elf4j-engine

An asynchronous Java log engine.

Implementing the elf4j (Easy Logging Facade for Java ) API, this is the log engine behind elf4j-provider - a native logging service provider of the elf4j logging facade.

A stand-alone log engine in the meantime, it is designed to be adaptable for servicing other Java logging APIs.

It is a log engine for the SLF4J API, as in slf4j-elf4j.
It is also a log engine for the Java Platform Logging (JPL) API introduced since Java 9, as in jpl-elf4j.

Getting started…

Install

To use this as a logging service provider in your application, see installation details here

Use it for logging in the application:

class Scratch {
   static Logger logger = Logger.instance();
   
   public static void main(String[] args) {
      logger.log("Hello, world!");
      logger.atInfo().log("It's a beautiful day");
      Logger info = logger.atInfo();
      info.log("... no matter on what level you say it");
      Logger warn = info.atWarn();
      warn.log("Houston, we do not have {} but let's do {}", "a problem", (Supplier) () -> "a drill");
      Throwable exception = new Exception("This is a drill");
      warn.atError().log(exception);
      logger.atInfo()
              .log(exception,
                      "i.e. Throwable always comes {}, then the {} message and arguments work {}",
                      "first",
                      "optional",
                      (Supplier) () -> "as usual");
      Logger.instance()
              .atInfo()
              .atError()
              .atWarn()
              .atTrace()
              .atDebug()
              .log("Not a practical example but now the severity level is DEBUG");
   }
}

The Logger instance is thread-safe, affording flexible usage.

Run that application, the follow output will appear in stdout:

2023-04-04T09:56:41.688-05:00 INFO Main - Hello, world!
2023-04-04T09:56:41.693-05:00 TRACE Main - It's a beautiful day
2023-04-04T09:56:41.693-05:00 INFO Main - ... no matter on what level you say it
2023-04-04T09:56:41.693-05:00 WARN Main - Houston, we do not have a problem but let's do a drill
2023-04-04T09:56:41.693-05:00 ERROR Main - 
java.lang.Exception: This is a drill
    at elf4j.engine.Main.main(Main.java:45)
   
2023-04-04T09:56:41.693-05:00 INFO Main - i.e. Throwable always comes first, then the following optional message and arguments work as usual
java.lang.Exception: This is a drill
    at elf4j.engine.Main.main(Main.java:45)
   
2023-04-04T09:56:41.694-05:00 DEBUG Main - Not a practical example but now the severity level is DEBUG

The output is always asynchronous and won’t block the application’s normal workflow.

The output format patterns can be configured by using a Properties file named elf4j.properties, placed in the root of the classpath.

e.g. with the elf4j.properties file:

pattern={timestamp} {level:5} {class:full}#{method}(L{linenumber}@{filename}) - {message}

The output is:

2023-04-04T09:55:04.857-05:00 INFO  elf4j.engine.Main#main(L39@Main.java) - Hello, world!
2023-04-04T09:55:04.864-05:00 TRACE elf4j.engine.Main#main(L40@Main.java) - It's a beautiful day
2023-04-04T09:55:04.864-05:00 INFO  elf4j.engine.Main#main(L42@Main.java) - ... no matter on what level you say it
2023-04-04T09:55:04.864-05:00 WARN  elf4j.engine.Main#main(L44@Main.java) - Houston, we do not have a problem but let's do a drill
2023-04-04T09:55:04.865-05:00 ERROR elf4j.engine.Main#main(L46@Main.java) - 
java.lang.Exception: This is a drill
    at elf4j.engine.Main.main(Main.java:45)
   
2023-04-04T09:55:04.865-05:00 INFO  elf4j.engine.Main#main(L48@Main.java) - i.e. Throwable always comes first, then the following optional message and arguments work as usual
java.lang.Exception: This is a drill
    at elf4j.engine.Main.main(Main.java:45)
   
2023-04-04T09:55:04.865-05:00 DEBUG elf4j.engine.Main#main(L59@Main.java) - Not a practical example but now the severity level is DEBUG

With the elf4j.properties file:

pattern={json}

The output becomes:

{"timestamp":"2023-10-07T20:11:44.0345848-05:00","message":"Hello, world!","level":"INFO","callerClass":"elf4j.engine.Main"}
{"timestamp":"2023-10-07T20:11:44.0375856-05:00","message":"It's a beautiful day","level":"TRACE","callerClass":"elf4j.engine.Main"}
{"timestamp":"2023-10-07T20:11:44.038585-05:00","message":"... no matter on what level you say it","level":"INFO","callerClass":"elf4j.engine.Main"}
{"timestamp":"2023-10-07T20:11:44.038585-05:00","message":"Houston, we do not have a problem but let's do a drill","level":"WARN","callerClass":"elf4j.engine.Main"}
{"timestamp":"2023-10-07T20:11:44.038585-05:00","message":"","level":"ERROR","callerClass":"elf4j.engine.Main","exception":"java.lang.Exception: This is a drill\r\n\tat elf4j.engine.Main.main(Main.java:43)\r\n"}
{"timestamp":"2023-10-07T20:11:44.038585-05:00","message":"i.e. Throwable always comes first, then the following optional message and arguments work as usual","level":"INFO","callerClass":"elf4j.engine.Main","exception":"java.lang.Exception: This is a drill\r\n\tat elf4j.engine.Main.main(Main.java:43)\r\n"}
{"timestamp":"2023-10-07T20:11:44.038585-05:00","message":"Not a practical example but now the severity level is DEBUG","level":"DEBUG","callerClass":"elf4j.engine.Main"}

The JSON pattern can be configured to pretty-print format, and/or mixed with other patterns.

Features, usage, and configuration details

For using elf4j as a logging facade API, see elf4j’s API description and sample usage.

For details of using this as a runtime log engine, see elf4j-provider for features and configuration.

“The performance talk”

It’s not how fast you fill up the target log file or repository, it’s how fast you relieve the application from logging duty back to its own business.

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