Swagger Codegen (with maven plugin) for OpenAPI 3.0 - maven

Question

I want to use Swagger Codegen for OpenAPI 3.0 YAML file. And I see Swagger Codegen 3.0.0-rc0 is available. But when I try to use that I run into issues. Following are the details:
My pom.xml file with swagger-codegen plugin:
<plugin>
<groupId>io.swagger</groupId>
<artifactId>swagger-codegen-maven-plugin</artifactId>
<version>3.0.0-rc0</version>
<executions>
<execution>
<goals>
<goal>generate</goal>
</goals>
<configuration>
<inputSpec>${basedir}/src/main/resources/mySpec.yaml</inputSpec>
<output>target/generated-sources</output>
<language>spring</language>
<generateApis>false</generateApis>
<modelPackage>com.kj.model</modelPackage>
<apiPackage>com.kj</apiPackage>
<configOptions>
<sourceFolder>swagger</sourceFolder>
<library>spring-mvc</library>
<interfaceOnly>true</interfaceOnly>
<useBeanValidation>true</useBeanValidation>
<dateLibrary>java8</dateLibrary>
<java8>true</java8>
</configOptions>
</configuration>
</execution>
</executions>
</plugin>
With the above plugin when I run the maven build, I got this ServiceConfigurationError, here is the stack trace:
Exception in thread "main" java.util.ServiceConfigurationError: io.swagger.codegen.CodegenConfig: Provider io.swagger.codegen.languages.java.JavaClientCodegen not found
at java.util.ServiceLoader.fail(ServiceLoader.java:239)
at java.util.ServiceLoader.access$300(ServiceLoader.java:185)
at java.util.ServiceLoader$LazyIterator.nextService(ServiceLoader.java:372)
at java.util.ServiceLoader$LazyIterator.next(ServiceLoader.java:404)
at java.util.ServiceLoader$1.next(ServiceLoader.java:480)
at io.swagger.codegen.CodegenConfigLoader.forName(CodegenConfigLoader.java:19)
at io.swagger.codegen.config.CodegenConfigurator.toClientOptInput(CodegenConfigurator.java:392)
at io.swagger.codegen.plugin.CodeGenMojo.execute(CodeGenMojo.java:512)
at org.apache.maven.plugin.DefaultBuildPluginManager.executeMojo(DefaultBuildPluginManager.java:134)
In order to fix this I added swagger-codegen-generators dependency within the maven plugin section of pom file:
<dependencies>
<dependency>
<groupId>io.swagger</groupId>
<artifactId>swagger-codegen-generators</artifactId>
<version>1.0.0-SNAPSHOT</version>
</dependency>
</dependencies>
So with this earlier mentioned issue got resolved but now I see this NPE
java.lang.NullPointerException
at io.swagger.codegen.languages.SpringCodegen.preprocessOpenAPI(SpringCodegen.java:429)
at io.swagger.codegen.DefaultGenerator.configureGeneratorProperties(DefaultGenerator.java:199)
at io.swagger.codegen.DefaultGenerator.generate(DefaultGenerator.java:716)
at io.swagger.codegen.plugin.CodeGenMojo.execute(CodeGenMojo.java:534)
at org.apache.maven.plugin.DefaultBuildPluginManager.executeMojo(DefaultBuildPluginManager.java:134)
at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:208)
at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:154)
at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:146)
at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject(LifecycleModuleBuilder.java:117)
As you would have noted already that I am using <language>spring</language> and <library>spring-mvc</library>. Please let me know if codegen has worked for someone for 3.0.0-rc0 with these configurations.
Note: I looked at this old post which is similar but at that time 3.0.0-rc0 was not available.

