For appender named appenderName , set its class. Note: The appender name can contain dots. Set appender specific options. Set options for appender named "A1". Appender "A1" will be a SyslogAppender log4j.
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Log4cxx has three main components: loggers , appenders and layouts. These three types of components work together to enable developers to log messages according to message type and level, and to control at runtime how these messages are formatted and where they are reported. The first and foremost advantage of any logging API over plain std::cout resides in its ability to disable certain log statements while allowing others to print unhindered.
This capability assumes that the logging space, that is, the space of all possible logging statements, is categorized according to some developer-chosen criteria. Loggers are named entities. Logger names are case-sensitive and they follow the hierarchical naming rule:. For example, the logger named "com. Similarly, "java" is a parent of "java. This naming scheme should be familiar to most developers. The root logger resides at the top of the logger hierarchy. It is exceptional in two ways:.
Invoking the class static log4cxx::Logger::getRootLogger method retrieves it. All other loggers are instantiated and retrieved with the class static log4cxx::Logger::getLogger method. This method takes the name of the desired logger as a parameter. Some of the basic methods in the Logger class are listed below. Loggers may be assigned levels. If a given logger is not assigned a level, then it inherits one from its closest ancestor with an assigned level. More formally:. To ensure that all loggers can eventually inherit a level, the root logger always has an assigned level.
Below are four tables with various assigned level values and the resulting inherited levels according to the above rule. In example 1 above, only the root logger is assigned a level. This level value, Proot , is inherited by the other loggers X , X.
Y and X. In example 2, all loggers have an assigned level value. There is no need for level inheritence. In example 3, the loggers root , X and X. Z are assigned the levels Proot , Px and Pxyz respectively. The logger X. Y inherits its level value from its parent X. In example 4, the loggers root and X and are assigned the levels Proot and Px respectively. The loggers X. Z inherits their level value from their nearest parent X having an assigned level.
A logging request is said to be enabled if its level is higher than or equal to the level of its logger. Otherwise, the request is said to be disabled. A logger without an assigned level will inherit one from the hierarchy. This rule is summarized below. This rule is at the heart of log4cxx.
It assumes that levels are ordered. Calling the getLogger method with the same name will always return a reference to the exact same logger object. Thus, it is possible to configure a logger and then to retrieve the same instance somewhere else in the code without passing around references.
In fundamental contradiction to biological parenthood, where parents always preceed their children, log4cxx loggers can be created and configured in any order. In particular, a "parent" logger will find and link to its descendants even if it is instantiated after them. Configuration of the log4cxx environment is typically done at application initialization. The preferred way is by reading a configuration file. This approach will be discussed shortly.
Log4cxx makes it easy to name loggers by software component. This can be accomplished by statically instantiating a logger in each class, with the logger name equal to the fully qualified name of the class. This is a useful and straightforward method of defining loggers. As the log output bears the name of the generating logger, this naming strategy makes it easy to identify the origin of a log message.
However, this is only one possible, albeit common, strategy for naming loggers. Log4cxx does not restrict the possible set of loggers. The developer is free to name the loggers as desired.
Nevertheless, naming loggers after the class where they are located seems to be the best strategy known so far. The ability to selectively enable or disable logging requests based on their logger is only part of the picture.
Log4cxx allows logging requests to print to multiple destinations. In log4cxx speak, an output destination is called an appender. It is also possible to log asynchronously. The addAppender method adds an appender to a given logger. Each enabled logging request for a given logger will be forwarded to all the appenders in that logger as well as the appenders higher in the hierarchy.
In other words, appenders are inherited additively from the logger hierarchy. For example, if a console appender is added to the root logger, then all enabled logging requests will at least print on the console.
If in addition a file appender is added to a logger, say C , then enabled logging requests for C and C 's children will print on a file and on the console. It is possible to override this default behavior so that appender accumulation is no longer additive by setting the additivity flag to false. More often than not, users wish to customize not only the output destination but also the output format.
This is accomplished by associating a layout with an appender. The layout is responsible for formatting the logging request according to the user's wishes, whereas an appender takes care of sending the formatted output to its destination. The PatternLayout , part of the standard log4cxx distribution, lets the user specify the output format according to conversion patterns similar to the C language printf function.
The first field is the number of milliseconds elapsed since the start of the program. The second field is the thread making the log request.
The third field is the level of the log statement. The fourth field is the name of the logger associated with the log request. The text after the '-' is the message of the statement. Inserting log requests into the application code requires a fair amount of planning and effort.
Observation shows that approximately 4 percent of code is dedicated to logging. Consequently, even moderately sized applications will have thousands of logging statements embedded within their code. Given their number, it becomes imperative to manage these log statements without the need to modify them manually. The log4cxx environment is fully configurable programmatically.
However, it is far more flexible to configure log4cxx using configuration files. Let us give a taste of how this is done with the help of an imaginary application MyApp that uses log4cxx. MyApp begins by including log4cxx headers. It then defines a static logger variable with the name MyApp which happens to be the fully qualified name of the class. The invocation of the BasicConfigurator::configure method creates a rather simple log4cxx setup.
This method is hardwired to add to the root logger a ConsoleAppender. The previous example always outputs the same log information. Fortunately, it is easy to modify MyApp so that the log output can be controlled at run-time. Here is a slightly modified version. This version of MyApp instructs PropertyConfigurator to parse a configuration file and set up logging accordingly. Here is a sample configuration file that results in exactly same output as the previous BasicConfigurator based example.
Suppose we are no longer interested in seeing the output of any component belonging to the com::foo package. The following configuration file shows one possible way of achieving this. As the logger com. Bar does not have an assigned level, it inherits its level from com. Consequently, doIt method's log request is suppressed. Calling the enhanced MyApp with the this configuration file will output the following on the console. In addition, as the root logger has been allocated a second appender, output will also be directed to the example.
This file will be rolled over when it reaches KB. When roll-over occurs, the old version of example. Note that to obtain these different logging behaviors we did not need to recompile code. The log4cxx library does not make any assumptions about its environment.
Logger Class Reference
Apache log4cxx is licensed under the Apache License , an open source license certified by the Open Source Initiative. Almost every large application includes its own logging or tracing API. Inserting log statements into code is a low-tech method for debugging it. It may also be the only way because debuggers are not always available or applicable. This is usually the case for multithreaded applications and distributed applications at large. Experience indicates that logging is an important component of the development cycle.
No API documentation available. Please see this page for information on how to submit your repository to our index. It provides a macro-based interface which allows both printf - and stream-style output. It also wraps log4cxx , which supports hierarchical loggers, verbosity levels and configuration-files. Code API rosconsole provides eight different types of logging statements, at 5 different verbosity levels, with both printf- and stream-style formatting.
PropertyConfigurator Class Reference
Apache Log4cxx is a framework which provides the capability to log messages in a variety of formats to the local console, local files, streamed over a socket or even launch an email based on a hierarchy of notification levels. Install RHEL5 example : rpm -ivh apr-devel Log4cxx can log to the console and log file as shown above. It can also log in XML format or a specified format, it can log time intervals with each interval logged to its' own log file time based logs with TimeBasedRollingPolicy or log to files of a specified size where upon reaching the size limit, it logs to a new file size based logs set MaxFileSize. Log4cxx can log to the Linux syslogd local or remote or to a socket stream.