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From tzolov <...@git.apache.org>
Subject [GitHub] incubator-hawq pull request: HAWQ-178: Add JSON plugin support in ...
Date Thu, 04 Feb 2016 13:23:50 GMT
Github user tzolov commented on a diff in the pull request:

    https://github.com/apache/incubator-hawq/pull/302#discussion_r51870749
  
    --- Diff: pxf/pxf-json/src/main/java/org/apache/hawq/pxf/plugins/json/JsonResolver.java
---
    @@ -0,0 +1,255 @@
    +package org.apache.hawq.pxf.plugins.json;
    +
    +/*
    + * Licensed to the Apache Software Foundation (ASF) under one
    + * 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
    + * specific language governing permissions and limitations
    + * under the License.
    + */
    +
    +import java.io.IOException;
    +import java.util.ArrayList;
    +import java.util.Iterator;
    +import java.util.List;
    +
    +import org.apache.commons.logging.Log;
    +import org.apache.commons.logging.LogFactory;
    +import org.apache.hawq.pxf.api.OneField;
    +import org.apache.hawq.pxf.api.OneRow;
    +import org.apache.hawq.pxf.api.ReadResolver;
    +import org.apache.hawq.pxf.api.io.DataType;
    +import org.apache.hawq.pxf.api.utilities.ColumnDescriptor;
    +import org.apache.hawq.pxf.api.utilities.InputData;
    +import org.apache.hawq.pxf.api.utilities.Plugin;
    +import org.codehaus.jackson.JsonFactory;
    +import org.codehaus.jackson.JsonNode;
    +import org.codehaus.jackson.map.ObjectMapper;
    +
    +/**
    + * This JSON resolver for PXF will decode a given object from the {@link JsonAccessor}
into a row for HAWQ. It will
    + * decode this data into a JsonNode and walk the tree for each column. It supports normal
value mapping via projections
    + * and JSON array indexing.
    + */
    +public class JsonResolver extends Plugin implements ReadResolver {
    +
    +	private static final Log LOG = LogFactory.getLog(JsonResolver.class);
    +
    +	private ArrayList<OneField> oneFieldList;
    +	private ColumnDescriptorCache[] columnDescriptorCache;
    +	private ObjectMapper mapper;
    +
    +	public JsonResolver(InputData inputData) throws Exception {
    +		super(inputData);
    +		oneFieldList = new ArrayList<OneField>();
    +		mapper = new ObjectMapper(new JsonFactory());
    +
    +		// Pre-generate all column structure attributes concerning the JSON to column value
resolution.
    +		columnDescriptorCache = new ColumnDescriptorCache[inputData.getColumns()];
    +		for (int i = 0; i < inputData.getColumns(); ++i) {
    +			ColumnDescriptor cd = inputData.getColumn(i);
    +			columnDescriptorCache[i] = new ColumnDescriptorCache(cd);
    +		}
    +	}
    +
    +	@Override
    +	public List<OneField> getFields(OneRow row) throws Exception {
    +		oneFieldList.clear();
    +
    +		String jsonRecordAsText = row.getData().toString();
    +
    +		JsonNode root = decodeLineToJsonNode(jsonRecordAsText);
    +
    +		if (root == null) {
    +			LOG.warn("Return null-fields row due to invalid JSON:" + jsonRecordAsText);
    +		}
    +
    +		// Iterate through the column definition and fetch our JSON data
    +		for (ColumnDescriptorCache column : columnDescriptorCache) {
    +
    +			// Get the current column description
    +
    +			if (root == null) {
    +				// Return empty (e.g. null) filed in case of malformed json.
    +				addNullField(column.getColumnType());
    +			} else {
    +
    +				// Move down the JSON path to the final name
    +				JsonNode node = getPriorJsonNode(root, column.getProjections());
    +
    +				// If this column is an array index, ex. "tweet.hashtags[0]"
    +				if (column.isArrayName()) {
    +
    +					// Move to the array node
    +					node = node.get(column.getArrayNodeName());
    +
    +					// If this node is null or missing, add a null value here
    +					if (node == null || node.isMissingNode()) {
    +						addNullField(column.getColumnType());
    +					} else if (node.isArray()) {
    +						// If the JSON node is an array, then add it to our list
    +						addFieldFromJsonArray(column.getColumnType(), node, column.getArrayIndex());
    +					} else {
    +						throw new IllegalStateException(column.getArrayNodeName() + " is not an array node");
    +					}
    +				} else {
    +					// This column is not an array type
    +					// Move to the final node
    +					node = node.get(column.getLastProjection());
    +
    +					// If this node is null or missing, add a null value here
    +					if (node == null || node.isMissingNode()) {
    +						addNullField(column.getColumnType());
    +					} else {
    +						// Else, add the value to the record
    +						addFieldFromJsonNode(column.getColumnType(), node);
    +					}
    +				}
    +			}
    +		}
    +
    +		return oneFieldList;
    +	}
    +
    +	/**
    +	 * Iterates down the root node to the child JSON node defined by the projs path.
    +	 * 
    +	 * @param root
    +	 *            node to to start the traversal from.
    +	 * @param projs
    +	 *            defines the path from the root to the desired child node.
    +	 * @return Returns the child node defined by the root and projs path.
    +	 */
    +	private JsonNode getPriorJsonNode(JsonNode root, String[] projs) {
    +
    +		// Iterate through all the tokens to the desired JSON node
    +		JsonNode node = root;
    +		for (int j = 0; j < projs.length - 1; ++j) {
    --- End diff --
    
    Update: I've refactored the ColumDescriptorCache to compute a *normalized* projections.
In case of array it substitutes the last path element with the name of the array. In this
way the JsonResolver#getFields() is simplified. (take a look)


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