[Java][Client] Add support for the new Spring RestClient (#18522)

* feat (JAVA SPRING RESTTEMPLATE) 17571: initial commit for Spring RestClient

* feat (JAVA SPRING RESTTEMPLATE) 17571: Copied and changed the webclient mustache files

The RestClient API is oriented on the WebClient API so many parts of the templates can be the same

* fix (JAVA SPRING RESTTEMPLATE) 17571: Renaming error & add README template

The README must be changed because the minimal Java Version for this client is 17

* fix (JAVA SPRING RESTTEMPLATE) 17571: Imports, compile errors and cookie setting

* feat (JAVA SPRING RESTTEMPLATE) 17571: Add generated samples

* test (JAVA SPRING RESTTEMPLATE) 17571: Add tests

* feat (JAVA SPRING RESTTEMPLATE) 17571: Update doc

* Add the restcilent to samples-java-client-jdk17.yam

The minimum Java version of the used Spring Version is 17

* fix (JAVA SPRING RESTTEMPLATE) 17571: Workflow paths to petstore samples

* fix (JAVA SPRING RESTTEMPLATE) 17571: Regenerated samples

* feat (JAVA SPRING RESTTEMPLATE) 17571: Generated echo-api sample for RestClient

* fix (JAVA SPRING RESTTEMPLATE) 17571: Missing import

* fix (JAVA SPRING RESTTEMPLATE) 17571: Missing body class exception when null body is set

* test (JAVA SPRING RESTTEMPLATE) 17571: Add echo-api Auth test

* fix (JAVA SPRING RESTTEMPLATE) 17571: Gradlew file permissions

* feat (JAVA SPRING RESTTEMPLATE) 17571: Reggenerate samples after rebase

* test (JAVA SPRING RESTTEMPLATE) 17571: Add echo-api Body gif test

* test (JAVA SPRING RESTTEMPLATE) 17571: Add echo-api octet stream body test

* test (JAVA SPRING RESTTEMPLATE) 17571: Add echo-api multipart form data test

* fix (JAVA SPRING RESTTEMPLATE) 17571: Form as body when body is null

Also regenerated the restclient samples

Author: Nicklas2751

.github/workflows/samples-java-client-echo-api-jdk17.yaml

@@ -0,0 +1,42 @@
+name: Java Client (Echo API) JDK17
+
+on:
+  push:
+    paths:
+      - samples/client/echo_api/java/restclient
+  pull_request:
+    paths:
+      - samples/client/echo_api/java/restclient
+jobs:
+  build:
+    name: Build Java Client JDK17
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        sample:
+          # clients
+          - samples/client/echo_api/java/restclient
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-java@v4
+        with:
+          distribution: 'temurin'
+          java-version: 17
+      - name: Cache maven dependencies
+        uses: actions/cache@v4
+        env:
+          cache-name: maven-repository
+        with:
+          path: |
+            ~/.m2
+          key: ${{ runner.os }}-${{ github.job }}-${{ env.cache-name }}-${{ hashFiles('**/pom.xml') }}
+      - name: Setup node.js
+        uses: actions/setup-node@v4
+      - name: Run echo server
+        run: |
+          git clone https://github.com/wing328/http-echo-server -b openapi-generator-test-server
+          (cd http-echo-server && npm install && npm start &)
+      - name: Build
+        working-directory: ${{ matrix.sample }}
+        run: mvn clean package

.github/workflows/samples-java-client-jdk17.yaml

@@ -5,10 +5,12 @@ on:
     paths:
       - samples/client/petstore/java/resttemplate-jakarta/**
       - samples/client/petstore/java/webclient-jakarta/**
+      - samples/client/petstore/java/restclient-*/** 
   pull_request:
     paths:
       - samples/client/petstore/java/resttemplate-jakarta/**
       - samples/client/petstore/java/webclient-jakarta/**
+      - samples/client/petstore/java/restclient-*/** 
 jobs:
   build:
     name: Build Java Client JDK17
@@ -20,6 +22,9 @@ jobs:
           # clients
           - samples/client/petstore/java/resttemplate-jakarta
           - samples/client/petstore/java/webclient-jakarta
+          - samples/client/petstore/java/restclient
+          - samples/client/petstore/java/restclient-nullable-arrays
+          - samples/client/petstore/java/restclient-swagger2
     steps:
       - uses: actions/checkout@v4
       - uses: actions/setup-java@v4

