About Struts—(六)-JSP教程,面向对象/设计

public actionerrors

  validate(actionmapping mapping,

    httpservletrequest request);

the validate() method is called by the controller servlet after the bean properties have been populated, but before the corresponding action classs perform() method is invoked. the validate() method has the following options:
·   执行适当的校验，没有发现问题 – 返回null or a zero-length actionerrors 实例，然后controller servlet 将调用action类的perform() 方法。
·   执行适当的校验，发现问题 – 返回一个包含有actionerror的actionerrors 实例，actionerror中包含了应该被显示的error message keys 。the controller servlet will store this array as a request attribute suitable for use by the <html:errors> tag, and will forward control back to the input form (identified by the input property for this actionmapping).
正如前面所提到的，这个特征是可选的。缺省的validate() 方法将返回null, and the controller servlet 将假定校验工作由action 类来做。
一个一般的做法是在actionform的validate方法中执行简单的校验，然后在action类中进行"business logic"校验。
an optional package for performing actionform validations is available in the nightly build and from david winterfeldts web site.