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
- Prerequisite: Java 8+ for versions older than 16.0.0 (exclusive); Java 21+ for versions newer than 16.0.0 (inclusive).
- To use this as a logging service provider in your application, see installation details here

Use it for logging in an application:

class ReadmeTest {
  static Logger logger = Logger.instance();
   
  @Test
  void readMe() {
    MDC.put("ctx-key", "ctx-value");
    logger.log("Hello, world!");
    logger.atTrace().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, "When being logged, the Throwable always comes {}", "first");
    logger.atInfo().log(
        exception, "The log {} and {} work as usual", () -> "message", () -> "arguments");
    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 following output will appear in stdout:

2025-07-13T11:54:40.384-05:00 INFO elf4j.engine.ReadmeTest - Hello, world!
2025-07-13T11:54:40.402-05:00 TRACE elf4j.engine.ReadmeTest - It's a beautiful day
2025-07-13T11:54:40.403-05:00 INFO elf4j.engine.ReadmeTest - ... no matter on what level you say it
2025-07-13T11:54:40.404-05:00 WARN elf4j.engine.ReadmeTest - Houston, we do not have a problem but let's do a drill
2025-07-13T11:54:40.404-05:00 ERROR elf4j.engine.ReadmeTest - 
java.lang.Exception: This is a drill
    at elf4j.engine.ReadmeTest.readMe(ReadmeTest.java:46)
    at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:103)
    at java.base/java.lang.reflect.Method.invoke(Method.java:580)
    at org.junit.platform.commons.util.ReflectionUtils.invokeMethod(ReflectionUtils.java:787)
    at org.junit.platform.commons.support.ReflectionSupport.invokeMethod(ReflectionSupport.java:478)
    (... full stack trace omitted for this README.md)
   
2025-07-13T11:54:40.405-05:00 INFO elf4j.engine.ReadmeTest - When being logged, the Throwable always comes first
java.lang.Exception: This is a drill
    at elf4j.engine.ReadmeTest.readMe(ReadmeTest.java:46)
    at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:103)
    at java.base/java.lang.reflect.Method.invoke(Method.java:580)
    at org.junit.platform.commons.util.ReflectionUtils.invokeMethod(ReflectionUtils.java:787)
    (... full stack trace omitted for this README.md)
   
2025-07-13T11:54:40.407-05:00 INFO elf4j.Logger - The log message and arguments work as usual
java.lang.Exception: This is a drill
    at elf4j.engine.ReadmeTest.readMe(ReadmeTest.java:46)
    at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:103)
    at java.base/java.lang.reflect.Method.invoke(Method.java:580)
    at org.junit.platform.commons.util.ReflectionUtils.invokeMethod(ReflectionUtils.java:787)
    (... full stack trace omitted for this README.md)
   
2025-07-13T11:54:40.408-05:00 DEBUG elf4j.engine.ReadmeTest - 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.

Configure output format patterns by using a Properties file named elf4j.properties, placed in the root of the classpath. For example, with the elf4j.properties file:

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

The output becomes:

2025-07-13T11:59:21.366-05:00 INFO ReadmeTest#readMe(L39@ReadmeTest.java) - Hello, world!
2025-07-13T11:59:21.392-05:00 TRACE ReadmeTest#readMe(L40@ReadmeTest.java) - It's a beautiful day
2025-07-13T11:59:21.393-05:00 INFO ReadmeTest#readMe(L42@ReadmeTest.java) - ... no matter on what level you say it
2025-07-13T11:59:21.393-05:00 WARN ReadmeTest#readMe(L44@ReadmeTest.java) - Houston, we do not have a problem but let's do a drill
2025-07-13T11:59:21.394-05:00 ERROR ReadmeTest#readMe(L47@ReadmeTest.java) -
    java.lang.Exception: This is a drill
    at elf4j.engine.ReadmeTest.readMe(ReadmeTest.java:46)
    at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:103)
    at java.base/java.lang.reflect.Method.invoke(Method.java:580)
    at org.junit.platform.commons.util.ReflectionUtils.invokeMethod(ReflectionUtils.java:787)
    (... full stack trace omitted for this README.md)
   
