logmemory.html
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<TITLE>Writing Log Records Only After a Condition Occurs
(Java Developers Almanac Example)
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<META CONTENT="Patrick Chan" NAME="AUTHOR">
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<h3>
e393.
Writing Log Records Only After a Condition Occurs</h3>
Suppose you are trying to track down an infrequent bug on a production
system with copious amounts of debug log messages. In most cases, when
the bug occurs, it is not necessary to have the entire history of log
messages; only a recent few are needed. To minimize the impact on the
system, a <code>MemoryHandler</code> can be used to store a number of log records
in memory and then dump them out only if the bug or other condition
occurs.
<pre>
try {
// Create a memory handler with a memory of 100 records
// and dumps the records into the file my.log when a
// SEVERE message is logged
FileHandler fhandler = new FileHandler(<font color="#0066ff"><i>"my.log"</i></font>);
int numRec = <font color="#0066ff"><i>100</i></font>;
MemoryHandler mhandler = new MemoryHandler(fhandler, numRec, Level.<font color="#0066ff"><i>SEVERE</i></font>);
// Add to the desired logger
Logger logger = Logger.getLogger(<font color="#0066ff"><i>"com.mycompany"</i></font>);
logger.addHandler(mhandler);
} catch (IOException e) {
}
try {
// Create a memory handler with a memory of 100 records
// and dumps the records into the file my.log when a
// some abitrary condition occurs
FileHandler fhandler = new FileHandler(<font color="#0066ff"><i>"my.log"</i></font>);
int numRec = <font color="#0066ff"><i>100</i></font>;
MemoryHandler mhandler = new MemoryHandler(fhandler, numRec, Level.OFF) {
public synchronized void publish(LogRecord record) {
// Log it before checking the condition
super.publish(record);
boolean condition = <font color="#0066ff"><i>false</i></font>;
if (condition) {
// Condition occurred so dump buffered records
push();
}
}
};
// Add to the desired logger
Logger logger = Logger.getLogger(<font color="#0066ff"><i>"com.mycompany"</i></font>);
logger.addHandler(mhandler);
} catch (IOException e) {
}
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Related Examples
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e385. <a class="eglink" href="BasicLogging.html?l=rel">
The Quintessential Logging Program
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e386. <a class="eglink" href="IsLog.html?l=rel">
Determining If a Message Will Be Logged
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e387. <a class="eglink" href="LogMethod.html?l=rel">
Logging a Method Call
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e388. <a class="eglink" href="LogExcept.html?l=rel">
Logging an Exception
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e389. <a class="eglink" href="Minimize.html?l=rel">
Minimizing the Impact of Logging Code
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e390. <a class="eglink" href="NoParent.html?l=rel">
Preventing a Logger from Forwarding Log Records to its Parent
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e391. <a class="eglink" href="LogFile.html?l=rel">
Writing Log Records to a Log File
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e392. <a class="eglink" href="LogConsole.html?l=rel">
Writing Log Records to Standard Error
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e394. <a class="eglink" href="SetFilter.html?l=rel">
Setting a Filter on a Logger Handler
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See also:
<a class="eglink" href="/egs/java.util.logging/pkg.html?l=rel#Configuration">
Configuration
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<a class="eglink" href="/egs/java.util.logging/pkg.html?l=rel#File%20Size">
File Size
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<a class="eglink" href="/egs/java.util.logging/pkg.html?l=rel#Formatters">
Formatters
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<a class="eglink" href="/egs/java.util.logging/pkg.html?l=rel#Levels">
Levels
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