Java tutorial
package com.fasterxml.jackson.core; import com.fasterxml.jackson.core.io.NumberInput; /** * Implementation of * <a href="http://tools.ietf.org/html/draft-ietf-appsawg-json-pointer-03">JSON Pointer</a> * specification. * Pointer instances can be used to locate logical JSON nodes for things like * tree traversal (see {@link TreeNode#at}). * It may be used in future for filtering of streaming JSON content * as well (not implemented yet for 2.3). *<p> * Instances are fully immutable and can be shared, cached. * * @author Tatu Saloranta * * @since 2.3 */ public class JsonPointer { /** * Marker instance used to represent segment that matches current * node or position (that is, returns true for * {@link #matches()}). */ protected final static JsonPointer EMPTY = new JsonPointer(); /** * Reference to rest of the pointer beyond currently matching * segment (if any); null if this pointer refers to the matching * segment. */ protected final JsonPointer _nextSegment; /** * Reference from currently matching segment (if any) to node * before leaf. * Lazily constructed if/as needed. *<p> * NOTE: we'll use `volatile` here assuming that this is unlikely to * become a performance bottleneck. If it becomes one we can probably * just drop it and things still should work (despite warnings as per JMM * regarding visibility (and lack thereof) of unguarded changes). * * @since 2.5 */ protected volatile JsonPointer _head; /** * We will retain representation of the pointer, as a String, * so that {@link #toString} should be as efficient as possible. */ protected final String _asString; protected final String _matchingPropertyName; protected final int _matchingElementIndex; /* /********************************************************** /* Cosntruction /********************************************************** */ /** * Constructor used for creating "empty" instance, used to represent * state that matches current node. */ protected JsonPointer() { _nextSegment = null; _matchingPropertyName = ""; _matchingElementIndex = -1; _asString = ""; } /** * Constructor used for creating non-empty Segments */ protected JsonPointer(String fullString, String segment, JsonPointer next) { _asString = fullString; _nextSegment = next; // Ok; may always be a property _matchingPropertyName = segment; // but could be an index, if parsable _matchingElementIndex = _parseIndex(segment); } /** * @since 2.5 */ protected JsonPointer(String fullString, String segment, int matchIndex, JsonPointer next) { _asString = fullString; _nextSegment = next; _matchingPropertyName = segment; _matchingElementIndex = matchIndex; } /* /********************************************************** /* Factory methods /********************************************************** */ /** * Factory method that parses given input and construct matching pointer * instance, if it represents a valid JSON Pointer: if not, a * {@link IllegalArgumentException} is thrown. * * @throws IllegalArgumentException Thrown if the input does not present a valid JSON Pointer * expression: currently the only such expression is one that does NOT start with * a slash ('/'). */ public static JsonPointer compile(String input) throws IllegalArgumentException { // First quick checks for well-known 'empty' pointer if ((input == null) || input.length() == 0) { return EMPTY; } // And then quick validity check: if (input.charAt(0) != '/') { throw new IllegalArgumentException( "Invalid input: JSON Pointer expression must start with '/': " + "\"" + input + "\""); } return _parseTail(input); } /** * Alias for {@link #compile}; added to make instances automatically * deserializable by Jackson databind. */ public static JsonPointer valueOf(String input) { return compile(input); } /* Factory method that composes a pointer instance, given a set * of 'raw' segments: raw meaning that no processing will be done, * no escaping may is present. * * @param segments * * @return Constructed path instance */ /* TODO! public static JsonPointer fromSegment(String... segments) { if (segments.length == 0) { return EMPTY; } JsonPointer prev = null; for (String segment : segments) { JsonPointer next = new JsonPointer() } } */ /* /********************************************************** /* Public API /********************************************************** */ public boolean matches() { return _nextSegment == null; } public String getMatchingProperty() { return _matchingPropertyName; } public int getMatchingIndex() { return _matchingElementIndex; } public boolean mayMatchProperty() { return _matchingPropertyName != null; } public boolean mayMatchElement() { return _matchingElementIndex >= 0; } /** * Returns the leaf of current JSON Pointer expression. * Leaf is the last non-null segment of current JSON Pointer. * * @since 2.5 */ public JsonPointer last() { JsonPointer current = this; if (current == EMPTY) { return null; } JsonPointer next; while ((next = current._nextSegment) != JsonPointer.EMPTY) { current = next; } return current; } public JsonPointer append(JsonPointer tail) { if (this == EMPTY) { return tail; } if (tail == EMPTY) { return this; } String currentJsonPointer = _asString; if (currentJsonPointer.endsWith("/")) { //removes final slash currentJsonPointer = currentJsonPointer.substring(0, currentJsonPointer.length() - 1); } return compile(currentJsonPointer + tail._asString); } /** * Method that may be called to see if the pointer would match property * (of a JSON Object) with given name. * * @since 2.5 */ public boolean matchesProperty(String name) { return (_nextSegment != null) && _matchingPropertyName.equals(name); } public JsonPointer matchProperty(String name) { if (_nextSegment == null || !