Java SecurityException: signer information does not match

This happens when classes belonging to the same package are loaded from different JAR files, and those JAR files have signatures signed with different certificates - or, perhaps more often, at least one is signed and one or more others are not (which includes classes loaded from directories since those AFAIK cannot be signed).

So either make sure all JARs (or at least those which contain classes from the same packages) are signed using the same certificate, or remove the signatures from the manifest of JAR files with overlapping packages.

A. If you use Maven, a useful way to debug clashing jars is:

mvn dependency:tree

For example, for an exception:

java.lang.SecurityException: class "javax.servlet.HttpConstraintElement"'s signer information does not match signer information of other classes in the same package

we do:

mvn dependency:tree|grep servlet

Its output:

[INFO] +- javax.servlet:servlet-api:jar:2.5:compile
[INFO] +- javax.servlet:jstl:jar:1.2:compile
[INFO] |  +- org.eclipse.jetty.orbit:javax.servlet.jsp:jar:2.2.0.v201112011158:compile
[INFO] |  +- org.eclipse.jetty.orbit:javax.servlet.jsp.jstl:jar:1.2.0.v201105211821:compile
[INFO] |  +- org.eclipse.jetty.orbit:javax.servlet:jar:3.0.0.v201112011016:compile
[INFO] +- org.eclipse.jetty:jetty-servlet:jar:9.0.0.RC2:compile

shows clashing servlet-api 2.5 and javax.servlet 3.0.0.x.

B. Other useful hints (how to debug the security exception and how to exclude Maven deps) are at the question Signer information does not match.

A simple way around it is just try changing the order of your imported jar files which can be done from (Eclipse). Right click on your package -> Build Path -> Configure build path -> References and Libraries -> Order and Export. Try changing the order of jars which contain signature files.