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最近对一个别人的WEB项目进行维护，看到这样的实现方法：
1.只有一个Controller的servlet 类
2.一个Service接口
3.一些实现Service接口的类

Controller类负责进行控制，动态产生业务逻辑的类的实例（所有的类需要实现Service接口)，然后通过
httpservletrequest.setAttribute("USERLIST", userList);向WEB端赋值，

具体的可以参考部分代码:
Controller 类(extends HttpServlet )

 protected void doPost(
 HttpServletRequest request,
 HttpServletResponse response)
 throws ServletException, IOException {
 //service name,example for packagename.ServiceName
 String serviceName = request.getParameter(Constant.SERVICE);
 if (serviceName == null)
 throw new ServletException("There isn't service parameter![?service=]");
 String targetName = request.getParameter(Constant.TARGET);
 //the targeted file name,example for /fileName.jsp
 if (targetName == null)
 throw new ServletException("There isn't target parameter![?target=]");
 ServletContext servletcontext = getServletContext();
 try {
 //TODO:hashmap to reduce the generated instance? 
 Class serviceClass = Class.forName(serviceName);
 Service service = (Service) serviceClass.newInstance();
 service.execute(request, response, servletcontext);
 } catch (ClassNotFoundException classnotfoundexception) {
 throw new ServletException(classnotfoundexception.getMessage());
 } catch (IllegalAccessException illegalaccessexception) {
 throw new ServletException(illegalaccessexception.getMessage());
 } catch (Exception exception) {
 throw new ServletException(exception.getMessage());
 }
 forward(request, response, targetName);
 }

Service 接口

public interface Service {
 public abstract void execute(
 HttpServletRequest httpservletrequest,
 HttpServletResponse httpservletresponse,
 ServletContext servletcontext)
 throws Exception;
}

一个实现service的类（相当于业务类)

public class StartService implements Service {
 public void execute(
 HttpServletRequest httpservletrequest,
 HttpServletResponse httpservletresponse,
 ServletContext servletcontext)
 throws Exception {
//test data
 List userList = new ArrayList();
 httpservletrequest.setAttribute("USERNAME", "TestUser");
 httpservletrequest.setAttribute("USERLIST", userList);
 }
}

JSP 页面文件

<%
String userName=(String)request.getAttribute("USERNAME");
List userList=(List)request.getAttribute("USERLIST");
%>

访问的时候：
/service.Controller?service=StartService&target=/StartPage.jsp