2025-07-13T11:59:21.395-05:00 INFO ReadmeTest#readMe(L48@ReadmeTest.java) - When being logged, the Throwable always comes first
    java.lang.Exception: This is a drill
    at elf4j.engine.ReadmeTest.readMe(ReadmeTest.java:46)
    at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:103)
    at java.base/java.lang.reflect.Method.invoke(Method.java:580)
    at org.junit.platform.commons.util.ReflectionUtils.invokeMethod(ReflectionUtils.java:787)
    (... full stack trace omitted for this README.md)
   
2025-07-13T11:59:21.398-05:00 INFO Logger#log(L169@Logger.java) - The log message and arguments work as usual
    java.lang.Exception: This is a drill
    at elf4j.engine.ReadmeTest.readMe(ReadmeTest.java:46)
    at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:103)
    at java.base/java.lang.reflect.Method.invoke(Method.java:580)
    at org.junit.platform.commons.util.ReflectionUtils.invokeMethod(ReflectionUtils.java:787)
    (... full stack trace omitted for this README.md)
   
2025-07-13T11:59:21.398-05:00 DEBUG ReadmeTest#readMe(L57@ReadmeTest.java) - Not a practical example but now the severity level is DEBUG

With the elf4j.properties file:

pattern={json}

The output becomes:

