【FAQ】SpingMVC實現集合參數（Could not instantiate bean class [java.util.List]）

需求，要求批量新增或者改動一個List，在Spring MVC中是不支持以下代碼的寫法

	@RequestMapping(value = "/update", method = RequestMethod.POST)
	public String update(List<ProductCollocation> productCollocations ,HttpServletRequest request, RedirectAttributes redirectAttributes) {
		for (ProductCollocation productCollocation : productCollocations) {
			productCollocation.setModifyDate(DateUtil.getDate());
			productCollocationService.update(productCollocation, "create_date","product","collocation","description");
		}
		addFlashMessage(redirectAttributes, SUCCESS_MESSAGE);
		return "redirect:list.jhtml";
	}

會拋出異常

nested exception is org.springframework.beans.BeanInstantiationException: Could not instantiate bean class [java.util.List]: 

是否事實上也非常easy，Spring MVC 須要支持Form表單對象的方式映射，使用get set器來填充對象。

新增一個Form

public class ProductCollocationForm {
	List<ProductCollocation> productCollocations;

	/**
	 * @return the productCollocations
	 */
	public List<ProductCollocation> getProductCollocations() {
		return productCollocations;
	}

	/**
	 * @param productCollocations the productCollocations to set
	 */
	public void setProductCollocations(List<ProductCollocation> productCollocations) {
		this.productCollocations = productCollocations;
	}
}

再使用Form來set對象

	@RequestMapping(value = "/update", method = RequestMethod.POST)
	public String update(ProductCollocationForm productCollocationForm ,HttpServletRequest request, RedirectAttributes redirectAttributes) {
		for (ProductCollocation productCollocation : productCollocationForm.getProductCollocations()) {
			productCollocation.setModifyDate(DateUtil.getDate());
			productCollocationService.update(productCollocation, "create_date","product","collocation","description");
		}
		addFlashMessage(redirectAttributes, SUCCESS_MESSAGE);
		return "redirect:list.jhtml";
	}

前台就能夠使用索引的方式對后台對象設置值了

<td>
				   <input type="text" name="productCollocations[${productCollocation_index}].displayName" class="text" maxlength="200"  style="width:100px"  value="${productCollocation.displayName}"/>
				   <input type="hidden" name="productCollocations[${productCollocation_index}].id" class="text" maxlength="200" value="${productCollocation.id}"/>
				</td>