log4net的appender和format

Appenders

The ability to selectively enable or disable logging requests based on their logger is only part of the picture. Log4net allows logging requests to print to multiple destinations. In log4net speak, an output destination is called an appender. Appenders must implement the log4net.Appenders.IAppender interface.

The following appenders are defined in the log4net package:

Type	Description
log4net.Appender.AdoNetAppender	Writes logging events to a database using either prepared statements or stored procedures.
log4net.Appender.AnsiColorTerminalAppender	Writes color highlighted logging events to a an ANSI terminal window.
log4net.Appender.AspNetTraceAppender	Writes logging events to the ASP trace context. These can then be rendered at the end of the ASP page or on the ASP trace page.
log4net.Appender.BufferingForwardingAppender	Buffers logging events before forwarding them to child appenders.
log4net.Appender.ColoredConsoleAppender	Writes logging events to the application's Console. The events may go to either the standard our stream or the standard error stream. The events may have configurable text and background colors defined for each level.
log4net.Appender.ConsoleAppender	Writes logging events to the application's Console. The events may go to either the standard our stream or the standard error stream.
log4net.Appender.DebugAppender	Writes logging events to the .NET system.
log4net.Appender.EventLogAppender	Writes logging events to the Windows Event Log.
log4net.Appender.FileAppender	Writes logging events to a file in the file system.
log4net.Appender.ForwardingAppender	Forwards logging events to child appenders.
log4net.Appender.LocalSyslogAppender	Writes logging events to the local syslog service (UNIX only).
log4net.Appender.MemoryAppender	Stores logging events in an in memory buffer.
log4net.Appender.NetSendAppender	Writes logging events to the Windows Messenger service. These messages are displayed in a dialog on a users terminal.
log4net.Appender.OutputDebugStringAppender	Writes logging events to the debugger. If the application has no debugger, the system debugger displays the string. If the application has no debugger and the system debugger is not active, the message is ignored.
log4net.Appender.RemoteSyslogAppender	Writes logging events to a remote syslog service using UDP networking.
log4net.Appender.RemotingAppender	Writes logging events to a remoting sink using .NET remoting.
log4net.Appender.RollingFileAppender	Writes logging events to a file in the file system. The RollingFileAppender can be configured to log to multiple files based upon date or file size constraints.
log4net.Appender.SmtpAppender	Sends logging events to an email address.
log4net.Appender.SmtpPickupDirAppender	Writes SMTP messages as files into a pickup directory. These files can then be read and sent by an SMTP agent such as the IIS SMTP agent.
log4net.Appender.TelnetAppender	Clients connect via Telnet to receive logging events.
log4net.Appender.TraceAppender	Writes logging events to the .NET trace system.
log4net.Appender.UdpAppender	Sends logging events as connectionless UDP datagrams to a remote host or a multicast group using a UdpClient.

More than one appender can be attached to a logger.              

 

 

 

 The recognized conversion pattern names are:

