Logging

CS 240 – Advanced Programming Concepts

Java Logging

Java Logging: Log Messages

• Java has built-in support for logging

​

• Logs contain messages that provide information to
• Software developers (e.g., debugging)
• System administrators
• Customer support agents

​

• Programs send log messages to “loggers”
• There can be one or more

​

• Each message has a “level”
• SEVERE, WARNING, INFO, CONFIG, FINE, FINER, FINEST

​

• We never remove debugging log messages from the code

3

Java Logging: Loggers

• Loggers have a method for each message level that are used to enter messages in the log
• severe, warning, info, config, fine, finer, finest

​

• Loggers can be configured to include or omit log messages based on their levels
• Logger.setLevel(level) method
• ALL (include all messages)
• OFF (omit all messages)
• SEVERE, WARNING, INFO, CONFIG, FINE, FINER, FINEST (include all messages at a particular level and higher)

​

​

4

Java Logging: Handlers

• Each logger has one or more “handlers” associated with it

​

• Handlers represent destinations to which the log messages should be sent
• ConsoleHandler (sends messages to the console)
• FileHandler (sends messages to a file)
• SocketHandler (sends messages to a network socket)

​

• Like loggers, handlers can also be configured to include or omit log messages based on their levels
• Handler.setLevel(level) method
• ALL (include all messages)
• OFF (omit all messages)
• SEVERE, WARNING, INFO, CONFIG, FINE, FINER, FINEST (include all messages at a particular level and higher)

​

5

Java Logging: Formatters

• Each handler has a “formatter” which defines the format used to encode its messages
• SimpleFormatter
• XMLFormatter

​

6

BLANK SLIDE

Configuration

Programmatic Configuration

public class ProgrammaticConfigurationExample {

� private static Logger logger;�� static {� try {� initLog();� } catch (IOException e) {� System.out.println("Could not initialize log: " + e.getMessage());� }� }�� private static void initLog() throws IOException {�� Level logLevel = Level.FINEST;�� logger = Logger.getLogger("ProgrammaticConfigurationExample");� logger.setLevel(logLevel);� logger.setUseParentHandlers(false);�� Handler consoleHandler = new ConsoleHandler();� consoleHandler.setLevel(logLevel);�// consoleHandler.setFormatter(new SimpleFormatter());� logger.addHandler(consoleHandler);�� FileHandler fileHandler = new FileHandler("log.txt", false);� fileHandler.setLevel(logLevel);�// fileHandler.setFormatter(new SimpleFormatter());� logger.addHandler(fileHandler);� }

}

​

9

Configuration File Example

import java.util.logging.Level;�import java.util.logging.Logger;��/**� * Specify the configuration file by adding the following VM option

* in the run configuration or you will get the default logging

* configuration:� *� * -Djava.util.logging.config.file=logging.properties� *� */�public class FileConfigurationExample {�� private static Logger logger =

Logger.getLogger("FileConfigurationExample");��}

10

Logging Configuration File

handlers=java.util.logging.FileHandler, java.util.logging.ConsoleHandler�java.util.logging.ConsoleHandler.level=FINE�java.util.logging.ConsoleHandler.formatter=java.util.logging.SimpleFormatter��java.util.logging.FileHandler.level=FINE�java.util.logging.FileHandler.pattern=log.txt��# Write 10MB before rotating this file�java.util.logging.FileHandler.limit=10000000��# Number of rotating files to be used�java.util.logging.FileHandler.count=4�java.util.logging.FileHandler.formatter=java.util.logging.SimpleFormatter��# Log format to use�java.util.logging.SimpleFormatter.format=%1$tY-%1$tm-%1$td %1$tH:%1$tM:%1$tS %4$s %2$s %5$s%6$s%n��.level=FINEST

11

Log Formatting

• Use format specifiers from the java.util.Formatter class
• Available variables to log:
• %1$ The date/time the message was created
• %2$ The method that called the log method
• %3$ The name of the logger
• %4$ The level the message was logged at
• %5$ The message
• %6$ The throwable

12

BLANK SLIDE

Logging Messages

Logging Methods

• Logging messages with specific levels
• severe(message)
• Same for warning, info, config, fine, finer, finest
• log(level, message)

​

• Logging method enter/exit
• entering(className, methodName)
• exiting(className, methodName)
• Logged at FINER level

​

​

• Logging throwing an exception
• throwing(className, methodName, throwable)
• Logged at FINER level

​

• Logging catching an exception
• log(level, message, throwable)

​

15

Logging Example 1

import java.util.logging.Level;�import java.util.logging.Logger;��/**� * Specify the configuration file by adding the following VM option in the run configuration� * or you will get the default logging configuration:� *� * -Djava.util.logging.config.file=logging.properties� *� */�public class FileConfigurationExample {�� private static Logger logger = Logger.getLogger("FileConfigurationExample");�� public static void main(String [] args) {� logger.info("This is my info log message.");� logger.fine("This is my fine log message");�� try {� throw new Exception("An exception occurred");� } catch (Exception ex) {� logger.severe("This is my exception message");� logger.log(Level.SEVERE, "This is my message logged with the exception", ex);� }� }�}

16

Logging Example 2

import java.util.logging.Level;�import java.util.logging.Logger;

​

public class Server {

​

private static Logger logger = Logger.getLogger(”Server");�

private void run() {

logger.info("Initializing HTTP Server");

try {

server = HttpServer.create(new InetSocketAddress(SERVER_PORT_NUMBER),

MAX_WAITING_CONNECTIONS);

} catch (IOException e) {

logger.log(Level.SEVERE, e.getMessage(), e);

return;

}

​

logger.info("Creating contexts");

server.createContext("/games/list", new ListGamesHandler());

server.createContext("/routes/claim", new ClaimRouteHandler());

logger.info("Starting HTTP Server");

server.start();

}

}

​

17

Logging Example 3

class ClaimRouteHandler implements HttpHandler {

​

private static Logger = Logger.getLogger("ClaimRouteHandler");

@Override

public void handle(HttpExchange exchange) throws IOException {

logger.entering("ClaimRouteHandler", "handle");

try {

...

logger.fine(reqData);

...

}

catch (IOException e) {

logger.log(Level.SEVERE, e.getMessage(), e);

...

}

logger.exiting("ClaimRouteHandler", "handle");

}

...

}

​

18

Log4J

• Java didn’t have a logging API until version 1.4
• Before 1.4, we had to log with System.out.println(…) or System.err.println(…)
• Or, use an external library
• Log4J became a very popular and widely used external logging library before 1.4
• Log4J is probably still more commonly used than the built-in java.util.logging API
• Log4J is very similar to java.util.logging

19

BLANK SLIDE