Key Words: Log copy Log4j-1.2.9.jar to/web-inf/lib directory
It's no use adding Log4j-1.2.9.jar references in Eclipse's Java builder path
Under the copy Log4j-1.2.9.jar to/web-inf/lib
TomcatYou need to automatically find the lib below this directory at startup, and the Eclipse reference is used in development use and, in the absence of a release,
TomcatThese classes are not found
# If programmed properly the most messages would is at DEBUG
# and the least at FATAL.
The use of log4j/log4e
Log4j is to help developers
LogThe API class library for output management. Its most important feature is the flexibility to configure the file settings
LogPriority of information,
LogThe output destination of the information and
LogThe output format of the information.
log4j in addition to recording program running
LogAnother important feature of information is that it is used to display debugging information.
Programmers often encounter situations that break out of the Java IDE Environment debugger, when most people choose to use System.out
The. println statement outputs a variable value method for debugging. This poses a very troubling question: once where
daysThe programmer decided not to display the System.out.println, but to comment out the spam statements on a line. If where
daysIf you want to debug variable values, you can only remove these comments in a row to recover the SYSTEM.OUT.PRINTLN statement.
Using log4j can be a good treatment for similar situations. Log4j use method The following is a log4j of some theoretical knowledge
To define a configuration file
Using a configuration file first will make our applications more flexible in configuring log
LogOutput mode includes output priority, output destination, output format. LOG4J supports two configuration file formats, one in XML format and one for Java attribute file Log4j.properties (key = value).
The following describes how to use the Log4j.properties file as a configuration file:
Configure Root Logger
Its syntax is: Log4j.rootlogger = [level], Appendername, Appendername, ...
L Output Priority level
[Level] is
LogThe priority of the record, which is divided into off, FATAL, ERROR, WARN, INFO, DEBUG, all, or custom levels.
LOG4J recommends using only four levels, from high to low, respectively, for error, WARN, INFO, and DEBUG.
By the level defined here, you can control the corresponding level in the application
LogInformation on the switch. For example, where the info level is defined, all debug levels in the application
LogInformation will not be printed.
L Output Destination
Output format configuration for specific output
L Output-type configuration
Appendername is the designation
LogWhere the information is being exported. Multiple output destinations can be specified at the same time.
Configuration
LogThe information output destination is Appender, and its syntax is:
Domconfigurator.configure (String filename): Reads a configuration file in XML form.
L Insert record information (format
LogInformation
When the two necessary steps are completed, you can easily use different priority levels
LogThe record statement is inserted where you want to record
LogAnywhere, its syntax is as follows:
Logger.debug (Object message);
Logger.info (Object message);
Logger.warn (Object message);
Logger.error (Object message);
LOG4J Sample Program
The following is a simple example program to further illustrate how log4j is used.
This means using the log4j.properties file in the SRC folder under the current engineering directory as the configuration file.
If you put the log4j.properties in the engineering root directory or do not write this sentence, the program will automatically find the configuration file.
③logger.debug is the information that outputs debug,
Logger.info is the output hint information,
Logger.warn is to display a warning message,
Logger.error is to display an error message.
The following are the contents of the configuration file log4j.properties: Log4j.rootlogger
Program Description:
L log4j. Rootlogger =debug, Stdout,r
That means I'm going to show all the priority equal to and above debug information. "stdout", "R" means that I have defined two outputs (whatever name is good). The following three lines say that the stdout output is actually the standard output console, which is the screen.
L The output format is patternlayout. The conversion mode is%5p (%f:%l)-%m%n,
The first five are used to display precedence, and then the current file name, plus the current number of rows, is displayed.
Finally, the information in Logger.debug () or logger.info () or Logger.warn () or Logger.error ().
%n indicates a carriage return blank line.
Plus the following six lines log information is not only displayed on the screen, but will be saved in a file called "Log.txt" with a maximum file of 100KB. If the file size exceeds 100KB, the file is backed up as "Log.txt.1", and the new "Log.txt" continues to log the log information. Next we can change the log4j.properties, without recompiling, we can control whether the log information is displayed, the output type of the log information, the output mode, the output format, and so on.
Examples are as follows:
Put "log4j" in the Log4j.properties file. Rootlogger =debug,stdout,r "
Rewrite it as "Log4j.rootcategory=off, stdout,r" so that all log information is not displayed;
Put "log4j" in the Log4j.properties file. Rootlogger =debug,stdout,r "Rewrite to" Log4j.rootcategory=info, stdout,r, so that only the log information of info, WARN and error is displayed, and DEBUG information is not displayed; Using log4j in Web programs attention issues
1, because the JSP or servlet in the execution state does not have the current path concept, all use
Propertyconfigurator.configure (String) statement when looking for a log4j.properties file, give the corresponding
The path to the current JSP or servlet translates into an absolute file system path.
method is to use the Servletcontext.getrealpath (string) statement.
2, the corresponding Log4j.properties set a property when you want to set the absolute path in the program.
Example: Log4j.appender.r.file property setting
LogThe location where the file is stored.
We can make flexible settings using the method of reading and writing. Properties configuration file.
log4e use instructions after understanding the features of the log4j
We will certainly write some log4j in our program
LogRecording.
For programmers who use Eclipse, log4e will be our most effective log4j
LogWriting Assistant, now start log4e trip. LOG4E is a free eclipse Plugin that helps you quickly add log to your Java project, and we can download the latest version of log4e on Http://log4e.jayefem.de/index.php/Download Web site.
After downloading, copy the appropriate folder to eclipse's plug-in directory, and then eclipse, with one more log4e option in the preferences. LOG4E can have multiple insert log as a method, class, and, of course, you can insert the log at the current location.
At the same time, it can also convert Sysout.out.println () to log; All of this only requires you to click the mouse or press a shortcut key, we only think of a method to insert log as an example of the Java Editor in the context of the right button,
Select log4e, you will see the following interface: Click Insert Log Statement for this method, you will see the verification page: After finish, you will see the following function inserted into the log:
log4e more instance references http://log4e.jayefem.de
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