ball_filteringobserver

Detailed Description

Outline

• Purpose
• Classes
• Description
  • Usage
    • Example 1: Basic Usage

Purpose

Provide an observer that filters log records.

Classes

• ball::FilteringObserver: observer that filters log records

See also

ball_record, ball_context, ball_loggermanager

Description

This component provides a concrete implementation of the ball::Observer protocol for receiving and processing log records:

             ,-----------------------.
            ( ball::FilteringObserver )
             `-----------------------'
                         |              ctor
                         V
                  ,--------------.
                 ( ball::Observer )
                  `--------------'
                                        publish
                                        dtor

ball::FilteringObserver processes the log records it receives through its publish method and conditionally forwards them to the inner observer supplied at construction.

Usage

This section illustrates intended use of this component.

Example 1: Basic Usage

This example shows how to use filtering observer to route some log records to a designated observer. A common use case is routing all log records for a given category (or category pattern) to a separate log file.

First, we create a filter that will match a log record's category against the pattern "EQUITY.*":

bool categoryFilter(const ball::Record& record, const ball::Context&)
{
    return ball::PatternUtil::isMatch(record.fixedFields().category(),
                                      "EQUITY.*");
}

Then, we create the observer that will receive filtered log records and create a filtering observer:

bsl::shared_ptr<ball::TestObserver> innerObserver(
                                       new ball::TestObserver(&bsl::cout));
 
ball::FilteringObserver filteringObserver(innerObserver, categoryFilter);

Next, we issue a series of log records and verify that only records with the category matching the pattern are published to the inner observer:

const ball::Context context(ball::Transmission::e_PASSTHROUGH, 0, 1);
 
ball::RecordAttributes fixedFields;
 
bsl::shared_ptr<ball::Record> record;
record.createInplace();
 
fixedFields.setCategory("CURNCY.USDGBP");
record->setFixedFields(fixedFields);
filteringObserver.publish(record, context);
 
assert(0 == innerObserver->numPublishedRecords());  // dropped
 
fixedFields.setCategory("EQUITY.NYSE");
record->setFixedFields(fixedFields);
filteringObserver.publish(record, context);
 
assert(1 == innerObserver->numPublishedRecords());  // forwarded
 
fixedFields.setCategory("EQUIT.");
record->setFixedFields(fixedFields);
filteringObserver.publish(record, context);
 
assert(1 == innerObserver->numPublishedRecords());  // dropped