springmvc上传下载文件

1、导入依赖；（jackson是因为在配置文件中添加了配置；）

<!--文件上传-->
<dependency>
    <groupId>commons-fileupload</groupId>
    <artifactId>commons-fileupload</artifactId>
    <version>1.3.3</version>
</dependency>
<!--servlet-api导入高版本的-->
<dependency>
    <groupId>javax.servlet</groupId>
    <artifactId>javax.servlet-api</artifactId>
    <version>4.0.1</version>
</dependency>
<dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-databind</artifactId>
    <version>2.10.0</version>
</dependency>

2、在applicationContext.xml添加相应配置（这里粘出完整配置）；

<?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/beans
        http://www.springframework.org/schema/beans/spring-beans.xsd
        http://www.springframework.org/schema/context
        http://www.springframework.org/schema/context/spring-context.xsd
        http://www.springframework.org/schema/mvc
        http://www.springframework.org/schema/mvc/spring-mvc.xsd">
    <!--自动扫描包，让指定包下的注解生效，由IOC统一管理-->
    <context:component-scan base-package="com.zhang.controller"/>
    <!--让springmvc不处理静态资源-->
    <mvc:default-servlet-handler/>
    <!-- JSON乱码问题配置 -->
    <mvc:annotation-driven>
        <mvc:message-converters register-defaults="true">
            <bean class="org.springframework.http.converter.StringHttpMessageConverter">
                <constructor-arg value="UTF-8"/>
            </bean>
            <bean class="org.springframework.http.converter.json.MappingJackson2HttpMessageConverter">
                <property name="objectMapper">
                    <bean class="org.springframework.http.converter.json.Jackson2ObjectMapperFactoryBean">
                        <property name="failOnEmptyBeans" value="false"/>
                    </bean>
                </property>
            </bean>
        </mvc:message-converters>
    </mvc:annotation-driven>

    <!--视图解析器-->
    <bean class="org.springframework.web.servlet.view.InternalResourceViewResolver" id="internalResourceViewResolver">
        <!--前缀-->
        <property name="prefix" value="/WEB-INF/jsp/"/>
        <!--后缀-->
        <property name="suffix" value=".jsp"/>
    </bean>

    <!--文件上传配置-->
    <bean class="org.springframework.web.multipart.commons.CommonsMultipartResolver" id="multipartResolver">
        <!--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"/>
        <!--上传文件大小上限，单位为字节（10485760=10M）-->
        <property name="maxUploadSize" value="10485760"/>
        <property name="maxInMemorySize" value="40960"/>
    </bean>
</beans>

上传有两种方式；

//@RequestMapping("/file") 将name=file控件得到的文件封装成CommonsMultipartFile 对象
//批量上传CommonsMultipartFile则为数组即可。
@PostMapping("/upload")
public String fileUpload(@RequestParam("file")CommonsMultipartFile file, HttpServletRequest request){

    //获取文件名：file.getOriginalFilename()
    String uploadFileName = file.getOriginalFilename();
    //如果文件名为空，直接返回首页！
    if("".equals(uploadFileName)){
//            return "redirect:/index.jsp";
        return "请选择文件。";
    }
    System.out.println("上传文件名：" + uploadFileName);

    //上传路径保存设置
    String path = request.getServletContext().getRealPath("/upload");
    //如果路径不存在，创建一个
    File realPath = new File(path);
    if(!realPath.exists()){
        realPath.mkdir();
    }
    System.out.println("上传文件保存地址：" + realPath);
    InputStream inputStream = null;
    OutputStream outputStream = null;
    try {
        inputStream = file.getInputStream();//文件输入流
        outputStream = new FileOutputStream(new File(realPath,uploadFileName));//文件输出流

        //读取写出
        int len = 0;
        byte[] buffer = new byte[1024];
        while ((len = inputStream.read(buffer)) != -1){
            outputStream.write(buffer,0,len);
            outputStream.flush();
        }
    } catch (IOException e) {
        e.printStackTrace();
    }finally {
        if(outputStream != null){
            try {
                outputStream.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        if(inputStream != null){
            try {
                inputStream.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
    return "上传成功";
//        return "redirect:/index.jsp";
}
//采用file.Transto来保存上传的文件
@PostMapping("/upload2")
public String fileUpload2(@RequestParam("file")CommonsMultipartFile file, HttpServletRequest request){
    //上传路径保存设置
    String path = request.getServletContext().getRealPath("/upload");
    //如果路径不存在，创建一个
    File realPath = new File(path);
    if(!realPath.exists()){
        realPath.mkdir();
    }
    System.out.println("上传文件保存地址：" + realPath);
    //通过CommonsMultipartFile的方法直接写文件（注意这个时候）
    try {
        file.transferTo(new File(realPath + "/" + file.getOriginalFilename()));
//            return "redirect:/index.jsp";
        return "上传成功";
    } catch (IOException e) {
        e.printStackTrace();
    }
    return "";
//        return "redirect:/index.jsp";
}

对应前端页面；

<form action="${pageContext.request.contextPath}/upload" enctype="multipart/form-data" method="post">
  <input type="file" name="file"/>
  <input type="submit" value="upload"/>
</form>
<form action="${pageContext.request.contextPath}/upload2" enctype="multipart/form-data" method="post">
  <input type="file" name="file"/>
  <input type="submit" value="upload"/>
</form>

下载

@RequestMapping("/download")
public String downloads(HttpServletResponse response,HttpServletRequest request){
    String path = request.getServletContext().getRealPath("/upload");
    //下载哪个文件，写哪个名字
    String filename ="L2Dwidget.min.js";

    //1、设置response响应头
    response.reset();//设置页面不缓存，清空buffer；
    response.setCharacterEncoding("UTF-8");//字符编码
    response.setContentType("multipart/form-data");//二进制传输数据

    try{
        response.setHeader("Content-Disposition",
                "attachment;filename=" + URLEncoder.encode(filename,"UTF-8"));
    }catch (UnsupportedEncodingException e){
        e.printStackTrace();
    }

    File file = new File(path, filename);
    InputStream inputStream = null;
    OutputStream outputStream = null;
    try {
        inputStream = new FileInputStream(file);//文件输入流
        outputStream = response.getOutputStream();//文件输出流

        //读取写出
        int len = 0;
        byte[] buffer = new byte[1024];
        while ((len = inputStream.read(buffer)) != -1){
            outputStream.write(buffer,0,len);
            outputStream.flush();
        }
    } catch (IOException e) {
        e.printStackTrace();
    }finally {
        if(outputStream != null){
            try {
                outputStream.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        if(inputStream != null){
            try {
                inputStream.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
    return "下载成功。";
}