bin/configs/java-restclient-echo-api.yaml

@@ -0,0 +1,13 @@
+generatorName: java
+outputDir: samples/client/echo_api/java/restclient
+library: restclient
+inputSpec: modules/openapi-generator/src/test/resources/3_0/echo_api.yaml
+templateDir: modules/openapi-generator/src/main/resources/Java
+additionalProperties:
+  artifactId: echo-api-native
+  hideGenerationTimestamp: "true"
+
+typeMappings:
+  OffsetDateTime: "Instant"
+importMappings:
+  OffsetDateTime: "java.time.Instant"

bin/configs/java-restclient-nullable-array.yaml

@@ -0,0 +1,8 @@
+generatorName: java
+outputDir: samples/client/petstore/java/restclient-nullable-arrays
+library: restclient
+inputSpec: modules/openapi-generator/src/test/resources/3_0/schema-with-nullable-arrays.yaml
+templateDir: modules/openapi-generator/src/main/resources/Java
+additionalProperties:
+  artifactId: petstore-restclient-nullable-arrays
+  hideGenerationTimestamp: "true"

bin/configs/java-restclient-swagger2.yaml

@@ -0,0 +1,10 @@
+generatorName: java
+outputDir: samples/client/petstore/java/restclient-swagger2
+library: restclient
+inputSpec: modules/openapi-generator/src/test/resources/3_0/petstore-with-fake-endpoints-models-for-testing.yaml
+templateDir: modules/openapi-generator/src/main/resources/Java
+additionalProperties:
+  artifactId: petstore-restclient
+  hideGenerationTimestamp: "true"
+  containerDefaultToNull: "true"
+  annotationLibrary: "swagger2"

bin/configs/java-restclient-useAbstractionForFiles.yaml

@@ -0,0 +1,9 @@
+generatorName: java
+outputDir: samples/client/others/java/restclient-useAbstractionForFiles
+library: restclient
+inputSpec: modules/openapi-generator/src/test/resources/3_0/issue13146_file_abstraction_response.yaml
+templateDir: modules/openapi-generator/src/main/resources/Java
+additionalProperties:
+  artifactId: file-restclient
+  hideGenerationTimestamp: "true"
+  useAbstractionForFiles: true

bin/configs/java-restclient.yaml

@@ -0,0 +1,9 @@
+generatorName: java
+outputDir: samples/client/petstore/java/restclient
+library: restclient
+inputSpec: modules/openapi-generator/src/test/resources/3_0/petstore-with-fake-endpoints-models-for-testing.yaml
+templateDir: modules/openapi-generator/src/main/resources/Java
+additionalProperties:
+  artifactId: petstore-restclient
+  hideGenerationTimestamp: "true"
+  containerDefaultToNull: "true"

