Create Sonar Plugin - Language class

 Language class contains the

1. Class extends AbstractLanguage  
2. defines KEY and Name for Language
3. File extensions for the specific language. ( here Foo.) Note we have used comma as seprator when you define multiple extensions.
4. We have injected "Configuration" - org.sonar.api.config.Configuration;
1. Basically at the  construction of the object, Key and Name for the language and configurations are set ( Constructor injection )

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package com.plugin.sonar.language.foo;

import org.apache.commons.lang.StringUtils;
import org.sonar.api.config.Configuration;
import org.sonar.api.resources.AbstractLanguage;

import java.util.ArrayList;
import java.util.List;
import java.util.Objects;

import static com.plugin.sonar.util.FooConstants.*;

public class FooLanguage extends AbstractLanguage {

    private Configuration config;

    public FooLanguage(Configuration configuration) {
        super(LANGUAGE_KEY, LANGUAGE_NAME);
        this.config = configuration;
    }

    @Override
    public String[] getFileSuffixes() {
        String[] suffixes = filterEmptyStrings(config.getStringArray(FILE_SUFFIXES_KEY));
        if (suffixes.length == 0) {
            suffixes = StringUtils.split(FILE_SUFFIXES_DEFAULT_VALUE, ",");
        }
        return suffixes;
    }

    private String[] filterEmptyStrings(String[] stringArray) {
        List<String> nonEmptyStrings = new ArrayList<>();
        for (String string : stringArray) {
            if (StringUtils.isNotBlank(string.trim())) {
                nonEmptyStrings.add(string.trim());
            }
        }
        return nonEmptyStrings.toArray(new String[0]);
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        if (!super.equals(o)) return false;
        FooLanguage that = (FooLanguage) o;
        return Objects.equals(config, that.config);
    }

    @Override
    public int hashCode() {
        return Objects.hash(super.hashCode(), config);
    }
}