JSP Whitespace reduction

I’ve often found that most JSP developers are uncertain as to why their HTML output contains a lot of extra blank-lines, tabs and carriage returns. White space included in the template text of JSP pages is preserved by default. This can have undesirable effects. For example, a carriage return added after a taglib directive would be added to the response output as an extra line. This cruft is known as WhiteSpace, and it is responsible for a lot of wasted bandwidth and many spacing issues in HTML designs.

The challenge:

  • Developers that only use WYSIWYG editors are never even aware of the extra spacing within JSP source code.
  • Developers that work in source code often want to format the markup to allow for better visualization and readability of the source code.
  • Most IDE’s do not show the developers the special characters within the editor environment, external text editors such as NotePad++ and TextPad can be configured to show them.

Here’s a few suggested approaches on removing these, first development items:

  1. Remove comments:
    • Remove any (and all) JSP style comments <%-- comment --%> as each line in them will result in a carriage return being sent to the browser.
    • While you are at it, remove HTML comments <!-- comment --> as they often expose potential attack vectors for individuals trying to hack your website.
  2. Combine your JSP directives, <%@page %> or <jsp:directive.page /> into a single entry.
  3. Open and close all tags on a single line when possible.

Compiler options are possible for some platforms:

  • The page directive on each JSP can contain the argument to tell the compiler to trim the space in individual JSP’s:
    <jsp:directive.page language="java" pageEncoding="utf-8" trimDirectiveWhitespaces="true" />
  • For Tomcat (and others?) web.xml can be edited to contain the following in the jsp-config section:

    <jsp-config>
    <jsp-property-group>
    <url-pattern>*.jsp</url-pattern>
    <trim-directive-whitespaces>true</trim-directive-whitespaces>
    </jsp-property-group>
    </jsp-config>
  • For Tomcat (and others?) web.xml can be edited to contain the following for the JSPServlet:

    <init-param>
    <param-name>trimSpaces</param-name>
    <param-value>true</param-value>
    </init-param>
  • The deployment descriptor can also be used to do so by adding a trim-directive-whitespaces element to a jsp-property-group element in the deployment descriptor and set it to true.
  • Some IDE’s expose the attribute, NetBeans 5.5 uses the following:
    1. Open the deployment descriptor file in the editor.
    2. Click the Pages button at the top of the editor.
    3. Select a JSP property group.
    4. Select the Trim Directive Whitespaces checkbox.
    5. Save the deployment descriptor.
  • Custom tag authors can eliminate white space from the output generated by a tag file by setting the trimDirectiveWhiteSpace attribute of the tag directive to true.

JSP Version Matrix for common servers:

Apache Tomcat 7.0.x JSP 2.2
Apache Tomcat 6.0.x JSP 2.1
Apache Tomcat 5.5.x JSP 2.0
Apache Tomcat 4.1.x JSP 1.2
Apache Tomcat 3.3.x JSP 1.1
IBM WebSphere Application Server 7.x JSP 2.x
IBM WebSphere Application Server 6.x JSP 2.0
IBM WebSphere Application Server 5.x JSP 1.2

REFERENCES:

Happy coding!

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