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Google API Client Library for Java. Supports Java 5 (or higher) desktop (SE) and web (EE), Android, and Google App Engine.

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/*
 * 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.api.client.googleapis.json;

import com.google.api.client.json.CustomizeJsonParser;
import com.google.api.client.json.Json;

import org.codehaus.jackson.JsonParser;
import org.codehaus.jackson.JsonToken;

import java.io.IOException;

/**
 * Abstract base class for a Google JSON-C feed parser when the feed class is
 * known in advance.
 * 
 * @since 1.0
 * @author Yaniv Inbar
 */
public abstract class AbstractJsonFeedParser {

  private boolean feedParsed;
  final JsonParser parser;
  final Class feedClass;

  AbstractJsonFeedParser(JsonParser parser, Class feedClass) {
    this.parser = parser;
    this.feedClass = feedClass;
  }

  /**
   * Parse the feed and return a new parsed instance of the feed class. This
   * method can be skipped if all you want are the items.
   */
  public T parseFeed() throws IOException {
    boolean close = true;
    try {
      this.feedParsed = true;
      T result = Json.parse(this.parser, this.feedClass, new StopAtItems());
      close = false;
      return result;
    } finally {
      if (close) {
        close();
      }
    }
  }

  final class StopAtItems extends CustomizeJsonParser {
    @Override
    public boolean stopAt(Object context, String key) {
      return "items".equals(key)
          && context.getClass().equals(AbstractJsonFeedParser.this.feedClass);
    }
  }

  /**
   * Parse the next item in the feed and return a new parsed instanceof of the
   * item class. If there is no item to parse, it will return {@code null} and
   * automatically close the parser (in which case there is no need to call
   * {@link #close()}.
   */
  public Object parseNextItem() throws IOException {
    JsonParser parser = this.parser;
    if (!this.feedParsed) {
      this.feedParsed = true;
      Json.skipToKey(parser, "items");
    }
    boolean close = true;
    try {
      if (parser.nextToken() == JsonToken.START_OBJECT) {
        Object result = parseItemInternal();
        close = false;
        return result;
      }
    } finally {
      if (close) {
        close();
      }
    }
    return null;
  }

  /** Closes the underlying parser. */
  public void close() throws IOException {
    this.parser.close();
  }

  abstract Object parseItemInternal() throws IOException;
}