JsonAccessor.java

// 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.
package com.cloud.bridge.util;

import java.math.BigDecimal;
import java.math.BigInteger;
import java.util.ArrayList;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

import com.google.gson.JsonArray;
import com.google.gson.JsonElement;
import com.google.gson.JsonObject;
import com.google.gson.JsonPrimitive;

import com.cloud.bridge.service.exception.InternalErrorException;

/**
 * JsonAccessor provides the functionality to allow navigating JSON object graph using simple expressions,
 * for example, following property access expressions are all valid ones
 *
 *         rootobj.level1obj[1].property
 *         this[0].level1obj[1].property
 *
 */
public class JsonAccessor {
    private JsonElement _json;

    Pattern _arrayAccessorMatcher = Pattern.compile("(.*)\\[(\\d+)\\]");

    public JsonAccessor(JsonElement json) {
        assert (json != null);
        _json = json;
    }

    public BigDecimal getAsBigDecimal(String propPath) {
        JsonElement jsonElement = eval(propPath);
        return jsonElement.getAsBigDecimal();
    }

    public BigInteger getAsBigInteger(String propPath) {
        JsonElement jsonElement = eval(propPath);
        return jsonElement.getAsBigInteger();
    }

    public boolean getAsBoolean(String propPath) {
        JsonElement jsonElement = eval(propPath);
        return jsonElement.getAsBoolean();
    }

    public byte getAsByte(String propPath) {
        JsonElement jsonElement = eval(propPath);
        return jsonElement.getAsByte();
    }

    public char getAsCharacter(String propPath) {
        JsonElement jsonElement = eval(propPath);
        return jsonElement.getAsCharacter();
    }

    public double getAsDouble(String propPath) {
        JsonElement jsonElement = eval(propPath);
        return jsonElement.getAsDouble();
    }

    public float getAsFloat(String propPath) {
        JsonElement jsonElement = eval(propPath);
        return jsonElement.getAsFloat();
    }

    public int getAsInt(String propPath) {
        JsonElement jsonElement = eval(propPath);
        return jsonElement.getAsInt();
    }

    public long getAsLong(String propPath) {
        JsonElement jsonElement = eval(propPath);
        return jsonElement.getAsLong();
    }

    public Number getAsNumber(String propPath) {
        JsonElement jsonElement = eval(propPath);
        return jsonElement.getAsNumber();
    }

    public short getAsShort(String propPath) {
        JsonElement jsonElement = eval(propPath);
        return jsonElement.getAsShort();
    }

    public String getAsString(String propPath) {
        JsonElement jsonElement = eval(propPath);
        return jsonElement.getAsString();
    }

    public boolean isBoolean(String propPath) {
        JsonElement jsonElement = eval(propPath);
        if (jsonElement instanceof JsonPrimitive)
            return ((JsonPrimitive)jsonElement).isBoolean();

        return false;
    }

    public boolean isNumber(String propPath) {
        JsonElement jsonElement = eval(propPath);

        if (jsonElement instanceof JsonPrimitive)
            return ((JsonPrimitive)jsonElement).isNumber();
        return false;
    }

    public boolean isString(String propPath) {
        JsonElement jsonElement = eval(propPath);

        if (jsonElement instanceof JsonPrimitive)
            return ((JsonPrimitive)jsonElement).isString();
        return false;
    }

    /*
     * Return
     *         -1    :    property expression can not be resolved
     *         0    :    match to a null JSON object
     *         1+    :    matched, for array element, the count of the elements inside the array
     */
    public int getMatchCount(String propPath) {
        JsonElement jsonElement = tryEval(propPath);
        if (jsonElement == null)
            return -1;

        if (jsonElement.isJsonNull())
            return 0;

        if (jsonElement.isJsonArray())
            return ((JsonArray)jsonElement).size();

        return 1;
    }

    public JsonElement eval(String propPath) {
        JsonElement jsonElement = tryEval(propPath);
        if (jsonElement == null)
            throw new InternalErrorException("Property " + propPath + " is resolved to null JSON element on object: " + _json.toString());

        return jsonElement;
    }

    public JsonElement tryEval(String propPath) {
        assert (propPath != null);
        String[] tokens = propPath.split("\\.");

        ArrayList<Resolver> resolverChain = new ArrayList<Resolver>();
        for (String token : tokens) {
            Matcher matcher = _arrayAccessorMatcher.matcher(token);
            if (matcher.find()) {
                String propStr = matcher.group(1);
                String indexStr = matcher.group(2);

                resolverChain.add(new ArrayPropertyResolver(propStr, Integer.parseInt(indexStr)));
            } else {
                resolverChain.add(new PropertyResolver(token));
            }
        }

        JsonElement jsonElementToResolveAt = _json;
        for (Resolver resolver : resolverChain) {
            jsonElementToResolveAt = resolver.resolve(jsonElementToResolveAt);

            if (jsonElementToResolveAt == null)
                break;
        }

        return jsonElementToResolveAt;
    }

    //
    // Property resolvers
    //
    private static interface Resolver {
        public JsonElement resolve(JsonElement jsonElementToResolveAt);
    }

    private static class PropertyResolver implements Resolver {
        protected String _propName;

        public PropertyResolver(String propName) {
            _propName = propName;
        }

        public JsonElement resolve(JsonElement jsonElementToResolveAt) {
            if ("this".equals(_propName))
                return jsonElementToResolveAt;

            if (jsonElementToResolveAt.isJsonObject())
                return ((JsonObject)jsonElementToResolveAt).get(_propName);

            if (jsonElementToResolveAt.isJsonNull())
                throw new NullPointerException(String.format("Property %s points to a null element on object: %s", _propName, jsonElementToResolveAt.toString()));

            throw new InternalErrorException("Unable to evaluate JSON accessor property: " + _propName + ", on object: " + jsonElementToResolveAt.toString());
        }
    }

    private static class ArrayPropertyResolver extends PropertyResolver {
        protected int _index;

        public ArrayPropertyResolver(String propName, int index) {
            super(propName);
            _index = index;
        }

        public JsonElement resolve(JsonElement jsonElementToResolveAt) {
            if (!"this".equals(_propName)) {
                if (jsonElementToResolveAt.isJsonObject()) {
                    jsonElementToResolveAt = ((JsonObject)jsonElementToResolveAt).get(_propName);
                } else {
                    if (jsonElementToResolveAt.isJsonNull())
                        throw new NullPointerException(String.format("Property %s points to a null element on object: %s", _propName, jsonElementToResolveAt.toString()));

                    throw new InternalErrorException("Unable to evaluate JSON accessor property: " + _propName + ", on object: " + jsonElementToResolveAt.toString());
                }
            }

            if (jsonElementToResolveAt instanceof JsonArray) {
                return ((JsonArray)jsonElementToResolveAt).get(_index);
            }

            if (jsonElementToResolveAt.isJsonNull())
                throw new NullPointerException(String.format("Property %s points to a null element on object: %s", _propName, jsonElementToResolveAt.toString()));

            throw new InternalErrorException("Unable to evaluate JSON accessor property: " + _propName + ", on object: " + jsonElementToResolveAt.toString());
        }
    }
}