采取的是spring action 中的例子
验证一个Student对象
   1.implements Validator接口(org.springframework.validation.Validator)
         public class StudentValidator implements Validator
         {
            public boolean supports(Class clazz)//必须实现的方法
            {return clazz.equals(Student.class) ;
            }
            public void validate(Object command,Errors errors)
           {
              Student student =(Student)command;
            // ValidationUtils.rejectIfEmpty  (Errors errors, String field, String errorCode, String defaultMessage)

               ValidationUtils.rejectIfEmpty(errors,"login","required.login","login is required");
               ValidationUtils.rejectIfEmpty(errors,"password","required.password","Password is required");
               ValidationUtils.rejectIfEmpty(errors,"firstName","required.firstName","firstNameis required");
               ValidationUtils.rejectIfEmpty(errors,"lastName","required.lastName","lastNameis required");
               ValidationUtils.rejectIfEmpty(errors,"city","required.login","cityis required");
                                            validateEmail(student .email,errors);
               validatePhone(student .phone,errors);
            }
            
            private static final String PHONE_REGXP="/(\\({0,1}(\\d{3})))/"
            private void validatePhone(String phone, Errors erros)
            {
             ValidationUtils.rejectIfEmpty(errors,"phone","required.phone","phoneis required");
             Perl5Util per5Util=new Perl5Util();
             if(!per5Util.math(PHONE_REGXP,phone))
            {
              errors.reject("invalid.phone","Phone number is invalid");
               }
               }    
              private static final String Email_REGXP="/(\\({0,1}(\\d{3})))/"
            private void validateEmail(String phone, Errors erros)
            {
             ValidationUtils.rejectIfEmpty(errors,"phone","required.phone","phoneis required");
             Perl5Util per5Util=new Perl5Util();
             if(!per5Util.math(Email_REGXP,email))
            {
              errors.reject("invalid.phone","Phone number is invalid");
               }
               }         
     

}
2.配置bean
      <bean id="methodNameResolver"
class="org.springframework.web.servlet.mvc.multiaction.ParameterMethodNameResolver">
<property name="paramName"><value>method</value>
</property>
<property name="defaultMethodName"><value>view</value>
</property>
</bean>
<property name="validator"><bean class="com.StudentValidator "/> 
</property>
<property name="defaultMethodName"><value>view</value>
</property>
<bean name="/jsp/test.do" class="org.nightwalker.spaces.web.controller.TestController">
<property name="methodNameResolver">
<ref local="methodNameResolver"/>
</property>
</bean>

查看源代码：
MultiActionController类：
  protected void bind(ServletRequest request, Object command) throws Exception {
  logger.debug("Binding request parameters onto MultiActionController command");
  ServletRequestDataBinder binder = createBinder(request, command);
  binder.bind(request);
  if (this.validators != null) {
   for (int i = 0; i < this.validators.length; i++) {
      //首先调用supports
      if (this.validators[i].supports(command.getClass())) {
     ValidationUtils.invokeValidator(this.validators[i], command, binder.getErrors());
    }
   }
  }
  binder.closeNoCatch();
 }

类ValidationUtils：
public static void invokeValidator(Validator validator, Object obj, Errors errors) {
  if (validator != null) {
   if (logger.isDebugEnabled()) {
    logger.debug("Invoking validator [" + validator + "]");
   }
   if (obj != null && !validator.supports(obj.getClass())) {
    throw new IllegalArgumentException("Validator " + validator.getClass() +
      " does not support " + obj.getClass());
   }
   validator.validate(obj, errors);
   if (logger.isDebugEnabled()) {
    if (errors.hasErrors()) {
     logger.debug("Validator found " + errors.getErrorCount() + " errors");
    }
    else {
     logger.debug("Validator found no errors");
    }
   }
  }
 }