第一步 导jar

commons-fileupload-1.3.3.jar
相关pom描述文件

    <!--文件上传  -->
    <dependency>
        <groupId>commons-fileupload</groupId>
        <artifactId>commons-fileupload</artifactId>
        <version>1.3.3</version>
    </dependency>

第二步 配置文件

springmvc.xml里配置文件上传解析器

 <bean id="multipartResolver"
    class="org.springframework.web.multipart.commons.CommonsMultipartResolver">

    <!-- one of the properties available; the maximum file size in bytes -->
<property name="maxUploadSize" value="1024000"/>
 </bean>

第三步 写前后台

前台

<form method="post" action="<%=request.getContextPath()%>/file/upload.action" enctype="multipart/form-data">
 真实姓名:<input type="text" name="userName"/> 
  头像：<input type="file" name="file"><br>
  <input type="submit"/>
</form> 

后台

建文件夹images/upload

public class UUIDGenerateUtil {
   public static String getUUID(){
       return UUID.randomUUID().toString().replaceAll("-", "");
   }
}

  @RequestMapping("/upload")
 public String fileUpload(MultipartFile file,String userName,HttpServletRequest request){
 System.out.println("文件到达后台");
 //要把文件存储到服务器 images/upload
 //首先要拿到/images/upload的绝对路径 
 //e:/tomcat/images/upload   /home/tomcat/images/upload
String path= request.getRealPath("/images/upload");
//生成文件名
//从用户传过来的file里可以拿到原始文件名，然后我们给他加上唯一标识，合成一个不会重复的文件名
String uuid=UUIDGenerateUtil.getUUID();
String old_file=file.getOriginalFilename();
String new_filename=uuid+old_file;
File f=new File(path,new_filename);
try {
    //文件持久化
    file.transferTo(f);
    //拼装一个user对象，持久化到数据库表(包括头像文件名)
} catch (IllegalStateException e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
} catch (IOException e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
}
request.setAttribute("filename", new_filename);
return "index";

}

Index.jsp

<img src="<%=request.getContextPath()%>/images/upload/${filename}"/>