SPI(Service Provider Interface)--通過接口獲取服務
阿新 • • 發佈：2018-07-17
obj 資源 源文件 tac bubuko 註解 nfa amp factory
spi 現在已有實現
- jdk 提供實現
- dubbo裏的spi實現
一、jdk實現
- 配置
- 定義接口
- 定義實現類
- 配置資源文件 classpath下創建（META-INF/services/接口全面：META-INF/services/spring.design.mode.test4.spi.DogService）
- 調用方法
ServiceLoader<DogService> loaders = ServiceLoader.load(DogService.class);
for (DogService d : loaders) {
d.sleep();
}
- 測試結果
黑色dog。。。汪汪叫，不睡覺... 白色dog。。。呼呼大睡覺...
- 代碼下載
https://files.cnblogs.com/files/z-test/spi-jdk.rar
二、dubbo 裏的spi實現。
- 用法介紹
//得到一個自適應實現類，用@Adaptive 註解的類，沒有就自動生產一個自適應類，可以根據調用方法的參數，動態獲取處理類 ExtensionLoader.getExtensionLoader(Protocol.class).getAdaptiveExtension();//得到默認的實現類 ExtensionLoader.getExtensionLoader(Protocol.class).getDefaultExtension(); //通過名字得到實現類。 ExtensionLoader.getExtensionLoader(Protocol.class).getExtension("name"); //通過url裏的 key對應的參數獲取實現類。1.先加載默認的激活實現，2加載key對應的value裏的值。 ExtensionLoader.getExtensionLoader(Protocol.class).getActivateExtension(url, key);
- 配置
- 文件位置
//加載順序 DUBBO_INTERNAL_DIRECTORY，DUBBO_DIRECTORY，SERVICES_DIRECTORY //即用戶可以覆蓋調源碼裏的實現。 private static final String DUBBO_DIRECTORY = "META-INF/dubbo/"; private static final String DUBBO_INTERNAL_DIRECTORY = DUBBO_DIRECTORY + "internal/"; private static final String SERVICES_DIRECTORY = "META-INF/services/";
-
- 配置文件內容如下 （文件名：接口全名；內容是key=value：自定義名稱：接口實現類全名）
- 註解解釋
- @SPI("dubbo") 標記接口，提供一個默認的實現 一便於getDefaultExtension()得到默認實現類
- @Adaptive
- 1.出現在實現類上，.getAdaptiveExtension() 可以得到對應的實現類，
- 2.出現在 接口裏的對應的方法上 強制要求對應的方法有URL參數，或者參數裏包含URL對象。（否則執行報錯）
- 實現類是com.alibaba.dubbo.rpc.Protocol 動態獲取協議 根據url.getProtocol() == null ? "dubbo" : url.getProtocol() 獲取協議名稱，url參數protocol 為空時使用默認名稱即@SPI("dubbo")中的名稱
-
public int getDefaultPort() { throw new UnsupportedOperationException( "method public abstract int com.alibaba.dubbo.rpc.Protocol.getDefaultPort() of interface com.alibaba.dubbo.rpc.Protocol is not adaptive method!"); } public com.alibaba.dubbo.rpc.Exporter export(com.alibaba.dubbo.rpc.Invoker arg0) throws com.alibaba.dubbo.rpc.RpcException { if (arg0 == null) throw new IllegalArgumentException("com.alibaba.dubbo.rpc.Invoker argument == null"); if (arg0.getUrl() == null) throw new IllegalArgumentException("com.alibaba.dubbo.rpc.Invoker argument getUrl() == null"); com.alibaba.dubbo.common.URL url = arg0.getUrl(); String extName = (url.getProtocol() == null ? "dubbo" : url.getProtocol()); if (extName == null) throw new IllegalStateException("Fail to get extension(com.alibaba.dubbo.rpc.Protocol) name from url(" + url.toString() + ") use keys([protocol])"); com.alibaba.dubbo.rpc.Protocol extension = (com.alibaba.dubbo.rpc.Protocol) ExtensionLoader .getExtensionLoader(com.alibaba.dubbo.rpc.Protocol.class).getExtension(extName); return extension.export(arg0); }
- 接口對應方法中含有com.alibaba.dubbo.rpc.Invocation的根據 url.getMethodParameter(methodName, "cache", "lru");“cache“為參數名，lru 為@spi中指定的默認值
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public com.alibaba.dubbo.cache.Cache getCache(com.alibaba.dubbo.common.URL arg0, com.alibaba.dubbo.rpc.Invocation arg1) { if (arg0 == null) throw new IllegalArgumentException("url == null"); com.alibaba.dubbo.common.URL url = arg0; if (arg1 == null) throw new IllegalArgumentException("invocation == null"); String methodName = arg1.getMethodName(); String extName = url.getMethodParameter(methodName, "cache", "lru"); if (extName == null) throw new IllegalStateException("Fail to get extension(com.alibaba.dubbo.cache.CacheFactory) name from url(" + url.toString() + ") use keys([cache])"); com.alibaba.dubbo.cache.CacheFactory extension = (com.alibaba.dubbo.cache.CacheFactory) ExtensionLoader .getExtensionLoader(com.alibaba.dubbo.cache.CacheFactory.class).getExtension(extName); return extension.getCache(arg0, arg1); }
