring-mvc-3.2.xsd">
<!-- 启动SpringMVC的注解功能 -->
<mvc:annotation-driven/>
<!-- 扫描controller（controller层注入） -->
<context:component-scan base-package="pers.chaffee.controller"/>
<!-- 对模型视图添加前后缀 -->
<bean id="viewResolver"
class="org.springframework.web.servlet.view.InternalResourceViewResolver"
p:prefix="/WEB-INF/view/jsp/" p:suffix=".jsp"/>
<!-- 静态资源不走controller -->
<mvc:resources mapping="/resources/**" location="/resources/"/>
</beans>
servlet实现:
@RequestMapping(value = "/upload2", method = RequestMethod.POST, consumes = {"multipart/form-data"})
public ModelAndView postUpload(HttpServletRequest request, HttpServletResponse response) {
//文件上传核心类
CommonsMultipartResolver multipartResolver = new CommonsMultipartResolver(request.getSession().getServletContext());
//判断request是否有文件上传
if (multipartResolver.isMultipart(request)) {
//通过MultipartHttpServletRequest解析上传请求中的文件
MultipartHttpServletRequest multiRequest = (MultipartHttpServletRequest) request;
//获取上传请求中的所有文件
Iterator<String> iter = multiRequest.getFileNames();
while (iter.hasNext()) {
//转换成spring支持的文件类型MultipartFile
MultipartFile file = multiRequest.getFile(iter.next());
if (file != null) {
File localFile = new File("F:\\f\\" + file.getOriginalFilename());
try {
//将上传文件写到指定位置,此处是本地文件夹
file.transferTo(localFile);
} catch (IllegalStateException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
ModelAndView modelAndView = new ModelAndView();
modelAndView.setViewName("upload/upload2");
return modelAndView;
}
@RequestMapping(value = "/download", method = RequestMethod.GET)
public ResponseEntity<byte[]> downLoad() throws IOException {
byte[] responseBody;
//获取文件
File file = new File("E:\\hello.txt");
InputStream is = new FileInputStream(file);
responseBody = new byte[is.available()];
is.read(responseBody);
HttpHeaders headers = new HttpHeaders();
//设置文件类型
headers.add("Content-Disposition", "attachment;filename=" + file.getName());
//设置Http状态码
HttpStatus stateCode = HttpStatus.OK;
//返回数据
ResponseEntity<byte[]> entity = new ResponseEntity<>(responseBody, headers, stateCode);
return entity;
}
小结
截至目前，只初步完成B/S方式的上传和下载，且文件存储方式仅限本地磁盘。而C/S方式的文件传输可以考虑thrift框架，thrift是一种跨平台跨语言的RPC框架，使用过程中发现在数据量不是很大的情况下thrift应用是一种比较合适的C/S解决方案；另外，文件存储方式可以根据具体情况选用文件服务器、数据库等。
详细的配置信息可以参考这篇文章：