I'm trying to setup slf4j to intercept all logging statements and then programmatically add the handlers based on certain conditions. My code is:
private void init()
{
SLF4JBridgeHandler.removeHandlersForRootLogger();
SLF4JBridgeHandler.install();
if(condition1)
appendHandler(console, Level.DEBUG);
if(condition2)
appendHandler(logfile1, Level.INFO);
...
}
How do I write the code for appendHandler
method? I've just spent a few hours trying to read through documentation and cannot find a solution. There are lots of references on how to do it in configuration files but not in code.
Also am I correct in that this code intercepts all logging statements for all the different logging frameworks?
SLF4J supports popular logging frameworks, namely log4j, java. util. logging, Simple logging and NOP. The logback project supports SLF4J natively.
If you used Log4j2 with SLF4J, the only thing you need is replacing Log4j2 JAR files (or maven dependencies) by JDK logger Binding. You do not want to touch any source files in order to replace your logger.
Unlike log4j, SLF4J (Simple Logging Facade for Java) is not an implementation of logging framework, it is an abstraction for all those logging frameworks in Java similar to log4J. Therefore, you cannot compare both. However, it is always difficult to prefer one between the two.
The SLF4J or the Simple Logging Facade for Java is an abstraction layer for various Java logging frameworks, like Log4j 2 or Logback. This allows for plugging different logging frameworks at deployment time without the need for code changes.
Also am I correct in that this code intercepts all logging statements for all the different logging frameworks?
SLF4JBridgeHandler is a java.util.logging
(JUL) logging bridge, which will "intercept" the JUL logging statements and route them to the SLF4J.
Other bridges available are jcl-over-slf4j
(Jakarta Commons Logging => SL4J) and log4j-over-slf4j
(Log4J => SL4J) (as well as their SLF4J => X counterparts).
Depending on which logging frameworks are used in your code (either directly or indirectly), you may want to include some or all of these, to capture all the logging statements, as detailed here.
How do I write the code for appendHandler method?
Once you have setup your bridges, you can then configure your SLF4J implementation in a usual way.
Below is an example of how to do this for Logback:
//Install the JUL Bridge
SLF4JBridgeHandler.removeHandlersForRootLogger();
SLF4JBridgeHandler.install();
//Obtain an instance of LoggerContext
LoggerContext context = (LoggerContext)LoggerFactory.getILoggerFactory();
//Create a new FileAppender
FileAppender<ILoggingEvent> file = new FileAppender<ILoggingEvent>();
file.setName("FileLogger");
file.setFile("error.log");
file.setContext(context);
file.setAppend(true);
//Filter out anything < WARN
ThresholdFilter warningFilter = new ThresholdFilter();
warningFilter.setLevel("WARN");
warningFilter.setContext(context);
warningFilter.start();
file.addFilter(warningFilter);
//Message Encoder
PatternLayoutEncoder ple = new PatternLayoutEncoder();
ple.setContext(context);
ple.setPattern("%date %level [%thread] %logger{10} %msg%n");
ple.start();
file.setEncoder(ple);
file.start();
//Get ROOT logger, and add appender to it
Logger root = context.getLogger(Logger.ROOT_LOGGER_NAME);
root.setLevel(Level.DEBUG);
root.addAppender(file);
If what you want is to use JUL (java.util.logging) as your primary logging framework, you do not need to register the SLF4JBridgeHandler at all.
Just configure JUL handlers as usual, and add the slf4j-jdk14
(i.e. SLF4J => JUL) bridge to your list of dependencies.
//Create a new Handler
Handler fh = new FileHandler("error.log");
fh.setLevel(Level.WARNING);
//Register it with the ROOT logger
Logger.getLogger("").addHandler(fh);
//Log some messages
Logger.getLogger("scratchpad").info("Info !");
Logger.getLogger("scratchpad").warning("Warning !");
Logger.getLogger("scratchpad").severe("Severe !");
//Log some messages via SL4J
LoggerFactory.getLogger("scratchpad").error("sl4j message");
This way any SL4J log statements will be redirected to the appropriate JUL handlers (you may also want to add jcl-over-slf4j
and log4j-over-sl4j
in the mix too).
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