org.powertac.common.spring.SpringApplicationContext.java Source code

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Here is the source code for org.powertac.common.spring.SpringApplicationContext.java

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/*
 * Copyright (c) 2011 by 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.powertac.common.spring;

import java.util.ArrayList;
import java.util.Collection;
import java.util.List;
import java.util.Map;

import org.springframework.beans.BeansException;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationContextAware;
import org.springframework.stereotype.Service;

/**
 * Static methods to access the Spring application context. It is set up
 * as a service so Spring will create and initialize it.
 * 
 * NOTE: These methods should NOT be used in constructors. Doing so makes it
 * vitually impossible to test with mocks, and makes transitive dependencies
 * very difficult in a test environment. Better to use them in individual
 * "service getter" methods that do nothing for dependencies that have
 * already been satisfied by test code using ReflectionTestUtils.setField().
 * 
 * ALSO NOTE: Even when used outside a constructor, there are still potential
 * problems in a test environment, because if any test in a suite initializes
 * Spring, then later tests that do not initialize Spring can retrieve
 * instances from earlier tests, which may not be what the test expects.
 * This can lead to baffling problems.
 * 
 * @author John Collins
 */
@Service
public class SpringApplicationContext implements ApplicationContextAware {
    private static ApplicationContext context;

    @Override
    public void setApplicationContext(ApplicationContext appContext) throws BeansException {
        context = appContext;
    }

    /**
     * Returns the Spring bean, if any, with the given name.
     */
    public static Object getBean(String beanName) {
        if (context != null)
            return context.getBean(beanName);
        else
            return null;
    }

    /**
     * Returns the first Spring bean found that is an instance of the 
     * given class.
     */
    public static <T> T getBeanByType(Class<T> type) {
        T bean = null;
        Collection<T> beans = context.getBeansOfType(type).values();
        if (beans.size() > 0) {
            bean = new ArrayList<T>(beans).get(0);
        }

        return bean;
    }

    /**
     * Returns all the Spring beans that are instances of the given type.
     */
    public static <T> List<T> listBeansOfType(Class<T> type) {
        return new ArrayList<T>(context.getBeansOfType(type).values());
    }

    /**
     * Returns a map of all the Spring beans that are instances of 
     * the given type.
     */
    public static <T> Map<String, T> mapBeansOfType(Class<T> type) {
        return context.getBeansOfType(type);
    }

    public static ApplicationContext getContext() {
        return context;
    }
}