github.com/keysonZZZ/kmg@v0.0.0-20151121023212-05317bfd7d39/kmgRpc/kmgRpcJava/java/src/com/google/gson/JsonStreamParser.java (about)

     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  }