Improve Registration.getSortedObjectLinks performance

[lhotari]

Leshan 1.0.0-M9

Current behaviour:
When using the Leshan Demo server, there are a lot of this type of exceptions when there are a lot of registrations:

java.lang.NumberFormatException.<init>(String)
at java.lang.NumberFormatException.forInputString(String)
at java.lang.Integer.parseInt(String, int)
at java.lang.Integer.parseInt(String)
at org.eclipse.leshan.server.registration.Registration.isNumber(String)
at org.eclipse.leshan.server.registration.Registration.access$000(String)
at org.eclipse.leshan.server.registration.Registration$1.compare(Link, Link)
at org.eclipse.leshan.server.registration.Registration$1.compare(Object, Object)
at java.util.TimSort.countRunAndMakeAscending(Object[], int, int, Comparator)
at java.util.TimSort.sort(Object[], int, int, Comparator, Object[], int, int)
at java.util.Arrays.sort(Object[], Comparator)
at org.eclipse.leshan.server.registration.Registration.getSortedObjectLinks()
at org.eclipse.leshan.server.demo.servlet.json.RegistrationSerializer.serialize(Registration, Type, JsonSerializationContext)
at org.eclipse.leshan.server.demo.servlet.json.RegistrationSerializer.serialize(Object, Type, JsonSerializationContext)

originating from https://github.com/eclipse/leshan/blob/e438d749ba997abb63ed49504ada17cde1240c1e/leshan-server-demo/src/main/java/org/eclipse/leshan/server/demo/servlet/EventServlet.java#L85

Expected behaviour:
Normal operations shouldn't create a large number of exceptions. It seems that Registration.isNumber could be improved so that it doesn't throw exceptions. A good example for a better approach is the one in Commons Lang StringUtils.isNumeric

[sbernard31]

Demo is just a demo. We don't aim to handle a lot of registrations.

Anyway, the fix proposed sounds good.

I made some bench ...

Benchmark                         Mode  Cnt         Score         Error  Units
IsNumericTest.testIsNumber       thrpt    3  26590429,681 ± 2885084,088  ops/s
IsNumericTest.testIsNumberFail   thrpt    3  26459725,741 ±  412815,205  ops/s
IsNumericTest.testIsNumeric      thrpt    3  41837663,625 ±  490409,437  ops/s
IsNumericTest.testIsNumericFail  thrpt    3  41675654,458 ±  663382,727  ops/s

... and write a PR about that : #506
Could you confirm this behave better ?

[lhotari]

LGTM , thank you @sbernard31

[sbernard31]

Integrated in master. (commit e57c417)