从源代码剖析Struts2中用户自定义配置转换器的两种方式——基于字段的配置转换器和基于类型的配置转换器（解决了实际系统中，因没有区分这两种工作方式的生命周期而引起的异常错误问题）

接口及类进行解析

TypeConverter（接口）

Interface for accessing the type conversion facilities within a context. This interface was copied from OGNL‘s TypeConverter

DefaultTypeConverter

public class DefaultTypeConverter implements TypeConverter

Default type conversion. Converts among numeric types and also strings. Contains the basic type mapping code from OGNL.

StrutsTypeConverter

public abstract class StrutsTypeConverter extends DefaultTypeConverter

Base class for type converters used in Struts. This class provides two abstract methods that are used to convert both to and from strings -- the critical functionality that is core to Struts‘s type coversion system.

ConversionAction.java文件

package com.atguigu.struts2.app;

import com.atguigu.struts2.model.Customer;

import com.opensymphony.xwork2.ActionSupport;

import com.opensymphony.xwork2.ModelDriven;

public class ConversionAction extends ActionSupport implements ModelDriven<Customer>{

    private static final long serialVersionUID = 1L;

    public String execute(){

       System.out.println("model: " + model);

       return "success";

    }

    private Customer model;

    @Override

    public Customer getModel() {

       model = new Customer();

       return model;

    }

}

DateConverter.java文件

package com.atguigu.struts2.app.converters;

import java.text.DateFormat;

import java.text.ParseException;

import java.text.SimpleDateFormat;

import java.util.Date;

import java.util.Map;

import javax.servlet.ServletContext;

import org.apache.struts2.ServletActionContext;

import org.apache.struts2.util.StrutsTypeConverter;

public class DateConverter extends StrutsTypeConverter {

    private DateFormat dateFormat;

    public DateConverter() {

       System.out.println("DateConverter‘s constructor...");

       /**

       //应用加载时机不同而产生的异常（NullException）

       //获取当前 WEB 应用的初始化参数 pattern(该参数在WEB-INF下的web.xml文件中)

       //这种方法使用/struts2-6/Customer-conversion.properties配置文件

       //Customer-conversion.properties配置文件的内容：

       //birth=com.atguigu.struts2.app.converters.DateConverter

       ServletContext servletContext = ServletActionContext.getServletContext();

       System.out.println(servletContext);

       String pattern = servletContext.getInitParameter("pattern");

       dateFormat = new SimpleDateFormat(pattern);

        *

        */

    }

    /**

     * 解决上面的问题，而重写的一个方法

     * @return

     */

    public DateFormat getDateFormat(){

       if(dateFormat == null){

           //获取当前 WEB 应用的初始化参数 pattern(该参数在WEB-INF下的web.xml文件中)

           //第一次用的时候获取，并加载相关的信息

           //这种方法是使用/struts2-6/src/xwork-conversion.properties配置文件

           //xwork-conversion.properties配置文件的内容：

           //java.util.Date=com.atguigu.struts2.app.converters.DateConverter

           ServletContext servletContext = ServletActionContext.getServletContext();

           System.out.println(servletContext);

           String pattern = servletContext.getInitParameter("pattern");

           dateFormat = new SimpleDateFormat(pattern);

       }

       return dateFormat;

    }

    @Override

    public Object convertFromString(Map context, String[] values, Class toClass) {

       System.out.println("convertFromString...");

       if(toClass == Date.class){

           if(values != null && values.length > 0){

              String value = values[0];

              try {

                  // return dateFormat.parseObject(value);

                  return getDateFormat().parseObject(value);

              } catch (ParseException e) {

                  e.printStackTrace();

              }

           }

       }

       //若没有转换成功, 则返回 values

       return values;

    }

    @Override

    public String convertToString(Map context, Object o) {

       System.out.println("convertToString...");

       if(o instanceof Date){

           Date date = (Date) o;

           //return dateFormat.format(date);

           return getDateFormat().format(date);

       }

       //若转换失败返回 null

       return null;

    }

}

<s:form action="testConversion" theme="simple">

       Age: <s:textfield name="age" label="Age"></s:textfield>

       ${fieldErrors.age[0] }

       ^<s:fielderror fieldName="age"></s:fielderror>

       <br><br>

       Birth: <s:textfield name="birth"></s:textfield>

       <s:fielderror fieldName="birth"></s:fielderror>

       <br><br>

       <s:submit></s:submit>

    </s:form>

<?xml version="1.0" encoding="UTF-8" ?>

<!DOCTYPE struts PUBLIC

    "-//Apache Software Foundation//DTD Struts Configuration 2.3//EN"

    "http://struts.apache.org/dtds/struts-2.3.dtd">

<struts>

    <package name="default" namespace="/" extends="struts-default">

       <action name="testConversion" class="com.atguigu.struts2.app.ConversionAction">

           <result>/success.jsp</result>

           <result name="input">/index.jsp</result>

       </action>

       <action name="testComplextProperty" class="com.atguigu.struts2.app.TestComplextPropertyAction">

           <result>/success.jsp</result>

       </action>

       <action name="testConversion2" class="com.atguigu.struts2.app.TestCollectionAction">

           <result>/success.jsp</result>

       </action>

    </package>

</struts>