How to use Logging

GeoTools provides extensive logging facilities, similar to commons-logging or sl4j, that allow applications to choose which logging implementation they wish to use.

• Logger: The java util logging api used to log messages and exceptions.

• Logging: GeoTools utility class used to produce Loggers

• LoggerFactory: Provide a bridge between logging implementation and Logger API.

Example use:

package org.geotools.tutorial;

import java.util.logging.Logger;
import org.geotools.util.logging.Logging:

public class Example {
  void method() {
     final Logger LOGGER = Logging.getLogger("org.geotools.tutorial");
     LOGGER.config("Welcome to GeoTools");
  }
}

The logger may be declared in the class’s static fields or returned by a class’s static method. This is not mandatory but suggested if it is going to be used is several methods:

package org.geotools.image;

import java.util.logging.Logger;
import org.geotools.util.logging.Logging:

public class ImageWorker {
    /** ImageWorker.class package name "org.geotools.image" used for Logger */
    private static final Logger LOGGER = Logging.getLogger(ImageWorker.class);
}

Logger

Messages are logged using one of the predefined levels:

Level	Displayed on standard output	Comments
OFF	yes by default	highest value, used turn off all output
FATAL	yes by default	fatal problem preventing application from continuing
SEVERE	yes by default	serious failure, operation unable to continue
WARNING	yes by default	non-fatal warning to bring to user attention
INFO	yes by default	message for end users (not debugging information)
OPERATION	no unless configured	operation configuration
CONFIG	no unless configured	configuration information (services available, etc.)
FINE	no unless configured	information for developers (high level)
FINER	no unless configured	common when entering, returning, or an exception
FINEST	no unless configured	most verbose output
ALL	no unless configured	lowest value, used to enable all output

Levels are used with the log methods when logging messages:

LOGGER.log(Level.INFO,"Hello world");

LOGGER.log(Level.INFO,"Welcome ", System.getProperty("user.name","Friend"));

This technique can be used with the custom level Logging.FATAL:

LOGGER.log(Logging.FATAL, "I’m sorry Dave, I’m afraid I can’t do that.");

The INFO level is for end users. Use the FINE, FINER or FINEST levels for debug information, and setup yours logging.properties file accordingly (see Logging Configuration below).

Convenience method exists in Logger for each of buil-in levels.

LOGGER.severe("Et tu, Brute?" );

LOGGER.warnning("Birds Aren't Real");

LOGGER.info("Hello world");

LOGGER.config("Application settings loaded");

LOGGER.fine("Starting to process the internet");

LOGGER.finer("The internet is full of cat pictures");

if( LOGGER.isLoggableLevel(Level.FINEST)){
    LOGGER.finest("percent processed:"+progress);
}

There are three more FINER convenience methods for tracing program execution:

public Object myMethod(String myArgument) {
    LOGGER.entering("MyClass", "MyMethod", myArgument);
    try {
       // ... do some process here
       LOGGER.exiting("MyClass", "MyMethod", myReturnValue);
       return myReturnValue;
    }
    catch (Throwable myThrowable){
       LOGGER.throwing("MyClass", "MyMethod", myThrowable);
    }
}