https://tomcat.apache.org/: Interface code to the native connector 
public interface org.apache.tomcat.jni.PoolCallback
  minor version: 0
  major version: 59
  flags: flags: (0x0601) ACC_PUBLIC, ACC_INTERFACE, ACC_ABSTRACT
  this_class: org.apache.tomcat.jni.PoolCallback
  super_class: java.lang.Object
{
  public abstract int callback();
    descriptor: ()I
    flags: (0x0401) ACC_PUBLIC, ACC_ABSTRACT
}
SourceFile: "PoolCallback.java"