如何告诉castor将一个空字段编组为一个空标签? [英] How to tell castor to marshall a null field to an empty tag?

问题描述

我正在整理一个可以将某些字段设置为null的对象.我正在使用带有xml映射文件的castor进行配置.我正在编组的课程是这样的:

I'm marshalling an object that can have some field set to null. I'm using castor with a xml-mapping file for the configuration. The class I'm marshalling is like this:

class Entity {
    private int id;
    private String name;
    private String description; // THIS CAN BE NULL
    /* ... getters and setters follow ... */
}

...以及这样的映射文件:

...and a mapping file like this:

<mapping>
    <class name="Entity">
        <field name="id" type="integer"/>
        <field name="name" type="string"/>
        <field name="description" type="string"/>
    </class>
</mapping>

如果该字段为空(简化示例)，我现在会得到什么:

What I'm getting at the moment if the field is null (simplified example):

<entity>
   <id>123</id>
   <name>Some Name</name>
</entity>

尽管我希望在结果XML中有一个空标记，即使description字段为null.

while I want to have an empty tag in the resulting XML, even if the description field is null.

<entity>
   <id>123</id>
   <name>Some Name</name>
   <description /> <!-- open/close tags would be ok -->
</entity>

推荐答案

一种方法是使用GeneralizedFieldHandler.有点hack，但是它可以用于其他字符串类型的字段.

One way to do this is with a GeneralizedFieldHandler. It's a bit of a hack but it will work for other fields that are Strings.

示例:

<mapping>
    <class name="Entity">
        <field name="id" type="integer"/>
        <field name="name" type="string"/>
        <field name="description" type="string" handler="NullHandler"/>
    </class>
</mapping>


public class NullHandler extends GeneralizedFieldHandler {

    @Override
    public Object convertUponGet( Object arg0 )
    {
        if( arg0 == null )
        {
            return "";
        }

        return arg0;
    }

    @Override
    public Object convertUponSet( Object arg0 )
    {
        return arg0;
    }

    @Override
    public Class getFieldType()
    {
        return String.class;
    }

}

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