SPI

docs/Java/SPI.md

@@ -0,0 +1,85 @@
+---
+layout: default
+title: SPI
+parent: Java
+
+---
+
+# maven库
+
+```xml
+
+<dependency>
+    <groupId>org.kohsuke.metainf-services</groupId>
+    <artifactId>metainf-services</artifactId>
+    <version>${metainf-services.version}</version>
+    <scope>compile</scope>
+</dependency>
+
+```
+
+> @MetaInfServices(InspectorPlugin.class)
+
+
+# java加载SPI
+
+Java的SPI机制就是指：针对一个接口，我们需要加载外部对该接口的实现，
+只要约定好将该实现配置在classPath路径下的META-INF/services文件夹的文件，使用方就可以自动加载文件里所定义的类。
+
+SPI中三个重要的角色：
+
+- 接口
+```java
+
+public interface InspectorPlugin {
+
+    String identify();
+
+    boolean enable(List<String> plugins);
+
+    boolean entrance();
+
+    int watch(ModuleEventWatcher watcher,InvocationSendService service);
+
+}
+```
+- 配置文件
+```java
+@MetaInfServices(InspectorPlugin.class)
+public class DubboProviderPlugin extends BasePlugin {
+    public DubboProviderPlugin( InvocationSendService invocationSendService) {
+        super(Constant.DUBBO_PROVIDER,true,invocationSendService);
+    }
+
+
+
+    @Override
+    public void watch(ModuleEventWatcher watcher) {
+        new EventWatchBuilder(watcher)
+                .onClass("org.apache.dubbo.rpc.filter.ContextFilter").includeBootstrap()
+                .onBehavior("invoke")
+                .onWatch(new DubboProviderEventListener(entrance, protocol,invocationSendService), Event.Type.BEFORE, Event.Type.RETURN, Event.Type.THROWS);
+    }
+}
+```
+- ServiceLoader反射获取
+
+``` java
+private List<InspectorPlugin> loadInspectorPluginBySPI( ClassLoader classLoader) {
+        ServiceLoader<InspectorPlugin> loaded = ServiceLoader.load(InspectorPlugin.class, classLoader);
+        Iterator<InspectorPlugin> spiIterator = loaded.iterator();
+        List<InspectorPlugin> target = Lists.newArrayList();
+        while (spiIterator.hasNext()) {
+            try {
+                target.add(spiIterator.next());
+            } catch (Throwable e) {
+                log.error("Error load spi InspectorPlugin >>> ", e);
+            }
+        }
+        return target;
+    }
+
+
+```
+
+