The same cmd work in shell but not in subprocess.Popen() for a matlab-based java program under Django

Background: Ubuntu 64bit machine. I need to call a matlab-based jar from django(deployed on apache). Here is the problem, when I run the command on the shell, it works; however, when I call subprocess.Popen({{cmd}}) inside django code, an exception is thrown.
Edit: I try to open a python shell and call subprocess.Popen({{cmd}}). I write a single python script file and put the same code in it. They all work. It's so weird that the code just fail when run on django!!!!!!
For details:

The cmd: java -jar A.jar param1 param2 param3 param4
When run directly in shell, everything is normal. When run with python code, the exception is:

Exception in thread "main" java.lang.ExceptionInInitializerError
    at com.mathworks.toolbox.javabuilder.internal.MCRConfiguration.getProxyLibraryDir(MCRConfiguration.java:178)
    at com.mathworks.toolbox.javabuilder.internal.MCRConfiguration$MCRRoot.get(MCRConfiguration.java:77)
    at com.mathworks.toolbox.javabuilder.internal.MCRConfiguration$MCRRoot.<clinit>(MCRConfiguration.java:87)
    at com.mathworks.toolbox.javabuilder.internal.MCRConfiguration.getMCRRoot(MCRConfiguration.java:92)
    at com.mathworks.toolbox.javabuilder.internal.MCRConfiguration$ModuleDir.<clinit>(MCRConfiguration.java:66)
    at com.mathworks.toolbox.javabuilder.internal.MCRConfiguration.getModuleDir(MCRConfiguration.java:71)
    at com.mathworks.toolbox.javabuilder.internal.MWMCR.<clinit>(MWMCR.java:1466)
    at autoBlockJava.AutoBlockJavaMCRFactory.newInstance(AutoBlockJavaMCRFactory.java:83)
    at autoBlockJava.AutoBlockJavaMCRFactory.newInstance(AutoBlockJavaMCRFactory.java:94)
    at autoBlockJava.AutoBlockJavaSharedMCRFactory$3.call(AutoBlockJavaSharedMCRFactory.java:95)
    at autoBlockJava.AutoBlockJavaSharedMCRFactory$3.call(AutoBlockJavaSharedMCRFactory.java:93)
    at autoBlockJava.AutoBlockJavaSharedMCRFactory.getInstance(AutoBlockJavaSharedMCRFactory.java:72)
    at autoBlockJava.AutoBlockJavaSharedMCRFactory.newInstance(AutoBlockJavaSharedMCRFactory.java:93)
    at autoBlockJava.manualMain.<init>(manualMain.java:97)
    at autoblock.AutoBlock.main(AutoBlock.java:29)
Caused by: java.lang.NullPointerException
    at com.mathworks.toolbox.javabuilder.internal.MCRConfiguration$ProxyLibraryDir.get(MCRConfiguration.java:143)
    at com.mathworks.toolbox.javabuilder.internal.MCRConfiguration$ProxyLibraryDir.<clinit>(MCRConfiguration.java:173)
    ... 15 more

I'm totally confused. I really don't know what's the reason for it now.