mesclient-op060B-P02/skills/java-client-file-logging/assets/AppLog.java

package com.example.client.util;

import java.io.File;
import java.io.FileOutputStream;
import java.io.PrintStream;
import java.text.SimpleDateFormat;
import java.util.Date;

/**
 * Lightweight local logging for a standalone Java desktop client.
 * Change APP_NAME and package before use.
 */
public final class AppLog {
    private static final String APP_NAME = "client";
    private static final Object LOCK = new Object();
    private static final SimpleDateFormat TIME = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss.SSS");
    private static PrintStream out;
    private static volatile String exitReason;
    private static volatile String uncaughtThread;
    private static volatile Throwable uncaughtException;

    private AppLog() { }

    public static void init() {
        synchronized (LOCK) {
            if (out != null) return;
            try {
                File code = new File(AppLog.class.getProtectionDomain().getCodeSource().getLocation().toURI());
                File base = code.isFile() ? code.getParentFile() : new File(System.getProperty("user.dir"));
                File dir = new File(base, "logs");
                if (!dir.exists() && !dir.mkdirs()) return;

                String day = new SimpleDateFormat("yyyy-MM-dd").format(new Date());
                out = new PrintStream(new FileOutputStream(new File(dir, APP_NAME + "-" + day + ".log"), true), true, "UTF-8");
                Thread.setDefaultUncaughtExceptionHandler(new Thread.UncaughtExceptionHandler() {
                    public void uncaughtException(Thread thread, Throwable exception) {
                        exitReason = "UNCAUGHT_EXCEPTION";
                        uncaughtThread = thread.getName();
                        uncaughtException = exception;
                    }
                });
                Runtime.getRuntime().addShutdownHook(new Thread(new Runnable() {
                    public void run() {
                        if ("USER_CLOSE".equals(exitReason)) {
                            log("INFO", "Client exited, reason=user-close", null);
                        } else if ("UNCAUGHT_EXCEPTION".equals(exitReason)) {
                            log("ERROR", "Client exited, reason=uncaught-exception, thread=" + clean(uncaughtThread), uncaughtException);
                        }
                    }
                }, APP_NAME + "-log-shutdown"));
            } catch (Exception ignored) {
                // Logging is best-effort and must not stop client startup.
            }
        }
    }

    public static void login(String userId, String method, boolean success) {
        log(success ? "INFO" : "WARN", "Login " + (success ? "succeeded" : "failed")
                + ", method=" + clean(method) + ", user=" + clean(userId), null);
    }

    public static void scan(String type, String code) {
        log("INFO", "Scan, type=" + clean(type) + ", code=" + clean(code), null);
    }

    public static void work(String action, String code, boolean success) {
        log(success ? "INFO" : "WARN", "Operation " + (success ? "succeeded" : "failed")
                + ", action=" + clean(action) + ", code=" + clean(code), null);
    }

    public static void markUserClose() {
        exitReason = "USER_CLOSE";
    }

    private static String clean(String value) {
        return value == null ? "" : value.replace('\r', ' ').replace('\n', ' ');
    }

    private static void log(String level, String message, Throwable exception) {
        synchronized (LOCK) {
            if (out == null) return;
            out.println("[" + TIME.format(new Date()) + "][" + level + "]["
                    + Thread.currentThread().getName() + "] " + message);
            if (exception != null) exception.printStackTrace(out);
            out.flush();
        }
    }
}