Spring上传文件，图片，以及常见的问题

1. 在工程依赖库下添加文件上传jar包

　　commons-fileupload-1.2.2.jar
　　commons-io-2.4.jar

2.在springMVC配置文件中配置视图解析multipartResolver

<bean id="multipartResolver" class="org.springframework.web.multipart.commons.CommonsMultipartResolver">
        <property name="maxUploadSize" value="5000000" />
        <property name="defaultEncoding" value="UTF-8" />
    </bean>

　　这里有个问题需要注意一下，Bean 的id必须为multipartResolver，因为在项目初始化的时候，Spring容器会通过这个id来进行注入，下面是Spring源码：

 public static final String MULTIPART_RESOLVER_BEAN_NAME = "multipartResolver";
/** MultipartResolver used by this servlet */
    private MultipartResolver multipartResolver;
/*
   省略一大堆代码
*/
/**
     * Initialize the MultipartResolver used by this class.
     * <p>If no bean is defined with the given name in the BeanFactory for this namespace,
     * no multipart handling is provided.
     */
    private void initMultipartResolver(ApplicationContext context) {
        try {
            this.multipartResolver = context.getBean(MULTIPART_RESOLVER_BEAN_NAME, MultipartResolver.class);
            if (logger.isDebugEnabled()) {
                logger.debug("Using MultipartResolver [" + this.multipartResolver + "]");
            }
        }
        catch (NoSuchBeanDefinitionException ex) {
            // Default is no multipart resolver.
            this.multipartResolver = null;
            if (logger.isDebugEnabled()) {
                logger.debug("Unable to locate MultipartResolver with name ‘" + MULTIPART_RESOLVER_BEAN_NAME +
                        "‘: no multipart request handling provided");
            }
        }
    }

　　接下来，我们测试一下如果写错之后会报什么错误

　　上面只是DEBUG， 查看源码就会知道会DEBUG输出这一句，

　　下面是具体报的错误：预期的MultipartHttpServletRequest：是否配置了MultipartResolver？

下面依次是jsp代码和后台实现上传的java代码：

<form id="userForm" name="userForm" method="post"
        action="${pageContext.request.contextPath }/user/useraddsave.html"
        enctype="multipart/form-data">
            <div>
                <label for="a_idPicPath">证件照：</label> <input type="file"
                    name="a_idPicPath" id="a_idPicPath" /> <font color="red"></font>
            </div>
            <div class="providerAddBtn">
                <input type="button" name="add" id="add" value="保存"> <input
                    type="button" id="back" name="back" value="返回">
            </div>
        </form>

//保存新增用户信息
    @RequestMapping(value="/useraddsave.html",method=RequestMethod.POST)
    public String addUserSave(User user,HttpServletRequest request,@RequestParam(value="a_idPicPath",required=false) MultipartFile multipartFile){

        if(!multipartFile.isEmpty()){
            String path = "/statics"+File.separator+"upload"; //文件或者图片上传到的位置
            String oldName = multipartFile.getOriginalFilename(); //上传的文件名
            String prefix = FilenameUtils.getExtension(oldName); //文件的后缀名
            int maxSize =5000000;
            if(multipartFile.getSize()<maxSize){
                if(prefix.equalsIgnoreCase("jpg")|| prefix.equalsIgnoreCase("png")){
                    String fileName = System.currentTimeMillis()+RandomUtils.nextInt(1000000)+"_Personal."+prefix; // 为避免文件名一样随机生成的文件名保存在服务器
                    File targetFile = new File(path,fileName);
                    if(!targetFile.exists()){
                        targetFile.mkdirs();
                    }
                    try {
                        multipartFile.transferTo(targetFile); //开始上传
                    } catch (Exception e) {
                        // TODO Auto-generated catch block
                        e.printStackTrace();
                        request.setAttribute("uploadFileError", "上傳出現異常，上傳失敗");
                    }
                    String idPicPath= path+File.separator+fileName;
                    user.setIdPicPath(idPicPath);
                    user.setCreationDate(new Date());
                    userService.add(user);
                    return "redirect:/user/userlist.html";
                } else {
                    request.setAttribute("uploadFileError", "文件格式錯誤,上傳失敗");
                }
            } else {
                request.setAttribute("uploadFileError", "文件太大,上傳失敗");
            }
        }
        return "useradd";//新增失败返回到useradd.jsp
    }

　　方法需要添加参数 @RequestParam(value="a_idPicPath",required=false) MultipartFile multipartFile

　　　　　　　　　　　　　　The end......