Recipe 13.5. Troubleshooting JSP Pages

Recipe 13.5. Troubleshooting JSP Pages Problem You want to see a dump of the names and values of servlet request and HTTP session attributes and for a particular JSP page so you can troubleshoot rendering problems. Solution Include the debug.jsp file shown on the JSP page (see Example 13-5). Example 13-5. JSP dump of request, session, and context data <hr width="3px"> Debug Information:<br> <table border="1" width="50%" class="debug"> <tr> <th colspan="3" style="background:orange"> <b>Request Parameters</b> </th> </tr> <c:forEach items="${paramValues}" var="parameter"> <tr> <td><c:out value="${parameter.key}"/></td> <td colspan="2"> <c:forEach var="value" items="${parameter.value}"> <textarea rows="2" cols="50"> <c:out value="${value}"/> </textarea> </c:forEach> </td> </tr> </c:forEach> <tr> <th colspan="3" style="background:orange"> <b>Header Values</b> </th> </tr> <c:forEach items="${header}" var="h"> <tr> <td><c:out value="${h.key}"/></td> <td colspan="2"> <textarea rows="2" cols="50"> <c:out value="${h.value}"/> </textarea> </td> </tr> </c:forEach> <tr> <th colspan="3" style="background:orange"> <b>Initialization Parameters</b> </th> </tr> <c:forEach items="${initParam}" var="parameter"> <tr> <td><c:out value="${parameter.key}"/></td> <td colspan="2"> <textarea rows="2" cols="50"> <c:out value="${parameter.value}"/> </textarea> </td> </tr> </c:forEach> <tr> <th colspan="3" style="background:orange"> <b>Cookies</b> </th> </tr> <c:forEach items="${cookie}" var="mapEntry"> <tr> <td rowspan="8"><c:out value="${mapEntry.key}"/></td> <td align="right">Name:</td> <td><c:out value="${mapEntry.value.name}"/></td> </tr> <tr> <td align="right">Value:</td> <td><c:out value="${mapEntry.value.value}"/></td> </tr> <tr> <td align="right">Domain:</td> <td><c:out value="${mapEntry.value.domain}"/></td> </tr> <tr> <td align="right">Max Age:</td> <td><c:out value="${mapEntry.value.maxAge}"/></td> </tr> <tr> <td align="right">Path:</td> <td><c:out value="${mapEntry.value.path}"/></td> </tr> <tr> <td align="right">Secure:</td> <td><c:out value="${mapEntry.value.secure}"/></td> </tr> <tr> <td align="right">Version:</td> <td><c:out value="${mapEntry.value.version}"/></td> </tr> <tr> <td align="right">Comment:</td> <td><c:out value="${mapEntry.value.comment}"/></td> </tr> </c:forEach> <tr> <th colspan="3" style="background:orange"> <b>Page Scope Attributes</b> </th> </tr> <c:forEach items="${pageScope}" var="itm"> <c:if test="${itm.key != 'javax.servlet.jsp.jspResponse'}"> <tr> <td><c:out value="${itm.key}"/></td> <td colspan="2"> <textarea rows="2" cols="50"> <c:out value="${itm.value}"/> </textarea> </td> </tr> </c:if> </c:forEach> <tr> <th colspan="3" style="background:orange"> <b>Request Scope Attributes</b> </th> </tr> <c:forEach items="${requestScope}" var="itm"> <tr> <td><c:out value="${itm.key}"/></td> <td colspan="2"> <textarea rows="2" cols="50"> <c:out value="${itm.value}"/> </textarea> </td> </tr> </c:forEach> <tr> <th colspan="3" style="background:orange"> <b>Session Scoped Attributes</b> </th> </tr> <c:forEach items="${sessionScope}" var="itm"> <tr> <td><c:out value="${itm.key}"/></td> <td colspan="2"> <textarea rows="2" cols="50"> <c:out value="${itm.value}"/> </textarea> </td> </tr> </c:forEach> <tr> <th colspan="3" style="background:orange"> <b>Application Scope Attributes</b> </th> </tr> <c:forEach items="${applicationScope}" var="itm"> <tr> <td><c:out value="${itm.key}"/></td> <td colspan="2"> <c:choose> <c:when test="${itm.key eq 'org.apache.struts.action. PLUG_INS'}"> <c:forEach items="${itm.value}" var="subitm"> <textarea rows="2" cols="50"> <c:out value="${subitm}"/> </textarea> </c:forEach> </c:when> <c:otherwise> <textarea rows="2" cols="50"> <c:out value="${itm.value}"/> </textarea> </c:otherwise> </c:choose> </td> </tr> </c:forEach> </table> Discussion During development, JSP pages commonly show incorrect data, to render halfway, or to throw an exception. Developers troubleshoot these problems by commenting out portions of the page that appear to be causing the problem, and then entering scriptlet to display the values of request and session attributes used on the page. This is the equivalent of commenting out troublesome Java code and adding System.out.println( ) statements. This solution doesn't replace this arcane approach but makes it easier to apply. You have to comment out the failing portion of the page, but you can use the JSP fragment in Example 13-5 to eliminate the handcoded scriptlet. This reusable JSP fragment, derived from work by James Mitchell, displays request headers, scoped attributes, and other Struts-specific information to help you debug your problem. You can include the fragment anywhere on the page though, typically, it would be placed near the bottom of the page using the include directive: ... <!-- Debug Data --> <%@ include file="debug.jsp" %> <!-- End Debug Data --> </body> </html:html> The debug.jsp displays the following data: Request parameter values Request header values Application initialization parameters Cookies Page-scope attributes Request-scope attributes Session-scope attributes Application-scope attributes You can modify debug.jsp to display custom attributes that you may use in your application. Figure 13-6 shows a sample of the displayed information when debug.jsp is included at the bottom of the Registration.jsp file from the struts-example web application. Figure 13-6. Request parameters and header values The debug.jsp page displays detailed information about cookies, as shown in Figure 13-7. Figure 13-7. Cookie details and page-scoped attributes The debug.jsp page fragment should only be used in development; leaving this information displayed in production will make you look silly and will open a major security hole. See Also The debug.jsp page uses JSTL. You can use JSTL tags in your own application using the Solution shown in Recipe 3.1.