Log4j-one of the "weapons" required by the system

Introduction

Log4j is an open-source project of Apache. By using log4j, we can control the log information delivery destination, such as the console, file, database, and even the interface server; you can also control the output format of each log. By defining the level of each log information, you can control the log generation process in greater detail. When necessary, you can use a configuration file to flexibly configure the program without modifying the program code.

Install

Slave Decompress the archive file to a suitable directory. Add the file Dist/lib/log4j-1.2.11.jar to the classpath environment variable

Our concerns

For a log processing function, we have three main concerns:

Who will record logs? -- Logger

How to obtain a logger instance? 1. There are many ways to create a logger. The following method can retrieve the root logger: Logger logger = logger. getrootlogger (); 2. Create a New logger as follows: Logger logger = logger. getlogger ("logtest "); 3. A common usage is to instantiate a static global Logger Based on the class name: Static logger = logger. getlogger (logtest. Class ); How to record logs? Log Level) Corresponding logging method (logger) Fatal (0) Log. Fatal () Error (3) Log. Error () Warn (4) Log. Warn () Warn (6) Log.info () Debug (7) Log. debug ()

Where is the record? -- Appender

1. eagleappender uses the layout (layout) specified by the user to output log events to system. out or system. Err. The default target is system. Out. 2. dailyrollingfileappender extends fileappender. Therefore, multiple log files can be recorded cyclically at a frequency selected by one user. 3. fileappender writes log events to a file 4. rollingfileappender extends the fileappender backup capacity to a certain size of log files. 5. writerappender writes log events to writer or outputstream based on the user's choice. 6. jdbcappender writes log events to the database.

Log format? -- Logger

1. HTML layout formatted log output is an HTML table. 2. patternlayout format the log output based on the specified conversion mode, or use the default conversion mode if no conversion mode is specified. 3. simplelayout format the log output in a very simple way. It prints the level, and then follows a break "-". Finally, it is the log message.

Configuration File description

The ease-of-use of log4j is its configurability. By specifying problems 2 and 3 in the configuration file above, our system has a powerful and almost perfect logging function! The following is an example of a configuration file: logconfig. Properties

Log4j. rootlogger = debug, console, A1, Im Log4j.addivity.org. Apache = true # Apply to the console Log4j. appender. Console = org. Apache. log4j. leleappender Log4j. appender. Threshold = debug Log4j. appender. Console. Target = system. Out Log4j. appender. Console. layout = org. Apache. log4j. patternlayout Log4j. appender. Console. layout. conversionpattern = [framework] % d-% C-%-4r [% T] %-5 p % C % x-% m % N # Log4j. appender. console. layout. conversionpattern = [start] % d {date} [date] % N % P [Priority] % N % x [NDC] % N % T [thread] n % C [category] % N % m [Message] % N # Apply to files Log4j. appender. File = org. Apache. log4j. fileappender Log4j. appender. file. File = file. Log Log4j. appender. file. append = false Log4j. appender. file. layout = org. Apache. log4j. patternlayout Log4j. appender. file. layout. conversionpattern = [framework] % d-% C-%-4r [% T] %-5 p % C % x-% m % N # Used to generate files by day Log4j. appender. A1 = org. Apache. log4j. dailyrollingfileappender Log4j. appender. a1.file = samplemessages. log4j Log4j. appender. a1.datepattern = yyyymmdd-hh '. log4j' Log4j. appender. a1.layout = org. Apache. log4j. xml. xmllayout # Apply to file rollback Log4j. appender. rolling_file = org. Apache. log4j. rollingfileappender Log4j. appender. rolling_file.threshold = Error Log4j. appender. rolling_file.file = rolling. Log Log4j. appender. rolling_file.append = true Log4j. appender. rolling_file.maxfilesize = 10kb Log4j. appender. rolling_file.maxbackupindex = 1 Log4j. appender. rolling_file.layout = org. Apache. log4j. patternlayout Log4j. appender. rolling_file.layout.conversionpattern = [framework] % d-% C-%-4r [% T] %-5 p % C % x-% m % N # For Databases # Description: Database: MySQL # First create a database table (log4j) Description: # Field description # Guid serial number (auto-increment column) # Date time # Current thread # Level current level # Class current Java program/Method # Current message output Log4j. appender. Database = org. Apache. log4j. JDBC. jdbcappender Log4j. appender. database. url = JDBC: mysql: // localhost: 3306/test? Useunicode = true & characterencoding = GBK Log4j. appender. database. Driver = com. MySQL. JDBC. Driver Log4j. appender. database. User = root Log4j. appender. database. Password = Log4j. appender. database. SQL = insert into log4j (date, thread, level, class, message) values ('% d {yyyy-mm-dd hh: mm: SS}', '% t ', '% P',' % l', '% m ') Log4j. appender. database. layout = org. Apache. log4j. patternlayout Log4j. appender. database. layout. conversionpattern = [framework] % d-% C-%-4r [% T] %-5 p % C % x-% m % N # Custom appender Log4j. appender. Im = net. cybercorlin. util. Logger. appender. imappender Log4j. appender. Im. Host = mail.cybercorlin.net Log4j. appender. Im. Username = Username Log4j. appender. Im. Password = Password Log4j. appender. Im. Recipient = corlin@cybercorlin.net Log4j. appender. Im. layout = org. Apache. log4j. patternlayout Log4j. appender. Im. layout. conversionpattern = [framework] % d-% C-%-4r [% T] %-5 p % C % x-% m % N # Meaning of "% d % T % P % L % m % N: # % D date or time of the log output time point. The default format is iso8601. You can also specify the format after it, for example, % d {yyyy-mm-dd hh: mm: SS}, output is similar to: 17:49:27; # % T name of the thread that generates the log event; # % P the log_level of the log, such as debug, warn, Or info; # % C output category, usually the full name of the class, such as "iNotes. Default "; # % M log content; # % L location of log event output, including category name, thread, and number of lines in the code. For example, write2database. Main (write2database. Java: 33 ); # % N output a carriage return line break, which is "" on Windows and "" On Unix

Example

Package com. javer. Test. log4j; Import org. Apache. log4j. Logger; Import org. Apache. log4j. propertyconfigurator; Import org. Apache. log4j. htmllayout; /** * Javer's log4j example Program * @ Author javer QQ: 84831612 * @ Version 1.0 * @ Version http://blog.csdn.net/java008 */ Public class logtest { Public static void main (string [] ARGs) { String filepath = "F: // logconfig. properties "; Propertyconfigurator. Configure (filepath ); Logger log = logger. getlogger (logtest. Class ); // Log. addappender (New htmllayout ()); For (INT I = 0; I <10; I ++) { Log.info ("section" + (I + 1) + "debugging information "); Log. debug ("sqlexception:", new java. SQL. sqlexception ("SQL exception! ")); Log.info ("Hello log4j! "); } } }