gson/com/google/gson/JsonStreamParser.java

   1 /*
   2  * Copyright (C) 2009 Google Inc.
   3  *
   4  * Licensed under the Apache License, Version 2.0 (the "License");
   5  * you may not use this file except in compliance with the License.
   6  * You may obtain a copy of the License at
   7  *
   8  * http://www.apache.org/licenses/LICENSE-2.0
   9  *
  10  * Unless required by applicable law or agreed to in writing, software
  11  * distributed under the License is distributed on an "AS IS" BASIS,
  12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  13  * See the License for the specific language governing permissions and
  14  * limitations under the License.
  15  */
  16 package com.google.gson;
  17
  18 import java.io.EOFException;
  19 import java.io.IOException;
  20 import java.io.Reader;
  21 import java.io.StringReader;
  22 import java.util.Iterator;
  23 import java.util.NoSuchElementException;
  24
  25 import com.google.gson.internal.Streams;
  26 import com.google.gson.stream.JsonReader;
  27 import com.google.gson.stream.JsonToken;
  28 import com.google.gson.stream.MalformedJsonException;
  29
  30 /**
  31  * A streaming parser that allows reading of multiple {@link JsonElement}s from the specified reader
  32  * asynchronously.
  33  *
  34  * <p>This class is conditionally thread-safe (see Item 70, Effective Java second edition). To
  35  * properly use this class across multiple threads, you will need to add some external
  36  * synchronization.  For example:
  37  *
  38  * <pre>
  39  * JsonStreamParser parser = new JsonStreamParser("['first'] {'second':10} 'third'");
  40  * JsonElement element;
  41  * synchronized (parser) {  // synchronize on an object shared by threads
  42  *   if (parser.hasNext()) {
  43  *     element = parser.next();
  44  *   }
  45  * }
  46  * </pre>
  47  *
  48  * @author Inderjeet Singh
  49  * @author Joel Leitch
  50  * @since 1.4
  51  */
  52 public final class JsonStreamParser implements Iterator<JsonElement> {
  53   private final JsonReader parser;
  54   private final Object lock;
  55
  56   /**
  57    * @param json The string containing JSON elements concatenated to each other.
  58    * @since 1.4
  59    */
  60   public JsonStreamParser(String json) {
  61     this(new StringReader(json));
  62   }
  63
  64   /**
  65    * @param reader The data stream containing JSON elements concatenated to each other.
  66    * @since 1.4
  67    */
  68   public JsonStreamParser(Reader reader) {
  69     parser = new JsonReader(reader);
  70     parser.setLenient(true);
  71     lock = new Object();
  72   }
  73
  74   /**
  75    * Returns the next available {@link JsonElement} on the reader. Null if none available.
  76    *
  77    * @return the next available {@link JsonElement} on the reader. Null if none available.
  78    * @throws JsonParseException if the incoming stream is malformed JSON.
  79    * @since 1.4
  80    */
  81   public JsonElement next() throws JsonParseException {
  82     if (!hasNext()) {
  83       throw new NoSuchElementException();
  84     }
  85
  86     try {
  87       return Streams.parse(parser);
  88     } catch (StackOverflowError e) {
  89       throw new JsonParseException("Failed parsing JSON source to Json", e);
  90     } catch (OutOfMemoryError e) {
  91       throw new JsonParseException("Failed parsing JSON source to Json", e);
  92     } catch (JsonParseException e) {
  93       throw e.getCause() instanceof EOFException ? new NoSuchElementException() : e;
  94     }
  95   }
  96
  97   /**
  98    * Returns true if a {@link JsonElement} is available on the input for consumption
  99    * @return true if a {@link JsonElement} is available on the input, false otherwise
 100    * @since 1.4
 101    */
 102   public boolean hasNext() {
 103     synchronized (lock) {
 104       try {
 105         return parser.peek() != JsonToken.END_DOCUMENT;
 106       } catch (MalformedJsonException e) {
 107         throw new JsonSyntaxException(e);
 108       } catch (IOException e) {
 109         throw new JsonIOException(e);
 110       }
 111     }
 112   }
 113
 114   /**
 115    * This optional {@link Iterator} method is not relevant for stream parsing and hence is not
 116    * implemented.
 117    * @since 1.4
 118    */
 119   public void remove() {
 120     throw new UnsupportedOperationException();
 121   }
 122 }