Category: log4j

log4j – Configuration ”; Previous Next The previous chapter explained the core components of log4j. This chapter explains how you can configure the core components using a configuration file. Configuring log4j involves assigning the Level, defining Appender, and specifying Layout objects in a configuration file. The log4j.properties file is a log4j configuration file which keeps properties in key-value pairs. By default, the LogManager looks for a file named log4j.properties in the CLASSPATH. The level of the root logger is defined as DEBUG. The DEBUG attaches the appender named X to it. Set the appender named X to be a valid appender. Set the layout for the appender X. log4j.properties Syntax: Following is the syntax of log4j.properties file for an appender X: # Define the root logger with appender X log4j.rootLogger = DEBUG, X # Set the appender named X to be a File appender log4j.appender.X=org.apache.log4j.FileAppender # Define the layout for X appender log4j.appender.X.layout=org.apache.log4j.PatternLayout log4j.appender.X.layout.conversionPattern=%m%n log4j.properties Example Using the above syntax, we define the following in log4j.properties file: The level of the root logger is defined as DEBUG, The DEBUG appender named FILE to it. The appender FILE is defined as org.apache.log4j.FileAppender. It writes to a file named log.out located in the log directory. The layout pattern defined is %m%n, which means the printed logging message will be followed by a newline character. # Define the root logger with appender file log4j.rootLogger = DEBUG, FILE # Define the file appender log4j.appender.FILE=org.apache.log4j.FileAppender log4j.appender.FILE.File=${log}/log.out # Define the layout for file appender log4j.appender.FILE.layout=org.apache.log4j.PatternLayout log4j.appender.FILE.layout.conversionPattern=%m%n It is important to note that log4j supports UNIX-style variable substitution such as ${variableName}. Debug Level We have used DEBUG with both the appenders. All the possible options are: TRACE DEBUG INFO WARN ERROR FATAL ALL These levels are explained later in this tutorial. Appenders Apache log4j provides Appender objects which are primarily responsible for printing logging messages to different destinations such as consoles, files, sockets, NT event logs, etc. Each Appender object has different properties associated with it, and these properties indicate the behavior of that object. Property Description layout Appender uses the Layout objects and the conversion pattern associated with them to format the logging information. target The target may be a console, a file, or another item depending on the appender. level The level is required to control the filtration of the log messages. threshold Appender can have a threshold level associated with it independent of the logger level. The Appender ignores any logging messages that have a level lower than the threshold level. filter The Filter objects can analyze logging information beyond level matching and decide whether logging requests should be handled by a particular Appender or ignored. We can add an Appender object to a Logger by including the following setting in the configuration file with the following method: log4j.logger.[logger-name]=level, appender1,appender..n You can write same configuration in XML format as follows: <logger name=”com.apress.logging.log4j” additivity=”false”> <appender-ref ref=”appender1″/> <appender-ref ref=”appender2″/> </logger> If you are willing to add Appender object inside your program then you can use following method: public void addAppender(Appender appender); The addAppender() method adds an Appender to the Logger object. As the example configuration demonstrates, it is possible to add many Appender objects to a logger in a comma-separated list, each printing logging information to separate destinations. We have used only one appender FileAppender in our example above. All the possible appender options are: AppenderSkeleton AsyncAppender ConsoleAppender DailyRollingFileAppender ExternallyRolledFileAppender FileAppender JDBCAppender JMSAppender LF5Appender NTEventLogAppender NullAppender RollingFileAppender SMTPAppender SocketAppender SocketHubAppender SyslogAppender TelnetAppender WriterAppender We would cover FileAppender in Logging in Files and JDBC Appender would be covered in Logging in Database. Layout We have used PatternLayout with our appender. All the possible options are: DateLayout HTMLLayout PatternLayout SimpleLayout XMLLayout Using HTMLLayout and XMLLayout, you can generate log in HTML and in XML format as well. Layout Formatting You would learn how to format a log message in chapter: Log Formatting. Print Page Previous Next Advertisements ”;

