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Core processing architecture for json-schema-validator
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/*
 * Copyright (c) 2013, Francis Galiegue 
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the Lesser GNU General Public License as
 * published by the Free Software Foundation, either version 3 of the
 * License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * Lesser GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see .
 */

package com.github.fge.jsonschema.util;

import com.fasterxml.jackson.databind.DeserializationFeature;
import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.ObjectReader;
import com.fasterxml.jackson.databind.ObjectWriter;
import com.fasterxml.jackson.databind.node.JsonNodeFactory;
import com.google.common.collect.Maps;
import com.google.common.io.Closeables;

import java.io.IOException;
import java.io.StringWriter;
import java.math.BigDecimal;
import java.util.Collections;
import java.util.Iterator;
import java.util.Map;

/**
 * Utility class for Jackson
 *
 * This class provides a custom {@link JsonNodeFactory} and {@link
 * ObjectReader} which you should use preferably to your own (in particular,
 * the reader ensures that decimal values are read using {@link BigDecimal}.
 */
public final class JacksonUtils
{
    private static final JsonNodeFactory FACTORY
        = JsonNodeFactory.withExactBigDecimals(false);

    private static final ObjectReader READER;
    private static final ObjectWriter WRITER;

    static {
        final ObjectMapper mapper = new ObjectMapper().setNodeFactory(FACTORY)
            .enable(DeserializationFeature.USE_BIG_DECIMAL_FOR_FLOATS);
        READER = mapper.reader();
        WRITER = mapper.writerWithDefaultPrettyPrinter();
    }

    private JacksonUtils()
    {
    }

    /**
     * Return a preconfigured {@link ObjectReader} to read JSON inputs
     *
     * @return the reader
     */
    public static ObjectReader getReader()
    {
        return READER;
    }

    /**
     * Return a preconfigured {@link JsonNodeFactory} to generate JSON data as
     * {@link JsonNode}s
     *
     * @return the factory
     */
    public static JsonNodeFactory nodeFactory()
    {
        return FACTORY;
    }

    /**
     * Return a map out of an object's members
     *
     * If the node given as an argument is not a map, an empty map is
     * returned.
     *
     * @param node the node
     * @return a map
     */
    public static Map asMap(final JsonNode node)
    {
        if (!node.isObject())
            return Collections.emptyMap();

        final Iterator> iterator = node.fields();
        final Map ret = Maps.newHashMap();

        Map.Entry entry;

        while (iterator.hasNext()) {
            entry = iterator.next();
            ret.put(entry.getKey(), entry.getValue());
        }

        return ret;
    }

    /**
     * Pretty print a JSON value
     *
     * @param node the JSON value to print
     * @return the pretty printed value as a string
     */
    public static String prettyPrint(final JsonNode node)
    {
        final StringWriter writer = new StringWriter();

        try {
            WRITER.writeValue(writer, node);
            writer.flush();
        } catch (IOException ignored) {
            // cannot happen
        } finally {
            Closeables.closeQuietly(writer);
        }

        return writer.toString();
    }
}