ClassCastException: org.postgresql.jdbc4.Jdbc4Connection cannot be cast to org.postgresql.jdbc4.Jdbc4Connection

Question

I want to get PGConnection from PosgreSQL connection in JBOSS AS7 (Data source postgresql-9.0-801.jdbc4.jar)

I've got cast exception when used (WrappedConnection)connection . So now I use reflection (JDK 1.7):

private static PGConnection getPGConnction(Connection connection) throws SQLException {
    if(connection instanceof PGConnection) {
        return (PGConnection)connection;
    }
    try {
        Class[] parms = null;
        Method method =(connection.getClass()).getMethod("getUnderlyingConnection", parms);
        return (PGConnection) jdbc4Conn;
    } catch ...

and catch exception

java.lang.ClassCastException: org.postgresql.jdbc4.Jdbc4Connection cannot be cast to org.postgresql.jdbc4.Jdbc4Connection

It is the same class!!! How can it be?

Answer 1

When a class can not be cast to itself, if means you have 2 copies loaded by different classloaders. In a webapp, this can easily happen if you have the JDBC driver jar both in the application itself and in the app server's lib. Or, in case of .ear packaging, in both war/WEB-INF/lib and ear/lib . Make sure there is only a single jar on the classpath and you will get rid of the error. You can pass -verbose:class when starting Java to get more information on where the classes are being loaded from. Btw, what is the point of reflection in your code? Can't you just call getUnderlyingConnection normally?

Answer 2

Per kaqqao's advice , I

1. Deleted postgres as project library (changed scope from compile to provided)
2. Added jboss-deployment-structure.xml (with module name="deployment.postgresql-9.0-801.jdbc4.jar" dependency) to project web-inf.

   So problem is solved