json解析对应的value为null_Gson解析value为null情况下空指针问题

上周五，在解析json中遇到一个很坑的问题，就是解析Json字符串时出现value为null的时候，出现空指针异常。当时让

String password = jsonObject.get("password").getAsString();

JsonElement passwordJsonEle = jsonObject.get("password");

if(passwordJsonEle!=null){

String password = passwordJsonEle.getAsString();

System.out.println(password);

}

发现会进入if语句块，所以比较奇怪，查看源码，发现Gson解析Gson时底层解析的key:value是用Map装取，而当vaule为null时则装入的是Gson自定义的JsonNull类对象。

源代码：

/**

* Adds a member, which is a name-value pair, to self. The name must be a String, but the value

* can be an arbitrary JsonElement, thereby allowing you to build a full tree of JsonElements

* rooted at this node.

*

* @param property name of the member.

* @param value the member object.

*/

public void add(String property, JsonElement value) {

if (value == null) {

value = JsonNull.INSTANCE;

}

members.put(property, value);

}

下面是测试代码

public class GsonIsNull {

public static void testIsNull(){

Gson gson = new Gson();

String jsonString = "{\"name\":\"毛豆豆\",\"age\":24,\"password\":null}";

JsonObject jsonObject = gson.fromJson(jsonString, JsonObject.class);

String name = jsonObject.get("name").getAsString();

System.out.println(name);

String password = jsonObject.get("password").getAsString();

//空指针异常

//JsonElement passwordJsonEle = jsonObject.get("password");

//if(passwordJsonEle!=null){

//String password = passwordJsonEle.getAsString();

//System.out.println(password);

//}

//正常

JsonElement passwordJsonEle = jsonObject.get("password");

if(!passwordJsonEle.isJsonNull()){

String password = passwordJsonEle.getAsString();

System.out.println(password);

}

2017.3.14