mysql Communications link failure during commit(). Transaction resolution unknown when etl (no replies)

HI: We are working with mysql 5.6.21 and mysql-connector-java-5.1.17.jar. We do ETL operation, From source DB ingest 300000 data store at mysql. The situation is split data to 3000*100 records,every 100 records commit once at all. do 3000 loops insert operation.
We got the below exceptions high frequency,
com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException: Communications link failure during commit(). Transaction resolution unknown.
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method) ~[na:1.8.0_92]
at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62) ~[na:1.8.0_92]
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45) ~[na:1.8.0_92]
at java.lang.reflect.Constructor.newInstance(Constructor.java:423) ~[na:1.8.0_92]
at com.mysql.jdbc.Util.handleNewInstance(Util.java:411) ~[na:na]
at com.mysql.jdbc.Util.getInstance(Util.java:386) ~[na:na]
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1013) ~[na:na]
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:987) ~[na:na]
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:982) ~[na:na]
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:927) ~[na:na]
at com.mysql.jdbc.ConnectionImpl.commit(ConnectionImpl.java:1665) ~[na:na]
at org.apache.commons.dbcp.DelegatingConnection.commit(DelegatingConnection.java:334) ~[na:na]
at org.apache.commons.dbcp.PoolingDataSource$PoolGuardConnectionWrapper.commit(PoolingDataSource.java:211) ~[na:na]

what is the root cause?
Thank you very much.
Paul