Make RSQL visitor pluggable via a managed bean (#1145)

* Add a managed bean for a RsqlVisitorFactory

Signed-off-by: Stefan Behl <stefan.behl@bosch.io>

* Fix failing unit tests

* Fix Sonar findings

* Fix PR review findings

hawkbit-repository/hawkbit-repository-api/src/main/java/org/eclipse/hawkbit/repository/rsql/RsqlVisitorFactory.java

@@ -0,0 +1,37 @@
+/**
+ * Copyright (c) 2021 Bosch.IO GmbH and others.
+ *
+ * All rights reserved. This program and the accompanying materials
+ * are made available under the terms of the Eclipse Public License v1.0
+ * which accompanies this distribution, and is available at
+ * http://www.eclipse.org/legal/epl-v10.html
+ */
+package org.eclipse.hawkbit.repository.rsql;
+
+import org.eclipse.hawkbit.repository.FieldNameProvider;
+
+import cz.jirutka.rsql.parser.ast.Node;
+import cz.jirutka.rsql.parser.ast.RSQLVisitor;
+
+/**
+ * Factory to obtain {@link RSQLVisitor} instances that can be used to process
+ * the {@link Node}s representing an RSQL query.
+ */
+@FunctionalInterface
+public interface RsqlVisitorFactory {
+
+    /**
+     * Provides a {@link RSQLVisitor} instance for validating RSQL queries based
+     * on the given {@link FieldNameProvider}.
+     * 
+     * @param <A>
+     *            The type of the {@link FieldNameProvider}.
+     * @param fieldNameProvider
+     *            providing accessing to the relevant field names.
+     * 
+     * @return An {@link RSQLVisitor} to validate the {@link Node}s of an RSQL
+     *         query.
+     */
+    <A extends Enum<A> & FieldNameProvider> RSQLVisitor<Void, String> validationRsqlVisitor(Class<A> fieldNameProvider);
+
+}

hawkbit-repository/hawkbit-repository-api/src/main/java/org/eclipse/hawkbit/repository/rsql/RsqlVisitorFactoryHolder.java

@@ -0,0 +1,42 @@
+/**
+ * Copyright (c) 2021 Bosch.IO GmbH and others.
+ *
+ * All rights reserved. This program and the accompanying materials
+ * are made available under the terms of the Eclipse Public License v1.0
+ * which accompanies this distribution, and is available at
+ * http://www.eclipse.org/legal/epl-v10.html
+ */
+package org.eclipse.hawkbit.repository.rsql;
+
+import org.springframework.beans.factory.annotation.Autowired;
+
+/**
+ * Helper class providing static access to the managed
+ * {@link RsqlVisitorFactory} bean.
+ */
+public final class RsqlVisitorFactoryHolder {
+
+    private static final RsqlVisitorFactoryHolder SINGLETON = new RsqlVisitorFactoryHolder();
+
+    @Autowired
+    private RsqlVisitorFactory rsqlVisitorFactory;
+
+    private RsqlVisitorFactoryHolder() {
+
+    }
+
+    /**
+     * @return The holder singleton instance.
+     */
+    public static RsqlVisitorFactoryHolder getInstance() {
+        return SINGLETON;
+    }
+
+    /**
+     * @return The managed RsqlVisitorFactory bean
+     */
+    public RsqlVisitorFactory getRsqlVisitorFactory() {
+        return rsqlVisitorFactory;
+    }
+
+}