fix code

hutool-db/src/main/java/cn/hutool/db/dialect/DialectFactory.java

@@ -55,7 +55,7 @@ public class DialectFactory {
 	public final static String DRIVER_DM7 = "dm.jdbc.driver.DmDriver";
 	
 	private static Map<DataSource, Dialect> dialectPool = new ConcurrentHashMap<>();
-	private static Object lock = new Object();
+	private static final Object lock = new Object();
 
 	private DialectFactory() {
 	}

hutool-db/src/main/java/cn/hutool/db/dialect/DriverUtil.java

@@ -44,7 +44,7 @@ public class DriverUtil {
 		}
 		
 		Connection conn = null;
-		String driver = null;
+		String driver;
 		try {
 			try {
 				conn = ds.getConnection();
@@ -69,7 +69,7 @@ public class DriverUtil {
 	 * @throws DbRuntimeException SQL异常包装，获取元数据信息失败
 	 */
 	public static String identifyDriver(Connection conn) throws DbRuntimeException {
-		String driver = null;
+		String driver;
 		DatabaseMetaData meta;
 		try {
 			meta = conn.getMetaData();

hutool-db/src/main/java/cn/hutool/db/ds/GlobalDSFactory.java

@@ -12,7 +12,7 @@ import cn.hutool.log.StaticLog;
 public class GlobalDSFactory {
 
 	private static volatile DSFactory factory;
-	private static Object lock = new Object();
+	private static final Object lock = new Object();
 
 	/*
 	 * 设置在JVM关闭时关闭所有数据库连接