Here are a few title options, keeping in mind the question-and-answer format: Short and to the point: * ClassFormatException: Invalid Byte Tag in Constant Pool - Why and How to Fix it? * Tomcat 7 an

ClassFormatException: Invalid Byte Tag in Constant Pool

Background:

While porting a web application from Tomcat 7 to another server with the same Tomcat version but using Java 8, it was observed that Tomcat started successfully but produced an error in the catalina.out log:

org.apache.tomcat.util.bcel.classfile.ClassFormatException: Invalid byte tag in constant pool: 15

Cause:

The error originates from an issue with the Bytecode Engineering Library (BCEL), used by Tomcat, encountering difficulties processing the new Java 8 byte codes.

Solution 1: Disable Annotation Scanning

If annotation scanning is enabled in web.xml (metadata-complete="true"), disabling it allows the application to run without encountering the error.

Solution 2: Update to Tomcat 7.0.53 or Later

Starting with Tomcat 7.0.53, the compiler has been updated with improved Java 8 support. This update resolves the issue for applications using annotation scanning and non-Java 8 code.

Solution 3: Skip Certain Jar Files

For situations where annotation scanning is required and the application utilizes Java 8 code, add the following line to catalina.properties:

junit.jar,junit-*.jar,ant-launcher.jar,\
jfxrt.jar,nashorn.jar

to skip those Jar files during annotation scanning.

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