Not visible Interface on persistence query

Question

Calling a query on a table with BLOBs (Files in Tables) using the jTDS-Driver I get a class-loader error:

java.lang.IllegalArgumentException: interface org.hibernate.engine.jdbc.WrappedBlob is not visible from class loader

My Solution was to switch to an other classloader:

  public synchronized void method() {

        Thread thread = Thread.currentThread();
        ClassLoader tempLoader = thread.getContextClassLoader();
        thread.setContextClassLoader(null);

        entityManager.createNativeQuery("select * from TSRPTBLB where TSBID = 1 ")
                       .getSingleResult();

        thread.setContextClassLoader(tempLoader);
  }

Will there be any other, cleaner way than switsching the classloader?

Thank you in advance

Accepted Answer

Yes there is a better way:

You should explicitly set the correct ClassLoader to a class in the JAR where you run into problems (e.g set the class loader from WrappedBlob.class)
Add a finally statement so that in case of an exception you can still reset the original context ClassLoader or the server will be in a corrupt state

So if you consider both points the code could look as follows:

public synchronized void method() {
    Thread thread = Thread.currentThread();
    java.lang.ClassLoader originalClassLoader = thread.getContextClassLoader();
    thread.setContextClassLoader(WrappedBlob.class.getClassLoader());
    try {
        entityManager.createNativeQuery(
                "select * from TSRPTBLB where TSBID = 1 ")
                .getSingleResult();
    } finally {
        thread.setContextClassLoader(originalClassLoader);
    }
}

Not visible Interface on persistence query

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