szhem / log4j-json-layout

Log4J Layout to Format Logs into Logstash Json Format

Logstash Log4J Layout

1. What is it?
2. How to use?
3. Notes
4. License

What is it?

Log4J Layout to format logs according to the Logstash json format.

This layout does not have any external dependencies on 3rd party libraries, so it can be easily used within different environments, for example OSGi runtimes.

Currently the following features are available:

• Selecting what to log
• Adding tags and fields
• Logging source path

How to use?

Selecting what to log

It is possible to select what fields should be included or excluded from the logs.

By default the following fields are logged:

{
    "level": "ERROR",
    "logger": "root",
    "message": "Hello World!",
    "mdc": {
        "mdc_key_2": "mdc_val_2",
        "mdc_key_1": "mdc_val_1"
    },
    "ndc": "ndc_1 ndc_2 ndc_3",
    "host": "vm",
    "@timestamp": "2013-11-17T10:21:41.863Z",
    "thread": "main",
    "@version": "1"
}

If there is an exception, the logged message will look like the following one:

{
    "exception": {
        "message": "Test Exception",
        "class": "java.lang.RuntimeException",
        "stacktrace": "java.lang.RuntimeException: Test Exception\n\tat com.github.szhem.logstash.log4j.LogStashJsonLayoutTest.testSourcePath(LogStashJsonLayoutTest.java:193)\n\tat sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)\n\tat sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)\n\tat sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)\n\tat java.lang.reflect.Method.invoke(Method.java:601)\n\tat org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:47)\n\tat org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)\n\tat org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:44)\n\tat org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)\n\tat org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:26)\n\tat org.junit.rules.TestWatcher$1.evaluate(TestWatcher.java:55)\n\tat org.junit.rules.RunRules.evaluate(RunRules.java:20)\n\tat org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:271)\n\tat org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:70)\n\tat org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:50)\n\tat org.junit.runners.ParentRunner$3.run(ParentRunner.java:238)\n\tat org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:63)\n\tat org.junit.runners.ParentRunner.runChildren(ParentRunner.java:236)\n\tat org.junit.runners.ParentRunner.access$000(ParentRunner.java:53)\n\tat org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:229)\n\tat org.junit.runners.ParentRunner.run(ParentRunner.java:309)\n\tat org.junit.runner.JUnitCore.run(JUnitCore.java:160)\n\tat com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:76)\n\tat com.intellij.rt.execution.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:195)\n\tat com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:63)\n\tat sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)\n\tat sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)\n\tat sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)\n\tat java.lang.reflect.Method.invoke(Method.java:601)\n\tat com.intellij.rt.execution.application.AppMain.main(AppMain.java:120)"
    },
    "level": "ERROR",
    "logger": "root",
    "message": "Hello World!",
    "host": "vm",
    "@timestamp": "2013-11-17T10:21:41.863Z",
    "thread": "main",
    "@version": "1"
}

By default location is not logged as it's pretty expensive to resolve, but if you need to log it use includedFields property to specify the required fields to be included into the message

log4j.rootLogger = INFO, stdout

log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.layout=com.github.szhem.logstash.log4j.LogStashJsonLayout
log4j.appender.stdout.layout.includedFields=location

After that the location will be available in the message

{
    "level": "ERROR",
    "location": {
        "class": "com.github.szhem.logstash.log4j.LogStashJsonLayoutTest",
        "file": "LogStashJsonLayoutTest.java",
        "method": "testSourcePath",
        "line": "195"
    },
    "logger": "root",
    "message": "Hello World!",
    "host": "vm",
    "@timestamp": "2013-11-17T10:21:41.863Z",
    "thread": "main",
    "@version": "1"
}

Included and excluded fields can be combined together

log4j.rootLogger = INFO, stdout

log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.layout=com.github.szhem.logstash.log4j.LogStashJsonLayout
log4j.appender.stdout.layout.includedFields=location
log4j.appender.stdout.layout.excludedFields=exception,mdc,ndc

Adding tags and fields

Additional fields and tags which must be included into the logged message can be specified with tags and fields configuration properties of the layout:

log4j.rootLogger = INFO, stdout

log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.layout=com.github.szhem.logstash.log4j.LogStashJsonLayout
log4j.appender.stdout.layout.tags=spring,logstash
log4j.appender.stdout.layout.fields=type:log4j,format:json

The message will look like the following one:

{
    "format": "json",
    "type": "log4j",
    "level": "INFO",
    "logger": "root",
    "message": "Hello World",
    "host": "vm",
    "tags": ["spring", "logstash"],
    "@timestamp": "2013-11-17T11:03:02.025Z",
    "thread": "main",
    "@version": "1"
}

Logging source path

If the layout is configured with an instance of FileAppender or any of its subclasses then the path of the file, the log messages are sent to, will also be included into the message:

log4j.appender.out=org.apache.log4j.RollingFileAppender
log4j.appender.out.layout=com.github.szhem.logstash.log4j.LogStashJsonLayout
log4j.appender.out.file="/tmp/logger.log"
log4j.appender.out.append=true
log4j.appender.out.maxFileSize=100MB
log4j.appender.out.maxBackupIndex=10

With such a configuration the message will contain additional path field

{
    "level": "ERROR",
    "logger": "root",
    "message": "Hello World!",
    "host": "vm",
    "path": "/tmp/logger.log",
    "@timestamp": "2013-11-17T10:21:41.863Z",
    "thread": "main",
    "@version": "1"
}

Notes

The LogStashJsonLayout is not thread safe and a single instance of this layout must not be used with multiple appenders. Each appender must be configured with its own layout instance.

License

The component is distributed under Apache License 2.0.