android - 关于Gson解析json数据时如果属性值为null则会报空的问题

Question

想试试用Gson来解析json数据

这是data_info

{"careingpeople_id":"33","lovecode":null,"appellation":"父亲","name":"王健林","birthday":"2015-04-08","mobile":"15689653698","areano":"320583","communityno":"1","communityname":"测试小区","agency_id":"1","street":"","canselfcare":"0","language":"本地话","disease":"糖尿病","memo":"哈哈","ctime":"2015-04-08 10:22:33"}

这是解析的方法

 old_man_info_data = GsonUtil.getInstance().fromJson(data_info, OldManInfoData.class);

其中json数据中有一个字段的值是null

"lovecode":null

此时如果执行如下代码，就会报错

Log.e("这是什么鬼", old_info.getLovecode());

这是错误

 Caused by: java.lang.NullPointerException: println needs a message

想请问一下，有人碰到过类似问题吗？如何解决？

谢谢！

补充：Google了一下，有人说用下边这段代码

gson=new GsonBuilder().serializeNulls().create();

可以解决，但是我试过了，没用。

Answer 1

Post an answer from google+ and replace null with ""

import java.lang.reflect.Type;

public class StringConverter implements JsonSerializer<String>, 
    JsonDeserializer<String> { 
public JsonElement serialize(String src, Type typeOfSrc, 
    JsonSerializationContext context) { 
    if ( src == null ) { 
        return new JsonPrimitive(""); 
    } else { 
        return new JsonPrimitive(src.toString()); 
} 
public String deserialize(JsonElement json, Type typeOfT, 
    JsonDeserializationContext context) 
        throws JsonParseException { 
    return json.getAsJsonPrimitive().getAsString(); 
} 
}

Then use it like this:

GsonBuilder gb = new GsonBuilder(); 
gb.registerTypeAdapter(String.class, new StringConverter()); 
Gson gson = gb.create(); 

Answer 2

This kind of problem is an ordinary Java null pointer. Your object is null. Calling its get method will definitely result in a null pointer. The remedy is to add judgment or modify the data source

Answer 3

If the server cooperates with you, just change it to "" an empty string when encountering a null value.

If you can only change it locally, you have to make a judgment every time, and you cannot use Gson to analyze it

 if (dataObject.has("id") && !dataObject.isNull("id")) {
     dataObject.getString("id"));
 }

Answer 4

This is not Gson’s problem at all. . . .
The value that is obviously yours is null.
So your sentence

Log.e("这是什么鬼", old_info.getLovecode());

is equivalent to

Log.e("这是什么鬼", null);

If you change it to

Log.e("这是什么鬼", old_info.getLovecode()!=null?old_info.getLovecode():"");

It won’t be wrong. If I am wrong, hit me.