do not explode if mysql transient exception does not exist

extensions-core/mysql-metadata-storage/src/main/java/org/apache/druid/metadata/storage/mysql/MySQLConnector.java

@@ -19,7 +19,6 @@
 
 package org.apache.druid.metadata.storage.mysql;
 
-import com.google.common.annotations.VisibleForTesting;
 import com.google.common.base.Joiner;
 import com.google.common.base.Supplier;
 import com.google.common.collect.ImmutableList;
@@ -62,10 +61,10 @@ public MySQLConnector(
   {
     super(config, dbTables);
     log.info("Loading \"MySQL\" metadata connector driver %s", driverConfig.getDriverClassName());
-    tryLoadDriverClass(driverConfig.getDriverClassName());
+    tryLoadDriverClass(driverConfig.getDriverClassName(), true);
 
     if (driverConfig.getDriverClassName().contains("mysql")) {
-      myTransientExceptionClass = tryLoadDriverClass(MYSQL_TRANSIENT_EXCEPTION_CLASS_NAME);
+      myTransientExceptionClass = tryLoadDriverClass(MYSQL_TRANSIENT_EXCEPTION_CLASS_NAME, false);
     } else {
       myTransientExceptionClass = null;
     }
@@ -205,7 +204,11 @@ public boolean tableExists(Handle handle, String tableName)
   @Override
   protected boolean connectorIsTransientException(Throwable e)
   {
-    return isTransientException(myTransientExceptionClass, e);
+    if (myTransientExceptionClass != null) {
+      return myTransientExceptionClass.isAssignableFrom(e.getClass())
+             || e instanceof SQLException && ((SQLException) e).getErrorCode() == 1317 /* ER_QUERY_INTERRUPTED */;
+    }
+    return false;
   }
 
   @Override
@@ -241,28 +244,23 @@ public DBI getDBI()
     return dbi;
   }
 
-  private Class<?> tryLoadDriverClass(String className)
+  @Nullable
+  private Class<?> tryLoadDriverClass(String className, boolean failIfNotFound)
   {
     try {
       return Class.forName(className, false, getClass().getClassLoader());
     }
     catch (ClassNotFoundException e) {
-      throw new ISE(e, "Could not find %s on the classpath. The MySQL Connector library is not included in the Druid "
-                       + "distribution but is required to use MySQL. Please download a compatible library (for example "
-                       + "'mysql-connector-java-5.1.48.jar') and place it under 'extensions/mysql-metadata-storage/'. See "
-                       + "https://druid.apache.org/downloads for more details.",
-                    className
-      );
-    }
-  }
-
-  @VisibleForTesting
-  static boolean isTransientException(@Nullable Class<?> driverClazz, Throwable e)
-  {
-    if (driverClazz != null) {
-      return driverClazz.isAssignableFrom(e.getClass())
-             || e instanceof SQLException && ((SQLException) e).getErrorCode() == 1317 /* ER_QUERY_INTERRUPTED */;
+      if (failIfNotFound) {
+        throw new ISE(e, "Could not find %s on the classpath. The MySQL Connector library is not included in the Druid "
+                         + "distribution but is required to use MySQL. Please download a compatible library (for example "
+                         + "'mysql-connector-java-5.1.48.jar') and place it under 'extensions/mysql-metadata-storage/'. See "
+                         + "https://druid.apache.org/downloads for more details.",
+                      className
+        );
+      }
+      log.warn("Could not find %s on the classpath.", className);
+      return null;
     }
-    return false;
   }
 }

extensions-core/mysql-metadata-storage/src/test/java/org/apache/druid/metadata/storage/mysql/MySQLConnectorTest.java

@@ -19,8 +19,11 @@
 
 package org.apache.druid.metadata.storage.mysql;
 
+import com.google.common.base.Supplier;
 import com.mysql.jdbc.exceptions.MySQLTransactionRollbackException;
 import com.mysql.jdbc.exceptions.MySQLTransientException;
+import org.apache.druid.metadata.MetadataStorageConnectorConfig;
+import org.apache.druid.metadata.MetadataStorageTablesConfig;
 import org.junit.Assert;
 import org.junit.Test;
 
