Java EL Expression Performance Issue after Upgrade

Issue

• I recently updated to Liferay 7.4 and I'm seeing performance issues.
• I have custom JSP files with EL Expressions (expressions like ${expressionName}) deployed.
• In thread dumps taken during the performance issues, and I see a large number of threads that are in the BLOCKED state with stack traces that:
  • Mention custom JSP files
  • Contain the following calls:

at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Class.java)

• • Along with lines that appear to be related to EL resolution like:

at javax.el.CompositeELResolver.getValue(CompositeELResolver.java)

Environment

• DXP 7.4
• Quarterly Releases

Resolution

• Request a hotfix that includes LPD-21945

Additional Information

• This performance issue happens due to logic changes that were made in the third-party expression parser code here.
  • Because of this change, if the EL Expression evaluates to null, the expression parser will interpret it as a Java class name.
  • The parser will then begin looking inside every .jar file that it has access to for a class that has that name, but the name doesn’t exist.
  • Because this is a synchronized process, only one thread can perform it at a time, so if a large number of users are visiting the page where this .jsp file needs to be rendered, the threads will all block each other and it will be very slow.
• See this third-party JSP Tutorial page for an overview of EL Expressions