How can I set variables from within a custom tag and make them available to the including JSP page?

In 3 simple (and simplified) steps

• Create a TagExtraInfo subclass, defining the names and types of variables in the return value of the getVariableInfo(TagData) method

  public class MyTagExtraInfo extends TagExtraInfo {
      public VariableInfo[] getVariableInfo(TagData data) {
          return new VariableInfo[] {
              new VariableInfo("name", "java.lang.String", true, VariableInfo.NESTED)
          }
      }
  }
  

• In the tag handler class, add the variables to the PageContext as attributes

  public class MyTagHandler extends extends TagSupport {
      public int doStartTag() throws JspTagException {
          pageContext.setAttribute("name", "Duke");     
      }
  }
  

• In the TLD, add a <teiclass> tag specifying the TagExtraInfo subclass

  <tag>
      <name>myTag</name>
      <tagclass>MyTagHandler</tagclass>
      <teiclass>MyTagHandler</teiclass>        
  </tag>