Answer 1

To use Swagger Codegen with Maven plug-in for OpenAPI 3.0.0 spec, you may consider using OpenAPI Generator instead (which is a community-driven version of Swagger Codegen).
<dependency>
<groupId>org.openapitools</groupId>
<artifactId>openapi-generator-maven-plugin</artifactId>
<version>3.3.4</version>
</dependency>
Ref: https://github.com/OpenAPITools/openapi-generator#12---artifacts-on-maven-central
(please refer to the Q&A on why we forked Swagger Codegen)

Answer 2

The v3 swagger codegen maven plugin released April 2019 generates working Java client libraries from an OpenAPI 3.0 spec, I'm using this Maven pom.xml plugin config:
<plugin>
<groupId>io.swagger.codegen.v3</groupId>
<artifactId>swagger-codegen-maven-plugin</artifactId>
<version>3.0.8</version>
<executions>
..
All the rest of the configuration and configOptions entries are unchanged from version 2.4.5. I had to replace the old annotation dependency with the following so the client code would compile:
<dependency>
<groupId>io.swagger.core.v3</groupId>
<artifactId>swagger-annotations</artifactId>
<version>2.0.8</version>
</dependency>
Per request from #kozla13 below I added a complete POM example.
<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
<modelVersion>4.0.0</modelVersion>
<!-- This groupId will NOT allow deployment in LF -->
<groupId>org.example.swaggerapi.client</groupId>
<artifactId>swagger-client</artifactId>
<name>Example</name>
<version>0.0.1-SNAPSHOT</version>
<properties>
<java.version>11</java.version>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
<client.base.package.name>org.example.so</client.base.package.name>
</properties>
<dependencies>
<!-- Required for Java 9 and later -->
<dependency>
<groupId>javax.annotation</groupId>
<artifactId>javax.annotation-api</artifactId>
<version>1.3.2</version>
</dependency>
<dependency>
<groupId>io.swagger.core.v3</groupId>
<artifactId>swagger-annotations</artifactId>
<version>2.0.8</version>
</dependency>
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-context</artifactId>
<version>5.1.10.RELEASE</version>
</dependency>
<!-- HTTP client: Spring RestTemplate -->
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-web</artifactId>
<version>5.1.10.RELEASE</version>
</dependency>
<!-- JSON processing: jackson -->
<dependency>
<groupId>com.fasterxml.jackson.core</groupId>
<artifactId>jackson-core</artifactId>
<version>2.9.9</version>
</dependency>
<dependency>
<groupId>com.fasterxml.jackson.core</groupId>
<artifactId>jackson-annotations</artifactId>
<version>2.9.0</version>
</dependency>
<dependency>
<groupId>com.fasterxml.jackson.core</groupId>
<artifactId>jackson-databind</artifactId>
<version>2.9.9.3</version>
</dependency>
<dependency>
<groupId>com.fasterxml.jackson.jaxrs</groupId>
<artifactId>jackson-jaxrs-json-provider</artifactId>
<version>2.9.9</version>
</dependency>
<dependency>
<groupId>com.fasterxml.jackson.datatype</groupId>
<artifactId>jackson-datatype-jsr310</artifactId>
<version>2.9.9</version>
</dependency>
<!-- test dependencies -->
<dependency>
<groupId>org.junit.jupiter</groupId>
<artifactId>junit-jupiter-api</artifactId>
<version>5.3.2</version>
<scope>test</scope>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<!-- This 2019 version is required for OpenAPI 3 -->
<groupId>io.swagger.codegen.v3</groupId>
<artifactId>swagger-codegen-maven-plugin</artifactId>
<version>3.0.8</version>
<executions>
<execution>
<goals>
<goal>generate</goal>
</goals>
<configuration>
<inputSpec>${project.basedir}/ric-plt-a1/a1/openapi.yaml</inputSpec>
<language>java</language>
<packageName>${client.base.package.name}</packageName>
<modelPackage>${client.base.package.name}.model</modelPackage>
<apiPackage>${client.base.package.name}.api</apiPackage>
<invokerPackage>${client.base.package.name}.invoker</invokerPackage>
<configOptions>
<groupId>${project.groupId}</groupId>
<artifactId>${project.artifactId}</artifactId>
<artifactVersion>${project.version}</artifactVersion>
<library>resttemplate</library>
<java8>true</java8>
<dateLibrary>java8</dateLibrary>
<licenseName>Apache 2.0</licenseName>
<licenseUrl>https://www.apache.org/licenses/LICENSE-2.0</licenseUrl>
</configOptions>
</configuration>
</execution>
</executions>
</plugin>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<configuration>
<source>${java.version}</source>
<target>${java.version}</target>
</configuration>
</plugin>
</plugins>
</build>
</project>