GUACAMOLE-1407: Merge automatic detection of whether MySQL/MariaDB driver

extensions/guacamole-auth-jdbc/modules/guacamole-auth-jdbc-base/src/main/java/org/apache/guacamole/auth/jdbc/JDBCEnvironment.java

@@ -192,4 +192,24 @@ public abstract class JDBCEnvironment extends DelegatingEnvironment {
      */
     public abstract String getPassword() throws GuacamoleException;
 
+    /**
+     * Returns whether the given Java class is defined within the classpath.
+     *
+     * @param classname
+     *     The name of the Java class to check.
+     *
+     * @return
+     *     true if the given Java class is present within the classpath, false
+     *     otherwise.
+     */
+    public static boolean isClassDefined(String classname) {
+        try {
+            Class.forName(classname, false, JDBCEnvironment.class.getClassLoader());
+            return true;
+        }
+        catch (ClassNotFoundException e) {
+            return false;
+        }
+    }
+
 }

extensions/guacamole-auth-jdbc/modules/guacamole-auth-jdbc-mysql/src/main/java/org/apache/guacamole/auth/mysql/conf/MySQLDriver.java

@@ -19,6 +19,7 @@
 
 package org.apache.guacamole.auth.mysql.conf;
 
+import org.apache.guacamole.auth.jdbc.JDBCEnvironment;
 import org.apache.guacamole.properties.EnumGuacamoleProperty.PropertyValue;
 
 /**
@@ -31,11 +32,39 @@ public enum MySQLDriver {
      * MySQL driver.
      */
     @PropertyValue("mysql")
-    MYSQL,
+    MYSQL("com.mysql.jdbc.Driver"),
 
     /**
      * MariaDB driver.
      */
     @PropertyValue("mariadb")
-    MARIADB;
+    MARIADB("org.mariadb.jdbc.Driver");
+
+    /**
+     * The name of the JDBC driver class.
+     */
+    private final String driverClass;
+
+    /**
+     * Creates a new MySQLDriver that points to the given Java class as the
+     * entrypoint of the JDBC driver.
+     *
+     * @param classname
+     *     The name of the JDBC driver class.
+     */
+    private MySQLDriver(String classname) {
+        this.driverClass = classname;
+    }
+
+    /**
+     * Returns whether this MySQL JDBC driver is installed and can be found
+     * within the Java classpath.
+     *
+     * @return
+     *     true if this MySQL JDBC driver is installed, false otherwise.
+     */
+    public boolean isInstalled() {
+        return JDBCEnvironment.isClassDefined(driverClass);
+    }
+
 }

extensions/guacamole-auth-jdbc/modules/guacamole-auth-jdbc-mysql/src/main/java/org/apache/guacamole/auth/mysql/conf/MySQLEnvironment.java

@@ -25,6 +25,7 @@ import java.sql.DatabaseMetaData;
 import java.sql.SQLException;
 import java.util.TimeZone;
 import org.apache.guacamole.GuacamoleException;
+import org.apache.guacamole.GuacamoleServerException;
 import org.apache.guacamole.auth.jdbc.JDBCEnvironment;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
@@ -53,11 +54,6 @@ public class MySQLEnvironment extends JDBCEnvironment {
      */
     private static final MySQLVersion MYSQL_SUPPORTS_CTE = new MySQLVersion(8, 0, 1, false);
 
-    /**
-     * The default MySQL-compatible driver to use, if not specified.
-     */
-    private static final MySQLDriver DEFAULT_DRIVER = MySQLDriver.MYSQL;
-    
     /**
      * The default host to connect to, if MYSQL_HOSTNAME is not specified.
      */
@@ -178,21 +174,41 @@ public class MySQLEnvironment extends JDBCEnvironment {
 
     /**
      * Returns the MySQL driver that will be used to talk to the MySQL-compatible
-     * database server hosting the Guacamole Client database.  If unspecified
+     * database server hosting the Guacamole database. If unspecified, the
-     * a default value of MySQL will be used.
+     * installed MySQL driver will be automatically detected by inspecting the
+     * classes available in the classpath.
      * 
      * @return
      *     The MySQL driver that will be used to communicate with the MySQL-
      *     compatible server.
      * 
      * @throws GuacamoleException 
-     *     If guacamole.properties cannot be parsed.
+     *     If guacamole.properties cannot be parsed, or if no MySQL-compatible
+     *     JDBC driver is present.
      */
     public MySQLDriver getMySQLDriver() throws GuacamoleException {
-        return getProperty(
+
-            MySQLGuacamoleProperties.MYSQL_DRIVER,
+        // Use any explicitly-specified driver
-            DEFAULT_DRIVER
+        MySQLDriver driver = getProperty(MySQLGuacamoleProperties.MYSQL_DRIVER);
-        );
+        if (driver != null)
+            return driver;
+
+        // Attempt autodetection based on presence of JDBC driver within
+        // classpath...
+
+        if (MySQLDriver.MARIADB.isInstalled()) {
+            logger.info("Installed JDBC driver for MySQL/MariaDB detected as \"MariaDB Connector/J\".");
+            return MySQLDriver.MARIADB;
+        }
+
+        if (MySQLDriver.MYSQL.isInstalled()) {
+            logger.info("Installed JDBC driver for MySQL/MariaDB detected as \"MySQL Connector/J\".");
+            return MySQLDriver.MYSQL;
+        }
+
+        // No driver found at all
+        throw new GuacamoleServerException("No JDBC driver for MySQL/MariaDB is installed.");
+
     }
     
     /**