hengheng123456789

   在这里向初学者介绍一个简单使用日志记录程序信息的方法，希望有所帮助。


1、可以在main方法中书写以下语句进行log。

        final Logger baseLogger = Logger.getLogger("LogTest");
        baseLogger.setLevel(Level.INFO);//this set the log level to info. that means you can only pring info message to log file.
        final Handler[] handlers = baseLogger.getHandlers();
        for (int i = 0; i < handlers.length; i++) {
            baseLogger.removeHandler(handlers[i]);
        }

        try {
            baseLogger.addHandler(new DefaultHandler()); //class "DefaultHandler" is the default handler for log records. It currently only logs to a file in the format offered by TextFormatter.
        } catch (FreeColException e) {
            e.printStackTrace();
        }

2、可以在配置文件（${jdk}\jar\lib下面找到logging.properties文件）里面改日志记录的级别。

3、定义"DefaultHandler" 类，用于处理日志。

public final class DefaultHandler extends Handler {

    private static final String fileName = new String("test.log");

    private FileWriter fileWriter;

    /**
    * The constructor to use.
    * @throws Exception In case the log file could not be created/written to.
    */
    public DefaultHandler() throws Exception {
        File file = new File(fileName);

        if (file.exists()) {
            if (file.isDirectory()) {
                throw new Exception("Log file \"" + fileName + "\" could not be created.");
            } else if (file.isFile()) {
                file.delete();
            }
        }

        try {
            file.createNewFile();
        } catch (IOException e) {
            throw new Exception("Log file \"" + fileName + "\" could not be created.");
        }

        if (!file.canWrite()) {
            throw new Exception("Can not write in log file \"" + fileName + "\".");
        }

        try {
            fileWriter = new FileWriter(file);
        } catch (IOException e) {
            throw new Exception("Can not write in log file \"" + fileName + "\".");
        }

        // We  use TextFormatter that we build latter.
        setFormatter(new TextFormatter());
       
        try {
            String str = "version: 1.0\n" 
                        + "Java vendor: " + System.getProperty("java.vendor") + "\n"
                        + "Java version: " + System.getProperty("java.version") + "\n"
                        + "Java WM name: " + System.getProperty("java.vm.name") + "\n"
                        + "Java WM vendor: " + System.getProperty("java.vm.vendor") + "\n"
                        + "Java WM version: " + System.getProperty("java.vm.version") + "\n\n"
                        + "OS name: " + System.getProperty("os.name") + "\n"
                        + "OS architecture: " + System.getProperty("os.arch") + "\n"
                        + "OS version: " + System.getProperty("os.version") + "\n\n";
            fileWriter.write(str, 0, str.length());
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

     /**
    * Closes this handler so that it will stop handling log records.
    */
    public void close() {
        try {
            fileWriter.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    /**
    * Flushes the data that this handler has logged.
    */
    public void flush() {
        try {
            fileWriter.flush();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    /**
    * Publishes the given LogRecord by writing its data to a file using
    * a TextFormatter.
    *
    * @param record The log record to publish.
    */
    public void publish(LogRecord record) {
        if (record.getLevel().intValue() < getLevel().intValue()) {
            return;
        }

        String str = getFormatter().format(record);
        try {
            fileWriter.write(str, 0, str.length());
        } catch (IOException e) {
            e.printStackTrace();
        }
        flush();
    }
}
   
4、定义自己的Formatter格式。

/**
* Formats a log record's data into human-readable text.
*/
final class TextFormatter extends Formatter {

    /**
    * The constructor to use.
    */
    public TextFormatter() {
    }

    /**
    * Formats the given log record's data into human-readable text.
    *
    * @param record The log record whose data needs to be formatted.
    * @return The log record's data as a string.
    */
    public String format(LogRecord record) {
        String level;
        if (record.getLevel() == Level.INFO) {
            level = "INFO";
        } else if (record.getLevel() == Level.ALL) {
            level = "ALL";
        } else if (record.getLevel() == Level.SEVERE) {
            level = "SEVERE";
        } else if (record.getLevel() == Level.WARNING) {
            level = "WARNING";
        } else {
            level = "UNKNOWN";
        }

        //you can build your own result format

        String result = record.getSourceClassName() + ' ' + record.getSourceMethodName();
        result += "\n\t" + level + ": " + record.getMessage().replaceAll("\n", "\n\t");
        result += "\n\t" + new Date(record.getMillis()).toString();
        result += "\n\tThread ID: " + record.getThreadID() + '\n';

        return result;
    }
}

5、实际应用中的使用.

public class Client {
    private static final Logger logger = Logger.getLogger(Client.class.getName());

    private void createDirs() {
        String dir = System.getProperty("user.home");
        String fileSeparator = System.getProperty("file.separator");

        if (!dir.endsWith(fileSeparator)) {
            dir += fileSeparator;
        }
        dir += "test";

        File file = new File(dir);
        if (file.exists() && file.isFile()) {
            logger.warning("Could not create .freecol under ~ because there already exists a regular file with the same name.");
            return;
        } else if (!file.exists()) {
            file.mkdir();
           logger.info("Could not create .freecol under ~ because there already exists a regular file with the same name.");
         }
     }
}