From c5c65ba62601524ab09d7aa317689117676f2d4d Mon Sep 17 00:00:00 2001 From: Jesse Wilson Date: Sat, 25 Aug 2012 04:31:56 +0000 Subject: [PATCH] Add an experimental rewrite of JsonReader. The motivating difference is that JsonReaderV2 tries to read each character at most once. This means that when it reads literals, it also attempts to decode them to a keyword (true/false/null) or a number. This change also _doesn't_ read strings until demanded to do so. This should permit streaming access to strings down the road. This code is not yet complete, nor is has it been properly optimized. And the implementation is also quite a mess! It is a work in progress. --- .../com/google/gson/stream/JsonReaderV2.java | 1362 +++++++++++++++++ .../google/gson/stream/JsonReaderTest.java | 80 + 2 files changed, 1442 insertions(+) create mode 100644 gson/src/main/java/com/google/gson/stream/JsonReaderV2.java diff --git a/gson/src/main/java/com/google/gson/stream/JsonReaderV2.java b/gson/src/main/java/com/google/gson/stream/JsonReaderV2.java new file mode 100644 index 00000000..ec38c54d --- /dev/null +++ b/gson/src/main/java/com/google/gson/stream/JsonReaderV2.java @@ -0,0 +1,1362 @@ +/* + * Copyright (C) 2010 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.gson.stream; + +import java.io.Closeable; +import java.io.EOFException; +import java.io.IOException; +import java.io.Reader; + +/** + * Reads a JSON (RFC 4627) + * encoded value as a stream of tokens. This stream includes both literal + * values (strings, numbers, booleans, and nulls) as well as the begin and + * end delimiters of objects and arrays. The tokens are traversed in + * depth-first order, the same order that they appear in the JSON document. + * Within JSON objects, name/value pairs are represented by a single token. + * + *

Parsing JSON

+ * To create a recursive descent parser for your own JSON streams, first create + * an entry point method that creates a {@code JsonReader}. + * + *

Next, create handler methods for each structure in your JSON text. You'll + * need a method for each object type and for each array type. + *

+ *

When a nested object or array is encountered, delegate to the + * corresponding handler method. + * + *

When an unknown name is encountered, strict parsers should fail with an + * exception. Lenient parsers should call {@link #skipValue()} to recursively + * skip the value's nested tokens, which may otherwise conflict. + * + *

If a value may be null, you should first check using {@link #peek()}. + * Null literals can be consumed using either {@link #nextNull()} or {@link + * #skipValue()}. + * + *

Example

+ * Suppose we'd like to parse a stream of messages such as the following: 
 {@code
+ * [
+ *   {
+ *     "id": 912345678901,
+ *     "text": "How do I read a JSON stream in Java?",
+ *     "geo": null,
+ *     "user": {
+ *       "name": "json_newb",
+ *       "followers_count": 41
+ *      }
+ *   },
+ *   {
+ *     "id": 912345678902,
+ *     "text": "@json_newb just use JsonReader!",
+ *     "geo": [50.454722, -104.606667],
+ *     "user": {
+ *       "name": "jesse",
+ *       "followers_count": 2
+ *     }
+ *   }
+ * ]}
+ * This code implements the parser for the above structure: 
   {@code
+ *
+ *   public List readJsonStream(InputStream in) throws IOException {
+ *     JsonReader reader = new JsonReader(new InputStreamReader(in, "UTF-8"));
+ *     try {
+ *       return readMessagesArray(reader);
+ *     } finally {
+ *       reader.close();
+ *     }
+ *   }
+ *
+ *   public List readMessagesArray(JsonReader reader) throws IOException {
+ *     List messages = new ArrayList();
+ *
+ *     reader.beginArray();
+ *     while (reader.hasNext()) {
+ *       messages.add(readMessage(reader));
+ *     }
+ *     reader.endArray();
+ *     return messages;
+ *   }
+ *
+ *   public Message readMessage(JsonReader reader) throws IOException {
+ *     long id = -1;
+ *     String text = null;
+ *     User user = null;
+ *     List geo = null;
+ *
+ *     reader.beginObject();
+ *     while (reader.hasNext()) {
+ *       String name = reader.nextName();
+ *       if (name.equals("id")) {
+ *         id = reader.nextLong();
+ *       } else if (name.equals("text")) {
+ *         text = reader.nextString();
+ *       } else if (name.equals("geo") && reader.peek() != JsonToken.NULL) {
+ *         geo = readDoublesArray(reader);
+ *       } else if (name.equals("user")) {
+ *         user = readUser(reader);
+ *       } else {
+ *         reader.skipValue();
+ *       }
+ *     }
+ *     reader.endObject();
+ *     return new Message(id, text, user, geo);
+ *   }
+ *
+ *   public List readDoublesArray(JsonReader reader) throws IOException {
+ *     List doubles = new ArrayList();
+ *
+ *     reader.beginArray();
+ *     while (reader.hasNext()) {
+ *       doubles.add(reader.nextDouble());
+ *     }
+ *     reader.endArray();
+ *     return doubles;
+ *   }
+ *
+ *   public User readUser(JsonReader reader) throws IOException {
+ *     String username = null;
+ *     int followersCount = -1;
+ *
+ *     reader.beginObject();
+ *     while (reader.hasNext()) {
+ *       String name = reader.nextName();
+ *       if (name.equals("name")) {
+ *         username = reader.nextString();
+ *       } else if (name.equals("followers_count")) {
+ *         followersCount = reader.nextInt();
+ *       } else {
+ *         reader.skipValue();
+ *       }
+ *     }
+ *     reader.endObject();
+ *     return new User(username, followersCount);
+ *   }}
+ * + *

Number Handling

+ * This reader permits numeric values to be read as strings and string values to + * be read as numbers. For example, both elements of the JSON array {@code + * [1, "1"]} may be read using either {@link #nextInt} or {@link #nextString}. + * This behavior is intended to prevent lossy numeric conversions: double is + * JavaScript's only numeric type and very large values like {@code + * 9007199254740993} cannot be represented exactly on that platform. To minimize + * precision loss, extremely large values should be written and read as strings + * in JSON. + * + *

Non-Execute Prefix

+ * Web servers that serve private data using JSON may be vulnerable to Cross-site + * request forgery attacks. In such an attack, a malicious site gains access + * to a private JSON file by executing it with an HTML {@code