Abstract out concepts of DataSourceType and DatabaseConfigInitializer.

Encapsulate data source specific logic into subclasses of DataSourceType
and DatabaseConfigInitializer.  DataSourceType and
DatabaseConfigInitializer are separated because we need them at
different stages (init vs runtime) and they also need to exist in
different projects with different dependencies.

This is a first step toward providing support for different database
platforms as plugins.

Change-Id: I01ea666ef7f682d6137f0e64005d979dd706f67b
Signed-off-by: Edwin Kempin <edwin.kempin@sap.com>
Signed-off-by: Sasa Zivkov <sasa.zivkov@sap.com>

gerrit-server/src/main/java/com/google/gerrit/server/config/ConfigSection.java

@@ -0,0 +1,37 @@
+// Copyright (C) 2012 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package com.google.gerrit.server.config;
+
+import org.eclipse.jgit.lib.Config;
+
+/** Provides access to one section from {@link Config} */
+public class ConfigSection {
+
+  private final Config cfg;
+  private final String section;
+
+  public ConfigSection(Config cfg, String section) {
+    this.cfg = cfg;
+    this.section = section;
+  }
+
+  public String optional(String name) {
+    return cfg.getString(section, null, name);
+  }
+
+  public String required(String name) {
+    return ConfigUtil.getRequired(cfg, null, name);
+  }
+}