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Among the scans the annotation scanning is the slowest. That is because each class file (except ones in ignored JARs) has to be read and parsed looking for annotations in it.

An example of a container-provided SCI that triggers annotation scanning is the WebSocket API implementation which is included with standard distribution in all versions of Tomcat 8 and with Tomcat 7 starting with 7.0.47. An SCI class declared there triggers scanning for WebSocket endpoints (the classes annotated with @ServerEndpoint or implementing ServerApplicationConfig interface or extending the abstract Endpoint class). If you do not need support for WebSockets, you may remove the WebSocket API and WebSocket implementation JARs from Tomcat (websocket-api.jar and tomcat7-websocket.jar or tomcat-websocket.jar).

A note on TLD scanning: In Tomcat 7 and earlier the TLD scanning happens twice,

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The <absolute-ordering> element specifies which web fragment JARs (according to the names in their WEB-INF/web-fragment.xml files) have to be scanned for SCIs, fragments and annotations. An empty <absolute-ordering/> element configures that none are to be scanned.

Note: in Tomcat 8 the In Tomcat 7 the absolute-ordering option affects discovery both of SCIs provided by web application and ones provided by the container (i.e. by the libraries in $CATALINA_HOME/lib). In Tomcat 8 the option affects the web application ones only, while the container-provided SCIs are always discovered, regardless of absolute-ordering. It In such case the absolute-ordering option alone does not prevent scanning for annotations, but the list of JARs to be scanned will be empty, and thus it the scanning will complete quickly. The classes in WEB-INF/classes are always scanned regardless of absolute-ordering. An example of a container-provided SCI is in the WebSocket API implementation jar (tomcat-websocket.jar, tomcat7-websocket.jar) which is included with Tomcat 7 starting with 7.0.47. If you do not need support for WebSockets, you may remove it.

Scanning for web application resources and TLD scanning are not affected by these options.

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In Tomcat 7 JAR files can be excluded from scanning by listing their names or name patterns in a system property. Those are usually configured in the conf/catalina.properties file.

In Tomcat 8 you there are several options available. You can use a system property or configure a <JanScanFilter> element in the context file of your web application.

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