io.wcm.caravan.pipeline.impl.operators.MergeTransformer.java Source code

Introduction

Here is the source code for io.wcm.caravan.pipeline.impl.operators.MergeTransformer.java

Source

/*
 * #%L
 * wcm.io
 * %%
 * Copyright (C) 2014 wcm.io
 * %%
 * 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.
 * #L%
 */
package io.wcm.caravan.pipeline.impl.operators;

import static org.apache.commons.lang3.StringUtils.isNotBlank;
import io.wcm.caravan.pipeline.JsonPipeline;
import io.wcm.caravan.pipeline.JsonPipelineOutput;
import io.wcm.caravan.pipeline.JsonPipelineOutputException;

import java.util.Iterator;
import java.util.Map.Entry;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import rx.Observable;
import rx.Observable.Transformer;

import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.node.ObjectNode;

/**
 * a transformer that merges the output of a secondary {@link JsonPipeline} into the output of the primary pipeline.
 */
public class MergeTransformer implements Transformer<JsonPipelineOutput, JsonPipelineOutput> {

    private static final Logger log = LoggerFactory.getLogger(MergeTransformer.class);

    private final String primaryDescriptor;
    private final Observable<JsonPipelineOutput> secondaryOutput;
    private final String targetProperty;

    /**
     * @param primaryDescriptor the descriptor of the primary pipeline
     * @param secondaryOutput the observable that emits the output of the secondary pipeline
     * @param targetProperty the property that will be added to the primary pipeline'S output
     */
    public MergeTransformer(String primaryDescriptor, Observable<JsonPipelineOutput> secondaryOutput,
            String targetProperty) {
        this.primaryDescriptor = primaryDescriptor;
        this.secondaryOutput = secondaryOutput;
        this.targetProperty = targetProperty;
    }

    @Override
    public Observable<JsonPipelineOutput> call(Observable<JsonPipelineOutput> primaryOutput) {
        return primaryOutput.zipWith(secondaryOutput, (primaryModel, secondaryModel) -> {

            log.debug("zipping object from secondary source into target property " + targetProperty);

            JsonNode jsonFromPrimary = primaryModel.getPayload();
            JsonNode jsonFromSecondary = secondaryModel.getPayload();

            if (!(jsonFromPrimary.isObject())) {
                throw new JsonPipelineOutputException(
                        "Only pipelines with JSON *Objects* can be used as a target for a merge operation, but response data for "
                                + primaryDescriptor + " contained " + jsonFromPrimary.getClass().getSimpleName());
            }

            // start with cloning the the response of the primary pipeline
            ObjectNode mergedObject = jsonFromPrimary.deepCopy();

            // if a target property is specified, the JSON to be merged is inserted into this property
            if (isNotBlank(targetProperty)) {

                if (!mergedObject.has(targetProperty)) {
                    // the target property does not exist yet, so we just can set the property
                    mergedObject.set(targetProperty, jsonFromSecondary);
                } else {

                    // the target property already exists - let's hope we can merge!
                    JsonNode targetNode = mergedObject.get(targetProperty);

                    if (!targetNode.isObject()) {
                        throw new JsonPipelineOutputException(
                                "When merging two pipelines into the same target property, both most contain JSON *Object* responses");
                    }

                    if (!(jsonFromSecondary.isObject())) {
                        throw new JsonPipelineOutputException(
                                "Only pipelines with JSON *Object* responses can be merged into an existing target property");
                    }

                    mergeAllPropertiesInto((ObjectNode) jsonFromSecondary, (ObjectNode) targetNode);
                }
            } else {

                // if no target property is specified, all properties of the secondary pipeline are copied into the merged object
                if (!(jsonFromSecondary.isObject())) {
                    throw new JsonPipelineOutputException(
                            "Only pipelines with JSON *Object* responses can be merged without specify a target property");
                }

                mergeAllPropertiesInto((ObjectNode) jsonFromSecondary, mergedObject);
            }

            return primaryModel.withPayload(mergedObject)
                    .withMaxAge(Math.min(primaryModel.getMaxAge(), secondaryModel.getMaxAge()));
        });
    }

    private void mergeAllPropertiesInto(ObjectNode nodeToMerge, ObjectNode targetNode) {

        // iterate over all properties of the given node
        Iterator<Entry<String, JsonNode>> propertyIterator = nodeToMerge.fields();
        while (propertyIterator.hasNext()) {
            Entry<String, JsonNode> nextProperty = propertyIterator.next();
            String propertyName = nextProperty.getKey();

            if (targetNode.has(propertyName)) {
                // what to do if the property already exists? for now, just throw an exception,
                throw new JsonPipelineOutputException(
                        "Target pipeline " + primaryDescriptor + " already has a property named " + propertyName);
            }

            targetNode.set(propertyName, nextProperty.getValue());
        }
    }
}