Make some variables in BrokerController to be final.

[hzh0425]

FEATURE REQUEST

1. Please describe the feature you are requesting.
   make some variables in BrokerController to be final.

2. Provide any additional detail on your proposed use case for this feature.

3. Indicate the importance of this issue to you (blocker, must-have, should-have, nice-to-have). Are you currently using any workarounds to address this issue?

4. If there are some sub-tasks involved, use -[] for each sub-task and create a corresponding issue to map to the sub-task:

• sub-task1-issue-number: sub-task1 description here,
• sub-task2-issue-number: sub-task2 description here,
• ...

[RongtongJin]

Merged