CollectionToCollectionConverter.convert() improvement for untyped collections [SPR-11479]

[spring-projects-issues]

Gary Russell opened SPR-11479 and commented

Consider

• source : ArrayList
• sourceType : java.util.ArrayList<?>
• targetType : java.util.Collection<?>

Line #63...

https://github.com/spring-projects/spring-framework/blob/master/spring-core/src/main/java/org/springframework/core/convert/support/CollectionToCollectionConverter.java#L63

...determines that copyRequired == false .

However, line 70 then proceeds to copy the elements from the source to the target, which is eventually discarded, when line #84 simply returns the source.

It looks to me like it should have

if (copyRequired) {} 
``` around the for loop. The else clause needs to run, in case `copyRequired` gets changed to true.

---

Affects: 3.2.8, 4.0.2

Issue Links:

• INT-3306 Aggregator memory usage raises serious performance issue

Referenced from: commits bea94d5, d317b63

Backported to: 3.2.9

[spring-projects-issues]

Stéphane Nicoll commented

See PR: #483

[spring-projects-issues]

Juergen Hoeller commented

I've taken the tests from the pull request but eventually opted for a different implementation in CollectionToCollectionConverter, avoiding a collection copy for an untyped collection in the first place, and also avoiding repeated getElementTypeDescriptor calls (since that one re-introspects on every call).

The implementation also uses addAll instead of iteration over an untyped collection now, supporting a potentially optimized addAll implementation in the target collection type. No idea why that wasn't done years ago...

I've scheduled this for backporting to 3.2.9 as well, since the old behavior is suboptimal enough to become a performance concern in demanding scenarios with lots of on-the-fly collection conversions.

Juergen