src/main/java/org/apache/sling/scripting/sightly/impl/engine/extension/JoinFilterExtension.java

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 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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
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package org.apache.sling.scripting.sightly.impl.engine.extension;

import java.util.Collection;
import java.util.Iterator;

import org.apache.sling.scripting.sightly.extension.RuntimeExtension;
import org.apache.sling.scripting.sightly.render.RenderContext;
import org.apache.sling.scripting.sightly.render.RuntimeObjectModel;
import org.osgi.service.component.annotations.Component;

@Component(
        service = RuntimeExtension.class,
        property = {
                RuntimeExtension.NAME + "=" + RuntimeExtension.JOIN
        }
)
public class JoinFilterExtension implements RuntimeExtension {

    @Override
    public Object call(final RenderContext renderContext, Object... arguments) {
        ExtensionUtils.checkArgumentCount(RuntimeExtension.JOIN, arguments, 2);
        Object joinArgument = arguments[0];
        RuntimeObjectModel runtimeObjectModel = renderContext.getObjectModel();
        Collection<?> collection = runtimeObjectModel.toCollection(joinArgument);
        String joinString = runtimeObjectModel.toString(arguments[1]);
        return join(runtimeObjectModel, collection, joinString);
    }

    private String join(RuntimeObjectModel runtimeObjectModel, Collection<?> collection, String joinString) {
        StringBuilder sb = new StringBuilder();
        Iterator<?> iterator = collection.iterator();
        while (iterator.hasNext()) {
            String element = runtimeObjectModel.toString(iterator.next());
            sb.append(element);
            if (iterator.hasNext()) {
                sb.append(joinString);
            }
        }
        return sb.toString();
    }

}