for #1116, resolve transactionManager is null when receiving new request from client application.

this problem will be completely resolved in 3.1.0

sharding-jdbc/src/main/java/io/shardingsphere/core/jdbc/adapter/AbstractConnectionAdapter.java

@@ -89,6 +89,7 @@ public abstract class AbstractConnectionAdapter extends AbstractUnsupportedOpera
     @Override
     public final void setAutoCommit(final boolean autoCommit) {
         this.autoCommit = autoCommit;
+        TransactionContextHolder.set(new TransactionContext(new WeakXaTransactionManager(), TransactionType.XA, WeakXaTransactionEvent.class));
         recordMethodInvocation(Connection.class, "setAutoCommit", new Class[] {boolean.class}, new Object[] {autoCommit});
         EventBusInstance.getInstance().post(buildTransactionEvent(TCLType.BEGIN));
     }