Loading user classes in flink RichFilterFunction using User code classloader - apache-flink

Question

I am trying to use the flink's UserCodeClassLoader but since I am new to Flink I could not understand exactly how to use it.
Scenario:
In the open() method of RichFilterFunction(), I want to load an external jar.
To do so, I do the following in open():
#Override
public void open(Configuration parameters) throws Exception {
ClassLoader userClassLoader = getRuntimeContext().getUserCodeClassLoader();
URL url = userClassLoader.getResource("/tmp/rohit/FilterTest/FilterTest.jar");
klazz = userClassLoader.loadClass("FilterTest");
Constructor<?> ctor = klazz.getConstructor();
Object obj = ctor.newInstance(new Object[] {});
control = (MyRichFilterInterface)obj;
... etc
However, I am getting ClassNotFoundException:
Caused by: java.lang.ClassNotFoundException: FilterTest
at java.net.URLClassLoader.findClass(URLClassLoader.java:381)
at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
at org.apache.flink.runtime.execution.librarycache.FlinkUserCodeClassLoaders$ChildFirstClassLoader.loadClass(FlinkUserCodeClassLoaders.java:128)
at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
at MyRichFilterFunction.open(MyRichFilterFunction.java:24)
at org.apache.flink.api.common.functions.util.FunctionUtils.openFunction(FunctionUtils.java:36)
at org.apache.flink.streaming.api.operators.AbstractUdfStreamOperator.open(AbstractUdfStreamOperator.java:102)
at org.apache.flink.streaming.runtime.tasks.StreamTask.openAllOperators(StreamTask.java:393)
at org.apache.flink.streaming.runtime.tasks.StreamTask.invoke(StreamTask.java:254)
at org.apache.flink.runtime.taskmanager.Task.run(Task.java:718)
at java.lang.Thread.run(Thread.java:748)
My flink version is 1.4.0 & it is installed in /root/flink-1.4.0/
I have not changed any parameters in flink config specific to this issue.
If anyone knows what I am missing, that would be great!!!
I have used URLClassLoader earlier, but I am not sure how to use Flink's provided UserCodeClassLoader.