Besides writing your own Custom Tags in JSP, you will find that Java EE actually provides a set of Java Standard Tag Library (JSTL) ready for you to use. These built-in tags include repeating (for-loop) tags, if condition tags, variable declaration and output tags etc. The Libraries also come with many utility functions and international message formatting tags. Here is an example how it looks like.
01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 | <!DOCTYPE html><html> <body> <h1>JSTL Examples</h1> <h2>List of Application Context: ${applicationScope}</h2> <table> <c:forEach var="entry" items="${applicationScope}"> <tr> <td>${entry.key}</td> <td> <c:out value="${entry.value}"/> </td> </tr> </c:forEach> </table> <h2>List of Session Context: ${sessionScope}</h2> <table> <c:forEach var="entry" items="${sessionScope}"> <tr> <td>${entry.key}</td> <td> <c:out value="${entry.value}"/> </td> </tr> </c:forEach> </table> <h2>List of Page Context: ${pageScope}</h2> <table> <c:forEach var="entry" items="${pageScope}"> <tr> <td>${entry.key}</td> <td> <c:out value="${entry.value}"/> </td> </tr> </c:forEach> </table> <h2>List of Request Context: ${requestSope}</h2> <table> <c:forEach var="entry" items="${requestSope}"> <tr> <td>${entry.key}</td> <td> <c:out value="${entry.value}"/> </td> </tr> </c:forEach> </table> <h2>List of Query Parameters: ${param}</h2> <table> <c:forEach var="entry" items="${param}"> <tr> <td>${entry.key}</td> <td> <c:out value="${entry.value}"/> </td> </tr> </c:forEach> </table> <h2>List of Header Parameters: ${header}</h2> <table> <c:forEach var="entry" items="${header}"> <tr> <td>${entry.key}</td> <td> <c:out value="${entry.value}"/> </td> </tr> </c:forEach> </table> <h2>List of Cookies: ${cookie}</h2> <table> <c:forEach var="entry" items="${cookie}"> <tr> <td>${entry.key}</td> <td> <c:out value="${entry.value}"/> </td> </tr> </c:forEach> </table> </body></html> |
I used the core tag here to display map entries of few implicit variables. You may explore more on those tags declarations I have define on top of the example page from the Spec. These code are from the jsp-example from GitHub.
GLASSFISH NOTE: When deploying above example in GlassFish 3/4, you will run into a NullPointerException and causing the page resulted in error. It turns out that GF server added a internal variable named com.sun.jsp.taglibraryCache in ServletContext (Application Scope) that throws NPE when its toString() is called! To workaround this, I created jstl-example2.jsp
that wraps the ${entry.value} into a custom JSTL function so that it guarantees to return an output without throwing exception. So the lesson learned is that you should always return a String and not throw Exception when overriding
toString() of a Java class. It’s just bad practice.
| Reference: | EE JSP: Generating Dynamic Content with JSTL Tag Libraries from our JCG partner Zemian Deng at the A Programmer’s Journal blog. |
