log.java

java编写的简易留言本

package anni.tools;

import java.io.File;
import java.io.FileWriter;
import java.io.IOException;
import java.io.PrintWriter;

import java.text.SimpleDateFormat;

import java.util.Calendar;


/**
 * 日志.
 *
 * @author Lingo
 * @version 1.0
 * @since 2006-01-02 23:24
 */
public final class Log {
    /**
     * 日志文件最大限度.
     */
    public static final int LOG_FILE_MAX_SIZE = 1024 * 1024;

    /**
     * 日志显示的时间格式.
     */
    private static SimpleDateFormat sdf = new SimpleDateFormat(
            "yyyy-MM-dd HH:mm:ss");

    /**
     * 日志文件的时间格式.
     */
    private static SimpleDateFormat sdf2 = new SimpleDateFormat("yyyyMMdd");

    /**
     * 日志文件个数.
     */
    private static int count = 0;

    /**
     * 今天.
     */
    private static Calendar today = Calendar.getInstance();

    /**
     * 现在.
     */
    private static Calendar now;

    /**
     * 默认的日期文件.
     */
    private static File logFile = new File("log.txt");

    /**
     * 工具类隐藏构造方法.
     */
    private Log() {
    }

    /**
     * info级别的日志.
     * @param obj 信息
     */
    public static void info(final Object obj) {
        now = Calendar.getInstance();
        check();

        Throwable t = new Throwable();
        StackTraceElement[] element = t.getStackTrace();

        String msg;

        if (obj == null) {
            msg = null;
        } else {
            msg = obj.toString();
        }

        String message = "[" + sdf.format(now.getTime()) + "]["
            + element[1].getClassName() + "]["
            + element[1].getMethodName() + "] : " + msg;
        System.out.println(message);

        PrintWriter out = null;

        try {
            out = new PrintWriter(new FileWriter(logFile, true));
            out.println(message);
        } catch (IOException ex) {
            ex.printStackTrace();
        } finally {
            if (out != null) {
                out.flush();
                out.close();
                out = null;
            }
        }
    }

    /**
     * 检测日志文件是否超过最大限制.
     */
    private static void check() {
        long len = logFile.length();

        if (len > LOG_FILE_MAX_SIZE) {
            count++;

            File destFile = new File("log_" + sdf2.format(today) + "_"
                    + count + ".txt");
            logFile.renameTo(destFile);
            logFile = new File("log.txt");
        }

        if (today.DAY_OF_MONTH < now.DAY_OF_MONTH) {
            today = now;
            count = 0;
        }
    }

    /**
     * 测试用的main方法.
     * @param args 参数列表
     */
    public static void main(final String[] args) {
        Log.info("test");
    }
}