viirya commented on a change in pull request #29024:
URL: https://github.com/apache/spark/pull/29024#discussion_r495488559



##########
File path: 
sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/jdbc/connection/ConnectionProvider.scala
##########
@@ -18,60 +18,41 @@
 package org.apache.spark.sql.execution.datasources.jdbc.connection
 
 import java.sql.{Connection, Driver}
-import java.util.Properties
+import java.util.ServiceLoader
+
+import scala.collection.mutable
 
 import org.apache.spark.internal.Logging
 import org.apache.spark.sql.execution.datasources.jdbc.JDBCOptions
-
-/**
- * Connection provider which opens connection toward various databases 
(database specific instance
- * needed). If kerberos authentication required then it's the provider's 
responsibility to set all
- * the parameters.
- */
-private[jdbc] trait ConnectionProvider {
-  /**
-   * Additional properties for data connection (Data source property takes 
precedence).
-   */
-  def getAdditionalProperties(): Properties = new Properties()
-
-  /**
-   * Opens connection toward the database.
-   */
-  def getConnection(): Connection
-}
+import org.apache.spark.util.Utils
 
 private[jdbc] object ConnectionProvider extends Logging {
-  def create(driver: Driver, options: JDBCOptions): ConnectionProvider = {
-    if (options.keytab == null || options.principal == null) {
-      logDebug("No authentication configuration found, using basic connection 
provider")
-      new BasicConnectionProvider(driver, options)
-    } else {
-      logDebug("Authentication configuration found, using database specific 
connection provider")
-      options.driverClass match {
-        case PostgresConnectionProvider.driverClass =>
-          logDebug("Postgres connection provider found")
-          new PostgresConnectionProvider(driver, options)
-
-        case MariaDBConnectionProvider.driverClass =>
-          logDebug("MariaDB connection provider found")
-          new MariaDBConnectionProvider(driver, options)
-
-        case DB2ConnectionProvider.driverClass =>
-          logDebug("DB2 connection provider found")
-          new DB2ConnectionProvider(driver, options)
-
-        case MSSQLConnectionProvider.driverClass =>
-          logDebug("MS SQL connection provider found")
-          new MSSQLConnectionProvider(driver, options)
-
-        case OracleConnectionProvider.driverClass =>
-          logDebug("Oracle connection provider found")
-          new OracleConnectionProvider(driver, options)
-
-        case _ =>
-          throw new IllegalArgumentException(s"Driver ${options.driverClass} 
does not support " +
-            "Kerberos authentication")
+  private val providers = loadProviders()
+
+  def loadProviders(): Seq[JdbcConnectionProvider] = {
+    val loader = ServiceLoader.load(classOf[JdbcConnectionProvider],
+      Utils.getContextOrSparkClassLoader)
+    val providers = mutable.ArrayBuffer[JdbcConnectionProvider]()
+
+    val iterator = loader.iterator
+    while (iterator.hasNext) {
+      try {
+        val provider = iterator.next
+        logDebug(s"Loaded built in provider: $provider")
+        providers += provider
+      } catch {
+        case t: Throwable =>
+          logError(s"Failed to load built in provider.", t)
       }
     }
+    providers
+  }
+
+  def create(driver: Driver, options: JDBCOptions): Connection = {
+    val filteredProviders = providers.filter(_.canHandle(driver, options))
+    logDebug(s"Filtered providers: $filteredProviders")
+    require(filteredProviders.size == 1,
+      "JDBC connection initiated but not exactly one connection provider found 
which can handle it")

Review comment:
       Could you also show up in the err message what connect providers are 
found for the driver?




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