What's wrong with this picture.

Werner van Mook Thu, 18 Mar 2004 09:29:59 -0800

Hi all,

I created a jsp with this tag :

<ina:displayResponse />

I included a taglib directive and did all things I should do to get it working.

The class for this tag is :

import java.io.IOException;
import java.util.Enumeration;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.jsp.JspException;
import javax.servlet.jsp.JspWriter;
import javax.servlet.jsp.PageContext;
import javax.servlet.jsp.tagext.TagSupport;

import util.Message;

public class DisplayResponse extends TagSupport {

// The next line is line 54 Enumeration e = pageContext.getAttributeNamesInScope(PageContext.REQUEST_SCOPE);

        public int doStartTag() throws JspException {
                JspWriter out = pageContext.getOut();

                try {                   
                                if(e.hasMoreElements()) {
                                        out.println((String)e.nextElement());
                                } else {
                                        out.println("It has no more elements.");
                                }
                                out.println("Just transformed o into message.");
                } catch (IOException ioe) {
                        ioe.printStackTrace();
                }
                return SKIP_BODY;
        }
}

If I run this I get a nullPointerException on the line defining the enumeration. see :

javax.servlet.ServletException org.apache.jasper.runtime.PageContextImpl.doHandlePageException(PageCont extImpl.java:864) org.apache.jasper.runtime.PageContextImpl.handlePageException(PageContex tImpl.java:800) org.apache.jsp.view_jsp._jspService(view_jsp.java:67) org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:133) javax.servlet.http.HttpServlet.service(HttpServlet.java:856) org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.ja va:311) org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java: 301) org.apache.jasper.servlet.JspServlet.service(JspServlet.java:248) javax.servlet.http.HttpServlet.service(HttpServlet.java:856)

root cause java.lang.NullPointerException tags.DisplayResponse.(DisplayResponse.java:54) sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method) sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorA ccessorImpl.java:39) sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingCons tructorAccessorImpl.java:27) java.lang.reflect.Constructor.newInstance(Constructor.java:274) java.lang.Class.newInstance0(Class.java:308) java.lang.Class.newInstance(Class.java:261) org.apache.jasper.runtime.TagHandlerPool.get(TagHandlerPool.java:161) org.apache.jsp.view_jsp._jspx_meth_ina_displayResponse_0(view_jsp.java: 78) org.apache.jsp.view_jsp._jspService(view_jsp.java:59) org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:133) javax.servlet.http.HttpServlet.service(HttpServlet.java:856) org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.ja va:311) org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java: 301) org.apache.jasper.servlet.JspServlet.service(JspServlet.java:248) javax.servlet.http.HttpServlet.service(HttpServlet.java:856)

If I would change it to someting like :

Enumeration e = ((HttpServletRequest)pageContext.getRequest()).getAttributeNames(); I get the expected result. see :

message Just transformed o into message.


According to the docs getAttributeNamesInScope can only throw :
        java.lang.IllegalArgumentException or
        java.lang.IllegalStateException


So is this a bug?
Or did I miss something?

Werner van Mook
Java Lead Developer / Trainer
Connecties Voor Internet

What's wrong with this picture.

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