由Servlet到Struts（一）——之Servlet

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举一个简单的servlet的例子：比如查询用户。

（1）在页面输入用户名，点击查询按钮（<input type="submit" value="提交">）进行提交。

（2）根据配置文件web.xml。

  <servlet>  <servlet-name>TestServlet</servlet-name>  <servlet-class>com.ys.servlet.TestServlet</servlet-class>  </servlet>  <servlet-mapping>  <servlet-name>TestServlet</servlet-name>  <url-pattern>*.action</url-pattern>  </servlet-mapping>

（3）执行TestServlet.java

public class TestServlet extends HttpServlet{@Overrideprotected void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {String requestURI = request.getRequestURI();String path = requestURI.substring(requestURI.indexOf("/", 1), requestURI.indexOf("."));Action action = null;if ("/servlet/addUser".equals(path)) {action = new AddUserAction();}else if ("/servlet/delUser".equals(path)) {action = new DelUserAction();}else if ("/servlet/modifyUser".equals(path)) {action = new ModifyUserAction();}else if ("/servlet/queryUser".equals(path)) {action = new QueryUserAction();}else {throw new RuntimeException("请求失败！");}String forward = null;try {forward = action.execute(request, response);} catch (Exception e) {e.printStackTrace();}request.getRequestDispatcher(forward).forward(request, response);}}

在TestServlet中截取URL、根据URL分发到相应的Action，如（Action action = new QueryUserAction()）。

（4）执行QueryUserAction.java

public class QueryUserAction implements Action {@Overridepublic String execute(HttpServletRequest request,HttpServletResponse response) throws Exception {String userName = request.getParameter("userName");//其他查询条件......//调用业务逻辑UserManager userManager = new UserManager();List userList = userManager.query(userName);request.setAttribute("userList", userList);return "/query_success.jsp";//转向路径可以通过配置文件读取}}

（5）转向到相应的视图页面，渲染页面，进行显示。

<body>查询成功！<p><%=request.getAttribute("userList") %></body>

用时序图分析整个流程如下：