Don't run PreDecorationFilter if serviceId already set.

spring-cloud-netflix-core/src/main/java/org/springframework/cloud/netflix/zuul/filters/pre/PreDecorationFilter.java

@@ -58,7 +58,8 @@ public class PreDecorationFilter extends ZuulFilter {
 	@Override
 	public boolean shouldFilter() {
 		RequestContext ctx = RequestContext.getCurrentContext();
-		return !ctx.containsKey("forward.to");
+		return !ctx.containsKey("forward.to") // another filter has already forwarded
+				&& !ctx.containsKey("serviceId"); // another filter has already determined serviceId
 	}
 
 	@Override

spring-cloud-netflix-core/src/test/java/org/springframework/cloud/netflix/zuul/filters/pre/PreDecorationFilterTests.java

@@ -69,6 +69,18 @@ public class PreDecorationFilterTests {
 	}
 
 	@Test
+	public void skippedIfServiceIdSet() throws Exception {
+		RequestContext.getCurrentContext().set("serviceId", "myservice");
+		assertEquals(false, this.filter.shouldFilter());
+	}
+
+	@Test
+	public void skippedIfForwardToSet() throws Exception {
+		RequestContext.getCurrentContext().set("forward.to", "mycontext");
+		assertEquals(false, this.filter.shouldFilter());
+	}
+
+	@Test
 	public void prefixRouteAddsHeader() throws Exception {
 		this.properties.setPrefix("/api");
 		this.properties.setStripPrefix(true);