log4j – Sample Program ”; Previous Next We have seen how to create a configuration file. This chapter describe how to generate debug messages and log them in a simple text file. Following is a simple configuration file created for our example. Let us revise it once again: The level of the root logger is defined as DEBUG and attaches appender named FILE to it. The appender FILE is defined as org.apache.log4j.FileAppender and writes to a file named log.out located in the log directory. The layout pattern defined is %m%n, which means the printed logging message will be followed by a newline character. The contents of log4j.properties file are as follows − # Define the root logger with appender file log = /usr/home/log4j log4j.rootLogger = DEBUG, FILE # Define the file appender log4j.appender.FILE=org.apache.log4j.FileAppender log4j.appender.FILE.File=${log}/log.out # Define the layout for file appender log4j.appender.FILE.layout=org.apache.log4j.PatternLayout log4j.appender.FILE.layout.conversionPattern=%m%n Using log4j in Java Program The following Java class is a very simple example that initializes, and then uses, the log4j logging library for Java applications. import org.apache.log4j.Logger; import java.io.*; import java.sql.SQLException; import java.util.*; public class log4jExample{ /* Get actual class name to be printed on */ static Logger log = Logger.getLogger(log4jExample.class.getName()); public static void main(String[] args)throws IOException,SQLException{ log.debug(“Hello this is a debug message”); log.info(“Hello this is an info message”); } } Compile and Execute Here are the steps to compile and run the above-mentioned program. Make sure you have set PATH and CLASSPATH appropriately before proceeding for the compilation and execution. All the libraries should be available in CLASSPATH and your log4j.properties file should be available in PATH. Follow the steps give below − Create log4j.properties as shown above. Create log4jExample.java as shown above and compile it. Execute log4jExample binary to run the program. You would get the following result inside /usr/home/log4j/log.out file − Hello this is a debug message Hello this is an info message Print Page Previous Next Advertisements ”;

log4j – Logging Methods ”; Previous Next Logger class provides a variety of methods to handle logging activities. The Logger class does not allow us to instantiate a new Logger instance but it provides two static methods for obtaining a Logger object − public static Logger getRootLogger(); public static Logger getLogger(String name); The first of the two methods returns the application instance”s root logger and it does not have a name. Any other named Logger object instance is obtained through the second method by passing the name of the logger. The name of the logger can be any string you can pass, usually a class or a package name as we have used in the last chapter and it is mentioned below − static Logger log = Logger.getLogger(log4jExample.class.getName()); Logging Methods Once we obtain an instance of a named logger, we can use several methods of the logger to log messages. The Logger class has the following methods for printing the logging information. # Methods and Description 1 public void debug(Object message) It prints messages with the level Level.DEBUG. 2 public void error(Object message) It prints messages with the level Level.ERROR. 3 public void fatal(Object message) It prints messages with the level Level.FATAL. 4 public void info(Object message) It prints messages with the level Level.INFO. 5 public void warn(Object message) It prints messages with the level Level.WARN. 6 public void trace(Object message) It prints messages with the level Level.TRACE. All the levels are defined in the org.apache.log4j.Level class and any of the above mentioned methods can be called as follows − import org.apache.log4j.Logger; public class LogClass { private static org.apache.log4j.Logger log = Logger.getLogger(LogClass.class); public static void main(String[] args) { log.trace(“Trace Message!”); log.debug(“Debug Message!”); log.info(“Info Message!”); log.warn(“Warn Message!”); log.error(“Error Message!”); log.fatal(“Fatal Message!”); } } When you compile and run LogClass program, it would generate the following result − Debug Message! Info Message! Warn Message! Error Message! Fatal Message! All the debug messages make more sense when they are used in combination with levels. We will cover levels in the next chapter and then, you would have a good understanding of how to use these methods in combination with different levels of debugging. Print Page Previous Next Advertisements ”;

log4j Tutorial PDF Version Quick Guide Resources Job Search Discussion log4j is a reliable, fast and flexible logging framework (APIs) written in Java, which is distributed under the Apache Software License. log4j is a popular logging package written in Java. log4j has been ported to the C, C++, C#, Perl, Python, Ruby, and Eiffel languages. Audience This tutorial has been prepared for beginners to help them understand the basic functionality of log4J logging framework. Prerequisites As you are going to use Log4J logging framework in various Java-based application development, it is imperative that you should have a good understanding of Java programming language. Print Page Previous Next Advertisements ”;