feat: support option for setting client-id

Author: aakashanandg

google-cloud-spanner/clirr-ignored-differences.xml

@@ -957,4 +957,11 @@
     <className>com/google/cloud/spanner/DatabaseClient</className>
     <method>com.google.cloud.spanner.Statement$StatementFactory getStatementFactory()</method>
   </difference>
+
+  <difference>
+    <differenceType>7012</differenceType>
+    <className>com/google/cloud/spanner/Spanner</className>
+    <method>com.google.cloud.spanner.DatabaseClient getDatabaseClient(com.google.cloud.spanner.DatabaseId, java.lang.String)</method>
+    <justification>Added as default method for JDBC client ID support. Default implementation throws UnsupportedOperationException to maintain binary compatibility for existing implementers.</justification>
+  </difference>
 </differences>

google-cloud-spanner/src/main/java/com/google/cloud/spanner/Spanner.java

@@ -145,7 +145,9 @@ public interface Spanner extends Service<SpannerOptions>, AutoCloseable {
    *
    * <!--SNIPPET get_db_client-->
    */
-  DatabaseClient getDatabaseClient(DatabaseId db, String clientId);
+  default DatabaseClient getDatabaseClient(DatabaseId db, String clientId) {
+    throw new UnsupportedOperationException("getDatabaseClient with clientId is not supported by this default implementation.");
+  }
 
   /**
    * Returns a {@code BatchClient} to do batch operations on Cloud Spanner databases. Batch client

google-cloud-spanner/src/main/java/com/google/cloud/spanner/SpannerImpl.java

@@ -257,6 +257,7 @@ public DatabaseClient getDatabaseClient(DatabaseId db) {
     return getDatabaseClient(db, null);
   }
 
+  @Override
   public DatabaseClient getDatabaseClient(DatabaseId db, String clientId) {
     synchronized (this) {
       checkClosed();