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

     1  /*
     2   * Copyright (C) 2008 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  
    17  package com.google.gson;
    18  
    19  import java.lang.reflect.Type;
    20  
    21  /**
    22   * <p>Interface representing a custom deserializer for Json. You should write a custom
    23   * deserializer, if you are not happy with the default deserialization done by Gson. You will
    24   * also need to register this deserializer through
    25   * {@link GsonBuilder#registerTypeAdapter(Type, Object)}.</p>
    26   *
    27   * <p>Let us look at example where defining a deserializer will be useful. The {@code Id} class
    28   * defined below has two fields: {@code clazz} and {@code value}.</p>
    29   *
    30   * <pre>
    31   * public class Id&lt;T&gt; {
    32   *   private final Class&lt;T&gt; clazz;
    33   *   private final long value;
    34   *   public Id(Class&lt;T&gt; clazz, long value) {
    35   *     this.clazz = clazz;
    36   *     this.value = value;
    37   *   }
    38   *   public long getValue() {
    39   *     return value;
    40   *   }
    41   * }
    42   * </pre>
    43   *
    44   * <p>The default deserialization of {@code Id(com.foo.MyObject.class, 20L)} will require the
    45   * Json string to be <code>{"clazz":com.foo.MyObject,"value":20}</code>. Suppose, you already know
    46   * the type of the field that the {@code Id} will be deserialized into, and hence just want to
    47   * deserialize it from a Json string {@code 20}. You can achieve that by writing a custom
    48   * deserializer:</p>
    49   *
    50   * <pre>
    51   * class IdDeserializer implements JsonDeserializer&lt;Id&gt;() {
    52   *   public Id deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context)
    53   *       throws JsonParseException {
    54   *     return new Id((Class)typeOfT, id.getValue());
    55   *   }
    56   * </pre>
    57   *
    58   * <p>You will also need to register {@code IdDeserializer} with Gson as follows:</p>
    59   *
    60   * <pre>
    61   * Gson gson = new GsonBuilder().registerTypeAdapter(Id.class, new IdDeserializer()).create();
    62   * </pre>
    63   *
    64   * <p>New applications should prefer {@link TypeAdapter}, whose streaming API
    65   * is more efficient than this interface's tree API.
    66   *
    67   * @author Inderjeet Singh
    68   * @author Joel Leitch
    69   *
    70   * @param <T> type for which the deserializer is being registered. It is possible that a
    71   * deserializer may be asked to deserialize a specific generic type of the T.
    72   */
    73  public interface JsonDeserializer<T> {
    74  
    75    /**
    76     * Gson invokes this call-back method during deserialization when it encounters a field of the
    77     * specified type.
    78     * <p>In the implementation of this call-back method, you should consider invoking
    79     * {@link JsonDeserializationContext#deserialize(JsonElement, Type)} method to create objects
    80     * for any non-trivial field of the returned object. However, you should never invoke it on the
    81     * the same type passing {@code json} since that will cause an infinite loop (Gson will call your
    82     * call-back method again).
    83     *
    84     * @param json The Json data being deserialized
    85     * @param typeOfT The type of the Object to deserialize to
    86     * @return a deserialized object of the specified type typeOfT which is a subclass of {@code T}
    87     * @throws JsonParseException if json is not in the expected format of {@code typeofT}
    88     */
    89    public T deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context)
    90        throws JsonParseException;
    91  }