Call PHP from other languages

Hi all! We have developed a groupware web server written in PHP. We were interested in integrating some communication interfaces in Java, using Tomcat, in this application, but we have not found an efficient way to call PHP functions from a Java program. We would prefer not to use communication protocols like HTTP or RPC to do these calls. ¿Can anyone tell me if he/she has faced this problem, please? ¿Is it even possible? We can even use C/C++ instead of Java, but we still have the same problem. ¿Does anyone know if is there any way to call PHP functions from C, please? Thanks in advance. Germán