_matchingPropertyName.equals(name)) { return null; } return _nextSegment; } /** * Method that may be called to see if the pointer would match * array element (of a JSON Array) with given index. * * @since 2.5 */ public boolean matchesElement(int index) { return (index == _matchingElementIndex) && (index >= 0); } /** * Accessor for getting a "sub-pointer", instance where current segment * has been removed and pointer includes rest of segments. * For matching state, will return null. */ public JsonPointer tail() { return _nextSegment; } /** * Accessor for getting a pointer instance that is identical to this * instance except that the last segment has been dropped. * For example, for JSON Point "/root/branch/leaf", this method would * return pointer "/root/branch" (compared to {@link #tail()} that * would return "/branch/leaf"). * For leaf * * @since 2.5 */ public JsonPointer head() { JsonPointer h = _head; if (h == null) { if (this != EMPTY) { h = _constructHead(); } _head = h; } return h; } /* /********************************************************** /* Standard method overrides /********************************************************** */ @Override public String toString() { return _asString; } @Override public int hashCode() { return _asString.hashCode(); } @Override public boolean equals(Object o) { if (o == this) return true; if (o == null) return false; if (!(o instanceof JsonPointer)) return false; return _asString.equals(((JsonPointer) o)._asString); } /* /********************************************************** /* Internal methods /********************************************************** */ private final static int _parseIndex(String str) { final int len = str.length(); // [core#133]: beware of super long indexes; assume we never // have arrays over 2 billion entries so ints are fine. if (len == 0 || len > 10) { return -1; } // [core#176]: no leading zeroes allowed char c = str.charAt(0); if (c <= '0') { return (len == 1 && c == '0') ? 0 : -1; } if (c > '9') { return -1; } for (int i = 1; i < len; ++i) { c = str.charAt(i); if (c > '9' || c < '0') { return -1; } } if (len == 10) { long l = NumberInput.parseLong(str); if (l > Integer.MAX_VALUE) { return -1; } } return NumberInput.parseInt(str); } protected static JsonPointer _parseTail(String input) { final int end = input.length(); // first char is the contextual slash, skip for (int i = 1; i < end;) { char c = input.charAt(i); if (c == '/') { // common case, got a segment return new JsonPointer(input, input.substring(1, i), _parseTail(input.substring(i))); } ++i; // quoting is different; offline this case if (c == '~' && i < end) { // possibly, quote return _parseQuotedTail(input, i); } // otherwise, loop on } // end of the road, no escapes return new JsonPointer(input, input.substring(1), EMPTY); } /** * Method called to parse tail of pointer path, when a potentially * escaped character has been seen. * * @param input Full input for the tail being parsed * @param i Offset to character after tilde */ protected static JsonPointer _parseQuotedTail(String input, int i) { final int end = input.length(); StringBuilder sb = new StringBuilder(Math.max(16, end)); if (i > 2) { sb.append(input, 1, i - 1); } _appendEscape(sb, input.charAt(i++)); while (i < end) { char c = input.charAt(i); if (c == '/') { // end is nigh! return new JsonPointer(input, sb.toString(), _parseTail(input.substring(i))); } ++i; if (c == '~' && i < end) { _appendEscape(sb, input.charAt(i++)); continue; } sb.append(c); } // end of the road, last segment return new JsonPointer(input, sb.toString(), EMPTY); } protected JsonPointer _constructHead() { // ok; find out who we are to drop JsonPointer last = last(); if (last == this) { return EMPTY; } // and from that, length of suffix to drop int suffixLength = last._asString.length(); JsonPointer next = _nextSegment; return new JsonPointer(_asString.substring(0, _asString.length() - suffixLength), _matchingPropertyName, _matchingElementIndex, next._constructHead(suffixLength, last)); } protected JsonPointer _constructHead(int suffixLength, JsonPointer last) { if (this == last) { return EMPTY; } JsonPointer next = _nextSegment; String str = _asString; return new JsonPointer(str.substring(0, str.length() - suffixLength), _matchingPropertyName, _matchingElementIndex, next._constructHead(suffixLength, last)); } private static void _appendEscape(StringBuilder sb, char c) { if (c == '0') { c = '~'; } else if (c == '1') { c = '/'; } else { sb.append('~'); } sb.append(c); } }