增加AbstractDiscoveryEnabledStrategy抽象类，基于Header进行自定义路由更加方便

discovery-plugin-strategy/src/main/java/com/nepxion/discovery/plugin/strategy/adapter/AbstractDiscoveryEnabledStrategy.java

+package com.nepxion.discovery.plugin.strategy.adapter;
+
+/**
+ * <p>Title: Nepxion Discovery</p>
+ * <p>Description: Nepxion Discovery</p>
+ * <p>Copyright: Copyright (c) 2017-2050</p>
+ * <p>Company: Nepxion</p>
+ * @author Haojun Ren
+ * @version 1.0
+ */
+
+import java.util.Map;
+
+import javax.annotation.PostConstruct;
+
+import org.springframework.beans.factory.annotation.Autowired;
+
+import com.nepxion.discovery.plugin.framework.context.PluginContextAware;
+import com.nepxion.discovery.plugin.strategy.context.StrategyContextHolder;
+import com.netflix.loadbalancer.Server;
+
+public abstract class AbstractDiscoveryEnabledStrategy implements DiscoveryEnabledStrategy {
+    private StrategyContextHolder strategyContextHolder;
+
+    @Autowired
+    private PluginContextAware pluginContextAware;
+
+    @PostConstruct
+    public void initialize() {
+        strategyContextHolder = pluginContextAware.getBean(StrategyContextHolder.class);
+    }
+
+    @Override
+    public boolean apply(Server server, Map<String, String> metadata) {
+        return apply(server, metadata, strategyContextHolder);
+    }
+
+    public abstract boolean apply(Server server, Map<String, String> metadata, StrategyContextHolder strategyContextHolder);
+}
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