Address: http://www.vogella.com/articles/Logging/article.html
Java Logging
This article describes how to use the logging API in JDK in a Java program. An example of creating an HTML logger is provided later.
Directory
The JDK contains the Java logging API. With logger, you can not only collect log information into a file to report errors, but also add auxiliary information to the log. This logging API allows you to customize and use flexibility.
1.2. Create a loggerThe Java. util. Logging package provides the log function. You can use the code similar to the following to create a logger:
import java.util.logging.Logger;private final static Logger LOGGER = Logger.getLogger(MyClass.class .getName());1.3. Level
The log level reflects the severity of the problem. The level class is used to determine which information is written into the log. Below is a log level sorted in descending order of Severity:
Severe (highest)
Warning
Info
Config
Fine
Finer
Finest
In addition, you can use the off or all levels to close logs or open all logs.
The following code sets logger to the info level of the record:
LOGGER.setLevel(Level.INFO);1.4. Handler
You can set multiple handler for each logger.
Handler is used to receive logger information and send it to appropriate places in the appropriate format.
A handler can be disabled by setlevel (level. Off) and enabled by setlevel.
JDK provides several Standard handler, such:
Consolehandler: writes log information to the console
Filehandler: Write log information to the file
Information that exceeds info is automatically written to the console.
1.5. formatter
Each handler output can be configured with a formatter.
Existing formatter:
Simpleformatter orchestrates all log information in text format
Xmlformatter generates log information in XML format
You can also customize formatter. In the following example, formatter can encapsulate log information in HTML format:
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 lineclass MyHtmlFormatter extends Formatter{// This method is called for every log recordspublic String format(LogRecord rec){StringBuffer buf = new StringBuffer(1000);// Bold any levels >= WARNINGbuf.append("<tr>");buf.append("<td>");if (rec.getLevel().intValue() >= Level.WARNING.intValue()){buf.append("<b>");buf.append(rec.getLevel());buf.append("</b>");} else{buf.append(rec.getLevel());}buf.append("</td>");buf.append("<td>");buf.append(calcDate(rec.getMillis()));buf.append(' ');buf.append(formatMessage(rec));buf.append('\n');buf.append("<td>");buf.append("</tr>\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 createdpublic String getHead(Handler h){return "<HTML>\n<HEAD>\n" + (new Date()) + "\n</HEAD>\n<BODY>\n<PRE>\n"+ "<table border>\n "+ "<tr><th>Time</th><th>Log Message</th></tr>\n";}// This method is called just after the handler using this// formatter is closedpublic String getTail(Handler h){return "</table>\n </PRE></BODY>\n</HTML>\n";}}
1.6. Log Manager
Log manager is responsible for creating and managing logger and maintaining log configuration.
Using the logmanager. setlevel (string name, level) method, we can set the logging level for a package or a group of packages. For example, we can
Level is set to level. fine:
LogManager.getLogManager().setLevel("logging", Level.FINE)
1.7. Best practices
Using the class named logger by logged is a good way for programmers to better view logs and manage logger. At the same time, this is also a recommended method for logging APIs.
2. For example, you can find this example in the project "De. vogella. Logger:
Create your own 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 lineclass MyHtmlFormatter extends Formatter{// This method is called for every log recordspublic String format(LogRecord rec){StringBuffer buf = new StringBuffer(1000);// Bold any levels >= WARNINGbuf.append("<tr>");buf.append("<td>");if (rec.getLevel().intValue() >= Level.WARNING.intValue()){buf.append("<b>");buf.append(rec.getLevel());buf.append("</b>");} else{buf.append(rec.getLevel());}buf.append("</td>");buf.append("<td>");buf.append(calcDate(rec.getMillis()));buf.append(' ');buf.append(formatMessage(rec));buf.append('\n');buf.append("<td>");buf.append("</tr>\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 createdpublic String getHead(Handler h){return "<HTML>\n<HEAD>\n" + (new Date()) + "\n</HEAD>\n<BODY>\n<PRE>\n"+ "<table border>\n "+ "<tr><th>Time</th><th>Log Message</th></tr>\n";}// This method is called just after the handler using this// formatter is closedpublic String getTail(Handler h){return "</table>\n </PRE></BODY>\n</HTML>\n";}}
Initialize 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 LoggerLogger logger = Logger.getLogger("");logger.setLevel(Level.INFO);fileTxt = new FileHandler("Logging.txt");fileHTML = new FileHandler("Logging.html");// Create txt FormatterformatterTxt = new SimpleFormatter();fileTxt.setFormatter(formatterTxt);logger.addHandler(fileTxt);// Create HTML FormatterformatterHTML = new MyHtmlFormatter();fileHTML.setFormatter(formatterHTML);logger.addHandler(fileHTML);}}
Use 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 refactorprivate final static Logger LOGGER = Logger.getLogger(UseLogger.class.getName());public void writeLog() {// Set the LogLevel to Severe, only severe Messages will be writtenLOGGER.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 writtenLOGGER.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();}}
Start building with 50+ products and up to 12 months usage for Elastic Compute Service
1 on 1 presale consultation
24/7 Technical Support 6 Free Tickets per Quarter Faster Response
Alibaba Cloud offers highly flexible support services tailored to meet your exact needs.
A comprehensive suite of global cloud computing services to power your business
Payment Methods We Support
