Spring 7 WebClient Compatibility

[legion47T]

As addressed in #21628 Spring Framework 7 changes the HttpHeader type in a way that's not compatible with the current Spring WebClient ApiClient code generated by OpenAPI.
This PR adapts the changes from #21691 for WebClient.

The new HttpHeader methods become available with Spring Boot 3.2, which is why I updated from 3.0.12 to 3.2.12.

Similar to mentioned PR one can verify operation with

1. Generate a PetStore project with webclient for JakartaEE
2. Run integration-tests (mvn integration-test -f samples/client/petstore/java/webclient-jakarta/pom.xml)
3. Modify the project to use Spring Boot 4.0.0-M3 instead
4. Rerun integration tests

Unfortunately I wasn't able to run more than the integration tests, i.e. I did not spin up an actual server yet.

Mentioning Java Spring committee members: @cachescrubber , @welshm , @MelleD , @atextor , @manedev79 , @javisst , @borsch , @banlevente , @Zomzog , @martin-mfg

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  ./mvnw clean package || exit
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[wing328]

Thanks for the PR.

2. Run integration-tests (mvn integration-test -f samples/client/petstore/java/webclient-jakarta/pom.xml)
3. Modify the project to use Spring Boot 4.0.0-M3 instead

I ran the above against the master but the result is green (project compiles).

Am I supposed to get errors or the issues only occur during runtime?

[legion47T]

This should be a compile time error.

When I

1. replace <spring-boot-version>3.0.12</spring-boot-version> with <spring-boot-version>4.0.0-M3</spring-boot-version> in samples/client/petstore/java/webclient-jakarta/pom.xml and
2. execute mvn clean integration-test -f samples/client/petstore/java/webclient-jakarta/

I get

[ERROR] COMPILATION ERROR :
[INFO] -------------------------------------------------------------
[ERROR] /C:/Users/<user>/dev/projects/openapi-generator/samples/client/petstore/java/webclient-jakarta/src/main/java/org/openapitools/client/ApiClient.java:[349,27] Symbol nicht gefunden
  Symbol: Methode containsKey(java.lang.String)
  Ort: Variable defaultHeaders von Typ org.springframework.http.HttpHeaders
[ERROR] /C:/Users/<user>/dev/projects/openapi-generator/samples/client/petstore/java/webclient-jakarta/src/main/java/org/openapitools/client/ApiClient.java:[729,57] Symbol nicht gefunden
  Symbol: Methode entrySet()
  Ort: Variable headers von Typ org.springframework.http.HttpHeaders
[INFO] 2 errors

[wing328]

still no luck. it compiles fine:

[INFO]
[INFO] --- jar:3.3.0:jar (default-jar) @ petstore-webclient ---
[INFO] Building jar: C:\Users\wing3\Code\openapi-generator\samples\client\petstore\java\webclient-jakarta\target\petstore-webclient-1.0.0.jar
[INFO]
[INFO] --- source:3.3.1:jar-no-fork (attach-sources) @ petstore-webclient ---
[INFO] Building jar: C:\Users\wing3\Code\openapi-generator\samples\client\petstore\java\webclient-jakarta\target\petstore-webclient-1.0.0-sources.jar
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time:  13.664 s
[INFO] Finished at: 2025-10-06T16:53:39+08:00
[INFO] ------------------------------------------------------------------------
[INFO] 7 goals, 7 executed
[INFO]
[INFO] Publishing build scan...
[INFO] https://ge.openapi-generator.tech/s/awruj67pjmpgw
[INFO]

wing3@MSI MINGW64 ~/Code/openapi-generator (master)
$ git diff
diff --git a/samples/client/petstore/java/webclient-jakarta/pom.xml b/samples/client/petstore/java/webclient-jakarta/pom.xml
index 695f884ed60..ef2fa1939e9 100644
--- a/samples/client/petstore/java/webclient-jakarta/pom.xml
+++ b/samples/client/petstore/java/webclient-jakarta/pom.xml
@@ -123,7 +123,7 @@
         <jackson-version>2.19.2</jackson-version>
         <jackson-databind-version>2.19.2</jackson-databind-version>
         <jackson-databind-nullable-version>0.2.7</jackson-databind-nullable-version>
-        <spring-boot-version>3.0.12</spring-boot-version>
+        <spring-boot-version>4.0.0-M3</spring-boot-version>
         <jakarta-annotation-version>2.1.1</jakarta-annotation-version>
         <reactor-version>3.5.12</reactor-version>
         <reactor-netty-version>1.2.8</reactor-netty-version>

wing3@MSI MINGW64 ~/Code/openapi-generator (master)

I'm using JDK17 (on Windows). Not sure if it matters.

[legion47T]

I'm on 24. I'll test whether that makes a difference, but I'd be surprised honestly.
Spring Framework removed the necessary interface from the class, so it shouldn't compile irrespecitve of the Java version.

[legion47T]

Java 17 behaves identically.

[legion47T]

If I read your build correctly it seems you did not clean before testing. I would assume the JAR you're testing against is still depending on Spring Boot 3 and Maven didn't see the need for a rebuild to resolve against Spring Boot 4.

[wing328]

Ah you're right. Now I can reproduce the issue and able to confirm your fix addressed the compilation errors.

Thanks for the contribution. Let's give it a try