[java-micronaut] Support Optional for non-required properties (OpenAPITools#12144)

The Micronaut generator by default adds the @nullable annotation to
non-required properties and allows using the Jackson JsonNullable
wrapper but it is not possible to use java.util.Optional as a wrapper
for optional properties.

This change adds support for using the Optional wrapper for non-required
properties.

Author: auke-

docs/generators/java-micronaut-client.md

@@ -72,6 +72,7 @@ These options may be applied as additional-properties (cli) or configOptions (pl
 |testOutput|Set output folder for models and APIs tests| |${project.build.directory}/generated-test-sources/openapi|
 |title|Client service name| |null|
 |useBeanValidation|Use BeanValidation API annotations| |true|
+|useOptional|Use Optional container for optional parameters| |false|
 |withXml|whether to include support for application/xml content type and include XML annotations in the model (works with libraries that provide support for JSON and XML)| |false|
 
 ## SUPPORTED VENDOR EXTENSIONS

docs/generators/java-micronaut-server.md

@@ -74,6 +74,7 @@ These options may be applied as additional-properties (cli) or configOptions (pl
 |title|Client service name| |null|
 |useAuth|Whether to import authorization and to annotate controller methods accordingly| |true|
 |useBeanValidation|Use BeanValidation API annotations| |true|
+|useOptional|Use Optional container for optional parameters| |false|
 |withXml|whether to include support for application/xml content type and include XML annotations in the model (works with libraries that provide support for JSON and XML)| |false|
 
 ## SUPPORTED VENDOR EXTENSIONS

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

@@ -3,6 +3,7 @@
 import org.apache.commons.lang3.StringUtils;
 import org.openapitools.codegen.*;
 import org.openapitools.codegen.languages.features.BeanValidationFeatures;
+import org.openapitools.codegen.languages.features.OptionalFeatures;
 import org.openapitools.codegen.meta.features.DocumentationFeature;
 import org.openapitools.codegen.meta.features.SecurityFeature;
 import org.openapitools.codegen.model.ModelMap;
@@ -15,7 +16,7 @@
 
 import static org.openapitools.codegen.CodegenConstants.INVOKER_PACKAGE;
 
-public abstract class JavaMicronautAbstractCodegen extends AbstractJavaCodegen implements BeanValidationFeatures {
+public abstract class JavaMicronautAbstractCodegen extends AbstractJavaCodegen implements BeanValidationFeatures, OptionalFeatures {
     public static final String OPT_TITLE = "title";
     public static final String OPT_BUILD = "build";
     public static final String OPT_BUILD_GRADLE = "gradle";
@@ -34,6 +35,7 @@ public abstract class JavaMicronautAbstractCodegen extends AbstractJavaCodegen i
 
     protected String title;
     protected boolean useBeanValidation;
+    protected boolean useOptional;
     protected String buildTool;
     protected String testTool;
     protected boolean requiredPropertiesInConstructor = true;
@@ -52,6 +54,7 @@ public JavaMicronautAbstractCodegen() {
 
         // Set all the fields
         useBeanValidation = true;
+        useOptional = false;
         buildTool = OPT_BUILD_ALL;
         testTool = OPT_TEST_JUNIT;
         outputFolder = "generated-code/java-micronaut-client";
@@ -95,6 +98,7 @@ public JavaMicronautAbstractCodegen() {
         cliOptions.add(new CliOption(OPT_TITLE, "Client service name").defaultValue(title));
         cliOptions.add(new CliOption(OPT_MICRONAUT_VERSION, "Micronaut version, only >=3.0.0 versions are supported").defaultValue(micronautVersion));
         cliOptions.add(CliOption.newBoolean(USE_BEANVALIDATION, "Use BeanValidation API annotations", useBeanValidation));
+        cliOptions.add(CliOption.newBoolean(USE_OPTIONAL, "Use Optional container for optional parameters", useOptional));
         cliOptions.add(CliOption.newBoolean(OPT_REQUIRED_PROPERTIES_IN_CONSTRUCTOR, "Allow only to create models with all the required properties provided in constructor", requiredPropertiesInConstructor));
 
         CliOption buildToolOption = new CliOption(OPT_BUILD, "Specify for which build tool to generate files").defaultValue(buildTool);
@@ -158,6 +162,11 @@ public void processOpts() {
         }
         writePropertyBack(USE_BEANVALIDATION, useBeanValidation);
 
