log4j, logback, log4j2 and slf4j relations

1. The default is to achieve logback slf4j Interface Specification
2. log4j2 log4j and need to be added to achieve the connection packet, then the interface can be achieved using slf4j slf4j Interface Specification
3. If a project needs to rely on between slf4j interface specification, you can use log4j configuration file to a unified log format in the overall project
   1. If there is a conflict in which the package can use the exclusion conflict lifting, or using global (that is, using the wrong version number)
   2. Yet another situation is required log4j-over-slf4j package