Log Format Enforcer

The goal of this maven plugin is to provide teams with a way of enforcing a certain logging message style in their projects.

I often find myself working in projects where certain log guidelines were agreed upon. In my opinion this is awesome because this kind of logs are easier to parse, it introduces consistency amongst the logs created by every team member, etc, etc.

The only problem with this approach is that usually there's no way for enforcing these "agreed rules" which leads to problems of all sorts:

• typos in the log structure: "strings should be enclosed in double quotes" but someone missed the close double quote
• missing agreed log data: the team agreed that every log should have the 'userId' but someone forgot to add it in one particular log invocation
• new team members don't actually know what the agreed rules are
• you spend more time checking for log correctness in your code-reviews than actually reviewing interesting bits of the code logic
• if the team realizes that the log format should change a bit, it's already too late because you would have to go back to update every single log entry in your code base to make everything consistent again
• ...

All these are problems that this library tries to address.

Before

private static final Logger log = LoggerFactory.getLogger(MyClass.class); // or something similar
...
log.info("op=someMethod, msg='This is a message', someValue='{}'", someValue);
...
log.trace("op=otherMethod, msg='Other message', input='{}', output='{}'", input, output);
...
log.warn("op=otherMethod, msg='Something bad happened', input='{}', output='{}'", input, output, exception);
...

This is an actual example of some messages a team where I worked before agreed upon: 'msg' and 'op' would always be present. For some cases (typically trace messages) we would log 'input' and 'output'. Every message could have any number of unknown fields.

Note

Even with these simple rules there was always problems: some people would use 'message' instead of 'msg' or 'operation' instead of 'op', quotes were commonly forgotten, same for commas between each field

After

In your class:

private static final LogFormatEnforcer log = LogFormatEnforcer.loggerFor(MyClass.class); 
...
log.info(logMessage -> logMessage.op("someMethod").msg("This is a message").and("someValue", someValue));
...
log.trace(logMessage -> logMessage.op("otherMethod").msg("Other message").input(input).output(output));
...
log.warn(logMessage -> logMessage.op("otherMethod").msg("Something bad happened").input(input).output(output).exception(exception));
...

And I dare you trying to break the agreed rules now.

Note

If you do, please let me know; this is still an early prototype ;)

In the pom.xml:

<plugin>
    <groupId>com.leandronunes85.lfe</groupId>
    <artifactId>log-format-enforcer-maven-plugin</artifactId>
    <version>1.1</version>
    <configuration>
        <packageName>com.leandronunes85.tests</packageName>
        <mandatoryFields>
            <op />
            <msg />
        </mandatoryFields>
        <optionalFields>
            <input />
            <output />
        </optionalFields>
    </configuration>
    <executions>
        <execution>
            <goals>
                <goal>create</goal>
            </goals>
        </execution>
    </executions>
</plugin>

Now, do you want to enclose your values in square brackets (because it's easier for you to parse it) and use "->" to separate keys and values (because you fancy Java 8)? Just update your pom, like this:

<plugin>
    <groupId>com.leandronunes85.lfe</groupId>
    <artifactId>log-format-enforcer-maven-plugin</artifactId>
    <version>1.1</version>
    <configuration>
        <packageName>com.leandronunes85.tests</packageName>
        <mandatoryFields>
            <op />
            <msg />
        </mandatoryFields>
        <optionalFields>
            <input />
            <output />
        </optionalFields>
        <valueDelimiterPrefix>[</valueDelimiterPrefix>
        <valueDelimiterSuffix>]</valueDelimiterSuffix>
        <keyValueSeparator>-></keyValueSeparator>
    </configuration>
    <executions>
        <execution>
            <goals>
                <goal>create</goal>
            </goals>
        </execution>
    </executions>
</plugin>

Rebuild it, release it and that's it!

Note

Behind the scenes LogFormatEnforcer relies on slf4j for the actual logging work so you must provide it in your project dependencies.

Wrap up

As I said, this is still a prototype, there's still bugs that I'm aware of and many other that I'm not, for sure. Your comments, suggestions, concerns, etc, are all welcome so please drop me a line!