Bypass conversion when possible [SPR-9566]

[spring-projects-issues]

Gary Russell opened SPR-9566 and commented

1. A Map<?,?> that doesn't need conversion and does not have a no-arg constructor causes execution failure (works in 3.0). (INT-2630)
2. A large byte[] is unnecessarily copied, causing high cpu utilization (not copied in 3.0). (INT-2650).

A simple example showing #2 is provided in spring-framework-issues is shown here (to-be-supplied).

The parameter 'argumentsRequiringConversion' to ReflectionUtils.convertArguments is completely ignored.

Before reading #13163, I tried "fixing" this method, as shown here (to-be-supplied). This fixed the problem, but broke ExpressionTestsUsingCoreConversionService.testConvert, because the logic in ReflectiveMethodResolver.resolve, for the test case that fails (with my patch to ReflectionHelper), considers "Collection<String> foos" a "close match" to the parameter in the method

public void setFoos(Collection<Foo> foos)

which results in argumentsRequiringConversion being null. Seems to me this shouldn't be a CLOSE match, but a REQUIRES_CONVERSION match, in which case my suggested fix to ReflectionUtils would work.

We can work around these issues in Spring Integration, but the core issue remains.

---

Affects: 3.1.1

Reference URL: http://forum.springsource.org/showthread.php?127694-TCP-Endpoint-binary-incoming-transfer-high-cpu-load

Issue Links:

• Refactor GenericConversionService [SPR-9927] #14560 Refactor GenericConversionService ("depends on")
• INT-2650 TCP Endpoint - using SpEL in Spring 3.1 to convert byte[] to byte[] - high cpu load and handle time delay
• INT-2630 Unable to convert MessageHistory, MessageHeaders via bundled converters.

[spring-projects-issues]

Gary Russell commented

I don't have edit permissions:

repro PR: spring-attic/spring-framework-issues#27

My ReflectionHelper patch that "fixes" the problem, but breaks core tests is here garyrussell@9733431 (in my #14200 branch),

[spring-projects-issues]

Phil Webb commented

#132

[spring-projects-issues]

Chris Beams commented

commit a27d1a28ffb69aed618869d3815a3af7120effa2
Author: Phillip Webb <pwebb@vmware.com>
Commit: Chris Beams <cbeams@vmware.com>

    Bypass conversion when possible
    
    Prior to this commit conversion between like types would often result in
    a copy of the object. This can be problematic in the case of large byte
    arrays and objects that do not have a default constructor.
    
    The ConversionService SPI now includes canBypassConvert methods that can
    be used to deduce when conversion is not needed. Several existing
    converters have been updated to ensure they only apply when source and
    target types differ.
    
    This change introduces new methods to the ConversionService that will
    break existing implementations. However, it anticipated that most users
    are consuming the ConversionService interface rather then extending it.
    
    Issue: SPR-9566

[spring-projects-issues]

Phil Webb commented

Reopened following review as we do not want the ConversionService SPI to change.