Java Jsp Jstl Custom Tag

Introduction

In JavaServer Pages (JSP), it’s not uncommon to use custom tags for rendering dynamic content that’s pulled from a data source, such as a database. However, a common issue developers encounter is that nested custom tags within strings are not rendering correctly; instead, they appear as plain text. This can lead to frustrating situations, especially when you expect complex HTML output.

This blog post will address the problem of nested custom tags not rendering and provide a detailed solution to enable proper HTML tag processing.

The Problem: Nested Custom Tags Not Rendering

When you attempt to render dynamic content that includes custom tags, you may find that instead of producing the intended HTML, the tags are displayed as plain text. This often happens in scenarios where:

  1. Dynamic Data: You are fetching data from a database or bean containing user-generated or processed HTML.
  2. Custom Tag Output: The custom tag that should render inside your dynamic string isn’t processed by the JSP engine.

Example Scenario

Consider the following code snippet that retrieves important notices from a database:

<jsp:useBean id="ImportantNoticeBean" scope="page" class="com.mysite.beans.ImportantNoticeProcessBean"/>
<c:forEach var="noticeBean" items="${ImportantNoticeBean.importantNotices}">
    <mysite:notice importantNotice="${noticeBean}"/>
</c:forEach>

Here, while the custom tag <mysite:notice> may work perfectly, if importantNotice.getMessage() contains a custom tag, it will not be processed correctly and will be output as text, rather than being rendered.

The Solution: Enabling Nested Tag Rendering

To achieve the desired rendering of your nested custom tags, follow these steps:

Step 1: Use a JSP Fragment

Simply placing your dynamic content inside a single body content directive isn’t enough. You need to set up your custom tag to process nested content properly.

Instead of:

<bodycontent>JSP</bodycontent>

Utilize the JspFragment class as follows:

JspFragment body = getJspBody(); 
StringWriter stringWriter = new StringWriter(); 
StringBuffer buff = stringWriter.getBuffer(); 
buff.append("<h1>"); 
body.invoke(stringWriter); 
buff.append("</h1>"); 
out.println(stringWriter);

Step 2: Redesign Your Code

The initial approach contains hard-coded strings, which don’t undergo JSP’s processing. Redesign your code to utilize proper tag structure:

<jsp:useBean id="ImportantNoticeBean" scope="page" class="com.mysite.beans.ImportantNoticeProcessBean"/>
<c:forEach var="noticeBean" items="${ImportantNoticeBean.importantNotices}">
    <mysite:notice importantNotice="${noticeBean}">
        <mysite:quote author="Some Guy">Quote this</mysite:quote>
        <mysite:messagebody author="Some Guy" />
    </mysite:notice>
</c:forEach>

Step 3: Consider Regex for Processing Strings

If modifying the structure isn’t feasible, you can consider a regular expression to parse and replace custom tags within strings. This method requires careful implementation to ensure it matches and replaces tags accurately without side effects.

Conclusion

Rendering nested custom tags within dynamic content in JSP can be challenging, but by following the outlined solution steps, you can successfully overcome this issue. Utilizing JspFragment allows you to ensure that your tags are correctly rendered, while redesigning your setup helps achieve cleaner code that adheres to JSP standards.

For any additional questions or solutions related to JSP rendering issues, feel free to reach out in the comments!