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SPI(Service Provider Interface)--通过接口获取服务
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spi 现在已有实现
- jdk 提供实现
- dubbo里的spi实现
一、jdk实现
- 配置
- 定义接口
- 定义实现类
- 配置资源文件 classpath下创建（META-INF/services/接口全面：META-INF/services/spring.design.mode.test4.spi.DogService）
- 调用方法
ServiceLoader<DogService> loaders = ServiceLoader.load(DogService.class);
for (DogService d : loaders) {
d.sleep();
}
- 测试结果
黑色dog。。。汪汪叫，不睡觉...
白色dog。。。呼呼大睡觉...
- 代码下载
https://files.cnblogs.com/files/z-test/spi-jdk.rar
二、dubbo 里的spi实现。
- 用法介绍
//得到一个自适应实现类，用@Adaptive 注解的类，没有就自动生产一个自适应类，可以根据调用方法的参数，动态获取处理类
ExtensionLoader.getExtensionLoader(Protocol.class).getAdaptiveExtension(); //得到默认的实现类
ExtensionLoader.getExtensionLoader(Protocol.class).getDefaultExtension(); //通过名字得到实现类。得到实现类，先注入实现类，然后，使用它的包装类，进行包装。所以 返回的实例，也可能是包装类的实例
ExtensionLoader.getExtensionLoader(Protocol.class).getExtension("name"); //通过url里的 key对应的参数获取实现类。1.先加载默认的激活实现，2加载key对应的value里的值。
ExtensionLoader.getExtensionLoader(Protocol.class).getActivateExtension(url, key);
创建对应名称的扩展类代码
@SuppressWarnings("unchecked")
private T createExtension(String name) {
Class<?> clazz = getExtensionClasses().get(name);
if (clazz == null) {
throw findException(name);
}
try {
T instance = (T) EXTENSION_INSTANCES.get(clazz);
if (instance == null) {
EXTENSION_INSTANCES.putIfAbsent(clazz, clazz.newInstance());
instance = (T) EXTENSION_INSTANCES.get(clazz);
}
injectExtension(instance);
Set<Class<?>> wrapperClasses = cachedWrapperClasses;
if (wrapperClasses != null && !wrapperClasses.isEmpty()) {
for (Class<?> wrapperClass : wrapperClasses) {
instance = injectExtension((T) wrapperClass.getConstructor(type).newInstance(instance));
}
}
return instance;
} catch (Throwable t) {
throw new IllegalStateException("Extension instance(name: " + name + ", class: " +
type + ") could not be instantiated: " + t.getMessage(), t);
}
}
- 配置
- 文件位置
//加载顺序 DUBBO_INTERNAL_DIRECTORY，DUBBO_DIRECTORY，SERVICES_DIRECTORY
//即用户可以覆盖调源码里的实现。 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/";
- 配置文件内容如下 （文件名：接口全名；内容是key=value：自定义名称：接口实现类全名）
- 注解解释
- @SPI("dubbo") 标记接口，提供一个默认的实现 一便于getDefaultExtension()得到默认实现类
- @Adaptive
- 1.出现在实现类上，.getAdaptiveExtension() 可以得到对应的实现类，
- 2.出现在 接口里的对应的方法上 强制要求对应的方法有URL参数，或者参数里包含URL对象。（否则执行报错）
- 实现类是com.alibaba.dubbo.rpc.Protocol 动态获取协议 根据url.getProtocol() == null ? "dubbo" : url.getProtocol() 获取协议名称，url参数protocol 为空时使用默认名称即@SPI("dubbo")中的名称
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);
}- 接口对应方法中含有com.alibaba.dubbo.rpc.Invocation的根据 url.getMethodParameter(methodName, "cache", "lru");“cache“为参数名，lru 为@spi中指定的默认值
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);
}- 其他的实现为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")));
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);
}
@Activate(group = {Constants.PROVIDER, Constants.CONSUMER}) 激活的类，适用于getActivateExtension(url, key) 1.先查找适配的@activie对应的类，2，查找url里key的对应的value所对应的类。
- 动态注入属性（查找set方法，根据set方法参数类型和变量名查找可用对象注入到 spi生产的对象里面。可以注入spi里的对象和springcontext里的对象）
在 接口类对应的配置文件里，有两个实现类，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 获取需要注入的对象
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;
}}
大家可以看看源码，根据用法介绍里的方法，跟进看看。
