change to constructor autowiring mode for MetricsCollectController.java (#622)

diff --git a/dubbo-admin-server/src/main/java/org/apache/dubbo/admin/controller/MetricsCollectController.java b/dubbo-admin-server/src/main/java/org/apache/dubbo/admin/controller/MetricsCollectController.java
index 6acc0af..cdd129b 100644
--- a/dubbo-admin-server/src/main/java/org/apache/dubbo/admin/controller/MetricsCollectController.java
+++ b/dubbo-admin-server/src/main/java/org/apache/dubbo/admin/controller/MetricsCollectController.java
@@ -49,14 +49,16 @@
 @RequestMapping("/api/{env}/metrics")
 public class MetricsCollectController {
 
-    @Autowired
     private ProviderService providerService;
-
-    @Autowired
     private ConsumerService consumerService;
+    private MetricsService metricsService;
 
     @Autowired
-    private MetricsService metricsService;
+    public MetricsCollectController(ProviderService providerService, ConsumerService consumerService, MetricsService metricsService) {
+        this.providerService = providerService;
+        this.consumerService = consumerService;
+        this.metricsService = metricsService;
+    }
 
     @RequestMapping(method = RequestMethod.POST)
     public String metricsCollect(@RequestParam String group, @PathVariable String env) {