- 其他的實現為url.getParameter("channel.handler", "all") 如果@Adaptive({Constants.DISPATCHER_KEY, "dispather", "channel.handler"}) url.getParameter("dispatcher",url.getParameter("dispather", url.getParameter("channel.handler", "all")));
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public com.alibaba.dubbo.remoting.ChannelHandler dispatch(com.alibaba.dubbo.remoting.ChannelHandler arg0, com.alibaba.dubbo.common.URL arg1) { if (arg1 == null) throw new IllegalArgumentException("url == null"); com.alibaba.dubbo.common.URL url = arg1; String extName = url.getParameter("dispatcher", url.getParameter("dispather", url.getParameter("channel.handler", "all"))); if (extName == null) throw new IllegalStateException( "Fail to get extension(com.alibaba.dubbo.remoting.Dispatcher) name from url(" + url.toString() + ") use keys([dispatcher, dispather, channel.handler])"); com.alibaba.dubbo.remoting.Dispatcher extension = (com.alibaba.dubbo.remoting.Dispatcher) ExtensionLoader .getExtensionLoader(com.alibaba.dubbo.remoting.Dispatcher.class).getExtension(extName); return extension.dispatch(arg0, arg1); }
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@Activate(group = {Constants.PROVIDER, Constants.CONSUMER}) 激活的類，適用於getActivateExtension(url, key) 1.先查找適配的@activie對應的類，2，查找url裏key的對應的value所對應的類。
- 動態註入屬性（查找set方法，根據set方法參數類型和變量名查找可用對象註入到 spi生產的對象裏面。可以註入spi裏的對象和springcontext裏的對象）
在 接口類對應的配置文件裏，有兩個實現類，spi 和spring
@Adaptive public class AdaptiveExtensionFactory implements ExtensionFactory { private final List<ExtensionFactory> factories; public AdaptiveExtensionFactory() { ExtensionLoader<ExtensionFactory> loader = ExtensionLoader.getExtensionLoader(ExtensionFactory.class); List<ExtensionFactory> list = new ArrayList<ExtensionFactory>(); for (String name : loader.getSupportedExtensions()) { list.add(loader.getExtension(name)); } factories = Collections.unmodifiableList(list); } @Override public <T> T getExtension(Class<T> type, String name) { for (ExtensionFactory factory : factories) { T extension = factory.getExtension(type, name); if (extension != null) { return extension; } } return null; } }
spring 獲取需要註入的對象
public class SpringExtensionFactory implements ExtensionFactory { private static final Set<ApplicationContext> contexts = new ConcurrentHashSet<ApplicationContext>(); public static void addApplicationContext(ApplicationContext context) { contexts.add(context); } public static void removeApplicationContext(ApplicationContext context) { contexts.remove(context); } @Override @SuppressWarnings("unchecked") public <T> T getExtension(Class<T> type, String name) { for (ApplicationContext context : contexts) { if (context.containsBean(name)) { Object bean = context.getBean(name); if (type.isInstance(bean)) { return (T) bean; } } } return null; } }
spi
public class SpiExtensionFactory implements ExtensionFactory { @Override public <T> T getExtension(Class<T> type, String name) { if (type.isInterface() && type.isAnnotationPresent(SPI.class)) { ExtensionLoader<T> loader = ExtensionLoader.getExtensionLoader(type); if (!loader.getSupportedExtensions().isEmpty()) { return loader.getAdaptiveExtension(); } } return null; } }
大家可以看看源碼，根據用法介紹裏的方法，跟進看看。
SPI(Service Provider Interface)--通過接口獲取服務