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  • spring framework源码之SpringFactoriesLoader

    SpringFactoriesLoader

      查询META-INF/spring.factories的properties配置中指定class对应的所有实现类。

    public abstract class SpringFactoriesLoader {
        /** The location to look for the factories. Can be present in multiple JAR files. */
        private static final String FACTORIES_RESOURCE_LOCATION = "META-INF/spring.factories";
        private static final Log logger = LogFactory.getLog(SpringFactoriesLoader.class);
        /**
         * Loads the factory implementations of the given type from the default location, using
         * the given class loader.
         * <p>The returned factories are ordered in accordance with the {@link OrderComparator}.
         * @param factoryClass the interface or abstract class representing the factory
         * @param classLoader the ClassLoader to use for loading (can be {@code null} to use the default)
         */
        public static <T> List<T> loadFactories(Class<T> factoryClass, ClassLoader classLoader) {
            Assert.notNull(factoryClass, "'factoryClass' must not be null");
            if (classLoader == null) {
                classLoader = SpringFactoriesLoader.class.getClassLoader();
            }
            List<String> factoryNames = loadFactoryNames(factoryClass, classLoader);
            if (logger.isTraceEnabled()) {
                logger.trace("Loaded [" + factoryClass.getName() + "] names: " + factoryNames);
            }
            List<T> result = new ArrayList<T>(factoryNames.size());
            for (String factoryName : factoryNames) {
                result.add(instantiateFactory(factoryName, factoryClass, classLoader));
            }
            OrderComparator.sort(result);
            return result;
        }
        private static List<String> loadFactoryNames(Class<?> factoryClass, ClassLoader classLoader) {
            String factoryClassName = factoryClass.getName();
            try {
                List<String> result = new ArrayList<String>();
                Enumeration<URL> urls = classLoader.getResources(FACTORIES_RESOURCE_LOCATION);
                while (urls.hasMoreElements()) {
                    URL url = urls.nextElement();
                    Properties properties = PropertiesLoaderUtils.loadProperties(new UrlResource(url));
                    String factoryClassNames = properties.getProperty(factoryClassName);
                    result.addAll(Arrays.asList(StringUtils.commaDelimitedListToStringArray(factoryClassNames)));
                }
                return result;
            }
            catch (IOException ex) {
                throw new IllegalArgumentException("Unable to load [" + factoryClass.getName() +
                        "] factories from location [" + FACTORIES_RESOURCE_LOCATION + "]", ex);
            }
        }
        @SuppressWarnings("unchecked")
        private static <T> T instantiateFactory(String instanceClassName, Class<T> factoryClass, ClassLoader classLoader) {
            try {
                Class<?> instanceClass = ClassUtils.forName(instanceClassName, classLoader);
                if (!factoryClass.isAssignableFrom(instanceClass)) {
                    throw new IllegalArgumentException(
                            "Class [" + instanceClassName + "] is not assignable to [" + factoryClass.getName() + "]");
                }
                return (T) instanceClass.newInstance();
            }
            catch (Throwable ex) {
                throw new IllegalArgumentException("Cannot instantiate factory class: " + factoryClass.getName(), ex);
            }
        }
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  • 原文地址:https://www.cnblogs.com/zhangwanhua/p/7941034.html
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