Logging in CLIPS

Here’s the translation of the Go logging example to Java, with explanations in Markdown format suitable for Hugo:

Our Java program demonstrates various logging techniques using the built-in java.util.logging package and the more advanced org.slf4j with logback for structured logging.

import java.io.ByteArrayOutputStream;
import java.util.logging.*;
import org.slf4j.LoggerFactory;
import ch.qos.logback.classic.LoggerContext;
import ch.qos.logback.classic.encoder.JsonEncoder;
import ch.qos.logback.core.ConsoleAppender;

public class LoggingExample {
    public static void main(String[] args) {
        // Get the root logger and set its level
        Logger logger = Logger.getLogger("");
        logger.setLevel(Level.ALL);

        // Simply using the logger
        logger.info("standard logger");

        // Configure logger to show microseconds
        System.setProperty("java.util.logging.SimpleFormatter.format",
                "%1$tY-%1$tm-%1$td %1$tH:%1$tM:%1$tS.%1$tL %4$s %2$s %5$s%6$s%n");
        logger.info("with micro");

        // Add the class name and line number to the log output
        System.setProperty("java.util.logging.SimpleFormatter.format",
                "%1$tY-%1$tm-%1$td %1$tH:%1$tM:%1$tS %4$s %2$s %5$s%6$s%n");
        logger.info("with class/line");

        // Create a custom logger with a prefix
        Logger myLogger = Logger.getLogger("MyLogger");
        myLogger.setLevel(Level.ALL);
        ConsoleHandler handler = new ConsoleHandler();
        handler.setFormatter(new SimpleFormatter() {
            private static final String format = "my: [%1$tF %1$tT] %2$s %3$s%n";

            @Override
            public synchronized String format(LogRecord lr) {
                return String.format(format,
                        new java.util.Date(lr.getMillis()),
                        lr.getLevel().getLocalizedName(),
                        lr.getMessage()
                );
            }
        });
        myLogger.addHandler(handler);
        myLogger.setUseParentHandlers(false);
        myLogger.info("from myLogger");

        // Change the prefix of the custom logger
        handler.setFormatter(new SimpleFormatter() {
            private static final String format = "ohmy: [%1$tF %1$tT] %2$s %3$s%n";

            @Override
            public synchronized String format(LogRecord lr) {
                return String.format(format,
                        new java.util.Date(lr.getMillis()),
                        lr.getLevel().getLocalizedName(),
                        lr.getMessage()
                );
            }
        });
        myLogger.info("from myLogger");

        // Logging to a custom output (ByteArrayOutputStream in this case)
        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        Handler bufHandler = new StreamHandler(baos, new SimpleFormatter());
        Logger bufLogger = Logger.getLogger("BufferLogger");
        bufLogger.addHandler(bufHandler);
        bufLogger.setUseParentHandlers(false);
        bufLogger.info("hello");
        bufHandler.flush();
        System.out.print("from bufLogger: " + baos.toString());

        // Using SLF4J with Logback for JSON structured logging
        LoggerContext lc = (LoggerContext) LoggerFactory.getILoggerFactory();
        ch.qos.logback.classic.Logger rootLogger = lc.getLogger(org.slf4j.Logger.ROOT_LOGGER_NAME);

        ConsoleAppender<ch.qos.logback.classic.spi.ILoggingEvent> logConsoleAppender = new ConsoleAppender<>();
        logConsoleAppender.setContext(lc);
        logConsoleAppender.setName("console");
        JsonEncoder jsonEncoder = new JsonEncoder();
        jsonEncoder.setContext(lc);
        jsonEncoder.start();
        logConsoleAppender.setEncoder(jsonEncoder);
        logConsoleAppender.start();

        rootLogger.addAppender(logConsoleAppender);

        org.slf4j.Logger slf4jLogger = LoggerFactory.getLogger(LoggingExample.class);
        slf4jLogger.info("hi there");
        slf4jLogger.info("hello again", "key", "val", "age", 25);
    }
}

This Java program demonstrates various logging techniques:

We start by using the standard java.util.logging.Logger to output simple log messages.
We then configure the logger to show microseconds and file/line information by setting system properties.
A custom logger with a prefix is created, demonstrating how to customize log output format.
We show how to change the prefix of a custom logger.
Logging to a custom output (ByteArrayOutputStream) is demonstrated, which can be useful for capturing log output programmatically.
Finally, we use SLF4J with Logback to demonstrate structured logging in JSON format. This is similar to the slog package in Go, allowing for more complex log structures.

To run this program, you’ll need to include the SLF4J and Logback libraries in your classpath. The output will be similar to the Go example, with timestamps and structured JSON logs at the end.

This Java implementation provides equivalent functionality to the Go example, showcasing various logging techniques and customization options available in Java.

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