Java Logging - slf4j，log4j

Question

Is there a way to pass slf4j logger a map of properties?

for example, I would like to do something like this:

Logger logger = LoggerFactory.getLogger(SomeClass.class);

Map data = new HashMap<String, String>();
data["key1"] = "value1";
data["key2"] = "value2";

logger.info("my info message", data)

Then, I would like that my appender will receive log4j LoggingEvent with the above parameters, like this:

public class MyAppender extends AppenderSkeleton {
...
...

@Override
protected void append(LoggingEvent event) {
    Map properties = event.getProperties();
    String valueOfKey1 = (String) properties.get("key1");   
    //valueOfKey1 sould be equal to 'value1'
}
...
...    

UPDATE:

Is there any java logging framework that supports passing HashMap data (or similar in its interface)

Answer 1

From SLF4J Manual "Mapped Diagnostic Context" is essentially a map maintained by the logging framework where the application code provides key-value pairs which can then be inserted by the logging framework in log messages. MDC data can also be highly helpful in filtering messages or triggering certain actions.

SLF4J supports MDC, or mapped diagnostic context. If the underlying logging framework offers MDC functionality, then SLF4J will delegate to the underlying framework's MDC. Note that at this time, only log4j and logback offer MDC functionality.

As you tagged the question with log4j and as your example cites log4j classes, SLF4J will allow you to set values into the MDC map on a thread bases using slf4j API . Those values will then natively accessible at log4j level in the LoggingEvent .

Here is an example adapted from Logback manual cited in SLF4J manual (and also by @Seelenvirtuose in its comment) :

public class SimpleMDC {
  static public void main(String[] args) throws Exception {

    // You can put values in the MDC at any time. Before anything else
    // we put the first name
    MDC.put("key1", "value1");

    [ SNIP ]

    Logger logger = LoggerFactory.getLogger(SimpleMDC.class);
    // We now put the last name
    MDC.put("key2", "value2");

    logger.info("Info log message");
  }
}

Then, in your custom appender, you can easyly get the values :

public class MyAppender extends AppenderSkeleton {
...
...

@Override
protected void append(LoggingEvent event) {
    String valueOfKey1 = (String) event.getMDC("key1");   
    //valueOfKey1 should be equal to 'value1'
}
...
... 

Of course, same functionnality would be available through Logback ...