在SpringMVC框架下实现文件的 上传和 下载

<?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_2_5.xsd" 
id="WebApp_ID" version="2.5">
  
     <!-- 配置SpringMVC的DispatcherServlet -->
    <servlet>
        <servlet-name>springDispatcherServlet</servlet-name>
        <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
        <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>springDispatcherServlet</servlet-name>
        <url-pattern>/</url-pattern>
    </servlet-mapping>
  
    <!-- 配置 HiddenHttpMethodFilter: 把 POST 请求转为 DELETE、PUT 请求 -->
      <filter>
          <filter-name>HiddenHttpMethodFilter</filter-name>
          <filter-class>org.springframework.web.filter.HiddenHttpMethodFilter</filter-class>
      </filter>
      
      <filter-mapping>
          <filter-name>HiddenHttpMethodFilter</filter-name>
          <url-pattern>/*</url-pattern>
      </filter-mapping>
  
</web-app>

<?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:context="http://www.springframework.org/schema/context"
    xmlns:mvc="http://www.springframework.org/schema/mvc"
    xsi:schemaLocation="http://www.springframework.org/schema/mvc http://www.springframework.org/schema/mvc/spring-mvc-4.0.xsd
        http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
        http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-4.0.xsd">
    
    <!-- 配置自动扫描的包 -->
    <context:component-scan base-package="com.atguigu.springmvc"></context:component-scan>
    
    <!-- 配置视图解析器 -->
    <bean class="org.springframework.web.servlet.view.InternalResourceViewResolver">
        <property name="prefix" value="/WEB-INF/views/"></property>
        <property name="suffix" value=".jsp"></property>
    </bean>
    
    <!--  
        default-servlet-handler 将在 SpringMVC 上下文中定义一个 DefaultServletHttpRequestHandler,
        它会对进入 DispatcherServlet 的请求进行筛查, 如果发现是没有经过映射的请求, 就将该请求交由 WEB 应用服务器默认的 
        Servlet 处理. 如果不是静态资源的请求，才由 DispatcherServlet 继续处理

        一般 WEB 应用服务器默认的 Servlet 的名称都是 default.
        若所使用的 WEB 服务器的默认 Servlet 名称不是 default，则需要通过 default-servlet-name 属性显式指定
        
    -->
    <mvc:default-servlet-handler/>
    
    <!-- 一般都会配置这个 <mvc:annotation-driven ></mvc:annotation-driven>，
    由于。。。requestmapping请求实现不了，使用这个，会使requestmapping请求一定实现
    -->
    <mvc:annotation-driven ></mvc:annotation-driven>
    
   
</beans>

@Controller
public class SpringMVCTest {
    
    @Autowired
    private EmployeeDao employeeDao;
    //实现文件的下载
    //需要说明的是文件的上传和下载不需要其他配置
    @RequestMapping("testResponseEntity")
    public ResponseEntity<byte[]> testResponseEntity(HttpSession session) throws IOException{
        
        byte[] body=null;
        ServletContext servletContext=session.getServletContext();
        ///files/abc.txt：所要下载文件的地址
        InputStream in=servletContext.getResourceAsStream("/files/abc.txt");
        body=new byte[in.available()];
        in.read(body);
        
        HttpHeaders headers=new HttpHeaders();
        //响应头的名字和响应头的值
        headers.add("Content-Disposition", "attachment;filename=abc.txt");
        
        HttpStatus statusCode=HttpStatus.OK;
        
        ResponseEntity<byte[]> response=new ResponseEntity<byte[]>(body, headers, statusCode);
        return response;
    }
    
    //实现文件上传
    @ResponseBody
    @RequestMapping("/testHttpMessageConverter")
    public String testHttpMessageConverter(@RequestBody String body){
        System.out.println(body);
        return "helloworld!"+new Date();
    }
    

}

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>
    
    <center>
   
    <!-- 文件上传的表单 -->
    <form action="testHttpMessageConverter" method="post" enctype="multipart/form-data">
        File: <input type="file" name="file"/>
        Desc: <input type="text" name="desc"/>
        <input type="submit" value="Submit"/>
    </form>
    <br><br>
    
    <!-- 文件的下载 -->
    <a href="testResponseEntity">Test ResponseEntity</a>
    
    </center>
    
</body>
</html>