fix checkClosed usage

Author: Neenu1995

java-bigquery/google-cloud-bigquery-jdbc/src/main/java/com/google/cloud/bigquery/jdbc/BigQueryConnection.java

@@ -927,16 +927,14 @@ public void setHoldability(int holdability) throws SQLException {
   @Override
   public void close() throws SQLException {
     try {
-      BigQueryJdbcMdc.registerInstance(this, this.connectionId);
-      LOG.finest("++enter++");
-      LOG.fine("Closing Connection " + this);
-      // TODO(neenu-postMVP): Release all connection state objects
-      // check for and close all existing transactions
-
       if (isClosed()) {
         return;
       }
 
+      BigQueryJdbcMdc.registerInstance(this, this.connectionId);
+      LOG.finest("++enter++");
+      LOG.fine("Closing Connection " + this);
+
       try {
         if (this.bigQueryReadClient != null) {
           this.bigQueryReadClient.shutdown();
@@ -977,6 +975,7 @@ public boolean isClosed() {
 
   private void checkClosed() {
     if (isClosed()) {
+      LOG.severe("This " + getClass().getName() + " has been closed");
       throw new IllegalStateException("This " + getClass().getName() + " has been closed");
     }
   }

java-bigquery/google-cloud-bigquery-jdbc/src/main/java/com/google/cloud/bigquery/jdbc/BigQueryStatement.java

@@ -235,6 +235,7 @@ private BigQuerySettings generateBigQuerySettings() {
    */
   @Override
   public ResultSet executeQuery(String sql) throws SQLException {
+    checkClosed();
     try {
       BigQueryJdbcMdc.registerInstance(this.connection, this.connectionId);
       // TODO: write method to return state variables to original state.
@@ -262,6 +263,7 @@ public ResultSet executeQuery(String sql) throws SQLException {
 
   @Override
   public long executeLargeUpdate(String sql) throws SQLException {
+    checkClosed();
     try {
       BigQueryJdbcMdc.registerInstance(this.connection, this.connectionId);
       LOG.finest("++enter++");
@@ -306,6 +308,7 @@ int checkUpdateCount(long updateCount) {
 
   @Override
   public boolean execute(String sql) throws SQLException {
+    checkClosed();
     try {
       BigQueryJdbcMdc.registerInstance(this.connection, this.connectionId);
       LOG.finest("++enter++");
@@ -385,12 +388,12 @@ QueryStatistics getQueryStatistics(QueryJobConfiguration queryJobConfiguration)
    */
   @Override
   public void close() throws SQLException {
+    if (isClosed()) {
+      return;
+    }
     try {
       BigQueryJdbcMdc.registerInstance(this.connection, this.connectionId);
       LOG.fine("Closing Statement %s.", this);
-      if (isClosed()) {
-        return;
-      }
 
       boolean cancelSucceeded = false;
       try {
@@ -1571,6 +1574,7 @@ protected void logQueryExecutionStart(String sql) {
   /** Throws a {@link BigQueryJdbcException} if this object is closed */
   void checkClosed() throws SQLException {
     if (isClosed()) {
+      LOG.severe("This " + getClass().getName() + " has been closed");
       throw new BigQueryJdbcException("This " + getClass().getName() + " has been closed");
     }
   }