Changing Datatype in liferay service layer

your-portlet\docroot\WEB-INF\classes\META-INF
portlet-model-hints.xml

<model-hints>
    <model name="com.abc.portal.community.database.model.TwitterAccount">
        <field name="accountId" type="long" />
        <field name="twitterUserId" type="long" />
        <field name="imageUrl" type="String">
            <hint-collection name="TEXTAREA" />
        </field>
        <field name="twitterScreenName" type="String" />
        <field name="createDate" type="Date" />
        <field name="modifiedDate" type="Date" />
        <field name="lastStatusId" type="long" />
    </model>
    <model name="com.abc.portal.community.database.model.TwitterFeed">
        <field name="feedId" type="long" />
        <field name="accountId" type="long" />
        <field name="feedMessage" type="String">
            <hint-collection name="TEXTAREA" />
        </field>
        <field name="createDate" type="Date" />
    </model>
</model-hints>