Externalizable is an interface which contains two methods readExternal and writeExternal. These methods give you a control over the serialization mechanism. Thus if your class implements this interface, you can customize the serialization process by implementing these methods.
Java 接口传参 form data 和 json 的区别。题目问到Java接口，应该分三种情况。如果是JSP等服务器端模板技术，再加上一些jQuery AJAX。POST的时候，默认contentType都是application/x-www-form-urlencoded。可改成application/json，看自己。
