HttpMessageConverter read and write methods have restrictive type annotations [SPR-6848]

[spring-projects-issues]

Alex Antonov opened SPR-6848 and commented

When trying to implement a HttpMessageConverter for Google Protocol Buffers I've run into a limitation by the write and read method signatures that require an exact type T.
With Protocol Buffers, as with many other types of marshaling systems, there is a base class, Message in this case, that all exact classes extend or implement.
canRead and canWrite methods do declare the relaxed and appropriate signature of <? extends T>, however in the read and write methods its being set to exactly T.

This prevents of calling the converter's write and read methods with passing an implementation of Message as an argument, since it does not conform to the generic restrictions set forth by the interfaces.

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Affects: 3.0 GA

Issue Links:

• HttpMessageConverter should accept Class<? extends T> on can read [SPR-6771] #11437 HttpMessageConverter should accept Class<? extends T> on can read

Referenced from: commits 4ae1709

[spring-projects-issues]

Juergen Hoeller commented

Arjen, this is worth a quick look before we proceed with the 3.0.1 release: Since we relaxed the canRead and canWrite signatures for 3.0.1 already, we might also take this into account still.

Juergen

[spring-projects-issues]

Juergen Hoeller commented

We've relaxed read's Class parameter to:

T read(Class<? extends T> clazz, HttpInputMessage inputMessage)

This allows for specifying subtypes for reading as well, not just for writing (where it's already possibly to pass a subtype instance to the write method).

Note that the canRead and canWrite signatures have already been relaxed as part of #11437, fixed for the Spring 3.0.1 release as well.

This will be available in tonight's 3.0.1 snapshot (586). Feel free to give it an early try!

Juergen

[spring-projects-issues]

Alex Antonov commented

Juergen, thanks for the quick turn-around. I've given it a try and it works as expected.
Would SpringSource be interested in the code donation for the Google Protocol Buffers HttpMessageConverter to be included in the next Spring release (as proposed in earlier #10927)?