Conversion Pattern Name	Effect
a	Equivalent to appdomain
appdomain	Used to output the friendly name of the AppDomain where the logging event was generated.
aspnet-cache	Used to output all cache items in the case of %aspnet-cache or just one named item if used as %aspnet-cache{key} This pattern is not available for Compact Framework or Client Profile assemblies.
aspnet-context	Used to output all context items in the case of %aspnet-context or just one named item if used as %aspnet-context{key} This pattern is not available for Compact Framework or Client Profile assemblies.
aspnet-request	Used to output all request parameters in the case of %aspnet-request or just one named param if used as %aspnet-request{key} This pattern is not available for Compact Framework or Client Profile assemblies.
aspnet-session	Used to output all session items in the case of %aspnet-session or just one named item if used as %aspnet-session{key} This pattern is not available for Compact Framework or Client Profile assemblies.
c	Equivalent to logger
C	Equivalent to type
class	Equivalent to type
d	Equivalent to date
date	Used to output the date of the logging event in the local time zone. To output the date in universal time use the %utcdate pattern. The date conversion specifier may be followed by a date format specifier enclosed between braces. For example, %date{HH:mm:ss,fff} or %date{dd MMM yyyy HH:mm:ss,fff}. If no date format specifier is given then ISO8601 format is assumed (Iso8601DateFormatter). The date format specifier admits the same syntax as the time pattern string of the ToString. For better results it is recommended to use the log4net date formatters. These can be specified using one of the strings "ABSOLUTE", "DATE" and "ISO8601" for specifying AbsoluteTimeDateFormatter, DateTimeDateFormatter and respectively Iso8601DateFormatter. For example, %date{ISO8601} or %date{ABSOLUTE}. These dedicated date formatters perform significantly better than ToString.
exception	Used to output the exception passed in with the log message. If an exception object is stored in the logging event it will be rendered into the pattern output with a trailing newline. If there is no exception then nothing will be output and no trailing newline will be appended. It is typical to put a newline before the exception and to have the exception as the last data in the pattern.
F	Equivalent to file
file	Used to output the file name where the logging request was issued. WARNING Generating caller location information is extremely slow. Its use should be avoided unless execution speed is not an issue. See the note below on the availability of caller location information.
identity	Used to output the user name for the currently active user (Principal.Identity.Name). WARNING Generating caller information is extremely slow. Its use should be avoided unless execution speed is not an issue.
l	Equivalent to location
L	Equivalent to line
location	Used to output location information of the caller which generated the logging event. The location information depends on the CLI implementation but usually consists of the fully qualified name of the calling method followed by the callers source the file name and line number between parentheses. The location information can be very useful. However, its generation is extremely slow. Its use should be avoided unless execution speed is not an issue. See the note below on the availability of caller location information.
level	Used to output the level of the logging event.
line	Used to output the line number from where the logging request was issued. WARNING Generating caller location information is extremely slow. Its use should be avoided unless execution speed is not an issue. See the note below on the availability of caller location information.
logger	Used to output the logger of the logging event. The logger conversion specifier can be optionally followed by precision specifier, that is a decimal constant in brackets. If a precision specifier is given, then only the corresponding number of right most components of the logger name will be printed. By default the logger name is printed in full. For example, for the logger name "a.b.c" the pattern %logger{2} will output "b.c".
m	Equivalent to message
M	Equivalent to method
message	Used to output the application supplied message associated with the logging event.
mdc	The MDC (old name for the ThreadContext.Properties) is now part of the combined event properties. This pattern is supported for compatibility but is equivalent to property.
method	Used to output the method name where the logging request was issued. WARNING Generating caller location information is extremely slow. Its use should be avoided unless execution speed is not an issue. See the note below on the availability of caller location information.
n	Equivalent to newline
newline	Outputs the platform dependent line separator character or characters. This conversion pattern offers the same performance as using non-portable line separator strings such as "\n", or "\r\n". Thus, it is the preferred way of specifying a line separator.
ndc	Used to output the NDC (nested diagnostic context) associated with the thread that generated the logging event.
p	Equivalent to level
P	Equivalent to property
properties	Equivalent to property
property	Used to output the an event specific property. The key to lookup must be specified within braces and directly following the pattern specifier, e.g. %property{user} would include the value from the property that is keyed by the string 'user'. Each property value that is to be included in the log must be specified separately. Properties are added to events by loggers or appenders. By default the log4net:HostName property is set to the name of machine on which the event was originally logged. If no key is specified, e.g. %property then all the keys and their values are printed in a comma separated list. The properties of an event are combined from a number of different contexts. These are listed below in the order in which they are searched. the event properties The event has Properties that can be set. These properties are specific to this event only. the thread properties The Properties that are set on the current thread. These properties are shared by all events logged on this thread. the global properties The Properties that are set globally. These properties are shared by all the threads in the AppDomain.
r	Equivalent to timestamp
stacktrace	Used to output the stack trace of the logging event The stack trace level specifier may be enclosed between braces. For example, %stacktrace{level}. If no stack trace level specifier is given then 1 is assumed Output uses the format: type3.MethodCall3 > type2.MethodCall2 > type1.MethodCall1 This pattern is not available for Compact Framework assemblies.
stacktracedetail	Used to output the stack trace of the logging event The stack trace level specifier may be enclosed between braces. For example, %stacktracedetail{level}. If no stack trace level specifier is given then 1 is assumed Output uses the format: type3.MethodCall3(type param,...) > type2.MethodCall2(type param,...) > type1.MethodCall1(type param,...) This pattern is not available for Compact Framework assemblies.
t	Equivalent to thread
timestamp	Used to output the number of milliseconds elapsed since the start of the application until the creation of the logging event.
thread	Used to output the name of the thread that generated the logging event. Uses the thread number if no name is available.
type	Used to output the fully qualified type name of the caller issuing the logging request. This conversion specifier can be optionally followed by precision specifier, that is a decimal constant in brackets. If a precision specifier is given, then only the corresponding number of right most components of the class name will be printed. By default the class name is output in fully qualified form. For example, for the class name "log4net.Layout.PatternLayout", the pattern %type{1} will output "PatternLayout". WARNING Generating the caller class information is slow. Thus, its use should be avoided unless execution speed is not an issue. See the note below on the availability of caller location information.
u	Equivalent to identity
username	Used to output the WindowsIdentity for the currently active user. WARNING Generating caller WindowsIdentity information is extremely slow. Its use should be avoided unless execution speed is not an issue.
utcdate	Used to output the date of the logging event in universal time. The date conversion specifier may be followed by a date format specifier enclosed between braces. For example, %utcdate{HH:mm:ss,fff} or %utcdate{dd MMM yyyy HH:mm:ss,fff}. If no date format specifier is given then ISO8601 format is assumed (Iso8601DateFormatter). The date format specifier admits the same syntax as the time pattern string of the ToString. For better results it is recommended to use the log4net date formatters. These can be specified using one of the strings "ABSOLUTE", "DATE" and "ISO8601" for specifying AbsoluteTimeDateFormatter, DateTimeDateFormatter and respectively Iso8601DateFormatter. For example, %utcdate{ISO8601} or %utcdate{ABSOLUTE}. These dedicated date formatters perform significantly better than ToString.
w	Equivalent to username
x	Equivalent to ndc
X	Equivalent to mdc
%	The sequence %% outputs a single percent sign.

The single letter patterns are deprecated in favor of the longer more descriptive pattern names.

By default the relevant information is output as is. However, with the aid of format modifiers it is possible to change the minimum field width, the maximum field width and justification.

The optional format modifier is placed between the percent sign and the conversion pattern name.

The first optional format modifier is the left justification flag which is just the minus (-) character. Then comes the optional minimum field width modifier. This is a decimal constant that represents the minimum number of characters to output. If the data item requires fewer characters, it is padded on either the left or the right until the minimum width is reached. The default is to pad on the left (right justify) but you can specify right padding with the left justification flag. The padding character is space. If the data item is larger than the minimum field width, the field is expanded to accommodate the data. The value is never truncated.

This behavior can be changed using the maximum field width modifier which is designated by a period followed by a decimal constant. If the data item is longer than the maximum field, then the extra characters are removed from the beginning of the data item and not from the end. For example, it the maximum field width is eight and the data item is ten characters long, then the first two characters of the data item are dropped. This behavior deviates from the printf function in C where truncation is done from the end.

Below are various format modifier examples for the logger conversion specifier.

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

Note about caller location information.