log4j PatternLayout

http://www.yiibai.com/log4j/log4j_patternlayout.html

描述

log4j PatternLayout实例教程 - 如果想在一个特定的格式基础上一个模式产生的日志信息，那么可以使用org.apache.log4j.PatternLayout来格式化您的日志信息。

如果想在一个特定的格式基础上一个模式产生的日志信息，那么可以使用org.apache.log4j.PatternLayout来格式化日志信息。

PatternLayout类扩展了抽象org.apache.log4j.Layout类，并覆盖format()方法来结构日志信息根据提供的模式。

PatternLayout是一个简单的布局对象提供了以下Bean属性可以设置使用配置文件：

S.N.	Property & Description
1	conversionPattern 设置转换模式。默认值是 %r [%t] %p %c %x - %m%n

模式转换字符：

下面的表格解释在上述模式中使用的字符和所有其他字符，可以使用你自定义的模式：

Conversion Character	Meaning
c	Used to output the category of the logging event. For example, for the category name "a.b.c" the pattern %c{2} will output "b.c".
C	Used to output the fully qualified class name of the caller issuing the logging request. For example, for the class name "org.apache.xyz.SomeClass", the pattern %C{1} will output "SomeClass".
d	Used to output the date of the logging event. For example, %d{HH:mm:ss,SSS} or %d{dd MMM yyyy HH:mm:ss,SSS}.
F	Used to output the file name where the logging request was issued.
l	Used to output location information of the caller which generated the logging event.
L	Used to output the line number from where the logging request was issued.
m	Used to output the application supplied message associated with the logging event.
M	Used to output the method name where the logging request was issued.
n	Outputs the platform dependent line separator character or characters.
p	Used to output the priority of the logging event.
r	Used to output the number of milliseconds elapsed from the construction of the layout until the creation of the logging event.
t	Used to output the name of the thread that generated the logging event.
x	Used to output the NDC (nested diagnostic context) associated with the thread that generated the logging event.
X	The X conversion character is followed by the key for the MDC. For example, X{clientIP} will print the information stored in the MDC against the key clientIP.
%	The literal percent sign. %% will print a % sign.

格式修饰符：

默认情况下，相关的信息输出。在格式修饰符的帮助下，它是可以改变的最小字段宽度，最大字段宽度和对齐。

以下表涵盖了各种修饰符的情况：

Format modifier	left justify	minimum width	maximum width	comment
%20c	false	20	none	Left pad with spaces if the category name is less than 20 characters long.
%-20c	true	20	none	Right pad with spaces if the category name is less than 20 characters long.
%.30c	NA	none	30	Truncate from the beginning if the category name is longer than 30 characters.
%20.30c	false	20	30	Left pad with spaces if the category name is shorter than 20 characters. However, if category name is longer than 30 characters, hen truncate from the beginning.
%-20.30c	true	20	30	Right pad with spaces if the category name is shorter than 20 characters. However, if category name is longer than 30 characters, then truncate from the beginning.

PatternLayout 例子:

以下是一个简单的配置文件PatternLayout：

# Define the root logger with appender file
log = /usr/home/log4j
log4j.rootLogger = DEBUG, FILE
/* http://www.yiibai.com/log4j */
# 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=
      %d{yyyy-MM-dd}-%t-%x-%-5p-%-10c:%m%n

现在考虑下面的的Java示例将产生的日志信息：

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 an debug message");
     log.info("Hello this is an info message");
  }
}

编译并运行上述程序，将创建一个log.out文件在/usr/home/log4j目录，将看日志信息：

2010-03-23-main--DEBUG-log4jExample:Hello this is an debug message
2010-03-23-main--INFO -log4jExample:Hello this is an info message