opti test and add javadoc

Author: hqbfzwang

pulsar-client/src/main/java/org/apache/pulsar/client/impl/ProducerImpl.java

@@ -82,10 +82,10 @@
 import org.apache.pulsar.client.impl.crypto.MessageCryptoBc;
 import org.apache.pulsar.client.impl.metrics.InstrumentProvider;
 import org.apache.pulsar.client.impl.metrics.LatencyHistogram;
+import org.apache.pulsar.client.impl.metrics.ProducerMetrics;
 import org.apache.pulsar.client.impl.metrics.Unit;
 import org.apache.pulsar.client.impl.metrics.UpDownCounter;
 import org.apache.pulsar.client.impl.schema.AutoProduceBytesSchema;
-import org.apache.pulsar.client.impl.metrics.ProducerMetrics;
 import org.apache.pulsar.client.impl.schema.JSONSchema;
 import org.apache.pulsar.client.impl.schema.SchemaUtils;
 import org.apache.pulsar.client.impl.transaction.TransactionImpl;