[Java][WebClient][RestClient] Standardize useAbstractionForFiles behavior to use Resource interface

[Nawrok]

This PR updates the webclient and restclient Java generators to use Spring's org.springframework.core.io.Resource interface instead of AbstractResource when using useAbstractionForFiles property. This standardizes the file handling abstraction across all Spring-based HTTP clients, aligning them with the resttemplate implementation.

Fixes #23381

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---

Summary by cubic

Standardized file handling for Java webclient and restclient generators by using Spring’s org.springframework.core.io.Resource (instead of org.springframework.core.io.AbstractResource) when useAbstractionForFiles is enabled, matching resttemplate. Fixes #23381.

• Refactors

  • Replace org.springframework.core.io.AbstractResource with org.springframework.core.io.Resource for file parameters (single and collections) in webclient and restclient templates.
  • Update tests (re-enable WebClient case) and add samples/client/others/java/restclient-useAbstractionForFiles to the JDK17 workflow matrix.

• Migration

  • No changes required for most users. Code using AbstractResource can be passed to APIs expecting Resource. Recompile generated clients.

^{Written for commit cbf9c69. Summary will update on new commits.}

[cubic-dev-ai]

1 issue found across 8 files

Prompt for AI agents (unresolved issues)

Check if these issues are valid — if so, understand the root cause of each and fix them. If appropriate, use sub-agents to investigate and fix each issue separately.


<file name="modules/openapi-generator/src/main/resources/Java/libraries/restclient/single_request_parameter.mustache">

<violation number="1" location="modules/openapi-generator/src/main/resources/Java/libraries/restclient/single_request_parameter.mustache:5">
P2: Changing public collection parameter types from `Collection<AbstractResource>` to `Collection<Resource>` introduces a source-compatibility break for existing callers due to Java generic invariance.</violation>
</file>

_{Reply with feedback, questions, or to request a fix. Tag @cubic-dev-ai to re-run a review.}

[cubic-dev-ai]

P2: Changing public collection parameter types from Collection<AbstractResource> to Collection<Resource> introduces a source-compatibility break for existing callers due to Java generic invariance.

Prompt for AI agents

Check if this issue is valid — if so, understand the root cause and fix it. At modules/openapi-generator/src/main/resources/Java/libraries/restclient/single_request_parameter.mustache, line 5:

<comment>Changing public collection parameter types from `Collection<AbstractResource>` to `Collection<Resource>` introduces a source-compatibility break for existing callers due to Java generic invariance.</comment>

<file context>
@@ -2,27 +2,27 @@
 
     {{^staticRequest}}
-    public record {{#lambda.titlecase}}{{operationId}}{{/lambda.titlecase}}Request({{#allParams}}{{#isFile}}{{#useAbstractionForFiles}}{{#collectionFormat}}java.util.Collection<org.springframework.core.io.AbstractResource>{{/collectionFormat}}{{^collectionFormat}}org.springframework.core.io.AbstractResource{{/collectionFormat}}{{/useAbstractionForFiles}}{{^useAbstractionForFiles}}{{>nullable_var_annotations}} {{{dataType}}}{{/useAbstractionForFiles}}{{/isFile}}{{^isFile}}{{>nullable_var_annotations}} {{{dataType}}}{{/isFile}} {{paramName}}{{^-last}}, {{/-last}}{{/allParams}}){}
+    public record {{#lambda.titlecase}}{{operationId}}{{/lambda.titlecase}}Request({{#allParams}}{{#isFile}}{{#useAbstractionForFiles}}{{#collectionFormat}}java.util.Collection<org.springframework.core.io.Resource>{{/collectionFormat}}{{^collectionFormat}}org.springframework.core.io.Resource{{/collectionFormat}}{{/useAbstractionForFiles}}{{^useAbstractionForFiles}}{{>nullable_var_annotations}} {{{dataType}}}{{/useAbstractionForFiles}}{{/isFile}}{{^isFile}}{{>nullable_var_annotations}} {{{dataType}}}{{/isFile}} {{paramName}}{{^-last}}, {{/-last}}{{/allParams}}){}
     {{/staticRequest}}
     {{#staticRequest}}
</file context>

[Nawrok]

That is a valid point regarding the source-compatibility break caused by Java's generic invariance.

A backward-compatible solution would be to use an upper bound wildcard Collection<? extends Resource>. However, to keep the generated API unified across all Spring-based HTTP clients, we would need to apply this wildcard approach to all generators. This means we would also need to modify the resttemplate generator, which currently uses Collection<Resource> without wildcards.

We have two options: accept the breaking change here to align webclient and restclient with the current resttemplate implementation, or update all of them to use upper bounds.

What is the preferred direction for the project?