struts声明式异常

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Util

Struts Exception

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;
	}

	
}

上面注释部分就是采用编程式异常的代码.现在采用声明式异常就不用不需要再catch异常

package com.lwf.struts.util;

public class UserNotFoundException extends Exception {

	public UserNotFoundException(){}
	public UserNotFoundException(String message){
		super(message);
	}
}

查看配置文件中注意:

<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>

type异常类型,key消息文本.当struts碰到这个异常会默认转向到input指向的jsp页面.消息文本为key所指的值.
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
ApplicationResources.properties文件中内容:

error.login.usernull = user must not null

运行程序输出结果:

user must not null

看看struts源代码:

// 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>

那么当前应用如果配置了input属性,发生异常转向该属性所指页面,如果当前应用配置了exception配置了path则转向path所指页面,如果当前应用input,path都没有或者当前应用没配置exception,那么查找是否配置全局异常,如果有配置，那么转向到全局应用的path所指页面

在上面我们知道声明式异常默认采用ExceptionHandler来处理.但我们修改资源文件将

error.login.usernull = user must not null

改为

error.login.usernull = user must not null{0}

即增加参数我们会发现默认的异常处理并不能输出参数信息.

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2011-07-13 16:37
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