CODEWITHSUNDEEP
jspstruts2
Andrew Weir
Andrew Weir

Reputation: 1030

Should I use taglib or HTML? What's the purpose of Struts taglib?

I'm dabbling into JSP after having experienced most of life as a PHP developer. I'm quite comfortable with Java as it is, so I've started to get to know Struts as my MVC framework of choice.

I'm having trouble understanding the reasons why I should use the Struts taglib instead of standard HTML?

<s:textfield id="username" />

or 

<input type="text" id="username" name="username" />

What's the conceptual difference? Why should I use the taglib rather than HTML? Is there a preferred method within the world of Struts and the JSP community at large?

Upvotes: 2

Views: 4429

Answers (2)

Andrea Ligios
Andrea Ligios

Reputation: 50281

There is no way to access server data with pure HTML; the alternative to TagLibraries inside a JSP is not the HTML, but the old (and bad) Scriptlets.

Everything at the end will be transformed to HTML, but you need an intermediate tier to allow you handle business data.

How can you read serverside values with HTML ?

Long story short:

once was the Servlet, with its PrintWriters to output HTML:

public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws IOException, ServletException {

    String myServerSideValue = "StackOverflow";

    response.setContentType("text/html");
    PrintWriter writer = response.getWriter();        
    writer.println("<html>");
    writer.println("<head>");
    writer.println("<title>Wait, what... a Servlet in 2013?!</title>");
    writer.println("</head>");
    writer.println("<body>");
    writer.println("<span>Hello " + myServerSideValue + "</span>");
    writer.println("</body>");
    writer.println("</html>");
}

Clearly a nightmare, that led some smart guy to invent JSPs and Scriptlets:

<html>
   <head>
      <title>Wait, what... Scriptlets in 2013?!</title>
   </head>
   <body>
      <span>Hello <%= myServerSideValue %> </span>
   </body>
</html>

Then TagLibs like JSTL came out:

<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<html>
   <head>
      <title>you <i>may</i> still needs JSTL with, for example, Spring MVC</title>
   </head>
   <body>
      <span>Hello <c:out value="myServerSideValue" /> </span>
   </body>
</html>

And finally WebWork / Struts brought OGNL to us

<%@ taglib prefix="s" uri="/struts-tags" %>
<html>
   <head>
      <title>you still needs JSTL with, for example, Spring MVC</title>
   </head>
   <body>
      <span>Hello <s:property value="myServerSideValue" /> </span>
   </body>
</html>

Using OGNL inside Struts2 tags is similar to JSTL, but more powerful and fully integrated in Struts2 in several ways (Validation, Theming, etc).

Maybe this example is too nàive to understand why Struts2 Tags should be used instead Scriptlets or other TagLibs, but when coming to more complex, real-world scenarios, you will start to appreciate and maximize the usage of this great tool.

Upvotes: 0

Dave Newton
Dave Newton

Reputation: 160311

Struts 2 tags serve two primary purposes:

  1. Theming (e.g., "what's emitted")
  2. Framework integration (e.g., values, validation)

Struts 2 uses "themes" to determine what is output for view-oriented tags. The default "xhtml" theme, for example, wraps the input tags in table rows, sets the input field value, displays field validation errors if any, and probably a few other things I'm not recalling.

If you look at the page source you can see precisely what the differences are, except for the bits that are determined by back-end functionality like the if/then around validation messages.

In general, custom tags allow you to abstract view-layer functionality in arbitrary ways. The "preferred method" is to not do stuff by hand, which is what you'd need to do in order to duplicate even the simplest functionality like setting the value from the action and displaying error messages.

You can see what the custom tags do by looking at their FreeMarker templates (assuming you're not using the Java tags). You can extend those templates, create your own templates, etc. all under the framework's purview.

Even a cursory examination of the S2 tag and theming docs should answer this question.

Upvotes: 3

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