Gson使用总结

参考(不限于)：http://www.jianshu.com/p/e740196225a4

1.使用@SerializedName，处理客户端与服务端字段明命名不一致

@SerializedName(value = "emailAddress", alternate = {"email", "email_address"})
public String emailAddress;

2.使用TypeToken，处理泛型擦除

//方法声明
public <T> T fromJson(String json, Class<T> classOfT) throws JsonSyntaxException {  Object object = fromJson(json, (Type) classOfT);  return Primitives.wrap(classOfT).cast(object);}

Gson gson = new Gson();
String jsonArray = "[\"Android\",\"Java\",\"PHP\"]";
String[] strings = gson.fromJson(jsonArray, String[].class);
//错误写法
List<String> strings =gson.fromJson(jsonArray, String[].class); 
//正确写法
List<String> stringList = gson.fromJson(jsonArray, new TypeToken<List<String>>() {}.getType());

3.使用泛型，改善POJO的设计

//原设计
public class UserResult {    
    public int code;    
    public String message;    
    public User data;
}
public class UserListResult {    
    public int code;    
    public String message;    
    public List<User> data;
}
String json = "{..........}";
Gson gson = new Gson();
UserResult userResult = gson.fromJson(json,UserResult.class);
User user = userResult.data;UserListResult userListResult = gson.fromJson(json,UserListResult.class);
List<User> users = userListResult.data;
//新设计
public class Result<T> {    
    public int code;    
    public String message;      
    public T data;
}
Type userType = new TypeToken<Result<User>>(){}.getType();
Result<User> userResult = gson.fromJson(json,userType);User user = userResult.data;
Type userListType = new TypeToken<Result<List<User>>>(){}.getType();
Result<List<User>> userListResult = gson.fromJson(json,userType);
List<User> users = userListResult.data;

4.使用GsonBuilder导出null值、格式化输出、日期时间

Gson gson = new GsonBuilder()        
//序列化null 
.serializeNulls()        
// 设置日期时间格式，另有2个重载方法 
// 在序列化和反序化时均生效 
.setDateFormat("yyyy-MM-dd")        
// 禁此序列化内部类 
.disableInnerClassSerialization()        
//生成不可执行的Json（多了 )]}' 这4个字符） 
.generateNonExecutableJson()        
//禁止转义html标签 
.disableHtmlEscaping()        
//格式化输出 
.setPrettyPrinting()        
.create();

4.排除无用的字段

方案1.使用transient关键字

方案2.使用Modifier为指定类型的字段（excludeFieldsWithModifiers(Modifier.PROTECTED)）

方案3.使用@Expose，过滤无用(业务)字段

public class Category {    
  @Expose    
  public int id;    
  @Expose 
  public String name;    
  @Expose 
  public List<Category> children;    
  //不需要序列化,所以不加 @Expose 注解， 
  //等价于 @Expose(deserialize = false,serialize = false) 
  public Category parent;
}
Gson gson = new GsonBuilder()  
      .excludeFieldsWithoutExposeAnnotation() 
      .create();
gson.toJson(category);

方案4.基于策略（自定义规则），过滤无用(业务)字段

Gson gson = new GsonBuilder() 
      .addSerializationExclusionStrategy(new ExclusionStrategy() {            
        @Override            
        public boolean shouldSkipField(FieldAttributes f) { 
           // 这里作判断，决定要不要排除该字段,return true为排除 
           if ("finalField".equals(f.getName())) return true; 
           //按字段名排除 
           Expose expose = f.getAnnotation(Expose.class);                
           if (expose != null && expose.deserialize() == false) 
             return true; 
            //按注解排除 
         return false;           
       }            
       @Override            
       public boolean shouldSkipClass(Class<?> clazz) {                
         // 直接排除某个类 ，return true为排除 
         return (clazz == int.class || clazz == Integer.class);            }        
       })        
.create();

5.处理混合类型的bean

//原json
{
    "timestamp": 1449199363.89387,
    "message": "Succeed",
    "version": "1.0",
    "results": [
        {
            "data": {
                "recommended": 0,
                "video_type": 2,
                "vid": "23482078",
                "title": "破风",
                "movie_title": "破风",
                "duration": "126",
                "is_voted": 0,
                "image": "http://i1.letvimg.com/lc02_isvrs/201509/11/16/21/a4bdc7ff-6d69-4875-bff8-dbe136a533ff/thumb/2_960_540.jpg",
                "playcount": 3303475,
                "share_link": "http://leying.duohappy.cn",
                "desc": "无畏“破风手”传递正能量",
                "code_rate": [
                    9,
                    13,
                    21,
                    22,
                    51
                ],
                "is_downloadable": 0
            },
            "type": "video"
        },
        {
            "data": {
                "url": "http://www.baidu.com/",
                "image": "http://i0.letvimg.com/lc02_isvrs/201506/11/16/26/dbbebacb-12f5-4356-a364-c9a888b884ba/thumb/2_1440_810.jpg",
                "desc": "测试跳转描述",
                "recommended": 1,
                "title": "测试跳转"
            },
            "type": "link"
        }
    ]
}

问题点是这个data数据，由于返回data数据，受到type的影响。无法固定List 里的泛型T，只能用Object来代替。实际运行List里面的object,可能是video,也可能是link。需要自己定义json的反序列化过程。即实现JsonDeserializer接口，代码如下。

public class VideoList {
    public float timestamp;
    public String message;
    public String version;
    public List<Object> results;
}
public class VideoBean {
}
public class ChooseH5Bean {
}

public class VideoListJsonDeserializer implements JsonDeserializer<VideoList> {
        @Override
        public VideoList deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context) throws JsonParseException {
            VideoList videoList = new VideoList();
            if (json.isJsonObject()) {
                JsonObject jsonObject = json.getAsJsonObject();

                videoList.timestamp = jsonObject.get("timestamp").getAsFloat();
                videoList.message = jsonObject.get("message").getAsString();
                videoList.version = jsonObject.get("version").getAsString();

                JsonArray array = (JsonArray) jsonObject.get("results");
                List<Object> list = new ArrayList<Object>();
                for (int i = 0; i < array.size(); i++) {
                    JsonObject element = (JsonObject) array.get(i);
                    String type = element.get("type").getAsString();
                    Object item = null;
                    if ("video".equals(type)) {
                        item = context.deserialize(element.getAsJsonObject("data"), Video.class);
                    } else if ("link".equals(type)) {
                        item = context.deserialize(element.getAsJsonObject("data"), Link.class);
                    }
                    if (item != null) {
                        list.add(item);
                    }
                }
                videoList.results = list;
            }

            return videoList;
        }
    }

方案1.注册TypeAdapter

Gson gson = new GsonBuilder().registerTypeAdapter(VideoList.class, new VideoListJsonDeserializer()).create();
InputStream inputStream = getResources().openRawResource(R.raw.text);
VideoList videoList = gson.fromJson(new InputStreamReader(inputStream), VideoList.class);