A banking company is required to keep separate logs of all foreign transactions and of all foreign transactions greater than $10,000.

The foreign transactions to be logged are in the Smalltalk class Transaction. An instance of the class answers a string when sent the message #payee and a monetary amount when sent to message # amount.

Transaction has a method Transaction>> printOn

And a method Transaction>>printLog4s

 

One way to achieve this logging is to use two loggers, each with its own file appender set to record all transactions or only transactions above the $10,000 threshhold.

The figure below shows the structure of the log4s framework. One logger is the rootLogger; the second is a custom logger named ‘vast.’

The first step is to create a file appender named ForeignTxns with a level of Info and add it to the rootLogger: The pattern '%d %p [%c] %o' will log the time, the level, the logger name, and the transaction object. The message portion of the log event will be discarded.

In .ini file under the [log4s] stanza,

Equivalent Smalltalk code

The next step is to create a file appender named BigForeignTxns with a level of Warn and add it to a newly created logger called 'vast': The pattern of '%d %p [%c] %o' will log the time, the level, the Logger name, and the transaction object. The message portion of the log event will be discarded.

In .ini file under the [log4s] stanza,

Equivalent Smalltalk code

The actual application code might look like this method which decides whether the transaction presented should appear in one of the log files:

In the above example, all transactions result in an Info-level logging event. Only transactions with amounts greater than 10,000 result in a Warn-level logging event. The Info-level 'Foreign txn' logging event goes to the rootLogger and from there through the associated appender to the foreignTxns.log. The same logging event also goes to the vast logger, but this logger does not pass the logging event on to be written in the log file ‘foreignTxns.log.’

The Warn-level 'Large Foreign txn' logging event goes to the vast logger and from there through the associated appender to the bigForeignTxns.log. The same logging event also goes to the rootLogger, but this logger does not pass the logging event on to be written in the log file ‘bigForeignTxns.log.’

The output has three parts: the date, the logger name and the transaction. The transition is rendered as a payee and amount because of the method Transaction>>printLog4s. If the Transaction had no such method, the #printString method would record the transaction. If Transaction does not override #printOn:, it will record the transaction as 'aTransaction'

foreignTxns.log will have output like this.

bigForeignTxns.log will have output like this:

The same output can be achieved using just the rootLogger with two appenders. One of the appenders will have a level match filter. This configuration directs all warning log events, which are sent when a transaction amount exceeds $10,000, to one file and all informational level log events to another.

The figure below shows the structure of the log4s framework. The ForeignTxns appender has the filter and is on the right hand of the figure below. The BigForeignTxns appender is on the left side of the figure.

Just as for Method 1, the first step is to create a file appender named ForeignTxns with a level of Info and add it to the rootLogger. However for Method 2, this file appender has a level match filter to reject logging events of level Warn. Without the filter, the appender allows all logging events at level Info or greater to be written to the appender’s log file. Adding the filter will cause Warning-level logging events not to be output.

In the .ini file under [log4s],

Equivalent Smalltalk code (alternate 1)

Equivalent Smalltalk code (alternate 2)

Next, create a file appender named BigForeignTxns with a level of Info, but for Method 2, add it to the rootLogger rather than to a custom logger as in Method 1:

In .ini file under the [log4s] stanza,

Equivalent Smalltalk code

The Smalltalk application code might look like this method which decides whether the transaction presented should appear in one of the log files: The code is the same as for Method1, but when executed with Method 2’s arrangement of log4s players, the logging events go to the same logger. It is the appenders that decide the destination of the logging events.

In the above example, all transactions result in an Info-level logging event. Only transactions with amounts greater than 10,000 result in a Warn-level logging event. The Info-level 'Foreign txn' and Warn-level 'Large Foreign txn' logging events go through the rootLogger to both appenders. The Info-level logging events are output to the foreignTxns.log while the Warn-level logging events are output to the bigForeignTxns.log. How does this happen?

The ForeignTxns appender passes the Info-level logging event on to the levelMatchFilter which allows non-warning events to pass through to the log file for the appender, foreignTxns.log.

The ForeignTxns appender would normally log the Warn-level 'Large Foreign txn' logging event because its level allows logging events of Info or higher to be written, and Warn is higher. But the levelMatchFilter attached to the ForeignTxns appender ignores the logging event because it filters out logging events with a level of Warn. So the Warn-level 'Large Foreign txn' logging event does not appear in foreignTxns.log.

The BigForeignTxns appender ignores the Info-level logging event because the Info level of the event does not rise to the Warn-level required by the appender. So the Info-level 'Foreign txn' logging event does not appear in the bigForeignTxns.log.

The BigForeignTxns appender allows the Warn-level 'Large Foreign txn' logging event to be written to bigForeignTxns.log because the event level is greater or equal to the appender’s level.

Each output has three parts: the date, the logger name and the transaction. The transaction is rendered as a payee and amount because of the method Transaction>>printLog4s. Note that if there were no such method defined for class Transaction, then the method #printString would be called and the output would be 'aTransaction' unless Transaction overrides #printOn.

foreignTxns.log will have output like this:

bigForeignTxns.log will have output like this:

The configuration map ENVY/Image Logging Examples contains application EsLoggingFrameworkExamples which has many sample scripts that demonstrate the log4s functionality. See EsLogManager class>>readMe to get started.

EsSocketAppender>>readMe has a script you can use to start a socket listener.