初识Struts（十）------异常处理

在Struts框架中，对于异常的处理主要有两种机制：编程式和声明式。

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一、编程式异常处理：

??????????? *? 捕获异常

????? *? 创建相应的异常消息

????? *? 传递异常消息

* ?到相应的页面处理异常

如在Action中：

???????????????????????? try{

???????????????????????? ......

???????????????????????? }catch(UserNotFoundException unf){????????????????????????????????

??????????????????????????????????????? //创建国际化文本消息

??????????????????????????????????????? ActionMessage message = new ActionMessage("user.login.userNameNotFound",username);

???????????????????????????????????????

???????????????????????? ??? messages.add("error1", message);

???????????????????????? ???

???????????????????????? ??? //传递国际化文本消息

???????????????????????? ??? this.saveErrors(request, messages);

???????????????????????? }catch(PasswordErrorException pee){

???????????????????????????????????????

??????????????????????????????????????? //创建国际化文本

??????????????????????????????????????? ActionMessage message = new ActionMessage("user.login.passwordError");

??????????????????????????????????????? messages.add("error2",message);

??????????????????????????????????????? //传递国际化文本

??????????????????????????????????????? this.saveErrors(request, messages);

???????????????????????? }

然后再到页面处理:<html:errors/>

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二、声明式异常处理(即用<exception/>标签配置)：

? ???*? 在相应的action配置中添加<exception>配置(注意：要放在<forward>前面，这是由DTD决定的)

??? <action path="/login"

???????????? type="cn.huan.struts.LoginAction"

???????????? name="loginForm"

???????????? scope="request"

???????????? input="/login.jsp"

???????????? >

????????????

?????????? <exception type="cn.huan.struts.UserNotFoundException" key="user.login.userNameNotFound" path="/login_error.jsp"/>

?????????? <exception type="cn.huan.struts.PasswordErrorException" key="user.login.passwordError" path="/login_error.jsp"/>

??

?????????? <forward name="success" path="/login_success.jsp"/>

?????????? <forward name="error" path="/login_error.jsp"/>

????? </action>

????? ??????其中<exception>的type指定该Exception的类绝对路径(这里是我自己定义的两个RuntimeException)，key指定properties资源文件中的key值，path指定异常处理页面(没配该属性时会到input页面处理，因为默认异常处理类ExceptionHandler会先判断getPath是否有值，非空就new一个该getPath的ActionForward，为空就设置为mapping.getInputForward的值)

?????

????? *? 若多个action都需配同一个exception就可以将其设为全局exception来配置,mapping.findException方法会先到action中找局部exception，若没有就会找全局exception:

? <global-exceptions>

?

????? <exception type="cn.huan.struts.UserNotFoundException" key="user.login.userNameNotFound"/>

????? <exception type="cn.huan.struts.PasswordErrorException" key="user.login.passwordError"/>

?

?? </global-exceptions>

? ???????若没配path就会根据各action中的input属性配置处理异常

??????????

????? *?????? ?页面显示和编码方式一样用<html:messages/>标签或<html:errors/>标签

?

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另、自定义个性化异常

??? 若想把资源文件中配的异常信息都用一个异常来处理，就可自定义异常，并在struts-config.xml中配一处就ok….

?

?????? *? 自定义异常，如 ErrorCodeException.java:

package cn.huan.struts;

/**

?*

?* @author 刘银环

?*

?*/

public class ErrorCodeException extends RuntimeException {

????????? //错误码

????????? private String errorCode;

????????? //栈位符消息

????????? private Object[] args;

?????????

????????? /**

????????? ?* 构造函数一，根据错误码构造

????????? ?* @param errorCode:错误码

????????? ?*/

????????? public ErrorCodeException(String errorCode){

???????????????????????? this(errorCode,null);

????????? }

?????????

????????? /**

ActionForward forward;
ActionMessage error;
String property;

//如果不是自定义的ErrorCodeException，就抛给默认的ExceptionHandler处理
if(!(ex instanceof ErrorCodeException)){
return super.execute(ex, ae, mapping, formInstance, request, response);
}
// Build the forward from the exception mapping if it exists
// or from the form input
if (ae.getPath() != null) {
forward = new ActionForward(ae.getPath());
} else {
forward = mapping.getInputForward();
}

// Figure out the error
if (ex instanceof ModuleException) {
error = ((ModuleException) ex).getActionMessage();
property = ((ModuleException) ex).getProperty();
} else {
ErrorCodeException ece = (ErrorCodeException) ex;
String errorCode = ece.getErrorCode();
Object[] args = ece.getArgs();
error = new ActionMessage(errorCode,args);
property = error.getKey();

// error = new ActionMessage(ae.getKey(), ex.getMessage());
// 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;
}
(上面只给出了重写的execute方法)


* 配置，
<global-exceptions>

<exception key="error.exception" type="cn.huan.struts.ErrorCodeException" handler="cn.huan.struts.ErrorCodeExceptionHandler"/>

</global-exceptions>
上面的key指定properties资源文件中的key值，type指定异常类，handler指定异常的处理类(若没给出就会采用默认的ExceptionHandler)

* 使用：
if(!"admin".equals(username)){
throw new ErrorCodeException("user.login.userNameNotFound",username);
}
if(!"admin".equals(password)){
throw new ErrorCodeException("user.login.passwordError");
}

当然，这种自定义的异常也能处理没有配在资源文件中的异常信息..