+        if (additionalProperties.containsKey(USE_OPTIONAL)) {
+            this.setUseOptional(convertPropertyToBoolean(USE_OPTIONAL));
+        }
+        writePropertyBack(USE_OPTIONAL, useOptional);
+
         if (additionalProperties.containsKey(OPT_REQUIRED_PROPERTIES_IN_CONSTRUCTOR)) {
             this.requiredPropertiesInConstructor = convertPropertyToBoolean(OPT_REQUIRED_PROPERTIES_IN_CONSTRUCTOR);
         }
@@ -306,6 +315,11 @@ public void setUseBeanValidation(boolean useBeanValidation) {
         this.useBeanValidation = useBeanValidation;
     }
 
+    @Override
+    public void setUseOptional(boolean useOptional) {
+        this.useOptional = useOptional;
+    }
+
     @Override
     public String toApiVarName(String name) {
         String apiVarName = super.toApiVarName(name);
@@ -319,6 +333,10 @@ public boolean isUseBeanValidation() {
         return useBeanValidation;
     }
 
+    public boolean isUseOptional() {
+        return useOptional;
+    }
+
     @Override
     public OperationsMap postProcessOperationsWithModels(OperationsMap objs, List<ModelMap> allModels) {
         objs = super.postProcessOperationsWithModels(objs, allModels);

modules/openapi-generator/src/main/resources/java-micronaut/common/model/beanValidation.mustache

@@ -5,8 +5,8 @@ validate all pojos and enums
 nullable & nonnull
 }}{{#required}}{{#isNullable}}    @Nullable
 {{/isNullable}}{{^isNullable}}    @NotNull
-{{/isNullable}}{{/required}}{{^required}}    @Nullable
-{{/required}}{{!
+{{/isNullable}}{{/required}}{{^required}}{{^useOptional}}    @Nullable
+{{/useOptional}}{{/required}}{{!
 pattern
 }}{{#pattern}}{{^isByteArray}}    @Pattern(regexp="{{{pattern}}}")
 {{/isByteArray}}{{/pattern}}{{!

modules/openapi-generator/src/main/resources/java-micronaut/common/model/model.mustache

@@ -7,6 +7,9 @@ import org.apache.commons.lang3.builder.HashCodeBuilder;
 {{/useReflectionEqualsHashCode}}
 import java.util.Objects;
 import java.util.Arrays;
+{{#useOptional}}
+import java.util.Optional;
+{{/useOptional}}
 {{#imports}}
 import {{import}};
 {{/imports}}

modules/openapi-generator/src/main/resources/java-micronaut/common/model/pojo.mustache

@@ -186,7 +186,7 @@ Declare the class with extends and implements
         {{/vendorExtensions.x-is-jackson-optional-nullable}}
         {{^vendorExtensions.x-is-jackson-optional-nullable}}
             {{#jackson}}
-{{>common/model/jackson_annotations}}{{/jackson}}{{/vendorExtensions.x-is-jackson-optional-nullable}}       public {{{datatypeWithEnum}}} {{getter}}() {
+{{>common/model/jackson_annotations}}{{/jackson}}{{/vendorExtensions.x-is-jackson-optional-nullable}}    public {{#useOptional}}{{^required}}Optional<{{/required}}{{/useOptional}}{{{datatypeWithEnum}}}{{#useOptional}}{{^required}}>{{/required}}{{/useOptional}} {{getter}}() {
         {{#vendorExtensions.x-is-jackson-optional-nullable}}
             {{#isReadOnly}}
 {{! A readonly attribute doesn't have setter => jackson will set null directly if explicitly returned by API, so make sure we have an empty JsonNullable}}    if ({{name}} == null) {
@@ -196,7 +196,17 @@ Declare the class with extends and implements
         return {{name}}.orElse(null);
         {{/vendorExtensions.x-is-jackson-optional-nullable}}
         {{^vendorExtensions.x-is-jackson-optional-nullable}}
+          {{#useOptional}}
+            {{#required}}
         return {{name}};
+            {{/required}}
+            {{^required}}
+        return Optional.ofNullable({{name}});
+            {{/required}}
+          {{/useOptional}}
+          {{^useOptional}}
+        return {{name}};
+          {{/useOptional}}
         {{/vendorExtensions.x-is-jackson-optional-nullable}}
     }