Java tutorial
/* * Copyright 2008 Google Inc. * * Licensed 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.google.gwt.json.client; import com.google.gwt.core.client.JavaScriptException; import com.google.gwt.core.client.JavaScriptObject; /** * Parses the string representation of a JSON object into a set of * JSONValue-derived objects. * * @see com.google.gwt.json.client.JSONValue */ public class JSONParser { static final JavaScriptObject typeMap = initTypeMap(); /** * Evaluates a trusted JSON string and returns its JSONValue representation. * CAUTION! This method calls the JavaScript <code>eval()</code> function, * which can execute arbitrary script. DO NOT pass an untrusted string into * this method. * * <p> * This method has been deprecated. Please call either * {@link #parseStrict(String)} (for inputs that strictly follow the JSON * specification) or {@link #parseLenient(String)}. The implementation of this * method calls parseLenient. * * @param jsonString a JSON object to parse * @return a JSONValue that has been built by parsing the JSON string * @throws NullPointerException if <code>jsonString</code> is * <code>null</code> * @throws IllegalArgumentException if <code>jsonString</code> is empty * * @deprecated use {@link #parseStrict(String)} or * {@link #parseLenient(String)} */ @Deprecated public static JSONValue parse(String jsonString) { return parseLenient(jsonString); } /** * Evaluates a trusted JSON string and returns its JSONValue representation. * CAUTION! This method calls the JavaScript {@code eval()} function, which * can execute arbitrary script. DO NOT pass an untrusted string into this * method. * * @param jsonString a JSON object to parse * @return a JSONValue that has been built by parsing the JSON string * @throws NullPointerException if <code>jsonString</code> is * <code>null</code> * @throws IllegalArgumentException if <code>jsonString</code> is empty */ public static JSONValue parseLenient(String jsonString) { return parse(jsonString, false); } /** * Evaluates a JSON string and returns its JSONValue representation. Where * possible, the browser's {@code JSON.parse function} is used. For older * browsers including IE6 and IE7 that lack a {@code JSON.parse} function, the * input is validated as described in RFC 4627 for safety and passed to * {@code eval()}. * * @param jsonString a JSON object to parse * @return a JSONValue that has been built by parsing the JSON string * @throws NullPointerException if <code>jsonString</code> is * <code>null</code> * @throws IllegalArgumentException if <code>jsonString</code> is empty */ public static JSONValue parseStrict(String jsonString) { return parse(jsonString, true); } static void throwJSONException(String message) { throw new JSONException(message); } static void throwUnknownTypeException(String typeString) { throw new JSONException( "Unexpected typeof result '" + typeString + "'; please report this bug to the GWT team"); } /** * Called from {@link #initTypeMap()}. */ private static JSONValue createBoolean(boolean v) { return JSONBoolean.getInstance(v); } /** * Called from {@link #initTypeMap()}. */ private static JSONValue createNumber(double v) { return new JSONNumber(v); } /** * Called from {@link #initTypeMap()}. If we get here, <code>o</code> is * either <code>null</code> (not <code>undefined</code>) or a JavaScript * object. */ private static native JSONValue createObject(Object o) /*-{ if (!o) { return @com.google.gwt.json.client.JSONNull::getInstance()(); } var v = o.valueOf ? o.valueOf() : o; if (v !== o) { // It was a primitive wrapper, unwrap it and try again. var func = @com.google.gwt.json.client.JSONParser::typeMap[typeof v]; return func ? func(v) : @com.google.gwt.json.client.JSONParser::throwUnknownTypeException(Ljava/lang/String;)(typeof v); } else if (o instanceof Array || o instanceof $wnd.Array) { // Looks like an Array; wrap as JSONArray. // NOTE: this test can fail for objects coming from a different window, // but we know of no reliable tests to determine if something is an Array // in all cases. return @com.google.gwt.json.client.JSONArray::new(Lcom/google/gwt/core/client/JavaScriptObject;)(o); } else { // This is a basic JavaScript object; wrap as JSONObject. // Subobjects will be created on demand. return @com.google.gwt.json.client.JSONObject::new(Lcom/google/gwt/core/client/JavaScriptObject;)(o); } }-*/; /** * Called from {@link #initTypeMap()}. */ private static JSONValue createString(String v) { return new JSONString(v); } /** * Called from {@link #initTypeMap()}. This method returns a <code>null</code> * pointer, representing JavaScript <code>undefined</code>. */ private static JSONValue createUndefined() { return null; } /** * This method converts <code>jsonString</code> into a JSONValue. * In strict mode (strict == true), one of two code paths is taken: * 1) Call JSON.parse if available, or * 2) Validate the input and call eval() * * In lenient mode (strict == false), eval() is called without validation. * * @param strict if true, parse in strict mode. */ private static native JSONValue evaluate(String json, boolean strict) /*-{ // Note: we cannot simply call JsonUtils.unsafeEval because it is unable // to return a result for inputs whose outermost type is 'string' in // dev mode. var v; if (strict && @com.google.gwt.core.client.JsonUtils::hasJsonParse) { try { v = JSON.parse(json); } catch (e) { return @com.google.gwt.json.client.JSONParser::throwJSONException(Ljava/lang/String;)("Error parsing JSON: " + e); } } else { if (strict) { // Validate the input according to RFC 4627. if (!@com.google.gwt.core.client.JsonUtils::safeToEval(Ljava/lang/String;)(json)) { return @com.google.gwt.json.client.JSONParser::throwJSONException(Ljava/lang/String;)("Illegal character in JSON string"); } } json = @com.google.gwt.core.client.JsonUtils::escapeJsonForEval(Ljava/lang/String;)(json); try { v = eval('(' + json + ')'); } catch (e) { return @com.google.gwt.json.client.JSONParser::throwJSONException(Ljava/lang/String;)("Error parsing JSON: " + e); } } var func = @com.google.gwt.json.client.JSONParser::typeMap[typeof v]; return func ? func(v) : @com.google.gwt.json.client.JSONParser::throwUnknownTypeException(Ljava/lang/String;)(typeof v); }-*/; private static native JavaScriptObject initTypeMap() /*-{ return { "boolean": @com.google.gwt.json.client.JSONParser::createBoolean(Z), "number": @com.google.gwt.json.client.JSONParser::createNumber(D), "string": @com.google.gwt.json.client.JSONParser::createString(Ljava/lang/String;), "object": @com.google.gwt.json.client.JSONParser::createObject(Ljava/lang/Object;), "function": @com.google.gwt.json.client.JSONParser::createObject(Ljava/lang/Object;), "undefined": @com.google.gwt.json.client.JSONParser::createUndefined(), } }-*/; private static JSONValue parse(String jsonString, boolean strict) { if (jsonString == null) { throw new NullPointerException(); } if (jsonString.length() == 0) { throw new IllegalArgumentException("empty argument"); } try { return evaluate(jsonString, strict); } catch (JavaScriptException ex) { throw new JSONException(ex); } } /** * Not instantiable. */ private JSONParser() { } }