JSON如何反序列化数组？

Question

I am using fasterxml.jackson. I am confused about readValue() . Here is my question.

I know jackson deserialize normal JavaBean and Collection in two different ways. For JavaBean, we can pass MyBean.class or new TypeReference<MyBean> to readValue() . For Collections, we must pass new TypeReference<List<MyBean>> . That is because TypeReference saves the type erased by Collection. Am I right? :)

Now I am confused. If MyBean contains a list, then I can still pass MyBean.class and it works. How does jackson do that?

public class MyBean {
    String str;
    List<String> strList;
}

Answer 1

You are passing MyBean.class as the second argument to readValue() and Jackson can get the type from this through reflection. I'd guess Jackson does something like this :

MyBean.class.getDeclaredField("strList").getGenericType();

which will result in a type of java.util.List<java.lang.String> .

Note that you have a non generic class MyBean containing a List<String> . If you had for instance:

class MyGenBean<T> {
    List<T> list;
}

then

MyGenBean.class.getDeclaredField("list").getGenericType();

would return java.util.List<T> and you would need a TypeReference .