more flow control (#471)

flow control example better document

src/examples/java/io/nats/examples/jetstream/NatsJsPushSubFlowControl.java

@@ -65,7 +65,23 @@ public static void main(String[] args) {
                 // This is configured so the subscriber ends up being considered slow
                 JetStreamSubscription sub = js.subscribe(subject, pso);
                 nc.flush(Duration.ofSeconds(5));
-                sub.setPendingLimits(Consumer.DEFAULT_MAX_MESSAGES, 1024);
+
+                // ------------------------------------------------------------------------------------------
+                // Flow Control limit is set using pending limits. You can mix and match pending messages
+                // with total bytes or rely on one or the other.
+                // ------------------------------------------------------------------------------------------
+                // IMPORTANT!!!! THESE VALUES ARE EXAMPLE ONLY SO THE FLOW CONTROL MESSAGES
+                // SHOWS UP EASILY IN THIS DEMO. IN REAL SYSTEMS YOU WILL TYPICALLY HAVE MANY MORE
+                // MESSAGES AND MANY MORE BYTES AS YOUR LIMITS. FOR EXAMPLE THE DEFAULT VALUES
+                // AS SET IN io.nats.client.Consumer ARE
+                //     public static final long DEFAULT_MAX_MESSAGES = 64 * 1024;
+                //     public static final long DEFAULT_MAX_BYTES = 64 * 1024 * 1024;
+                // ------------------------------------------------------------------------------------------
+                // The example first version sets pending to 500 message with 1K total bytes
+                // The example second version (commented out) sets pending to 1 message with 500K total bytes
+                // ------------------------------------------------------------------------------------------
+                sub.setPendingLimits(500, 1024);
+                // sub.setPendingLimits(1, 500000);
 
                 // publish more message data than the subscriber will handle
                 byte[] data = new byte[1024];

src/test/java/io/nats/client/impl/JetStreamPushTests.java

@@ -13,7 +13,10 @@
 
 package io.nats.client.impl;
 
-import io.nats.client.*;
+import io.nats.client.JetStream;
+import io.nats.client.JetStreamSubscription;
+import io.nats.client.Message;
+import io.nats.client.PushSubscribeOptions;
 import io.nats.client.api.ConsumerConfiguration;
 import io.nats.client.api.ConsumerInfo;
 import org.junit.jupiter.api.Test;
@@ -294,8 +297,9 @@ public void testHeartbeat() throws Exception {
         });
     }
 
-    @Test
-    public void testFlowControl() throws Exception {
+    @ParameterizedTest
+    @ValueSource(strings = {"500,1024", "1,500000"})
+    public void testFlowControl(String pendingLimits) throws Exception {
         runInJsServer(nc -> {
             // Create our JetStream context to receive JetStream messages.
             JetStream js = nc.jetStream();
@@ -312,7 +316,8 @@ public void testFlowControl() throws Exception {
             // This is configured so the subscriber ends up being considered slow
             JetStreamSubscription sub = js.subscribe(SUBJECT, pso);
             nc.flush(Duration.ofSeconds(5));
-            sub.setPendingLimits(Consumer.DEFAULT_MAX_MESSAGES, 1024);
+            String[] split = pendingLimits.split(",");
+            sub.setPendingLimits(Integer.parseInt(split[0]), Integer.parseInt(split[1]));
 
             // publish more message data than the subscriber will handle
             byte[] data = new byte[1024];