Github user kl0u commented on a diff in the pull request:
https://github.com/apache/flink/pull/4901#discussion_r147649786
--- Diff:
flink-runtime/src/main/java/org/apache/flink/runtime/rest/handler/legacy/metrics/AbstractAggregatingMetricsHandler.java
---
@@ -0,0 +1,223 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements. See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership. The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.flink.runtime.rest.handler.legacy.metrics;
+
+import org.apache.flink.runtime.jobmaster.JobManagerGateway;
+import
org.apache.flink.runtime.rest.handler.legacy.AbstractJsonRequestHandler;
+import org.apache.flink.runtime.rest.handler.legacy.JsonFactory;
+import org.apache.flink.util.FlinkException;
+import org.apache.flink.util.Preconditions;
+
+import com.fasterxml.jackson.core.JsonGenerator;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.io.IOException;
+import java.io.StringWriter;
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.HashSet;
+import java.util.Iterator;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.CompletionException;
+import java.util.concurrent.Executor;
+
+/**
+ * Abstract request handler for querying metrics. Subclasses may either
that returns a list of all available metrics or
+ * the values for a set of metrics for a specific entity, or aggregate
them across several entities.
+ *
+ * <p>If the query parameters do not contain a "get" parameter the list of
all metrics is returned.
+ * {@code [ { "id" : "X" } ] }
+ *
+ * <p>If the query parameters do contain a "get" parameter, a
comma-separated list of metric names is expected as a value.
+ * {@code /metrics?get=X,Y}
+ * The handler will then return a list containing the values of the
requested metrics.
+ * {@code [ { "id" : "X", "value" : "S" }, { "id" : "Y", "value" : "T" } ]
}
+ *
+ * <p>If the query parameters do contain a "get" parameter a
comma-separate list of metric names is expected as a value.
--- End diff --
"get" parameter a comma-separate -> "get" parameter**,** a comma-separate
---
