struts声明式异常
struts声明式异常:
在配置文件中配置exception属性,并配以相应在的异常类型,那么程序中遇到这类异常就会自动处理异常信息.
如下例:登录action处理中会抛出UserNotFoundException,那么采用声明式异常:
<action path="/logon" type="com.lwf.struts.action.LogonAction" name="logonForm" input="/logon.jsp" scope="session" validate="true" > <exception key="error.login.usernull" type="com.lwf.struts.util.UserNotFoundException" path="/index.jsp" ></exception> </action>
<%@ page language="java" contentType="text/html; charset=UTF-8" pageEncoding="UTF-8"%><%@ taglib uri="/WEB-INF/struts-html.tld" prefix="html"%><%@ taglib uri="/WEB-INF/struts-bean.tld" prefix="bean" %><%@ taglib uri="/WEB-INF/struts-logic.tld" prefix="logic" %><!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"><html:html><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8"><title>logon</title></head><body><html:errors/><html:form action="logon"><table border="0" width="100%"><tr><th align="right"><bean:message key="login.user"/></th><td align="left"><html:text property="username" size="20" maxlength="20"></html:text></td></tr><tr><th align="right"><bean:message key="login.pwd"/></th><td align="left"><html:password property="password" size="20" maxlength="20"></html:password></td></tr><tr><td align="right"><html:submit>logonin</html:submit></td><td align="left"><html:button property="register" >register</html:button><html:reset>reset</html:reset></td></tr></table></html:form></body></html:html>
package com.lwf.struts.action;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import org.apache.struts.action.Action;import org.apache.struts.action.ActionForm;import org.apache.struts.action.ActionForward;import org.apache.struts.action.ActionMapping;import org.apache.struts.action.ActionMessage;import org.apache.struts.action.ActionMessages;import com.lwf.struts.form.LogonForm;import com.lwf.struts.util.UserManageEntity;import com.lwf.struts.util.UserNotFoundException;public class LogonAction extends Action {public ActionForward execute(ActionMapping mapping, ActionForm form,HttpServletRequest request, HttpServletResponse response)throws Exception {ActionMessages errors = new ActionMessages();ActionForward forward = new ActionForward();LogonForm logonForm = (LogonForm)form;String name = logonForm.getUsername();String pwd = logonForm.getPassword();UserManageEntity.UserManager(name);//try {//UserManageEntity.UserManager(name);//errors.add("logonerror1", new ActionMessage("error.login.user"," myerrmsg"));//this.saveMessages(request, errors);//request.getSession().setAttribute("user", logonForm);//forward = mapping.findForward("success");//} catch (UserNotFoundException e) {//errors.add("logonerror2", new ActionMessage("error.login.again"," error2"));//this.saveErrors(request, errors);//forward = mapping.findForward("error");//}//forward = mapping.findForward("success");return forward;}}package com.lwf.struts.util;public class UserNotFoundException extends Exception {public UserNotFoundException(){}public UserNotFoundException(String message){super(message);}}<action path="/logon" type="com.lwf.struts.action.LogonAction"name="logonForm" input="/logon.jsp" scope="session" validate="true" ><exception key="error.login.usernull" type="com.lwf.struts.util.UserNotFoundException" path="/index.jsp" ></exception></action>
error.login.usernull = user must not null
// Call the Action instance itself ActionForward forward = processActionPerform(request, response, action, form, mapping); protected ActionForward processActionPerform(HttpServletRequest request, HttpServletResponse response, Action action, ActionForm form, ActionMapping mapping) throws IOException, ServletException { try { return (action.execute(mapping, form, request, response)); } catch (Exception e) { return (processException(request, response, e, form, mapping)); } } protected ActionForward processException(HttpServletRequest request, HttpServletResponse response, Exception exception, ActionForm form, ActionMapping mapping) throws IOException, ServletException { // Is there a defined handler for this exception? ExceptionConfig config = mapping.findException(exception.getClass()); if (config == null) { log.warn(getInternal().getMessage("unhandledException", exception.getClass())); if (exception instanceof IOException) { throw (IOException) exception; } else if (exception instanceof ServletException) { throw (ServletException) exception; } else { throw new ServletException(exception); } } // Use the configured exception handling try { ExceptionHandler handler = (ExceptionHandler) RequestUtils.applicationInstance(config .getHandler()); return (handler.execute(exception, config, mapping, form, request, response)); } catch (Exception e) { throw new ServletException(e); } } /*从上面我们知道struts声明式异常默认使用ExceptionHandler 来处理,我们可以自己定义异常处理类,从而改变默认声明式异常处理的行为.在配置文件中exception 中增加handler属性*/ public ActionForward execute(Exception ex, ExceptionConfig ae, ActionMapping mapping, ActionForm formInstance, HttpServletRequest request, HttpServletResponse response) throws ServletException { LOG.debug("ExceptionHandler executing for exception " + ex); ActionForward forward; ActionMessage error; String property; // Build the forward from the exception mapping if it exists // or from the form input <strong> if (ae.getPath() != null) { forward = new ActionForward(ae.getPath()); } else { forward = mapping.getInputForward(); }</strong> // Figure out the error if (ex instanceof ModuleException) { error = ((ModuleException) ex).getActionMessage(); property = ((ModuleException) ex).getProperty(); } else { <strong> error = new ActionMessage(ae.getKey(), ex.getMessage());</strong> property = error.getKey(); } this.logException(ex); // Store the exception request.setAttribute(Globals.EXCEPTION_KEY, ex); this.storeException(request, property, error, forward, ae.getScope()); if (!response.isCommitted()) { return forward; } LOG.debug("Response is already committed, so forwarding will not work." + " Attempt alternate handling."); if (!silent(ae)) { handleCommittedResponse(ex, ae, mapping, formInstance, request, response, forward); } else { LOG.warn("ExceptionHandler configured with " + SILENT_IF_COMMITTED + " and response is committed.", ex); } return null; } /*以上代码是不是解释了异常会默认转向到input指向的jsp页面. 如果在exception添加path属性,如上面path="/index.jsp" 那么异常会转向到index.jsp而不是logon.jsp上面代码也解释了为什么配置文件exception的key属性在这里要与资源文件相对应。因为 */ error = new ActionMessage(ae.getKey(), ex.getMessage()); 这个方法传入的第一个参数为ae.getKey()即exception下的key值。如果我们继承ExceptionHandler并复写了excute方法，可以改变传入的参数值。 //我们也可以定义全局异常 <global-exceptions><exception key="error.login.usernull" type="com.lwf.struts.util.UserNotFoundException" path="/index.jsp" ></exception></global-exceptions>