struts2的XML校验框架小体会

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今天在学习struts2的XML校验框架时，略有晓得，记录下来：

对于如下一个XML配置文件：

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE validators PUBLIC "-//OpenSymphony Group//XWork Validator 1.0.2//EN" "http://www.opensymphony.com/xwork/xwork-validator-1.0.2.dtd">
<validators>
<field name="username">

  <field-validator type="requiredstring">
   <param name="trim">true</param>
   <message>username should not be blank!</message>
  </field-validator>

  <field-validator type="stringlength">
   <param name="minLength">6</param>
   <param name="maxLength">10</param>
   <message>
    username should between ${minLength} and ${maxLength}
   </message>

</field-validator>
</field>
</validators>

对于validator各个属性的确定，是要根据class文件所对应的源文件来解读的：

/*
* Copyright (c) 2002-2006 by OpenSymphony
* All rights reserved.
*/
package com.opensymphony.xwork2.validator.validators;

import com.opensymphony.xwork2.validator.ValidationException;

/**
* 
* StringLengthFieldValidator checks that a String field is of a certain length. If the "minLength"
* parameter is specified, it will make sure that the String has at least that many characters. If
* the "maxLength" parameter is specified, it will make sure that the String has at most that many
* characters. The "trim" parameter determines whether it will {@link String#trim() trim} the
* String before performing the length check. If unspecified, the String will be trimmed.
* 
* <p/>
*
*
* 
* <ul>
*    <li>fieldName - The field name this validator is validating. Required if using Plain-Validator Syntax otherwise not required</li>
*    <li>maxLength - The max length of the field value. Default ignore.</li>
*    <li>minLength - The min length of the field value. Default ignore.</li>
*    <li>trim - Trim the field value before evaluating its min/max length. Default true</li>
* </ul>
* 
*
*
* <pre>
* 
*      <validators>
*           
*           <validator type="stringlength">
*                <param name="fieldName">myPurchaseCode</param>
*                <param name="minLength">10</param>
*                <param name="maxLength">10</param>
*                <param name="trim">true</param>
*                <message>Your purchase code needs to be 10 characters long</message>
*            </validator>
*
*            
*            <field name="myPurchaseCode">
*                <field-validator type="stringlength">
*                     <param name="minLength">10</param>
*                     <param name="maxLength">10</param>
*                     <param name="trim">true</param>
*                     <message>Your purchase code needs to be 10 characters long</message>
*                </field-validator>
*            </field>
*      </validators>
* 
* </pre>
*
*
* @author Jason Carreira
* @author Mark Woon
* @author tmjee
* @version $Date: 2008-06-11 18:20:19 +0800 (鏄熸湡涓�, 11 鍏湀 2008) $ $Id: StringLengthFieldValidator.java 1786 2008-06-11 10:20:19Z rainerh $
*/
public class StringLengthFieldValidator extends FieldValidatorSupport {

    private boolean doTrim = true;
    private int maxLength = -1;
    private int minLength = -1;

    public void setMaxLength(int maxLength) {
        this.maxLength = maxLength;
    }

    public int getMaxLength() {
        return maxLength;
    }

    public void setMinLength(int minLength) {
        this.minLength = minLength;
    }

    public int getMinLength() {
        return minLength;
    }

    public void setTrim(boolean trim) {
        doTrim = trim;
    }

    public boolean getTrim() {
        return doTrim;
    }

    public void validate(Object object) throws ValidationException {
        String fieldName = getFieldName();
        String val = (String) getFieldValue(fieldName, object);

        if (val == null || val.length() <= 0) {
            // use a required validator for these
            return;
        }
        if (doTrim) {
            val = val.trim();
            if (val.length() <= 0) {
            // use a required validator
            return;
            }
        }

        if ((minLength > -1) && (val.length() < minLength)) {
            addFieldError(fieldName, object);
        } else if ((maxLength > -1) && (val.length() > maxLength)) {
            addFieldError(fieldName, object);
        }
    }
}

注意看红色部分标出的地方,这部分虽然是注释语句，但是却比源程序本身更能帮助理解各个param的要求和配置方法，所以这里注释语句是不应该被忽视的，而应该和源程序好好地结合起来，就更加有利于掌握好XML配置校验。