candyleer opened a new issue #1055: log toolkit may do not take effect in some 
case 
URL: https://github.com/apache/incubator-skywalking/issues/1055
 
 
   Please answer these questions before submitting your issue.
   
   - Why do you submit this issue?
   - [ ] Question or discussion
   - [x] Bug
   - [ ] Requirement
   - [ ] Feature or performance improvement
   
   ___
   ### Question
   - What do you want to know?
   
   ___
   ### Bug
   - Which version of SkyWalking, OS and JRE?
   
   - Which company or project?
   
   - What happen?
   #### Question
    when i start an app (called `test_app`) in IDE,i configure the logback file 
by following this 
[instruction](https://github.com/apache/incubator-skywalking/blob/master/docs/en/Application-toolkit-logback-1.x.md),but
 i found it didn't take effect.
   i debug this question step by step in `agent` jar. i found the class 
`org.apache.skywalking.apm.toolkit.log.logback.v1.x.TraceIdPatternLogbackLayout`
 didn't been transformed.this seems to be strange.what is it happened?
   then  i put an `break point` in this place, 
   
![image](https://user-images.githubusercontent.com/11530760/38506954-e09e8a0a-3c4d-11e8-9694-b6bcee17320b.png)
   and see the `debug` stack trace in ide ,Suddenly I understand.
   
![image](https://user-images.githubusercontent.com/11530760/38507096-246a5dae-3c4e-11e8-98a0-76d6dd81edc8.png)
   from this picture, we can see that the `TraceIdPatternLogbackLayout` class 
was loaded in `premain` method,and invoke by `boot` method.but at that time,the 
`byte buddy instrument` didn't work.because the code is
   ```
   ...
    ServiceManager.INSTANCE.boot();
   ...
    new AgentBuilder.Default()...
   .installOn(instrumentation);
   ```
   that is the class `TraceIdPatternLogbackLayout` loaded is before 
`instrumentation`.
   **this only happens when application code is loaded by 
`AppClassLoader`,because the `logback.xml` in this classpath.**
   
   in other cases,this code work fine cause their classloader is redefined like 
`spring boot` or `tomcat` etc. in this cases,the class 
`TraceIdPatternLogbackLayout` will be loaded only by app code invoke `logger` 
,when `agent` started by `AppClassLoader`,it can not see the `logback.xml` 
config file thus he dont know the class `TraceIdPatternLogbackLayout`,
   
   #### Solution
   To resolve this problem ,the simplest way is to change the order of 
   ```
   ...
    ServiceManager.INSTANCE.boot();
   ...
    new AgentBuilder.Default()...
   .installOn(instrumentation);
   ```
   to 
   ```
   ...
    new AgentBuilder.Default()...
   .installOn(instrumentation);
   ...
    ServiceManager.INSTANCE.boot();
   ```
   that is first invoke `instrumentation` then boot all service in case of the 
boot service contains some method need to be enhanced.
   but i dont know if there has some other problem will be caused?
   so please check
   ___
   ### Requirement or improvement
   - Please describe about your requirements or improvement suggestions.

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