Java allows logging configuration directly in code. This gives developers full control over loggers, handlers, formatters, and levels at runtime, useful for dynamically adjusting logs or when file-based config isn’t practical.
Simple Program
import java.util.logging.*;
public class SimpleProgrammaticLogging {
private static final Logger logger = Logger.getLogger(SimpleProgrammaticLogging.class.getName());
public static void main(String[] args) {
// Disable default console handler
Logger rootLogger = Logger.getLogger("");
for (Handler h : rootLogger.getHandlers()) {
rootLogger.removeHandler(h);
}
// Set custom ConsoleHandler
ConsoleHandler consoleHandler = new ConsoleHandler();
consoleHandler.setLevel(Level.INFO);
consoleHandler.setFormatter(new SimpleFormatter());
logger.setLevel(Level.INFO);
logger.addHandler(consoleHandler);
logger.fine("FINE: Hidden");
logger.info("INFO: Displayed");
logger.warning("WARNING: Displayed");
}
}Problem Statement
LotusJavaPrince wants to build a logger that logs all suspicious activity to a file for compliance purposes. Mahesh, the security officer, wants:
- Only
WARNINGandSEVEREmessages in the log file. - Console output must show everything from
FINEand above. - All configuration must be programmatic, without
.properties.
import java.io.IOException;
import java.util.logging.*;
public class BankAuditLogger {
private static final Logger logger = Logger.getLogger(BankAuditLogger.class.getName());
public static void main(String[] args) throws IOException {
// Disable root handlers
Logger rootLogger = Logger.getLogger("");
for (Handler h : rootLogger.getHandlers()) {
rootLogger.removeHandler(h);
}
// Console handler for detailed logs
ConsoleHandler consoleHandler = new ConsoleHandler();
consoleHandler.setLevel(Level.FINE);
consoleHandler.setFormatter(new SimpleFormatter());
// File handler for warnings and above
FileHandler fileHandler = new FileHandler("security-audit.log", true);
fileHandler.setLevel(Level.WARNING);
fileHandler.setFormatter(new XMLFormatter());
logger.setLevel(Level.FINE); // Allow FINE logs in the logger itself
logger.addHandler(consoleHandler);
logger.addHandler(fileHandler);
// Log simulation
logger.fine("FINE: Debugging transaction processing");
logger.info("INFO: User Mahesh performed login");
logger.warning("WARNING: Suspicious transaction pattern");
logger.severe("SEVERE: Fraudulent activity detected");
}
}
This will create security-audit.log with WARNING and SEVERE entries in XML format, while the console shows all logs starting from FINE.
Programmatic logging configuration is ideal when:
- Dynamic log behavior is needed.
- You want precise control over handler setup at runtime.
- Configuration files are not preferred or cannot be used.
It offers fine-grained control, is self-contained, and is suitable for embedded systems, testing, and microservices where environmental context drives logging.