spring-boot解析spring.factories文件

启动SpringBoot自动装配的工厂类方法实现

    /*** 解析 spring.factories 文件** @return 读取到的所有数据*/private static Map<String, List<String>> loadSpringFactories(ClassLoader classLoader){try {Enumeration<URL> urls = (classLoader != null ?classLoader.getResources("META-INF/spring.factories") :ClassLoader.getSystemResources("META-INF/spring.factories"));MultiValueMap<String, String> result = new LinkedMultiValueMap<>();while (urls.hasMoreElements()) {URL url = urls.nextElement();UrlResource resource = new UrlResource(url);Properties properties = PropertiesLoaderUtils.loadProperties(resource);for (Map.Entry<?, ?> entry : properties.entrySet()) {String factoryClassName = ((String) entry.getKey()).trim();for (String factoryName : StringUtils.commaDelimitedListToStringArray((String) entry.getValue())) {result.add(factoryClassName, factoryName.trim());}}}return result;}catch (IOException ex) {throw new IllegalArgumentException("Unable to load factories from location [META-INF/spring.factories]", ex);}}/*** 反射实例化*/private static <T> List<T> createSpringFactoriesInstances(Class<T> type, Class<?>[] parameterTypes,ClassLoader classLoader, Object[] args, Set<String> names) {List<T> instances = new ArrayList<>(names.size());for (String name : names) {try {Class<?> instanceClass = ClassUtils.forName(name, classLoader);Assert.isAssignable(type, instanceClass);Constructor<?> constructor = instanceClass.getDeclaredConstructor(parameterTypes);T instance = (T) BeanUtils.instantiateClass(constructor, args);instances.add(instance);}catch (Throwable ex) {throw new IllegalArgumentException("Cannot instantiate " + type + " : " + name, ex);}}return instances;}public static void main(String[] args) throws IOException {ClassLoader classLoader = ClassUtils.getDefaultClassLoader();// 解析 spring.factories 文件Map<String, List<String>> maps = loadSpringFactories(classLoader);// 获取指定的类 ApplicationContextInitializer 配置String className = ApplicationContextInitializer.class.getName();List<String> values = maps.getOrDefault(className,Collections.emptyList());// 反射实例化类Set<String> names = new LinkedHashSet<>(values);List<ApplicationContextInitializer> instances = createSpringFactoriesInstances(ApplicationContextInitializer.class, new Class<?>[]{}, classLoader, args, names);for (ApplicationContextInitializer instance : instances) {System.out.println(instance.toString());}}