Tomcat 7 - Servlet 3.0: Invalid byte tag in constant pool

Adding

metadata-complete="true" 

to your web.xml should sort the issue

<web-app version="3.0"
         xmlns="http://java.sun.com/xml/ns/javaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
         metadata-complete="true">

This tells tomcat not to scan classes for annotations: https://web.archive.org/web/20180510163848/http://www.tomcatexpert.com/blog/2011/10/12/how-use-fragments-and-annotations-configure-your-web-application

It may not be your issue, but mine was the same as this one -- an old version of com.ibm.icu:icu4j. I solved the problem by changing my build configuration to exclude the older transitive dependencies and explicitly depending upon the latest version (4.8).

Thanks James A Wilson for your answer - updating icu4j as you suggested worked for me and allows me to keep version="3.0" in my web.xml (which I prefer for the long run).

icu4j 2.6.1 was the version which did not work, upgrading to the NEXT version 3.4.4 will solve this problem. I did NOT go to the latest version of icu4j (49.1) because it is 4MB larger than version 3.4.4.

Here is a Maven configuration snippet to lock in your transitive dependency version (without adding an explicit dependency):

<dependencyManagement>
    <dependencies>
        <dependency>
            <groupId>com.ibm.icu</groupId>
            <artifactId>icu4j</artifactId>
            <version>3.4.4</version>
        </dependency>
    </dependencies>
</dependencyManagement>