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验证器 —— Validator

在执行Action时，输入验证时一个重要的步骤。验证范围从简单的任务到复杂的任务都有，例如简单的有检验某个输入域中是否有值，复杂的有验证信用卡号码等。

Java社区发布了 JSR 303 "Bean Validation"，将Java中的输入验证标准化。

现代的MVC框架经常同时提供编程式和声明式的验证方法。

示例

基于 MVC - 基于Filter Dispatcherr的Model2 - 示例 一节：

添加如下的Validator - ProductValidator.java

package com.gof.test.validator;import java.util.List;import java.util.ArrayList;import com.gof.test.bean.ProductForm;import com.sun.tools.javah.LLNI;public class ProductValidator {	public List
   
     validate(ProductForm productForm){	    List
    
      errors = new ArrayList
     
      ();	    	    String name = productForm.getName();	    if (name == null || name.trim().isEmpty()){	    	errors.add("Product must have a name");	    }	    	    String price = productForm.getPrice();	    if (price == null || price.trim().isEmpty()){	    	errors.add("Price must have a price");	    }else{	    	try{	    		Float.parseFloat(price);	    	}catch (NumberFormatException e){	    		errors.add("Invalid price value");	    	}	    }	    	    return errors;	}}
     
    
   

修改上一个的Filter为：

package com.gof.test.filter;import java.io.IOException;import java.util.List;import javax.servlet.Filter;import javax.servlet.FilterChain;import javax.servlet.FilterConfig;import javax.servlet.RequestDispatcher;import javax.servlet.ServletException;import javax.servlet.ServletRequest;import javax.servlet.ServletResponse;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import com.gof.test.action.SaveProductAction;import com.gof.test.bean.Product;import com.gof.test.bean.ProductForm;import com.gof.test.validator.ProductValidator;public class DispatcherFilter implements Filter {	public void init(FilterConfig filterConfig) throws ServletException {		// TODO Auto-generated method stub	}	public void doFilter(ServletRequest req, ServletResponse resp,			FilterChain chain) throws IOException, ServletException {		String uri = ((HttpServletRequest)req).getRequestURI();		int lastIndex = uri.lastIndexOf("/");		String action = uri.substring(lastIndex + 1);		String dispatchUrlString = null;				if (action.equals("product_input")){			dispatchUrlString = "/jsp/controller/ProductForm.jsp";		}else 		if (action.equals("product_save")){			ProductForm productForm = new ProductForm();						productForm.setName(req.getParameter("name"));			productForm.setDescription(req.getParameter("description"));			productForm.setPrice(req.getParameter("price"));						// begin validate			ProductValidator productValidator = new ProductValidator();			List
   
     errors = productValidator.validate(productForm);			// end validate			if (errors.isEmpty()){				Product product = new Product();				product.setName(productForm.getName());				product.setDescription(productForm.getDescription());				product.setPrice(Float.parseFloat(productForm.getPrice()));								SaveProductAction saveProductAction = new SaveProductAction();				saveProductAction.save(product);								req.setAttribute("product", product);				dispatchUrlString = "/jsp/controller/ProductDetails.jsp";			}else{				req.setAttribute("errors", errors);				req.setAttribute("form", productForm);				dispatchUrlString = "/jsp/controller/ProductForm.jsp";			}					}        		if (dispatchUrlString != null){			RequestDispatcher rDispatcher = req.getRequestDispatcher(dispatchUrlString);			rDispatcher.forward(req, resp);		}else{			chain.doFilter(req, resp);		}	}	public void destroy() {		// TODO Auto-generated method stub	}}
   

修改 ProductForm.jsp如下：

<%@ page language="java" contentType="text/html; charset=utf-8"    pageEncoding="utf-8"%><%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
   
   
    
    
Add a product
    
            
     
            
     
                
                          
       
${error}
                
                  
     
        
     
    
        
    
        
     
                  
       
                        
Product Name:
                        
                   
                   
                        
Description:
                        
                   
                   
                        
Price:
                        
                   
                   
                        
                        
                   
              
     
    
    
   

访问如下URL:

http://localhost:8080/base-webapp/product_input

输入错误信息，提交：