Custom JSP Tag Extension

Question

How to extend an existing custom JSP tag?

As you know, a user tag consists of two parts: an implementation class and a TLD file. I can extend the parent custom tag class, but how do you “extend” its TLD file? One obvious solution is to cut and paste it and then add my stuff, but I am wondering if there is a more elegant solution, for example, how do you expand the definition of a tile in Apache Tiles.

Thanks.

Answer 1

I don't think you can extend an existing tag, but a similar approach is to use a common abstract superclass for two tag implementation classes:

// define repetitive stuff in abstract class public abstract class TextConverterTag extends TagSupport{ private final long serialVersionUID = 1L; private String text; public String getText(){ return text; } public void setText(final String text){ this.text = text; } @Override public final int doStartTag() throws JspException{ if(text != null){ try{ pageContext.getOut().append(process(text)); } catch(final IOException e){ throw new JspException(e); } } return TagSupport.SKIP_BODY; } protected abstract CharSequence process(String input); } // implementing class defines core functionality only public class UpperCaseConverter extends TextConverterTag{ private final long serialVersionUID = 1L; @Override protected CharSequence process(final String input){ return input.toUpperCase(); } } // implementing class defines core functionality only public class LowerCaseConverter extends TextConverterTag{ private final long serialVersionUID = 1L; @Override protected CharSequence process(final String input){ return input.toLowerCase(); } } 

But I'm afraid you will have to configure each tag class separately, since I don't think that taglib has abstract tag definitions.