code: /*
   * Copyright (C) 2009 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 tools.com.google.gson;
  
  import java.io.EOFException;
  import java.io.IOException;
  import java.io.Reader;
  import java.io.StringReader;
  import java.util.Iterator;
  import java.util.NoSuchElementException;
  
  import tools.com.google.gson.internal.Streams;
  import tools.com.google.gson.stream.JsonReader;
  import tools.com.google.gson.stream.JsonToken;
  import tools.com.google.gson.stream.MalformedJsonException;
  
  /**
   * A streaming parser that allows reading of multiple {@link JsonElement}s from the specified reader
   * asynchronously.
   * 
   * <p>This class is conditionally thread-safe (see Item 70, Effective Java second edition). To
   * properly use this class across multiple threads, you will need to add some external
   * synchronization.  For example:
   * 
   * <pre>
   * JsonStreamParser parser = new JsonStreamParser("['first'] {'second':10} 'third'");
   * JsonElement element;
   * synchronized (parser) {  // synchronize on an object shared by threads
   *   if (parser.hasNext()) {
   *     element = parser.next();
   *   }
   * }
   * </pre>
   *
   * @author Inderjeet Singh
   * @author Joel Leitch
   * @since 1.4
   */
  public final class JsonStreamParser implements Iterator<JsonElement> {
    private final JsonReader parser;
    private final Object lock;
  
    /**
     * @param json The string containing JSON elements concatenated to each other.
     * @since 1.4
     */
    public JsonStreamParser(String json) {
      this(new StringReader(json));      
    }
    
    /**
     * @param reader The data stream containing JSON elements concatenated to each other.
     * @since 1.4
     */
    public JsonStreamParser(Reader reader) {
      parser = new JsonReader(reader);
      parser.setLenient(true);
      lock = new Object();
    }
    
    /**
     * Returns the next available {@link JsonElement} on the reader. Null if none available.
     * 
     * @return the next available {@link JsonElement} on the reader. Null if none available.
     * @throws JsonParseException if the incoming stream is malformed JSON.
     * @since 1.4
     */
    public JsonElement next() throws JsonParseException {
      if (!hasNext()) {
        throw new NoSuchElementException();
      }
      
      try {
        return Streams.parse(parser);
      } catch (StackOverflowError e) {
        throw new JsonParseException("Failed parsing JSON source to Json", e);
      } catch (OutOfMemoryError e) {
        throw new JsonParseException("Failed parsing JSON source to Json", e);
      } catch (JsonParseException e) {
        throw e.getCause() instanceof EOFException ? new NoSuchElementException() : e;
      }
    }
  
    /**
     * Returns true if a {@link JsonElement} is available on the input for consumption
     * @return true if a {@link JsonElement} is available on the input, false otherwise
     * @since 1.4
     */
    public boolean hasNext() {
      synchronized (lock) {
        try {
          return parser.peek() != JsonToken.END_DOCUMENT;
        } catch (MalformedJsonException e) {
          throw new JsonSyntaxException(e);
        } catch (IOException e) {
          throw new JsonIOException(e);
        }
      }
    }
  
    /**
     * This optional {@link Iterator} method is not relevant for stream parsing and hence is not
     * implemented.
     * @since 1.4
     */
    public void remove() {
      throw new UnsupportedOperationException();
    }
  }
  