本节书摘来自异步社区《Spring MVC学习指南（第2版）》一书中的第2章，第2.4节，作者：【美】Paul Deck著，更多章节内容可以访问云栖社区“异步社区”公众号查看
2.4 模型2之Filter分发器
虽然servlet是模型2应用程序中最常见的控制器，但过滤器也可以充当控制器。但请注意，过滤器没有作为欢迎页面的权限。仅输入域名时不会调用过滤器分派器。Struts 2使用过滤器作为控制器，是因为该过滤器也用于提供静态内容。
下面的例子（appdesign2）是一个采用filter分发器的模型2应用，目录结构如图2.5所示。
图2.5 appdesign2目录结构
JSP页面和Product类同appdesign1相同，但没有采用servlet作为控制器，而是使用了一个名为FilterDispatcher的过滤器（见清单2.7）。
清单2.7 DispatcherFilter类
package appdesign2.filter;
import java.io.IOException;
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.annotation.WebFilter;
import javax.servlet.http.HttpServletRequest;
import appdesign2.action.SaveProductAction;
import appdesign2.form.ProductForm;
import appdesign2.model.Product;
import java.math.BigDecimal;
@WebFilter(filterName = "DispatcherFilter",
urlPatterns = { "/*" })
public class DispatcherFilter implements Filter {
@Override
public void init(FilterConfig filterConfig)
throws ServletException {
}
@Override
public void destroy() {
}
@Override
public void doFilter(ServletRequest request,
ServletResponse response, FilterChain filterChain)
throws IOException, ServletException {
HttpServletRequest req = (HttpServletRequest) request;
String uri = req.getRequestURI();
/*
* uri is in this form: /contextName/resourceName, for
* example /appdesign2/input-product. However, in the
* case of a default context, the context name is empty,
* and uri has this form /resourceName, e.g.:
* /input-product
*/
// action processing
int lastIndex = uri.lastIndexOf("/");
String action = uri.substring(lastIndex + 1);
String dispatchUrl = null;
if ("input-product".equals(action)) {
// do nothing
dispatchUrl = "/jsp/ProductForm.jsp";
}else if("save-product".equals(action)) {
// create form
ProductForm productForm = new ProductForm();
// populate action properties
productForm.setName(request.getParameter("name"));
productForm.setDescription(
request.getParameter("description"));
productForm.setPrice(request.getParameter("price"));
// create model
Product product = new Product();
product.setName(productForm.getName());
product.setDescription(product.getDescription());
try {
product.setPrice(new BigDecimal(productForm.getPrice()));
} catch (NumberFormatException e) {
}
// execute action method
SaveProductAction saveProductAction =
new SaveProductAction();
saveProductAction.save(product);
// store model in a scope variable for the view
request.setAttribute("product", product);
dispatchUrl = "/jsp/ProductDetails.jsp";
}
// forward to a view
if (dispatchUrl != null) {
RequestDispatcher rd = request
.getRequestDispatcher(dispatchUrl);
rd.forward(request, response);
} else {
// let static contents pass
filterChain.doFilter(request, response);
}
}
}
doFilter方法的内容同appdesign1中process方法。
由于过滤器的过滤目标是包括静态内容在内的所有网址，因此，若没有相应的action则需要调用filterChain.doFilter()。
} else {
// let static contents pass
filterChain.doFilter(request, response);
}
要测试应用，可以用浏览器访问如下URL：
http://localhost:8080/appdesign2/input-product