{"timestamp":"2025-07-13T12:38:08.478009-05:00","level":"INFO","loggerName":"elf4j.engine.ReadmeTest","context":{"ctx-key":"ctx-value"},"message":"Hello, world!"}
{"timestamp":"2025-07-13T12:38:08.4963095-05:00","level":"TRACE","loggerName":"elf4j.engine.ReadmeTest","context":{"ctx-key":"ctx-value"},"message":"It's a beautiful day"}
{"timestamp":"2025-07-13T12:38:08.4968277-05:00","level":"INFO","loggerName":"elf4j.engine.ReadmeTest","context":{"ctx-key":"ctx-value"},"message":"... no matter on what level you say it"}
{"timestamp":"2025-07-13T12:38:08.4968277-05:00","level":"WARN","loggerName":"elf4j.engine.ReadmeTest","context":{"ctx-key":"ctx-value"},"message":"Houston, we do not have a problem but let's do a drill"}
{"timestamp":"2025-07-13T12:38:08.4974686-05:00","level":"ERROR","loggerName":"elf4j.engine.ReadmeTest","context":{"ctx-key":"ctx-value"},"message":"","exception":"java.lang.Exception: This is a drill\r\n\tat elf4j.engine.ReadmeTest.readMe(ReadmeTest.java:46)\r\n\tat java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:103)\r\n\tat java.base/java.lang.reflect.Method.invoke(Method.java:580)\r\n\tat org.junit.platform.commons.util.ReflectionUtils.invokeMethod(ReflectionUtils.java:787)\r\n\tat org.junit.platform.commons.support.ReflectionSupport.invokeMethod(ReflectionSupport.java:478)\r\n\tat org.junit.jupiter.engine.execution.MethodInvocation.proceed(MethodInvocation.java:60)\r\n\tat org.junit.jupiter.engine.execution.InvocationInterceptorChain$ValidatingInvocation.proceed(InvocationInterceptorChain.java:131)\r\n\tat org.junit.jupiter.engine.extension.TimeoutExtension.intercept(TimeoutExtension.java:161)\r\n\tat org.junit.jupiter.engine.extension.TimeoutExtension.interceptTestableMethod(TimeoutExtension.java:152)\r\n\tat org.junit.jupiter.engine.extension.TimeoutExtension.interceptTestMethod(TimeoutExtension.java:91)\r\n\tat org.junit.jupiter.engine.execution.InterceptingExecutableInvoker$ReflectiveInterceptorCall.lambda$ofVoidMethod$0(InterceptingExecutableInvoker.java:112)\r\n\tat org.junit.jupiter.engine.execution.InterceptingExecutableInvoker.lambda$invoke$0(InterceptingExecutableInvoker.java:94)\r\n\tat org.junit.jupiter.engine.execution.InvocationInterceptorChain$InterceptedInvocation.proceed(InvocationInterceptorChain.java:106)\r\n\tat org.junit.jupiter.engine.execution.InvocationInterceptorChain.proceed(InvocationInterceptorChain.java:64)\r\n\tat org.junit.jupiter.engine.execution.InvocationInterceptorChain.chainAndInvoke(InvocationInterceptorChain.java:45)\r\n\tat org.junit.jupiter.engine.execution.InvocationInterceptorChain.invoke(InvocationInterceptorChain.java:37)\r\n\tat org.junit.jupiter.engine.execution.InterceptingExecutableInvoker.invoke(InterceptingExecutableInvoker.java:93)\r\n\tat org.junit.jupiter.engine.execution.InterceptingExecutableInvoker.invoke(InterceptingExecutableInvoker.java:87)\r\n\tat org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.lambda$invokeTestMethod$4(TestMethodTestDescriptor.java:221)\r\n\tat org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)\r\n\tat org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.invokeTestMethod(TestMethodTestDescriptor.java:217)\r\n\tat org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.execute(TestMethodTestDescriptor.java:159)\r\n\tat org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.execute(TestMethodTestDescriptor.java:70)\r\n\tat org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$6(NodeTestTask.java:157)\r\n\tat org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)\r\n\tat org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:147)\r\n\tat org.junit.platform.engine.support.hierarchical.Node.around(Node.java:137)\r\n\tat org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$9(NodeTestTask.java:145)\r\n\tat org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)\r\n\tat org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:144)\r\n\tat org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:101)\r\n\tat java.base/java.util.ArrayList.forEach(ArrayList.java:1596)\r\n\tat org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.invokeAll(SameThreadHierarchicalTestExecutorService.java:41)\r\n\tat org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$6(NodeTestTask.java:161)\r\n\tat org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)\r\n\tat org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:147)\r\n\tat org.junit.platform.engine.support.hierarchical.Node.around(Node.java:137)\r\n\tat org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$9(NodeTestTask.java:145)\r\n\tat org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)\r\n\tat