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(ns
#^{:author "Alex Taggart, Timothy Pratley",
:doc "Logging macros which delegate to a specific logging implementation.
At runtime a specific implementation is selected from, in order, Apache
commons-logging, log4j, and finally java.util.logging.
Logging levels are specified by clojure keywords corresponding to the
values used in log4j/commons-logging:
:trace, :debug, :info, :warn, :error, :fatal
Unless otherwise specified, the current namespace will be used as the log-name
(similar to how the java class name is usually used).
Logging occurs with the log macro which writes either directly or via an
agent. By default direct logging is disabled, but can be enabled via the
*allow-direct-logging* boolean ref. If log is invoked within a transaction it
will always use an agent.
The logging macros will not evaluate their 'message' unless the specific
logging level is in effect.
Use the enabled? function to write conditional code against the logging level
(beyond simply whether or not to call log/send-log).
You can redirect all java writes of System.out and System.err to the log
system by calling log-capture!. To rebind *out* and *err* to the log system
invoke with-logs."
}
clojure.contrib.logging)
(defstruct log-system
:name ; the name of the logging system used
:get-log ; fn [name] to obtain a log by string name
:enabled? ; fn [log lvl] to check if a particular level is emabled
:write) ; fn [log lvl msg ex] to a log a message
(defmacro commons-logging
"Creates a log-system struct using the Apache commons-logging API,
if present; otherwise nil."
[]
(try
(import (org.apache.commons.logging LogFactory Log))
`(letfn [(get-log# [name#]
(LogFactory/getLog name#))
(enabled?# [log# level#]
(condp = level#
:trace (.isTraceEnabled log#)
:debug (.isDebugEnabled log#)
:info (.isInfoEnabled log#)
:warn (.isWarnEnabled log#)
:error (.isErrorEnabled log#)
:fatal (.isFatalEnabled log#)))
(write# [log# level# msg# e#]
(condp = level#
:trace (.trace log# msg# e#)
:debug (.debug log# msg# e#)
:info (.info log# msg# e#)
:warn (.warn log# msg# e#)
:error (.error log# msg# e#)
:fatal (.fatal log# msg# e#)))]
(struct log-system "commons-logging" get-log# enabled?# write#))
(catch Exception e nil)))
(defmacro log4j-logging
"Creates a log-system struct using the log4j API, if present; otherwise nil."
[]
(try
(import (org.apache.log4j Logger Level))
`(let [levels# {:trace Level/TRACE
:debug Level/DEBUG
:info Level/INFO
:warn Level/WARN
:error Level/ERROR
:fatal Level/FATAL}]
(letfn [(get-log# [name#]
(Logger/getLogger name#))
(enabled?# [log# level#]
(.isEnabledFor log# (levels# level#)))
(write# [log# level# msg# e#]
(if-not e#
(.log log# (levels# level#) msg#)
(.log log# (levels# level#) msg# e#)))]
(struct log-system "log4j-logging" get-log# enabled?# write#)))
(catch Exception e nil)))
(defmacro java-logging
"Creates a log-system struct using the java.util.logging API."
[]
(try
(import (java.util.logging Logger Level))
`(let [levels# {:trace Level/FINEST
:debug Level/FINE
:info Level/INFO
:warn Level/WARNING
:error Level/SEVERE
:fatal Level/SEVERE}]
(letfn [(get-log# [name#]
(Logger/getLogger name#))
(enabled?# [log# level#]
(.isLoggable log# (levels# level#)))
(write# [log# level# msg# e#]
(if-not e#
(.log log# (levels# level#) (str msg#))
(.log log# (levels# level#) (str msg#) e#)))]
(struct log-system "java-logging" get-log# enabled?# write#)))
(catch Exception e nil)))
(defmacro direct-log
"Logs the message immediately if the specific logging level is enabled. Use
the log macro in prefernce to this."
[level message throwable log-name system]
`(let [log# ((~system :get-log) ~log-name)]
(if ((~system :enabled?) log# ~level)
((~system :write) log# ~level ~message ~throwable))))
(defmacro send-log
"Sends the message to a logging agent. Use the log macro in preference to
this."
[level message throwable log-name system-agent]
(defn agent-log [sys# lvl# msg# th# ln#]
(let [log# ((sys# :get-log) ln#)]
(if ((sys# :enabled?) log# lvl#)
((sys# :write) log# lvl# (force msg#) th#))
sys#))
`(send-off ~system-agent
agent-log ~level (delay ~message) ~throwable ~log-name))
(def *log-system*
(ref (some eval ['(commons-logging)
'(log4j-logging)
'(java-logging)])))
(def *log-system-agent* (agent *log-system*))
(def *allow-direct-logging* (ref false))
(defmacro log
"Logs a message, either directly or via an agent."
([level message]
`(log ~level ~message nil))
([level message throwable]
`(log ~level ~message ~throwable (str *ns*)))
([level message throwable log-name]
`(if (and @*allow-direct-logging*
(not (clojure.lang.LockingTransaction/isRunning)))
(direct-log ~level ~message ~throwable ~log-name @*log-system*)
(send-log ~level ~message ~throwable ~log-name *log-system-agent*))))
(defn enabled?
"Returns true if the specific logging level is enabled."
([level]
(enabled? level (str *ns*)))
([level log-name]
(let [sys @*log-system*]
((sys :enabled?) ((sys :get-log) log-name) level))))
(defmacro spy
"Evaluates expr and outputs the form and its result to the debug log; returns
the result of expr."
[expr]
`(let [a# ~expr] (log :debug (str '~expr " => " a#)) a#))
(defn log-stream
"Creates a logging output stream that will output to the log."
[level log-name]
(java.io.PrintStream.
(proxy [java.io.ByteArrayOutputStream] []
(flush []
(proxy-super flush)
(let [s (.trim (.toString this))]
(proxy-super reset)
(if (> (.length s) 0)
(log level s nil log-name)))))
true))
(def *old-std-streams* (ref nil))
(defn log-capture!
"Captures System/out and System/err, redirecting all writes of those streams
to :info and :error logging, respectively. The specified log-name value will
be used for all redirected logging. NOTE: this will not redirect output of
*out* or *err*; for that use with-logs"
[log-name]
(dosync
(let [new-out (log-stream :info log-name)
new-err (log-stream :error log-name)]
; don't overwrite if something is already there
(if (nil? @*old-std-streams*)
(ref-set *old-std-streams* {:out System/out :err System/err}))
(System/setOut new-out)
(System/setErr new-err))))
(defn log-uncapture!
"Restores System/out and System/err to their original values."
[]
(dosync
(when-let [{old-out :out old-err :err} @*old-std-streams*]
(ref-set *old-std-streams* nil)
(System/setOut old-out)
(System/setErr old-err))))
(defmacro with-logs
"Evaluates exprs in a context in which *out* and *err* are bound to :info and
:error logging, respectively."
[log-name & body]
`(let [new-out# (java.io.PrintWriter.
(log-stream :info ~log-name) true)
new-err# (java.io.PrintWriter.
(log-stream :error ~log-name) true)]
(binding [*out* new-out#
*err* new-err#]
~@body)))
|