docs/generators/java.md

@@ -58,7 +58,7 @@ These options may be applied as additional-properties (cli) or configOptions (pl
 |implicitHeadersRegex|Skip header parameters that matches given regex in the generated API methods using @ApiImplicitParams annotation. Note: this parameter is ignored when implicitHeaders=true| |null|
 |invokerPackage|root package for generated code| |org.openapitools.client|
 |legacyDiscriminatorBehavior|Set to false for generators with better support for discriminators. (Python, Java, Go, PowerShell, C# have this enabled by default).|<dl><dt>**true**</dt><dd>The mapping in the discriminator includes descendent schemas that allOf inherit from self and the discriminator mapping schemas in the OAS document.</dd><dt>**false**</dt><dd>The mapping in the discriminator includes any descendent schemas that allOf inherit from self, any oneOf schemas, any anyOf schemas, any x-discriminator-values, and the discriminator mapping schemas in the OAS document AND Codegen validates that oneOf and anyOf schemas contain the required discriminator and throws an error if the discriminator is missing.</dd></dl>|true|
-|library|library template (sub-template) to use|<dl><dt>**jersey2**</dt><dd>HTTP client: Jersey client 2.25.1. JSON processing: Jackson 2.9.x</dd><dt>**jersey3**</dt><dd>HTTP client: Jersey client 3.x. JSON processing: Jackson 2.x</dd><dt>**feign**</dt><dd>HTTP client: OpenFeign 10.x. JSON processing: Jackson 2.9.x. or Gson 2.x</dd><dt>**okhttp-gson**</dt><dd>[DEFAULT] HTTP client: OkHttp 3.x. JSON processing: Gson 2.8.x. Enable Parcelable models on Android using '-DparcelableModel=true'. Enable gzip request encoding using '-DuseGzipFeature=true'.</dd><dt>**retrofit2**</dt><dd>HTTP client: OkHttp 3.x. JSON processing: Gson 2.x (Retrofit 2.3.0). Enable the RxJava adapter using '-DuseRxJava[2/3]=true'. (RxJava 1.x or 2.x or 3.x)</dd><dt>**resttemplate**</dt><dd>HTTP client: Spring RestTemplate 4.x. JSON processing: Jackson 2.9.x</dd><dt>**webclient**</dt><dd>HTTP client: Spring WebClient 5.x. JSON processing: Jackson 2.9.x</dd><dt>**resteasy**</dt><dd>HTTP client: Resteasy client 3.x. JSON processing: Jackson 2.9.x</dd><dt>**vertx**</dt><dd>HTTP client: VertX client 3.x. JSON processing: Jackson 2.9.x</dd><dt>**google-api-client**</dt><dd>HTTP client: Google API client 1.x. JSON processing: Jackson 2.9.x</dd><dt>**rest-assured**</dt><dd>HTTP client: rest-assured : 4.x. JSON processing: Gson 2.x or Jackson 2.10.x. Only for Java 8</dd><dt>**native**</dt><dd>HTTP client: Java native HttpClient. JSON processing: Jackson 2.9.x. Only for Java11+</dd><dt>**microprofile**</dt><dd>HTTP client: Microprofile client 1.x. JSON processing: JSON-B or Jackson 2.9.x</dd><dt>**apache-httpclient**</dt><dd>HTTP client: Apache httpclient 5.x</dd></dl>|okhttp-gson|
+|library|library template (sub-template) to use|<dl><dt>**jersey2**</dt><dd>HTTP client: Jersey client 2.25.1. JSON processing: Jackson 2.9.x</dd><dt>**jersey3**</dt><dd>HTTP client: Jersey client 3.x. JSON processing: Jackson 2.x</dd><dt>**feign**</dt><dd>HTTP client: OpenFeign 10.x. JSON processing: Jackson 2.9.x. or Gson 2.x</dd><dt>**okhttp-gson**</dt><dd>[DEFAULT] HTTP client: OkHttp 3.x. JSON processing: Gson 2.8.x. Enable Parcelable models on Android using '-DparcelableModel=true'. Enable gzip request encoding using '-DuseGzipFeature=true'.</dd><dt>**retrofit2**</dt><dd>HTTP client: OkHttp 3.x. JSON processing: Gson 2.x (Retrofit 2.3.0). Enable the RxJava adapter using '-DuseRxJava[2/3]=true'. (RxJava 1.x or 2.x or 3.x)</dd><dt>**resttemplate**</dt><dd>HTTP client: Spring RestTemplate 4.x. JSON processing: Jackson 2.9.x</dd><dt>**webclient**</dt><dd>HTTP client: Spring WebClient 5.x. JSON processing: Jackson 2.9.x</dd><dt>**restclient**</dt><dd>HTTP client: Spring RestClient 6.1. JSON processing: Jackson 2.9.x</dd><dt>**resteasy**</dt><dd>HTTP client: Resteasy client 3.x. JSON processing: Jackson 2.9.x</dd><dt>**vertx**</dt><dd>HTTP client: VertX client 3.x. JSON processing: Jackson 2.9.x</dd><dt>**google-api-client**</dt><dd>HTTP client: Google API client 1.x. JSON processing: Jackson 2.9.x</dd><dt>**rest-assured**</dt><dd>HTTP client: rest-assured : 4.x. JSON processing: Gson 2.x or Jackson 2.10.x. Only for Java 8</dd><dt>**native**</dt><dd>HTTP client: Java native HttpClient. JSON processing: Jackson 2.9.x. Only for Java11+</dd><dt>**microprofile**</dt><dd>HTTP client: Microprofile client 1.x. JSON processing: JSON-B or Jackson 2.9.x</dd><dt>**apache-httpclient**</dt><dd>HTTP client: Apache httpclient 5.x</dd></dl>|okhttp-gson|
 |licenseName|The name of the license| |Unlicense|
 |licenseUrl|The URL of the license| |http://unlicense.org|
 |microprofileFramework|Framework for microprofile. Possible values &quot;kumuluzee&quot;| |null|
@@ -84,7 +84,7 @@ These options may be applied as additional-properties (cli) or configOptions (pl
 |supportStreaming|Support streaming endpoint (beta)| |false|
 |supportUrlQuery|Generate toUrlQueryString in POJO (default to true). Available on `native`, `apache-httpclient` libraries.| |false|
 |testOutput|Set output folder for models and APIs tests| |${project.build.directory}/generated-test-sources/openapi|
-|useAbstractionForFiles|Use alternative types instead of java.io.File to allow passing bytes without a file on disk. Available on resttemplate, webclient, libraries| |false|
+|useAbstractionForFiles|Use alternative types instead of java.io.File to allow passing bytes without a file on disk. Available on resttemplate, webclient, restclient, libraries| |false|
 |useBeanValidation|Use BeanValidation API annotations| |false|
 |useEnumCaseInsensitive|Use `equalsIgnoreCase` when String for enum comparison| |false|
 |useGzipFeature|Send gzip-encoded requests| |false|

modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/JavaClientCodegen.java

@@ -83,6 +83,7 @@ public class JavaClientCodegen extends AbstractJavaCodegen
     public static final String RESTEASY = "resteasy";
     public static final String RESTTEMPLATE = "resttemplate";
     public static final String WEBCLIENT = "webclient";
+    public static final String RESTCLIENT = "restclient";
     public static final String REST_ASSURED = "rest-assured";
     public static final String RETROFIT_2 = "retrofit2";
     public static final String VERTX = "vertx";
@@ -216,7 +217,7 @@ public JavaClientCodegen() {
         cliOptions.add(CliOption.newBoolean(CASE_INSENSITIVE_RESPONSE_HEADERS, "Make API response's headers case-insensitive. Available on " + OKHTTP_GSON + ", " + JERSEY2 + " libraries"));
         cliOptions.add(CliOption.newString(MICROPROFILE_FRAMEWORK, "Framework for microprofile. Possible values \"kumuluzee\""));
         cliOptions.add(CliOption.newString(MICROPROFILE_MUTINY, "Whether to use async types for microprofile (currently only Smallrye Mutiny is supported)."));
-        cliOptions.add(CliOption.newBoolean(USE_ABSTRACTION_FOR_FILES, "Use alternative types instead of java.io.File to allow passing bytes without a file on disk. Available on resttemplate, webclient, libraries"));
+        cliOptions.add(CliOption.newBoolean(USE_ABSTRACTION_FOR_FILES, "Use alternative types instead of java.io.File to allow passing bytes without a file on disk. Available on resttemplate, webclient, restclient, libraries"));
         cliOptions.add(CliOption.newBoolean(DYNAMIC_OPERATIONS, "Generate operations dynamically at runtime from an OAS", this.dynamicOperations));
         cliOptions.add(CliOption.newBoolean(SUPPORT_STREAMING, "Support streaming endpoint (beta)", this.supportStreaming));
         cliOptions.add(CliOption.newBoolean(CodegenConstants.WITH_AWSV4_SIGNATURE_COMMENT, CodegenConstants.WITH_AWSV4_SIGNATURE_COMMENT_DESC + " (only available for okhttp-gson library)", this.withAWSV4Signature));
@@ -238,6 +239,7 @@ public JavaClientCodegen() {
         supportedLibraries.put(RETROFIT_2, "HTTP client: OkHttp 3.x. JSON processing: Gson 2.x (Retrofit 2.3.0). Enable the RxJava adapter using '-DuseRxJava[2/3]=true'. (RxJava 1.x or 2.x or 3.x)");
         supportedLibraries.put(RESTTEMPLATE, "HTTP client: Spring RestTemplate 4.x. JSON processing: Jackson 2.9.x");
         supportedLibraries.put(WEBCLIENT, "HTTP client: Spring WebClient 5.x. JSON processing: Jackson 2.9.x");
+        supportedLibraries.put(RESTCLIENT, "HTTP client: Spring RestClient 6.1. JSON processing: Jackson 2.9.x");
         supportedLibraries.put(RESTEASY, "HTTP client: Resteasy client 3.x. JSON processing: Jackson 2.9.x");
         supportedLibraries.put(VERTX, "HTTP client: VertX client 3.x. JSON processing: Jackson 2.9.x");
         supportedLibraries.put(GOOGLE_API_CLIENT, "HTTP client: Google API client 1.x. JSON processing: Jackson 2.9.x");
@@ -300,7 +302,7 @@ public void addOperationToGroup(String tag, String resourcePath, Operation opera
 