org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:144)\r\n\tat org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:101)\r\n\tat java.base/java.util.ArrayList.forEach(ArrayList.java:1596)\r\n\tat org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.invokeAll(SameThreadHierarchicalTestExecutorService.java:41)\r\n\tat org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$6(NodeTestTask.java:161)\r\n\tat org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)\r\n\tat org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:147)\r\n\tat org.junit.platform.engine.support.hierarchical.Node.around(Node.java:137)\r\n\tat org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$9(NodeTestTask.java:145)\r\n\tat org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)\r\n\tat org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:144)\r\n\tat org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:101)\r\n\tat org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.submit(SameThreadHierarchicalTestExecutorService.java:35)\r\n\tat org.junit.platform.engine.support.hierarchical.HierarchicalTestExecutor.execute(HierarchicalTestExecutor.java:57)\r\n\tat org.junit.platform.engine.support.hierarchical.HierarchicalTestEngine.execute(HierarchicalTestEngine.java:54)\r\n\tat org.junit.platform.launcher.core.EngineExecutionOrchestrator.executeEngine(EngineExecutionOrchestrator.java:230)\r\n\tat org.junit.platform.launcher.core.EngineExecutionOrchestrator.failOrExecuteEngine(EngineExecutionOrchestrator.java:204)\r\n\tat org.junit.platform.launcher.core.EngineExecutionOrchestrator.execute(EngineExecutionOrchestrator.java:172)\r\n\tat org.junit.platform.launcher.core.EngineExecutionOrchestrator.execute(EngineExecutionOrchestrator.java:101)\r\n\tat org.junit.platform.launcher.core.EngineExecutionOrchestrator.lambda$execute$0(EngineExecutionOrchestrator.java:64)\r\n\tat org.junit.platform.launcher.core.EngineExecutionOrchestrator.withInterceptedStreams(EngineExecutionOrchestrator.java:150)\r\n\tat org.junit.platform.launcher.core.EngineExecutionOrchestrator.execute(EngineExecutionOrchestrator.java:63)\r\n\tat org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:109)\r\n\tat org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:91)\r\n\tat org.junit.platform.launcher.core.DelegatingLauncher.execute(DelegatingLauncher.java:47)\r\n\tat org.junit.platform.launcher.core.InterceptingLauncher.lambda$execute$1(InterceptingLauncher.java:39)\r\n\tat org.junit.platform.launcher.core.ClasspathAlignmentCheckingLauncherInterceptor.intercept(ClasspathAlignmentCheckingLauncherInterceptor.java:25)\r\n\tat org.junit.platform.launcher.core.InterceptingLauncher.execute(InterceptingLauncher.java:38)\r\n\tat org.junit.platform.launcher.core.DelegatingLauncher.execute(DelegatingLauncher.java:47)\r\n\tat org.junit.platform.launcher.core.SessionPerRequestLauncher.execute(SessionPerRequestLauncher.java:66)\r\n\tat com.intellij.junit5.JUnit5IdeaTestRunner.startRunnerWithArgs(JUnit5IdeaTestRunner.java:57)\r\n\tat com.intellij.rt.junit.IdeaTestRunner$Repeater$1.execute(IdeaTestRunner.java:38)\r\n\tat com.intellij.rt.execution.junit.TestsRepeater.repeat(TestsRepeater.java:11)\r\n\tat com.intellij.rt.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:35)\r\n\tat com.intellij.rt.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:231)\r\n\tat com.intellij.rt.junit.JUnitStarter.main(JUnitStarter.java:55)\r\n"}
{"timestamp":"2025-07-13T12:38:08.4974686-05:00","level":"INFO","loggerName":"elf4j.engine.ReadmeTest","context":{"ctx-key":"ctx-value"},"message":"When being logged, the Throwable always comes first","exception":"java.lang.Exception: This is a drill\r\n\tat elf4j.engine.ReadmeTest.readMe(ReadmeTest.java:46)\r\n\tat java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:103)\r\n\tat java.base/java.lang.reflect.Method.invoke(Method.java:580)\r\n\tat org.junit.platform.commons.util.ReflectionUtils.invokeMethod(ReflectionUtils.java:787)\r\n\tat org.junit.platform.commons.support.ReflectionSupport.invokeMethod(ReflectionSupport.java:478)\r\n\tat org.junit.jupiter.engine.execution.MethodInvocation.proceed(MethodInvocation.java:60)\r\n\tat org.junit.jupiter.engine.execution.InvocationInterceptorChain$ValidatingInvocation.proceed(InvocationInterceptorChain.java:131)\r\n\tat org.junit.jupiter.engine.extension.TimeoutExtension.intercept(TimeoutExtension.java:161)\r\n\tat org.junit.jupiter.engine.extension.TimeoutExtension.interceptTestableMethod(TimeoutExtension.java:152)\r\n\tat org.junit.jupiter.engine.extension.TimeoutExtension.interceptTestMethod(TimeoutExtension.java:91)\r\n\tat