A slightly different question that I looked for here: “How do you pass an object to a tag file?”
Answer: Use the “type” attribute of the attribute directive:
<%@ attribute name="field"
required="true"
type="com.mycompany.MyClass" %>
The type defaults to java.lang.String, so without it you’ll get an error if you try to access object fields saying that it can’t find the field from type String.