Non-Field Validator Vs Field-Validator--字段校验和非字段校验

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本文详细介绍了Struts2框架中两种校验器的使用方法：非字段校验器和字段校验器。非字段校验器适用于不特定字段的情况，而字段校验器专门用于指定字段的校验。

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原文：http://struts.apache.org/2.2.1/docs/validation.html

There are two ways you can define validators in your -validation.xml file:

<validator>
<field-validator>

Keep the following in mind when using either syntax:

Non-Field-Validator: The <validator> element allows you to declare both types of validators (either a plain Validator a field-specific FieldValidator). <validator type="expression> <param name="expression">foo gt bar</param> <message>foo must be great than bar.</message> </validator> <validator type="required"> <param name="fieldName">bar</param> <message>You must enter a value for bar.</message> </validator>

fiel d -validator : The <field-validator> elements are basically the same as the <validator> elements except that they inherit the fieldName attribute from the enclosing <field> element. FieldValidators defined within a <field-validator> element will have their fieldName automatically filled with the value of the parent <field> element's fieldName attribute. The reason for this structure is to conveniently group the validators for a particular field under one element, otherwise the fieldName attribute would have to be repeated, over and over, for each individual <validator>.

It is always better to defined field-validator inside a <field> tag instead of using a <validator> tag and supplying fieldName as its param as the xml code itself is clearer (grouping of field is clearer)

Note that you should only use FieldValidators (not plain Validators) within a block. A plain Validator inside a <field> will not be allowed and would generate error when parsing the xml, as it is not allowed in the defined dtd (xwork-validator-1.0.2.dtd)

Declaring a FieldValidator using the <field-validator> syntax

<field name="email_address"> 
    <field-validator type="required"> 
        <message>You cannot leave the email address field empty.</message> 
    </field-validator> 
    <field-validator type="email"> 
        <message>The email address you entered is not valid.</message> 
    </field-validator> 
</field> 







      
       The
 choice is yours. It's perfectly legal to only use elements without the 
elements and set the fieldName attribute for each of them. The following
 are effectively equal:




       

        

          <field name="email_address"> 
    <field-validator type="required"> 
        <message>You cannot leave the email address field empty.</message> 
    </field-validator> 
    <field-validator type="email"> 
        <message>The email address you entered is not valid.</message> 
    </field-validator> 
</field> 
 
<validator type="required"> 
    <param name="fieldName">email_address</param> 
    <message>You cannot leave the email address field empty.</message> 
</validator> 
<validator type="email"> 
    <param name="fieldName">email_address</param> 
    <message>The email address you entered is not valid.</message> 
</validator> 







                
                 
                  
                   译文：





                                   
                                    
                                     
                                                                             




                                     

                                    

                                   




非字段校验器vs字段校验器



这里有两种方法在你的-validation.xml文件里定义校验器

1.<validator>

2.<field-validator>



当你使用这两种方法时请将下面的禁忌于心。



非字段校验器：你可以使用<validator>标签定义两种类型的校验器（抽象出来的校验器或具体字段的校验器）





---------------------------这个没有绑定到具体的字段
<validator type="expression>
    <param name="expression">foo gt bar</param>
    <message>foo must be great than bar.</message>
</validator>
---------------------------这个绑定到了bar字段
<validator type="required">
    <param name="fieldName">bar</param>
    <message>You must enter a value for bar.</message>
</validator> 
 





字段校验器：<field-validator>和<validator>只有一点不同， 那就是<field-validator>的

fieldName属性继承自他的父标签<field>标签。<field>标签通过制定name属性为他的子标签

绑定该指定字段，如：<field name="email_address"> 。采用这种结构的好处，很容易

把针对某一个字段的校验器集合到一个校验器组，否则的话你每个<validator>标签都要写一个

name属性，我的天啊。



在<field>标签下定义<field-validator>标签比在每一个<validator>标签下定义fieldname

参数更清晰。（字段组更清晰）



注意：你只能在field标签里面定义<field-validator>元素，而不能定义抽象的<validator>

元素。如果你在<field>标签里面定义<validator>将导致错误，因为这在 xwork-validator-1.0.2.dtd

是不允许的



在定义 字段校验器时请遵循以下语法规则：

<field name="email_address">
    <field-validator type="required">
        <message>You cannot leave the email address field empty.</message>
    </field-validator>
    <field-validator type="email">
        <message>The email address you entered is not valid.</message>
    </field-validator>
</field>

 

你可以选择之一。你使用非字段校验，并且每一次都为他设定fieldname属性是完全合法的。

下面两种方式是一样的。





<field name="email_address">
    <field-validator type="required">
        <message>You cannot leave the email address field empty.</message>
    </field-validator>
    <field-validator type="email">
        <message>The email address you entered is not valid.</message>
    </field-validator>
</field>
 
<validator type="required">
    <param name="fieldName">email_address</param>
    <message>You cannot leave the email address field empty.</message>
</validator>
<validator type="email">
    <param name="fieldName">email_address</param>
    <message>The email address you entered is not valid.</message>
</validator> 








 
 
 





 
 
字段校验器：

    一个<field>绑定一个字段，一个<field>可以有多个<field-validator>,对一个字段可以有多个校验。

    结构清晰，方便浏览和检查。易于维护。





非字段校验器：



   一个<validator>标签下面只能对一个字段进行校验，如果对一个字段进行多次校验，需要写很多个<validator>,很繁琐。而且不利于维护。

 
 
 
 
 




 
by loverszhaokai