Question

I’ve examined various questions about taglibs and implicit objects here. While many of the answers present interesting ideas, I haven’t been able to find one that answers this question directly.

So to illustrate my dilemma, say I have a Java class that implements the javax.servlet.jsp.tagext.Tag interface…

import javax.servlet.ServletRequest;
import javax.servlet.jsp.JspException;
import javax.servlet.jsp.PageContext;
import javax.servlet.jsp.tagext.Tag;

class MyTag implements Tag {
    private PageContext _pageContext;

    public void setPageContext(PageContext pageContext) {
        _pageContext = pageContext;
    }
    .
    .
    .

This gives me access to a PageContext object, which provides some useful information about the calling JSP. Problem is, PageContext doesn’t seem to provide access to many of the JSP’s actual implicit objects…

.
.
.
public int doEndTag() throws JspException {
    ServletRequest req = _pageContext.getRequest();
    .
    .
    .
    return EVAL_PAGE;
}

The ServletRequest object depicted above is quite different from HttpServletRequest, which is implemented by the implicit object “request” in the JSP itself. This makes calling such handy methods as HttpServletRequest.getRequestURI() problematic inside my class.

So from reading the answers to several other questions here, I’m left with the impression that there is no out-of-the-box way of getting at the actual implicit objects. I either have to pass them explicitly as attributes of the custom tag in my JSP…

<mc:mytag request="<%=request%>"/>

…or perhaps store them in the hash of some other implicit object I do have access to…

<% session.setAttribute("request", request); %>

Which, if true, naturally leads me to the question… are you friggin’ kidding me?? There’s got to be something key that I’m missing here. Access to the JSP’s implicit objects seems like such a reasonably common thing for me to want in my custom taglib classes. It strikes me as immensely kludgy to have to take such steps every time I require them — especially when I’m being passed something like the PageContext object that could conceivably provide them for me, but doesn’t seem to.

I really feel like I’m missing something basic here, but I can’t for the life of me figure out what that might be. Can someone shed some light on this?

Answer 1

The PageContext does give you access to the current HttpServletRequest, you just need to cast it:

HttpServletRequest req = (HttpServletRequest )_pageContext.getRequest();

This isn’t great, but dates back to a time when people thought there might one day be non-HTTP stuff in the Servlet API.

As for the use of the term “implicit objects”, this only makes sense within the context of the JSP page itself. The term has no meaning beyond that. The “implicit object” representing the current HttpServletRequest is the same object you get from the PageContext.