Castor使用之：映射Clob字段到xml文件

在使用Castor将java对象转换为xml文件时，会遇到Clob类型的属性的转换。Castor中没有Clob类型的处理器，因此需要我们自己实现一个ClobFieldHandler。

例如：我们要将Root.java转换成一个xml文件。

1.Root.java

package lab.castor.lab01;

import java.sql.Clob;

public class Root {
	private Clob comment;

	public Clob getComment() {
		return comment;
	}

	public void setComment(Clob comment) {
		this.comment = comment;
	}
}

2.mapping.xml

<?xml version="1.0"?>
<mapping>
  <class name="lab.castor.lab01.Root">
     <field name="comment" type="string" handler="lab.castor.lab01.ClobFieldHandler">
        <bind-xml node="comment"/>
     </field>
  </class>
</mapping>

3.ClobFieldHandler.java

package lab.castor.lab01;

import java.io.Reader;
import java.sql.Clob;

import org.exolab.castor.mapping.GeneralizedFieldHandler;

public class ClobFieldHandler extends GeneralizedFieldHandler {

	/**
	 * Creates a new ClobFieldHandler instance
	 */
	public ClobFieldHandler() {
		super();
	}

	/**
	 * This method is used to convert the value when the getValue method is called. The getValue method will obtain the
	 * actual field value from given 'parent' object. This convert method is then invoked with the field's value. The
	 * value returned from this method will be the actual value returned by getValue method.
	 * 
	 * @param value the object value to convert after performing a get operation
	 * @return the converted value.
	 */
	public Object convertUponGet(Object value) {
		if (value == null) {
			return null;
		}

		StringBuffer sb = new StringBuffer();
		try {
			Clob clob = (Clob) value;
			Reader reader = clob.getCharacterStream();
			if (reader == null) {
				return null;
			}

			char[] charbuf = new char[4096];
			// 解决4096字节大小的限制
			for (int i = reader.read(charbuf); i > 0; i = reader.read(charbuf)) {
				sb.append(charbuf, 0, i);
			}
		} catch (Exception e) {
			//
		}
		return sb.toString();
	}

	/**
	 * This method is used to convert the value when the setValue method is called. The setValue method will call this
	 * method to obtain the converted value. The converted value will then be used as the value to set for the field.
	 * 
	 * @param value the object value to convert before performing a set operation
	 * @return the converted value.
	 */
	public Object convertUponSet(Object value) {
		return null;
	}

	/**
	 * Returns the class type for the field that this GeneralizedFieldHandler converts to and from. This should be the
	 * type that is used in the object model.
	 * 
	 * @return the class type of of the field
	 */
	public Class getFieldType() {
		return Clob.class;
	}

	/**
	 * Creates a new instance of the object described by this field.
	 * 
	 * @param parent The object for which the field is created
	 * @return A new instance of the field's value
	 * @throws IllegalStateException This field is a simple type and cannot be instantiated
	 */
	public Object newInstance(Object parent) throws IllegalStateException {
		// -- Since it's marked as a string...just return null,
		// -- it's not needed.
		return null;
	}

}

没有实现String到Clob的转换。