重温经典struts1之自定义全局异常处理类处理异常以及＜exeception＞标签的配置

提示：文章写完后，目录可以自动生成，如何生成可参考右边的帮助文档

前言

前面的文章，我们学习了，Action类中调用Service，通过try…catch代码块，catch自定义异常类，通过ActionMessage类，进行错误信息页面显示，
今天我们来学习，自定义全局异常处理类，无需try…catch代码块，通过配置struts-config.xml文件中的< exeception>标签，统一处理异常，将错误信息显示到页面

需求

如下图所示，
写一个login页面
当用户名和密码不等于admin时，
login页面上显示错误信息：用户名和密码错误

在这里插入图片描述

具体实现步骤

自定义MyException异常类
继承RuntimeException类，定义messageKey和args变量，提供get和set方法，来接收错误消息key和参数内容
这里注意args变量是object数组类型，可以接收多个参数

MyException异常类代码如下：

package xxx.xxx.exception;

public class MyException extends RuntimeException {

	private String messageKey;

	private Object[] args;

	public String getMessageKey() {
		return messageKey;
	}

	public void setMessageKey(String messageKey) {
		this.messageKey = messageKey;
	}

	public Object[] getArgs() {
		return args;
	}

	public void setArgs(Object[] args) {
		this.args = args;
	}

	public MyException(String messageKey) {
		this(messageKey, null);
	}

	public MyException(String messageKey, Object arg) {
		this(messageKey, new Object[] { arg });
	}

	public MyException(String messageKey, Object[] args) {
		this.messageKey = messageKey;
		this.args = args;
	}

}

自定义MyExceptionHandler全局异常处理类
继承ExceptionHandler类，放行自定义MyException以外的异常类，处理我们自定义的异常类,同样，将自定义异常类的消息key和参数赋值到ActionMessage类，返回到页面显示

MyExceptionHandler异常处理类代码如下：

package xxx.xxx.handler;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.apache.struts.Globals;
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.ExceptionHandler;
import org.apache.struts.config.ExceptionConfig;
import org.apache.struts.util.ModuleException;

import xxx.xxx.exception.MyException;

public class MyExceptionHandler extends ExceptionHandler {

	public ActionForward execute(Exception ex, ExceptionConfig ae, ActionMapping mapping, ActionForm formInstance,
			HttpServletRequest request, HttpServletResponse response) throws ServletException {

		if (!(ex instanceof MyException)) {
			return super.execute(ex, ae, mapping, formInstance, request, response);
		}

		ActionForward forward = null;
		ActionMessage error = null;
		String property = null;

		if (ae.getPath() != null) {
			forward = new ActionForward(ae.getPath());
		} else {
			forward = mapping.getInputForward();
		}

		MyException ece = (MyException) ex;
			error = new ActionMessage(ece.getMessageKey(), ece.getArgs());
			property = error.getKey();

		this.logException(ex);

		request.setAttribute(Globals.EXCEPTION_KEY, ex);
		this.storeException(request, property, error, forward, ae.getScope());

		return forward;
	}
}

将自定义MyException异常类和MyExceptionHandler异常处理类，配置到struts-config.xml文件中的< global-exceptions>< exception>标签内，交给struts管理

struts-config.xml代码如下：

	<global-exceptions>
		<exception key=""
		           type="xxx.xxx.exception.MyException"
		           handler="xxx.xxx.handler.MyExceptionHandler"/>
	</global-exceptions>

UserService类中验证用户名和密码，错误时，抛出自定义MyException的异常类
错误消息内容的login.error，是定义在国际化资源文件中。
具体内容参看我之前的文章
重温经典struts1之国际化(I18N)

UserService 代码如下：

package xxx.xxx.service;

import xxx.xxx.exception.MyException;

public class UserService {

	public void login(String username, String password) {
		if (!"admin".equals(username) || !"admin".equals(password)) {
			throw new MyException("login.error", username);
		}
	}

}

action类调用UserService类完成用户名和密码验证
通过下边的示例，可以看到，action中调用service的异常处理代码变得比较简洁。

Action类代码如下：

package xxx.xxx.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 xxx.xxx.form.LoginForm;
import xxx.xxx.service.UserService;

public class LoginAction extends Action {

	@Override
	public ActionForward execute(ActionMapping mapping, ActionForm form, HttpServletRequest request,
			HttpServletResponse response) {

		LoginForm lf = (LoginForm) form;
		String username = lf.getUsername();
		String password = lf.getPassword();

		UserService userService = new UserService();

		ActionMessages messages = new ActionMessages();

		userService.login(username, password);

		ActionMessage message = new ActionMessage("login.success", username);
		messages.add("login.success", message);
		this.saveMessages(request, messages);

		return mapping.findForward("success");

	}
}