org.junit.jupiter.engine.execution.InterceptingExecutableInvoker$ReflectiveInterceptorCall.lambda$ofVoidMethod$0(InterceptingExecutableInvoker.java:112)\r\n\tat org.junit.jupiter.engine.execution.InterceptingExecutableInvoker.lambda$invoke$0(InterceptingExecutableInvoker.java:94)\r\n\tat org.junit.jupiter.engine.execution.InvocationInterceptorChain$InterceptedInvocation.proceed(InvocationInterceptorChain.java:106)\r\n\tat org.junit.jupiter.engine.execution.InvocationInterceptorChain.proceed(InvocationInterceptorChain.java:64)\r\n\tat org.junit.jupiter.engine.execution.InvocationInterceptorChain.chainAndInvoke(InvocationInterceptorChain.java:45)\r\n\tat org.junit.jupiter.engine.execution.InvocationInterceptorChain.invoke(InvocationInterceptorChain.java:37)\r\n\tat org.junit.jupiter.engine.execution.InterceptingExecutableInvoker.invoke(InterceptingExecutableInvoker.java:93)\r\n\tat org.junit.jupiter.engine.execution.InterceptingExecutableInvoker.invoke(InterceptingExecutableInvoker.java:87)\r\n\tat org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.lambda$invokeTestMethod$4(TestMethodTestDescriptor.java:221)\r\n\tat org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)\r\n\tat org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.invokeTestMethod(TestMethodTestDescriptor.java:217)\r\n\tat org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.execute(TestMethodTestDescriptor.java:159)\r\n\tat org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.execute(TestMethodTestDescriptor.java:70)\r\n\tat org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$6(NodeTestTask.java:157)\r\n\tat org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)\r\n\tat org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:147)\r\n\tat org.junit.platform.engine.support.hierarchical.Node.around(Node.java:137)\r\n\tat org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$9(NodeTestTask.java:145)\r\n\tat org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)\r\n\tat org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:144)\r\n\tat org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:101)\r\n\tat java.base/java.util.ArrayList.forEach(ArrayList.java:1596)\r\n\tat org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.invokeAll(SameThreadHierarchicalTestExecutorService.java:41)\r\n\tat org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$6(NodeTestTask.java:161)\r\n\tat org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)\r\n\tat org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:147)\r\n\tat org.junit.platform.engine.support.hierarchical.Node.around(Node.java:137)\r\n\tat org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$9(NodeTestTask.java:145)\r\n\tat org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)\r\n\tat org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:144)\r\n\tat org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:101)\r\n\tat java.base/java.util.ArrayList.forEach(ArrayList.java:1596)\r\n\tat org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.invokeAll(SameThreadHierarchicalTestExecutorService.java:41)\r\n\tat org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$6(NodeTestTask.java:161)\r\n\tat org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)\r\n\tat org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:147)\r\n\tat org.junit.platform.engine.support.hierarchical.Node.around(Node.java:137)\r\n\tat org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$9(NodeTestTask.java:145)\r\n\tat org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)\r\n\tat org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:144)\r\n\tat org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:101)\r\n\tat org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.submit(SameThreadHierarchicalTestExecutorService.java:35)\r\n\tat org.junit.platform.engine.support.hierarchical.HierarchicalTestExecutor.execute(HierarchicalTestExecutor.java:57)\r\n\tat org.junit.platform.engine.support.hierarchical.HierarchicalTestEngine.execute(HierarchicalTestEngine.java:54)\r\n\tat org.junit.platform.launcher.core.EngineExecutionOrchestrator.executeEngine(EngineExecutionOrchestrator.java:230)\r\n\tat org.junit.platform.launcher.core.EngineExecutionOrchestrator.failOrExecuteEngine(EngineExecutionOrchestrator.java:204)\r\n\tat org.junit.platform.launcher.core.EngineExecutionOrchestrator.execute(EngineExecutionOrchestrator.java:172)\r\n\tat org.junit.platform.launcher.core.EngineExecutionOrchestrator.execute(EngineExecutionOrchestrator.java:101)\r\n\tat org.junit.platform.launcher.core.EngineExecutionOrchestrator.lambda$execute$0(EngineExecutionOrchestrator.java:64)\r\n\tat