How to Disable Tomcat TLD Scanning for Faster Startup

Background

Tomcat, as an implementation of the Servlet specification, scans JAR files for .tld files and loads the defined tag libraries when the application starts. When developers use template engines such as Velocity instead of JSP, disabling this scan can speed up startup.

Method

According to Tomcat's configuration documentation, the processTlds attribute of <Context> controls whether TLDs are processed on startup. Setting it to false disables the scan. To apply this to all applications, edit conf/context.xml as follows:

<?xml version='1.0' encoding='utf-8'?> <Context processTlds="false"> <WatchedResource>WEB-INF/web.xml</WatchedResource> </Context>

Pitfall

In Tomcat 6 the setting does not take effect because the StandardContext initialization processes TLDs before the lifecycle event where the configuration is applied. The relevant code is:

if (processTlds) { this.addLifecycleListener(new TldConfig()); } super.init(); // Notify our interested LifecycleListeners lifecycle.fireLifecycleEvent(INIT_EVENT, null);

Since processTlds is evaluated before the INIT_EVENT, the configuration is ignored.

Workaround: define an empty JarScanner in context.xml to prevent TLD scanning:

<?xml version='1.0' encoding='utf-8'?> <Context processTlds="false"> <JarScanner className="com.alipay.sofa.runtime.test.patch.tomcat.NullJarScanner"/> </Context>

The NullJarScanner implementation simply does nothing:

package com.alipay.sofa.runtime.test.patch.tomcat; import org.apache.tomcat.JarScanner; import org.apache.tomcat.JarScannerCallback; import javax.servlet.ServletContext; import java.util.Set; public class NullJarScanner implements JarScanner { @Override public void scan(ServletContext context, ClassLoader classloader, JarScannerCallback callback, Set<String> jarsToSkip) { // Do nothing at all. } }

Tomcat 7 does not exhibit this issue; setting processTlds="false" works out of the box.