JSONPointer.java

package org.json;

import static java.lang.String.format;
import static java.util.Collections.emptyList;

import java.io.UnsupportedEncodingException;
import java.net.URLDecoder;
import java.util.ArrayList;
import java.util.List;

/*
Copyright (c) 2002 JSON.org

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

The Software shall be used for Good, not Evil.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.
*/

/**
 * A JSON Pointer is a simple query language defined for JSON documents by
 * <a href="https://tools.ietf.org/html/rfc6901">RFC 6901</a>. 
 */
public class JSONPointer {

    private List<String> refTokens;

    /**
     * Pre-parses and initializes a new {@code JSONPointer} instance. If you want to
     * evaluate the same JSON Pointer on different JSON documents then it is recommended
     * to keep the {@code JSONPointer} instances due to performance considerations.
     * 
     * @param pointer the JSON String or URI Fragment representation of the JSON pointer.
     * @throws IllegalArgumentException if {@code pointer} is not a valid JSON pointer
     */
    public JSONPointer(String pointer) {
        if (pointer == null) {
            throw new NullPointerException("pointer cannot be null");
        }
        if (pointer.isEmpty()) {
            refTokens = emptyList();
            return;
        }
        if (pointer.startsWith("#/")) {
            pointer = pointer.substring(2);
            try {
                pointer = URLDecoder.decode(pointer, "utf-8");
            } catch (UnsupportedEncodingException e) {
                throw new RuntimeException(e);
            }
        } else if (pointer.startsWith("/")) {
            pointer = pointer.substring(1);
        } else {
            throw new IllegalArgumentException("a JSON pointer should start with '/' or '#/'");
        }
        refTokens = new ArrayList<String>();
        for (String token : pointer.split("/")) {
            refTokens.add(unescape(token));
        }
    }

    private String unescape(String token) {
        return token.replace("~1", "/").replace("~0", "~")
                .replace("\\\"", "\"")
                .replace("\\\\", "\\");
    }

    /**
     * Evaluates this JSON Pointer on the given {@code document}. The {@code document}
     * is usually a {@link JSONObject} or a {@link JSONArray} instance, but the empty
     * JSON Pointer ({@code ""}) can be evaluated on any JSON values and in such case the
     * returned value will be {@code document} itself. 
     * 
     * @param document the JSON document which should be the subject of querying.
     * @return the result of the evaluation
     * @throws JSONPointerException if an error occurs during evaluation
     */
    public Object queryFrom(Object document) {
        if (refTokens.isEmpty()) {
            return document;
        }
        Object current = document;
        for (String token : refTokens) {
            if (current instanceof JSONObject) {
                current = ((JSONObject) current).opt(unescape(token));
            } else if (current instanceof JSONArray) {
                current = readByIndexToken(current, token);
            } else {
                throw new JSONPointerException(format(
                        "value [%s] is not an array or object therefore its key %s cannot be resolved", current,
                        token));
            }
        }
        return current;
    }

    private Object readByIndexToken(Object current, String indexToken) {
        try {
            int index = Integer.parseInt(indexToken);
            JSONArray currentArr = (JSONArray) current;
            if (index >= currentArr.length()) {
                throw new JSONPointerException(format("index %d is out of bounds - the array has %d elements", index,
                        currentArr.length()));
            }
            return currentArr.get(index);
        } catch (NumberFormatException e) {
            throw new JSONPointerException(format("%s is not an array index", indexToken), e);
        }
    }
}