doc: spring-SpringFactoriesLoader.md

docs/Spring/clazz/Spring-SpringFactoriesLoader.md

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+# SpringFactoriesLoader
+- Author: [HuiFer](https://github.com/huifer)
+- 源码阅读仓库: [SourceHot-spring-boot](https://github.com/SourceHot/spring-boot-read)
+
+
+- 全路径 : `org.springframework.core.io.support.SpringFactoriesLoader`
+- 测试类 : `org.springframework.core.io.support.SpringFactoriesLoaderTests`
+
+
+## loadFactories
+
+- **加载并实例化工厂**
+
+```java
+public static <T> List<T> loadFactories(Class<T> factoryType, @Nullable ClassLoader classLoader) {
+		Assert.notNull(factoryType, "'factoryType' must not be null");
+		ClassLoader classLoaderToUse = classLoader;
+		if (classLoaderToUse == null) {
+			classLoaderToUse = SpringFactoriesLoader.class.getClassLoader();
+		}
+		// 工厂实现类名称
+		List<String> factoryImplementationNames = loadFactoryNames(factoryType, classLoaderToUse);
+		if (logger.isTraceEnabled()) {
+			logger.trace("Loaded [" + factoryType.getName() + "] names: " + factoryImplementationNames);
+		}
+		List<T> result = new ArrayList<>(factoryImplementationNames.size());
+		for (String factoryImplementationName : factoryImplementationNames) {
+			// 将实例化的工厂放入结果集合
+			result.add(instantiateFactory(factoryImplementationName, factoryType, classLoaderToUse));
+		}
+		// 排序
+		AnnotationAwareOrderComparator.sort(result);
+		return result;
+	}
+```
+
+
+
+
+
+## loadSpringFactories
+
+- 获取接口的实现类名
+
+```java
+	private static Map<String, List<String>> loadSpringFactories(@Nullable ClassLoader classLoader) {
+		MultiValueMap<String, String> result = cache.get(classLoader);
+		if (result != null) {
+			return result;
+		}
+
+		try {
+			// 找 META-INF/spring.factories
+			Enumeration<URL> urls = (classLoader != null ?
+					classLoader.getResources(FACTORIES_RESOURCE_LOCATION) :
+					ClassLoader.getSystemResources(FACTORIES_RESOURCE_LOCATION));
+			result = new LinkedMultiValueMap<>();
+			while (urls.hasMoreElements()) {
+				// 获取 路由地址
+				URL url = urls.nextElement();
+				// url 解析
+				UrlResource resource = new UrlResource(url);
+				// Properties 解析
+				Properties properties = PropertiesLoaderUtils.loadProperties(resource);
+				// 循环解析结果
+				for (Map.Entry<?, ?> entry : properties.entrySet()) {
+					String factoryTypeName = ((String) entry.getKey()).trim();
+					for (String factoryImplementationName : StringUtils.commaDelimitedListToStringArray((String) entry.getValue())) {
+						// 放入list
+						result.add(factoryTypeName, factoryImplementationName.trim());
+					}
+				}
+			}
+			// 放入缓存
+			cache.put(classLoader, result);
+			return result;
+		}
+		catch (IOException ex) {
+			throw new IllegalArgumentException("Unable to load factories from location [" +
+													   FACTORIES_RESOURCE_LOCATION + "]", ex);
+		}
+	}
+
+```
+
+- 存放在 测试目录下的`META-INF/spring.factories`
+
+  ```properties
+  org.springframework.core.io.support.DummyFactory =\
+  org.springframework.core.io.support.MyDummyFactory2, \
+  org.springframework.core.io.support.MyDummyFactory1
+  
+  java.lang.String=\
+  org.springframework.core.io.support.MyDummyFactory1
+  
+  org.springframework.core.io.support.DummyPackagePrivateFactory=\
+  org.springframework.core.io.support.DummyPackagePrivateFactory
+  
+  ```
+
+  
+
+- `Enumeration<URL> urls ` 变量存放的是 扫描到的`META-INF/spring.factories` 路径
+
+- while 代码简单描述
+  1. 获取文件路径
+  2. 文件路径解析
+  3. 读取文件 Properties 解析
+  4. 放入返回结果
+  5. 放入缓存
+
+
+
+## instantiateFactory
+
+```java
+@SuppressWarnings("unchecked")
+private static <T> T instantiateFactory(String factoryImplementationName, Class<T> factoryType, ClassLoader classLoader) {
+   try {
+      Class<?> factoryImplementationClass = ClassUtils.forName(factoryImplementationName, classLoader);
+      if (!factoryType.isAssignableFrom(factoryImplementationClass)) {
+         throw new IllegalArgumentException(
+               "Class [" + factoryImplementationName + "] is not assignable to factory type [" + factoryType.getName() + "]");
+      }
+      return (T) ReflectionUtils.accessibleConstructor(factoryImplementationClass).newInstance();
+   }
+   catch (Throwable ex) {
+      throw new IllegalArgumentException(
+            "Unable to instantiate factory class [" + factoryImplementationName + "] for factory type [" + factoryType.getName() + "]",
+            ex
+      );
+   }
+}
+```
+
+- 反射创建
+
+
+