@@ -29,37 +32,63 @@
 
 public class MySQLConnectorTest
 {
+  private static final MySQLConnectorDriverConfig MYSQL_DRIVER_CONFIG = new MySQLConnectorDriverConfig();
+  private static final MySQLConnectorDriverConfig MARIADB_DRIVER_CONFIG = new MySQLConnectorDriverConfig()
+  {
+    @Override
+    public String getDriverClassName()
+    {
+      return "org.mariadb.jdbc.Driver";
+    }
+  };
+  private static final Supplier<MetadataStorageConnectorConfig> CONNECTOR_CONFIG_SUPPLIER =
+      MetadataStorageConnectorConfig::new;
+  private static final Supplier<MetadataStorageTablesConfig> TABLES_CONFIG_SUPPLIER =
+      () -> new MetadataStorageTablesConfig(null, null, null, null, null, null, null, null, null, null, null);
+
+
   @Test
-  public void testIsExceptionTransient()
+  public void testIsExceptionTransientMySql()
   {
-    final Class<?> clazz = MySQLTransientException.class;
-    Assert.assertTrue(MySQLConnector.isTransientException(clazz, new MySQLTransientException()));
-    Assert.assertTrue(MySQLConnector.isTransientException(clazz, new MySQLTransactionRollbackException()));
+    MySQLConnector connector = new MySQLConnector(
+        CONNECTOR_CONFIG_SUPPLIER,
+        TABLES_CONFIG_SUPPLIER,
+        new MySQLConnectorSslConfig(),
+        MYSQL_DRIVER_CONFIG
+    );
+    Assert.assertTrue(connector.connectorIsTransientException(new MySQLTransientException()));
+    Assert.assertTrue(connector.connectorIsTransientException(new MySQLTransactionRollbackException()));
     Assert.assertTrue(
-        MySQLConnector.isTransientException(clazz, new SQLException("some transient failure", "wtf", 1317))
+        connector.connectorIsTransientException(new SQLException("some transient failure", "wtf", 1317))
     );
     Assert.assertFalse(
-        MySQLConnector.isTransientException(clazz, new SQLException("totally realistic test data", "wtf", 1337))
+        connector.connectorIsTransientException(new SQLException("totally realistic test data", "wtf", 1337))
     );
     // this method does not specially handle normal transient exceptions either, since it is not vendor specific
     Assert.assertFalse(
-        MySQLConnector.isTransientException(clazz, new SQLTransientConnectionException("transient"))
+        connector.connectorIsTransientException(new SQLTransientConnectionException("transient"))
     );
   }
 
   @Test
   public void testIsExceptionTransientNoMySqlClazz()
   {
+    MySQLConnector connector = new MySQLConnector(
+        CONNECTOR_CONFIG_SUPPLIER,
+        TABLES_CONFIG_SUPPLIER,
+        new MySQLConnectorSslConfig(),
+        MARIADB_DRIVER_CONFIG
+    );
     // no vendor specific for MariaDb, so should always be false
-    Assert.assertFalse(MySQLConnector.isTransientException(null, new MySQLTransientException()));
+    Assert.assertFalse(connector.connectorIsTransientException(new MySQLTransientException()));
     Assert.assertFalse(
-        MySQLConnector.isTransientException(null, new SQLException("some transient failure", "wtf", 1317))
+        connector.connectorIsTransientException(new SQLException("some transient failure", "wtf", 1317))
     );
     Assert.assertFalse(
-        MySQLConnector.isTransientException(null, new SQLException("totally realistic test data", "wtf", 1337))
+        connector.connectorIsTransientException(new SQLException("totally realistic test data", "wtf", 1337))
     );
     Assert.assertFalse(
-        MySQLConnector.isTransientException(null, new SQLTransientConnectionException("transient"))
+        connector.connectorIsTransientException(new SQLTransientConnectionException("transient"))
     );
   }
 }