didyhu/logging-best-practices.md

## logging-best-practices.md

      
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              logging-best-practices.md
            
          
    #Logging Best Practices
Always log, and always log in right place, on right level.
Error
Unexcepted exceptions happened, should write down the error message and the call stacks.
log.error(ex.getMessage(),ex);
Warn
Something dosen't break the process, but worth to log down. eg, In weixin api, when we find the accessToken expires Unexpectedly, we get another new one, the write down a warning.
if(accessToken==null){
  accessToken=getAccessToken();
  log.warn("AccessToken Expires Unexpectedly, got a new one.");
}

INFO
Log when there is a side effect process done. eg, user logged in, someting written to the database, some order or payment created or updated.
orderRepository.save(order);
log.info("Saved Order{id:{}, userId:{}, state:{}}", order.getId(), order.getUserId(), order.getState());
DEBUG/TRACE
To log some key intermediate variables, to remind the developer what action is taking place
public Boolean login(String code){
  log.trace("Entering login(code:{})",code)
  UserInfo userInfo=weixinAdapter.getUserInfo(code);
  log.debug("Got UserInfo:{}",userInfo)
  boolean subscribe=userInfo.subscribe==1
  log.trace("Leaving login():{}",subscribe);
  return subscribe;
}