二、出錯管理(Managing Errors)
Struts框架有兩個主要的類來管理出錯，一個是org.apache.struts.action.ActionError類，它對錯誤信息進行包裝。另一個是org.apache.struts.action.ActionErrors類，它是ActionError實例的容器。這兩個類經常要在ActionForm及Action類中使用。其具體的使用如下：
ActionErrors errors = new ActionErrors();
errors.add("propertyname", new ActionError("key");
errors.add(ActionErrors.GLOBAL_ERROR,new ActionError("key");
關于"propertyname"和ActionErrors.GLOBAL_ERROR，對前者用在ActionForm中，這里是對應表現層（JSP）中的屬性值。而對后者則用在Action中，它對應struts-config.xml的<global-forwards />中描述的信息。例子：
ActionForm類：
public class LoginForm extends ActionForm {
…………………
public ActionErrors validate(ActionMapping mapping,HttpServletRequest request) {
ActionErrors errors = new ActionErrors();
if ( (username == null ) || (username.length() == 0) ) {
errors.add("username",new ActionError("errors.username.required"));
}
if ( (password == null ) || (password.length() == 0) ) {
errors.add("password",new ActionError("errors.password.required"));
}
return errors;
}
…………………
}

Action類：
public class LoginAction extends Action {
……………………
public ActionForward execute(ActionMapping mapping,ActionForm form,HttpServletRequest request, HttpServletResponseresponse) throws IOException, ServletException {
String user = null;
// Default target to success
String target = "success";
// Use the LoginForm to get the request parameters
String username = ((LoginForm)form).getUsername();
String password = ((LoginForm)form).getPassword();
user = getUser(username, password);
// Set the target to failure
if ( user == null ) {
target = "login";
ActionErrors errors = new ActionErrors();
errors.add(ActionErrors.GLOBAL_ERROR,new ActionError("errors.login.unknown",username));
// Report any errors we have discovered back to the
// original form
if (!errors.empty()) {
saveErrors(request, errors);
}
}
else {
HttpSession session = request.getSession();
session.setAttribute("USER", user);
}
// Forward to the appropriate View
return (mapping.findForward(target));
}
}
在表現層中表現錯誤只須要寫上<html:error />標簽即可。