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CDS4J API

There is a newer version: 3.6.1

/************************************************************************
 * © 2019-2024 SAP SE or an SAP affiliate company. All rights reserved. *
 ************************************************************************/
package com.sap.cds;

import java.util.Collection;
import java.util.Iterator;
import java.util.Map;
import java.util.Optional;
import java.util.ServiceLoader;
import java.util.concurrent.ConcurrentHashMap;

import com.google.common.collect.ImmutableList;

/**
 * Internal ServiceLoader class.
 */
public final class Cds4jServiceLoader {

	private static final Map> implementations = new ConcurrentHashMap<>();

	private Cds4jServiceLoader() {
	}

	@SuppressWarnings("unchecked")
	public static  T load(Class clazz) {
		Class impl = implementations.computeIfAbsent(clazz.getCanonicalName(), c -> findImpl(clazz));
		try {
			return (T) impl.getDeclaredConstructor().newInstance();

		} catch (Exception e) {
			throw new CdsException("Failed to instantiate " + impl.getCanonicalName(), e);
		}
	}

	@SuppressWarnings("unchecked")
	private static  Class findImpl(Class clazz) {
		Iterator implClasses = ServiceLoader.load(clazz).iterator();
		if (implClasses.hasNext()) {
			return (Class) implClasses.next().getClass();
		} else {
			// Try same classloader as the requested Class
			implClasses = ServiceLoader.load(clazz, clazz.getClassLoader()).iterator();
			if (implClasses.hasNext()) {
				return (Class) implClasses.next().getClass();
			}
			throw new CdsException("Cannot find implementation of " + clazz.getCanonicalName());
		}
	}

	public static  Optional find(Class clazz) {
		try {
			return Optional.of(load(clazz));

		} catch (Exception e) {
			return Optional.empty();
		}
	}

	public static  Collection loadAll(Class clazz) {
		Iterator implClasses = ServiceLoader.load(clazz).iterator();
		if (!implClasses.hasNext()) {
			implClasses = ServiceLoader.load(clazz, clazz.getClassLoader()).iterator();
		}
		return ImmutableList.copyOf(implClasses);
	}

}