[JAVA] selectHeaderAccept is removing values of the accept header

Description

T.L.D.R.: The selectHeaderAccept is removing values of the accept header

When working in JAVA and generating code using swagger-codegen-maven-plugin, the code generated contains in ApiClient.java the method public List<MediaType> selectHeaderAccept(String[] accepts):

public List<MediaType> selectHeaderAccept(String[] accepts) {
        if (accepts.length == 0) {
            return null;
        }
        for (String accept : accepts) {
            MediaType mediaType = MediaType.parseMediaType(accept);
            if (isJsonMime(mediaType)) {
                return Collections.singletonList(mediaType);
            }
        }
        return MediaType.parseMediaTypes(StringUtils.arrayToCommaDelimitedString(accepts));
    }

This method iterates over the values of accept header and returns early if JSON exists in the array. This verification is done using the public boolean isJsonMime(MediaType mediaType):

public boolean isJsonMime(MediaType mediaType) {
        return mediaType != null && (MediaType.APPLICATION_JSON.isCompatibleWith(mediaType) || mediaType.getSubtype().matches("^.*\\+json[;]?\\s*$"));
    }

If the Accept header contains application/problem+json and application/json, and the client expects application/json, an error will occur since the selectHeaderAccept method returns early with a single value (effectively removing other possible JSON values) when it shouldn't.

Swagger-codegen version

latest, 3.0.58

Command line used for generation

Generated using swagger-codegen-maven-plugin

Steps to reproduce

<plugin>
    <groupId>io.swagger.codegen.v3</groupId>
    <artifactId>swagger-codegen-maven-plugin</artifactId>
    <version>3.0.58</version>
    <executions>
        <execution>
            <id>ExampleClient</id>
            <phase>process-resources</phase>
            <goals>
                <goal>generate</goal>
            </goals>
            <configuration>
                <inputSpec>${project.build.directory}/${swagger.rest.client.example}</inputSpec>
                <language>java</language>
                <library>resttemplate</library>
                <modelPackage>com.kn.example.client.model</modelPackage>
                <apiPackage>com.kn.example.client.api</apiPackage>
                <generateModelTests>false</generateModelTests>
                <generateModelDocumentation>false</generateModelDocumentation>
                <generateApiTests>false</generateApiTests>
                <generateApiDocumentation>false</generateApiDocumentation>
                <configOptions>
                    <hideGenerationTimestamp>true</hideGenerationTimestamp>
                    <dateLibrary>java8-localdatetime</dateLibrary>
                    <interfaceOnly>true</interfaceOnly>
                    <defaultInterfaces>false</defaultInterfaces>
                </configOptions>
            </configuration>
        </execution>
    </executions>
</plugin>

Suggest a fix/enhancement

Consider avoiding the premature optimization of returning the first isJsonMime found in the given Accept header array.

Start with the generated ApiClient.java method selectHeaderAccept and its isJsonMime check, then reproduce the behavior through swagger-codegen-maven-plugin using the provided configuration and Accept values. Trace the corresponding Java generation template and verify that generated clients retain all applicable Accept values instead of returning prematurely.