将每个用户/每个请求的Java servlet中的日志分组

Question

I have a simple servlet that does some calculations, and logs the intermediate results to a file using slf4j as the facade and a simple logging binder (also from slf4j) to log to the file. This works fine, but when multiple users are sending requests simultaneously, their logs get interwoven with each other. Below is a dummy example to show the problem: the logging from both user alice and bob gets mixed up:

log: phase1 of user alice
log: phase2 of user alice
log: phase1 of user bob
log: phase3 of user alice
log: phase2 of user bob
log: phase3 of user bob
...

This is really troublesome if the amount of users involved and the complexity of the log statements increases.

A possible solution is to create a logfile for each user, and when a request enters by user X (this can be detected by my code), append it to logfile X. The problem is I don't see how to do this with simple logging. Is is possible, and if not, is there another way?

Answer 1

您可以将每个用户阶段的条目存储在某种结构中，然后在上一个阶段结束时或在发生错误时（如果发生错误）立即将所有阶段记录为单个日志条目。

Answer 2

You might want to look at the "MDC" (Mapped Diagnostic Context) class in SLF4J (other logging frameworks also support this).

It allows you to set custom logging context data and then you can get that data to appear in your messages.

For example, you could do...

import org.slf4j.MDC;

...
    private static final USER_NAME_MDC_KEY = "USRKEY";

    servlet method {
        MDC.put(USER_NAME_MDC_KEY, user.getUserId());

        ...rest of logic...

    }

If you have a pattern set up like this...

        <PatternLayout pattern="[UID=%X{USRKEY}] %d{HH:mm} [%t] %-level %c{1} - %m%n" />

...then each line in your log will contain...

[UID=<whatever has been set in the MDC>]

You could then GREP your logs for the particular user Id in order to get the messages logged just for them.

(I think this is sort of what you wanted, I might be wrong!)