Convert local variable to field

Instead of instantiating the variable every time the method is called,
do it once in the constructor.

Change-Id: I524ef5a3a5fb47c6f82be4f167900ec868279c34
diff --git a/src/main/java/com/ericsson/gerrit/plugins/eventslog/sql/SQLClient.java b/src/main/java/com/ericsson/gerrit/plugins/eventslog/sql/SQLClient.java
index d0e5d94..e950dcd 100644
--- a/src/main/java/com/ericsson/gerrit/plugins/eventslog/sql/SQLClient.java
+++ b/src/main/java/com/ericsson/gerrit/plugins/eventslog/sql/SQLClient.java
@@ -47,6 +47,8 @@
 class SQLClient {
   private static final Logger log = LoggerFactory.getLogger(SQLClient.class);
   private final Gson gson;
+  private final boolean isPostgresql;
+
   private BasicDataSource ds;
 
   SQLClient(String storeUrl, String urlOptions) {
@@ -59,6 +61,7 @@
     ds.setValidationQueryTimeout(5);
 
     gson = new GsonBuilder().registerTypeAdapter(Supplier.class, new SupplierSerializer()).create();
+    isPostgresql = storeUrl.contains("postgresql");
   }
 
   /**
@@ -106,9 +109,8 @@
    * @throws SQLException If there was a problem with the database
    */
   void createDBIfNotCreated() throws SQLException {
-    boolean postgresql = ds.getUrl().contains("postgresql");
-    execute(SQLTable.createTableQuery(postgresql));
-    execute(SQLTable.createIndexes(postgresql));
+    execute(SQLTable.createTableQuery(isPostgresql));
+    execute(SQLTable.createIndexes(isPostgresql));
   }
 
   /**