How to set global config in the rich functions

[zhen li]

Hi:
    I want to set some configs in the source functions use 
getRuntimeContext().getExecutionConfig().setGlobalJobParameters(parameterTool)
    And  used the configs in the downstream operators such as filter function 
through the getGlobalJobParameters, But it returns null pointer exception.Is 
the global config  only can set in the start of streams?