1.2. 創建一個logger

包 java.util.logging提供了日志的功能，可以使用類似于下面的代碼來創建一個logger：

import java.util.logging.Logger;

private final static Logger LOGGER = Logger.getLogger(MyClass.class .getName());

1.3.?Level

Log的等級反映了問題的嚴重程度。Level類用于決定哪些信息被寫入到log中。下面是一個按嚴重程度的降序排列的Log Level：

SEVERE (highest)

WARNING

INFO

CONFIG

FINE

FINER

FINEST

除此之外，您還可以使用OFF或ALL這兩個level來關閉log或打開所有log。

下面這行代碼是將logger設置為記錄INFO級別：

LOGGER.setLevel(Level.INFO);

1.4.?Handler

每個logger可以設置多個Handler。

Handler的作用是接收logger的信息，并將其以合適的格式發送到合適的地方。

一個Handler可以用setLevel(Level.OFF)來關閉，用setLevel(...)開啟。

JDK提供了幾個標準的handler，例如：

ConsoleHandler: 將log信息寫到Console

FileHandler: 將log信息寫到文件中

超過INFO(包含INFO)的信息將自動被寫入到Console中。

1.5.?Formatter

每個Handler的輸出都可以使用一個formatter來配置

已有的formatter：

SimpleFormatter 將所有的log信息以文本格式編排

XMLFormatter 生成XML格式的log信息

您還可以自定義Formatter，下面的這個示例Formatter可以將log信息用html的格式包裝：

package logging;

import java.text.SimpleDateFormat;

import java.util.Date;

import java.util.logging.Formatter;

import java.util.logging.Handler;

import java.util.logging.Level;

import java.util.logging.LogRecord;

//This custom formatter formats parts of a log record to a single line

class MyHtmlFormatter extends Formatter

{

// This method is called for every log records

public String format(LogRecord rec)

{

StringBuffer buf = new StringBuffer(1000);

// Bold any levels >= WARNING

buf.append("

");

buf.append("

");

if (rec.getLevel().intValue() >= Level.WARNING.intValue())

{

buf.append("");

buf.append(rec.getLevel());

buf.append("");

} else

{

buf.append(rec.getLevel());

}

buf.append("

");

buf.append("

");

buf.append(calcDate(rec.getMillis()));

buf.append(' ');

buf.append(formatMessage(rec));

buf.append('\n');

buf.append("

");

buf.append("

\n");

return buf.toString();

}

private String calcDate(long millisecs)

{

SimpleDateFormat date_format = new SimpleDateFormat("MMM dd,yyyy HH:mm");

Date resultdate = new Date(millisecs);

return date_format.format(resultdate);

}

// This method is called just after the handler using this

// formatter is created

public String getHead(Handler h)

{

return "\n

\n" + (new Date()) + "\n\n\n

\n"

+ "

+ "

TimeLog Message\n";

}

// This method is called just after the handler using this

// formatter is closed

public String getTail(Handler h)

{

return "

\n \n\n";

}

}

1.6.?Log Manager

log manager的職責是創建和管理logger，并負責維護log配置。

使用LogManager.setLevel(String name, Level level)方法，我們可以為一個包或一組包設置logging level。例如，我們可以將所有logger的logging

level設為Level.FINE：

LogManager.getLogManager().setLevel("logging", Level.FINE)

1.7.?Best Practices

使用被logged的那個類的名稱為logger命名是一種很好的方法，這種方法可以使程序員更好地查看日志和管理logger，同時，這也是Logging API推薦的一種方式。

2. 示例

您可以在項目“de.vogella.logger”中找到這個例子：

創建你自己的formatter：

package logging;

import java.text.SimpleDateFormat;

import java.util.Date;

import java.util.logging.Formatter;

import java.util.logging.Handler;

import java.util.logging.Level;

import java.util.logging.LogRecord;

//This custom formatter formats parts of a log record to a single line

class MyHtmlFormatter extends Formatter

{

// This method is called for every log records

public String format(LogRecord rec)

{

StringBuffer buf = new StringBuffer(1000);

// Bold any levels >= WARNING

buf.append("

");

buf.append("

");

if (rec.getLevel().intValue() >= Level.WARNING.intValue())

{

buf.append("");

buf.append(rec.getLevel());

buf.append("");

} else

{

buf.append(rec.getLevel());

}

buf.append("

");

buf.append("

");

buf.append(calcDate(rec.getMillis()));

buf.append(' ');

buf.append(formatMessage(rec));

buf.append('\n');

buf.append("

");

buf.append("

\n");

return buf.toString();

}

private String calcDate(long millisecs)

{

SimpleDateFormat date_format = new SimpleDateFormat("MMM dd,yyyy HH:mm");

Date resultdate = new Date(millisecs);

return date_format.format(resultdate);

}

// This method is called just after the handler using this

// formatter is created

public String getHead(Handler h)

{

return "\n

\n" + (new Date()) + "\n\n\n

\n"

+ "

+ "

TimeLog Message\n";

}

// This method is called just after the handler using this

// formatter is closed

public String getTail(Handler h)

{

return "

\n \n\n";

}

}初始化logger

package logging;

import java.io.IOException;

import java.util.logging.FileHandler;

import java.util.logging.Formatter;

import java.util.logging.Level;

import java.util.logging.Logger;

import java.util.logging.SimpleFormatter;

public class MyLogger {

static private FileHandler fileTxt;

static private SimpleFormatter formatterTxt;

static private FileHandler fileHTML;

static private Formatter formatterHTML;

static public void setup() throws IOException {

// Create Logger

Logger logger = Logger.getLogger("");

logger.setLevel(Level.INFO);

fileTxt = new FileHandler("Logging.txt");

fileHTML = new FileHandler("Logging.html");

// Create txt Formatter

formatterTxt = new SimpleFormatter();

fileTxt.setFormatter(formatterTxt);

logger.addHandler(fileTxt);

// Create HTML Formatter

formatterHTML = new MyHtmlFormatter();

fileHTML.setFormatter(formatterHTML);

logger.addHandler(fileHTML);

}

}使用logger

package logging;

import java.io.IOException;

import java.util.logging.Level;

import java.util.logging.Logger;

public class UseLogger {

// Always use the classname, this way you can refactor

private final static Logger LOGGER = Logger.getLogger(UseLogger.class

.getName());

public void writeLog() {

// Set the LogLevel to Severe, only severe Messages will be written

LOGGER.setLevel(Level.SEVERE);

LOGGER.severe("Info Log");

LOGGER.warning("Info Log");

LOGGER.info("Info Log");

LOGGER.finest("Really not important");

// Set the LogLevel to Info, severe, warning and info will be written

// Finest is still not written

LOGGER.setLevel(Level.INFO);

LOGGER.severe("Info Log");

LOGGER.warning("Info Log");

LOGGER.info("Info Log");

LOGGER.finest("Really not important");

}

public static void main(String[] args) {

UseLogger logger = new UseLogger();

try {

MyLogger.setup();

} catch (IOException e) {

e.printStackTrace();

throw new RuntimeException("Problems with creating the log files");

}

logger.writeLog();

}

}