org.junit.platform.launcher.core.EngineExecutionOrchestrator.withInterceptedStreams(EngineExecutionOrchestrator.java:150)\r\n\tat org.junit.platform.launcher.core.EngineExecutionOrchestrator.execute(EngineExecutionOrchestrator.java:63)\r\n\tat org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:109)\r\n\tat org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:91)\r\n\tat org.junit.platform.launcher.core.DelegatingLauncher.execute(DelegatingLauncher.java:47)\r\n\tat org.junit.platform.launcher.core.InterceptingLauncher.lambda$execute$1(InterceptingLauncher.java:39)\r\n\tat org.junit.platform.launcher.core.ClasspathAlignmentCheckingLauncherInterceptor.intercept(ClasspathAlignmentCheckingLauncherInterceptor.java:25)\r\n\tat org.junit.platform.launcher.core.InterceptingLauncher.execute(InterceptingLauncher.java:38)\r\n\tat org.junit.platform.launcher.core.DelegatingLauncher.execute(DelegatingLauncher.java:47)\r\n\tat org.junit.platform.launcher.core.SessionPerRequestLauncher.execute(SessionPerRequestLauncher.java:66)\r\n\tat com.intellij.junit5.JUnit5IdeaTestRunner.startRunnerWithArgs(JUnit5IdeaTestRunner.java:57)\r\n\tat com.intellij.rt.junit.IdeaTestRunner$Repeater$1.execute(IdeaTestRunner.java:38)\r\n\tat com.intellij.rt.execution.junit.TestsRepeater.repeat(TestsRepeater.java:11)\r\n\tat com.intellij.rt.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:35)\r\n\tat com.intellij.rt.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:231)\r\n\tat com.intellij.rt.junit.JUnitStarter.main(JUnitStarter.java:55)\r\n"}
{"timestamp":"2025-07-13T12:38:08.4981677-05:00","level":"INFO","loggerName":"elf4j.engine.ReadmeTest","context":{"ctx-key":"ctx-value"},"message":"The log message and arguments work as usual","exception":"java.lang.Exception: This is a drill\r\n\tat elf4j.engine.ReadmeTest.readMe(ReadmeTest.java:46)\r\n\tat java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:103)\r\n\tat java.base/java.lang.reflect.Method.invoke(Method.java:580)\r\n\tat org.junit.platform.commons.util.ReflectionUtils.invokeMethod(ReflectionUtils.java:787)\r\n\tat org.junit.platform.commons.support.ReflectionSupport.invokeMethod(ReflectionSupport.java:478)\r\n\tat org.junit.jupiter.engine.execution.MethodInvocation.proceed(MethodInvocation.java:60)\r\n\tat org.junit.jupiter.engine.execution.InvocationInterceptorChain$ValidatingInvocation.proceed(InvocationInterceptorChain.java:131)\r\n\tat org.junit.jupiter.engine.extension.TimeoutExtension.intercept(TimeoutExtension.java:161)\r\n\tat org.junit.jupiter.engine.extension.TimeoutExtension.interceptTestableMethod(TimeoutExtension.java:152)\r\n\tat org.junit.jupiter.engine.extension.TimeoutExtension.interceptTestMethod(TimeoutExtension.java:91)\r\n\tat org.junit.jupiter.engine.execution.InterceptingExecutableInvoker$ReflectiveInterceptorCall.lambda$ofVoidMethod$0(InterceptingExecutableInvoker.java:112)\r\n\tat org.junit.jupiter.engine.execution.InterceptingExecutableInvoker.lambda$invoke$0(InterceptingExecutableInvoker.java:94)\r\n\tat org.junit.jupiter.engine.execution.InvocationInterceptorChain$InterceptedInvocation.proceed(InvocationInterceptorChain.java:106)\r\n\tat org.junit.jupiter.engine.execution.InvocationInterceptorChain.proceed(InvocationInterceptorChain.java:64)\r\n\tat org.junit.jupiter.engine.execution.InvocationInterceptorChain.chainAndInvoke(InvocationInterceptorChain.java:45)\r\n\tat org.junit.jupiter.engine.execution.InvocationInterceptorChain.invoke(InvocationInterceptorChain.java:37)\r\n\tat org.junit.jupiter.engine.execution.InterceptingExecutableInvoker.invoke(InterceptingExecutableInvoker.java:93)\r\n\tat org.junit.jupiter.engine.execution.InterceptingExecutableInvoker.invoke(InterceptingExecutableInvoker.java:87)\r\n\tat org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.lambda$invokeTestMethod$4(TestMethodTestDescriptor.java:221)\r\n\tat org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)\r\n\tat org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.invokeTestMethod(TestMethodTestDescriptor.java:217)\r\n\tat org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.execute(TestMethodTestDescriptor.java:159)\r\n\tat org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.execute(TestMethodTestDescriptor.java:70)\r\n\tat org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$6(NodeTestTask.java:157)\r\n\tat org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)\r\n\tat org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:147)\r\n\tat org.junit.platform.engine.support.hierarchical.Node.around(Node.java:137)\r\n\tat org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$9(NodeTestTask.java:145)\r\n\tat