在Spring MVC 5中使用MultipartFile总是返回null

Question

我无法将图像上传到服务器中的特定目录。多部分文件变量总是空的，这里我的代码

配置Bean

 @Bean
public CommonsMultipartResolver multipartResolver()
{
    CommonsMultipartResolver resolver = new CommonsMultipartResolver();
    resolver.setDefaultEncoding("utf-8");
    return resolver;
}

领域类别

private MultipartFile producImage;

public MultipartFile getProductImage() {
    return producImage;
}

public void setProducImage(MultipartFile producImage) {
    this.producImage = producImage;
}

控制器类

   @RequestMapping(value = "/products/add", method = RequestMethod.POST)
public String processAddNewProductForm(@ModelAttribute("newProduct") Product newProduct, BindingResult result, HttpServletRequest request)
{
    String[] suppressedFields = result.getSuppressedFields();
    if(suppressedFields.length > 0)
    {
        throw new RuntimeException("Attempting to bind disallowed fields " + StringUtils.arrayToCommaDelimitedString(suppressedFields));
    }
    // productImage always receive null value !!!!!!
    MultipartFile productImage = newProduct.getProductImage();
    String rootDirectory = request.getSession().getServletContext().getRealPath("/");
    if(productImage != null && !productImage.isEmpty())
    {
        try
        {
            productImage.transferTo(new File(rootDirectory + "resources\\images\\" + newProduct.getProductId() + ".png"));
        }
        catch(Exception ex)
        {
            throw new RuntimeException("Product Image Saving failed", ex);
        }
    }

    productService.addProduct(newProduct);
    return "redirect:/market/products";
}

前端：addproduct.jsp

  <form:form method="POST" modelAttribute="newProduct" class="form-horizontal" enctype="multipart/form-data">
            <fieldset>
                <legend>Add New Product</legend>
                <div class="form-group">
                    <label class="control-label col-lg-2" for="productImage">
                        <spring:message code="addProduct.form.productImage.label" />
                    </label>
                    <div class="col-lg-10">
                        <form:input id="productImage" path="productImage" type="file" class="form:input-large" />
                    </div>
                </div>
                <div class="form-group">
                    <div class="col-lg-offset-2 col-lg-10">
                        <input type="submit" id="btnAdd" class="btn btn-primary" value ="Add"/>
                    </div>
                </div>
            </fieldset>
        </form:form>

我不知道为什么不工作。提前感谢您的帮助。

Answer 1

您必须初始化MultipartFilter类型的bean并设置multipart解析器，使Spring能够处理包含文件的请求：

@Bean
public MultipartFilter multipartFilter(){

    MultipartFilter multipartFilter = new MultipartFilter();
    multipartFilter.setMultipartResolverBeanName("multipartResolver");
    return multipartFilter;
}