Github user tzolov commented on a diff in the pull request:
https://github.com/apache/incubator-hawq/pull/302#discussion_r51870529
--- 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 --
Not it points to the element before the last. This is because the last
element could either a simple node name or array reference (e.g. name[index]).
Later the JsornResovler#getFields handles both cases separately to resolve the
last node element.
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