org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)\r\n\tat org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:144)\r\n\tat org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:101)\r\n\tat java.base/java.util.ArrayList.forEach(ArrayList.java:1596)\r\n\tat org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.invokeAll(SameThreadHierarchicalTestExecutorService.java:41)\r\n\tat org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$6(NodeTestTask.java:161)\r\n\tat org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)\r\n\tat org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:147)\r\n\tat org.junit.platform.engine.support.hierarchical.Node.around(Node.java:137)\r\n\tat org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$9(NodeTestTask.java:145)\r\n\tat org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)\r\n\tat org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:144)\r\n\tat org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:101)\r\n\tat java.base/java.util.ArrayList.forEach(ArrayList.java:1596)\r\n\tat org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.invokeAll(SameThreadHierarchicalTestExecutorService.java:41)\r\n\tat org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$6(NodeTestTask.java:161)\r\n\tat org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)\r\n\tat org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:147)\r\n\tat org.junit.platform.engine.support.hierarchical.Node.around(Node.java:137)\r\n\tat org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$9(NodeTestTask.java:145)\r\n\tat org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)\r\n\tat org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:144)\r\n\tat org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:101)\r\n\tat org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.submit(SameThreadHierarchicalTestExecutorService.java:35)\r\n\tat org.junit.platform.engine.support.hierarchical.HierarchicalTestExecutor.execute(HierarchicalTestExecutor.java:57)\r\n\tat org.junit.platform.engine.support.hierarchical.HierarchicalTestEngine.execute(HierarchicalTestEngine.java:54)\r\n\tat org.junit.platform.launcher.core.EngineExecutionOrchestrator.executeEngine(EngineExecutionOrchestrator.java:230)\r\n\tat org.junit.platform.launcher.core.EngineExecutionOrchestrator.failOrExecuteEngine(EngineExecutionOrchestrator.java:204)\r\n\tat org.junit.platform.launcher.core.EngineExecutionOrchestrator.execute(EngineExecutionOrchestrator.java:172)\r\n\tat org.junit.platform.launcher.core.EngineExecutionOrchestrator.execute(EngineExecutionOrchestrator.java:101)\r\n\tat org.junit.platform.launcher.core.EngineExecutionOrchestrator.lambda$execute$0(EngineExecutionOrchestrator.java:64)\r\n\tat org.junit.platform.launcher.core.EngineExecutionOrchestrator.withInterceptedStreams(EngineExecutionOrchestrator.java:150)\r\n\tat org.junit.platform.launcher.core.EngineExecutionOrchestrator.execute(EngineExecutionOrchestrator.java:63)\r\n\tat org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:109)\r\n\tat org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:91)\r\n\tat org.junit.platform.launcher.core.DelegatingLauncher.execute(DelegatingLauncher.java:47)\r\n\tat org.junit.platform.launcher.core.InterceptingLauncher.lambda$execute$1(InterceptingLauncher.java:39)\r\n\tat org.junit.platform.launcher.core.ClasspathAlignmentCheckingLauncherInterceptor.intercept(ClasspathAlignmentCheckingLauncherInterceptor.java:25)\r\n\tat org.junit.platform.launcher.core.InterceptingLauncher.execute(InterceptingLauncher.java:38)\r\n\tat org.junit.platform.launcher.core.DelegatingLauncher.execute(DelegatingLauncher.java:47)\r\n\tat org.junit.platform.launcher.core.SessionPerRequestLauncher.execute(SessionPerRequestLauncher.java:66)\r\n\tat com.intellij.junit5.JUnit5IdeaTestRunner.startRunnerWithArgs(JUnit5IdeaTestRunner.java:57)\r\n\tat com.intellij.rt.junit.IdeaTestRunner$Repeater$1.execute(IdeaTestRunner.java:38)\r\n\tat com.intellij.rt.execution.junit.TestsRepeater.repeat(TestsRepeater.java:11)\r\n\tat com.intellij.rt.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:35)\r\n\tat com.intellij.rt.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:231)\r\n\tat com.intellij.rt.junit.JUnitStarter.main(JUnitStarter.java:55)\r\n"}
{"timestamp":"2025-07-13T12:38:08.4981677-05:00","level":"DEBUG","loggerName":"elf4j.engine.ReadmeTest","context":{"ctx-key":"ctx-value"},"message":"Not a practical example but now the severity level is DEBUG"}

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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