Reading Files cross jars

To my somewhat annoyance I discovered that reading files from the current package is done with a normal FileReader but if you want to read the same file from a different jar you have to use the getResourceAsStream() method.


public class Read {
public static void main(String[] args) {
System.out.println(doRead());
}

public static String doRead() {
String result = "";
try {
BufferedReader fr;

InputStream inputStream = Read.class.getResourceAsStream("/data.txt");
if (inputStream != null) {
fr = new BufferedReader(new InputStreamReader(inputStream));
} else {
fr = new BufferedReader(new FileReader(new File("resources/data.txt")));
}

result = fr.readLine();
fr.close();
} catch (IOException e) {
e.printStackTrace();
}
return result;
}

}


Active MQ topics & Queues

Topics - go to all
Queues - go to one (usually round robin)

Active MQ topics VS Queue

SVN revert!

Tortoise:

Undo changes:
Tortoise SVN -> update to revision -> select revision -> RIGHT click -> revert to this revision.

Undo 1 change
Tortoise SVN -> Merge -> Reverse Merge (tick) -> select revision to remove

Command line:

Reverse Merge

Situation: Trunk was good upto 497 and now its all gone wrong. To revert everything and set the HEAD back to 497 do:
svn merge -r HEAD:497 .

Debug - Heap and memory allocation

So Java comes with these tools now:

jconsole
jvisualvm


But there is also this neat little tool allowing you to look inside the heap and see how the memory is allocated

jmap -heap <process id>


Free simple profiler - JIP

'Heavy' profiling

Collections and ConcurrentModificationExceptions

Unmodifiable collections can STILL throw ConcurrentModificationExceptions

Please remember this and use CopyOnWriteArrayList instead.

Log4j to different files

How to log to different files based on packages.

Sample log4j.properties file:

log4j.rootLogger=WARN,

#Overriding log levels in certain packages:
log4j.logger = INFO, all
log4j.logger.com.drkw.swaptradesubscriber=INFO, tradeReadingFile
log4j.logger.com.drkw.tibco=INFO, tibcoMessages

# For stdout use this one:
#log4j.appender.stdout=org.apache.log4j.ConsoleAppender

log4j.appender.tibcoMessages=org.apache.log4j.FileAppender
log4j.appender.tibcoMessages.File=C:/temp/tradeSubscriber-tibco.log
log4j.appender.tibcoMessages.layout=org.apache.log4j.PatternLayout
log4j.appender.tibcoMessages.layout.ConversionPattern=%d{ISO8601} %p %t %c - %m%n
log4j.appender.tibcoMessages.Append=false
log4j.appender.tibcoMessages.Threshold=DEBUG

log4j.appender.tradeReadingFile=org.apache.log4j.FileAppender
log4j.appender.tradeReadingFile.File=C:/temp/tradeSubscriber-load.log
log4j.appender.tradeReadingFile.layout=org.apache.log4j.PatternLayout
log4j.appender.tradeReadingFile.layout.ConversionPattern=%d{ISO8601} %p %t %c - %m%n
log4j.appender.tradeReadingFile.Append=false

log4j.appender.all=org.apache.log4j.FileAppender
log4j.appender.all.File=C:/temp/tradeSubscriber-all.log
log4j.appender.all.layout=org.apache.log4j.PatternLayout
log4j.appender.all.layout.ConversionPattern=%d{ISO8601} %p %t %c - %m%n
log4j.appender.all.Append=false

Multi-threading with JMock

A way to make jmock 'pause' when running a test:

http://www.jmock.org/threading-scheduler.html


DeterministicScheduler scheduler = new DeterministicScheduler();
scheduler.tick(500, TimeUnit.MILLISECONDS);