     @Override
     public void processOpts() {
-        if (WEBCLIENT.equals(getLibrary()) || NATIVE.equals(getLibrary())) {
+        if (WEBCLIENT.equals(getLibrary()) || NATIVE.equals(getLibrary()) || RESTCLIENT.equals(getLibrary())) {
             dateLibrary = "java8";
         } else if (MICROPROFILE.equals(getLibrary())) {
             dateLibrary = "legacy";
@@ -508,7 +510,7 @@ public void processOpts() {
         }
 
         // helper for client library that allow to parse/format java.time.OffsetDateTime or org.threeten.bp.OffsetDateTime
-        if (additionalProperties.containsKey("jsr310") && (isLibrary(WEBCLIENT) || isLibrary(VERTX) || isLibrary(RESTTEMPLATE) || isLibrary(RESTEASY) || isLibrary(MICROPROFILE) || isLibrary(JERSEY2) || isLibrary(JERSEY3) || isLibrary(APACHE))) {
+        if (additionalProperties.containsKey("jsr310") && (isLibrary(WEBCLIENT) || isLibrary(VERTX) || isLibrary(RESTTEMPLATE) || isLibrary(RESTEASY) || isLibrary(MICROPROFILE) || isLibrary(JERSEY2) || isLibrary(JERSEY3) || isLibrary(APACHE) || isLibrary(RESTCLIENT))) {
             supportingFiles.add(new SupportingFile("JavaTimeFormatter.mustache", invokerFolder, "JavaTimeFormatter.java"));
         }
 
@@ -556,7 +558,7 @@ public void processOpts() {
             reservedWords.remove("file");
         }
 
-        if (!(FEIGN.equals(getLibrary()) || RESTTEMPLATE.equals(getLibrary()) || RETROFIT_2.equals(getLibrary()) || GOOGLE_API_CLIENT.equals(getLibrary()) || REST_ASSURED.equals(getLibrary()) || WEBCLIENT.equals(getLibrary()) || MICROPROFILE.equals(getLibrary()))) {
+        if (!(FEIGN.equals(getLibrary()) || RESTTEMPLATE.equals(getLibrary()) || RETROFIT_2.equals(getLibrary()) || GOOGLE_API_CLIENT.equals(getLibrary()) || REST_ASSURED.equals(getLibrary()) || WEBCLIENT.equals(getLibrary()) || MICROPROFILE.equals(getLibrary()) || RESTCLIENT.equals(getLibrary()))) {
             supportingFiles.add(new SupportingFile("apiException.mustache", invokerFolder, "ApiException.java"));
             supportingFiles.add(new SupportingFile("Configuration.mustache", invokerFolder, "Configuration.java"));
             supportingFiles.add(new SupportingFile("Pair.mustache", invokerFolder, "Pair.java"));
@@ -659,6 +661,9 @@ public void processOpts() {
             supportingFiles.add(new SupportingFile("auth/Authentication.mustache", authFolder, "Authentication.java"));
         } else if (WEBCLIENT.equals(getLibrary())) {
             forceSerializationLibrary(SERIALIZATION_LIBRARY_JACKSON);
+        } else if (RESTCLIENT.equals(getLibrary())) {
+            forceSerializationLibrary(SERIALIZATION_LIBRARY_JACKSON);
+            applyJakartaPackage();
         } else if (VERTX.equals(getLibrary())) {
             typeMapping.put("file", "AsyncFile");
             importMapping.put("AsyncFile", "io.vertx.core.file.AsyncFile");