Logging Context

Context definition

As a developer, you often need to comprehend multiple log entries in a context (web request, web session, etc). For instance, in the context of a single web request you want to see a sequence of log statements as they are emitted by various layers of technology in the same order as they are being executed.

Adding context values to log statements

You can use a class Context to do just that.

Context adds parameters that will be mixed-in to all log statements down stream in the stack trace.

Here is an example:

Logger logger = LoggerFactory.getLogger(getClass());
Context.put("user", "joeschmoe", "user_id", "234", "email", "joe@schmoe.me");
logger.info("hello");
logger.error("world");
Context.clear();

will print the following into a log:

{"level":"INFO","timestamp":"Fri Feb 24 15:20:15 CST 2017","thread":"main","logger":"org.javalite.activejdbc.logging.JsonLog4jLayoutSpec","message":"hello", "context":{"user":"joeschmoe","user_id":"234","email":"joe@schmoe.me"}}
{"level":"ERROR","timestamp":"Fri Feb 24 15:20:15 CST 2017","thread":"main","logger":"org.javalite.activejdbc.logging.JsonLog4jLayoutSpec","message":"world", "context":{"user":"joeschmoe","user_id":"234","email":"joe@schmoe.me"}}

As you can see, every log line now includes an object context with corresponding values.

• Class Context attaches parameters to a current thread, making them available to execution down the stack trace.

• Class org.javalite.logging.JsonLog4j(2)Layout locates context values on the current thread and appends them to every log line.

Cleaning context

The context parameters are attached to a Thread and will remain there till they are removed.

If you are using ActiveWeb, the context is cleaned automatically at the end of each HTTP request processing. If you are not using ActiveWeb, you can do it by executing:

Context.clean();