org.springframework.cloud.commons.util.SpringFactoryImportSelector.java Source code

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Here is the source code for org.springframework.cloud.commons.util.SpringFactoryImportSelector.java

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/*
 * Copyright 2013-2017 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.cloud.commons.util;

import java.util.ArrayList;
import java.util.LinkedHashSet;
import java.util.List;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.springframework.beans.factory.BeanClassLoaderAware;
import org.springframework.context.EnvironmentAware;
import org.springframework.context.annotation.DeferredImportSelector;
import org.springframework.core.GenericTypeResolver;
import org.springframework.core.annotation.AnnotationAttributes;
import org.springframework.core.env.Environment;
import org.springframework.core.io.support.SpringFactoriesLoader;
import org.springframework.core.type.AnnotationMetadata;
import org.springframework.util.Assert;

/**
 * Selects configurations to load defined by the generic type T. Loads implementations
 * using {@link SpringFactoriesLoader}.
 *
 * @author Spencer Gibb
 * @author Dave Syer
 */
public abstract class SpringFactoryImportSelector<T>
        implements DeferredImportSelector, BeanClassLoaderAware, EnvironmentAware {

    private ClassLoader beanClassLoader;

    private Class<T> annotationClass;

    private Environment environment;

    private final Log log = LogFactory.getLog(SpringFactoryImportSelector.class);

    @SuppressWarnings("unchecked")
    protected SpringFactoryImportSelector() {
        this.annotationClass = (Class<T>) GenericTypeResolver.resolveTypeArgument(this.getClass(),
                SpringFactoryImportSelector.class);
    }

    @Override
    public String[] selectImports(AnnotationMetadata metadata) {
        if (!isEnabled()) {
            return new String[0];
        }
        AnnotationAttributes attributes = AnnotationAttributes
                .fromMap(metadata.getAnnotationAttributes(this.annotationClass.getName(), true));

        Assert.notNull(attributes, "No " + getSimpleName() + " attributes found. Is " + metadata.getClassName()
                + " annotated with @" + getSimpleName() + "?");

        // Find all possible auto configuration classes, filtering duplicates
        List<String> factories = new ArrayList<>(new LinkedHashSet<>(
                SpringFactoriesLoader.loadFactoryNames(this.annotationClass, this.beanClassLoader)));

        if (factories.isEmpty() && !hasDefaultFactory()) {
            throw new IllegalStateException("Annotation @" + getSimpleName()
                    + " found, but there are no implementations. Did you forget to include a starter?");
        }

        if (factories.size() > 1) {
            // there should only ever be one DiscoveryClient, but there might be more than
            // one factory
            log.warn("More than one implementation " + "of @" + getSimpleName()
                    + " (now relying on @Conditionals to pick one): " + factories);
        }

        return factories.toArray(new String[factories.size()]);
    }

    protected boolean hasDefaultFactory() {
        return false;
    }

    protected abstract boolean isEnabled();

    protected String getSimpleName() {
        return this.annotationClass.getSimpleName();
    }

    protected Class<T> getAnnotationClass() {
        return this.annotationClass;
    }

    protected Environment getEnvironment() {
        return this.environment;
    }

    @Override
    public void setEnvironment(Environment environment) {
        this.environment = environment;
    }

    @Override
    public void setBeanClassLoader(ClassLoader classLoader) {
        this.beanClassLoader = classLoader;
    }

}