本文通过老王使用纸质书籍阅读小王使用电子书籍的故事，详细说明设计模式中的结构型设计模式之适配器模式，分别对对象适配器和类适配器代码实现，最后为了加深理解，会列举适配器设计模式在JDK和Spring源码中的应用。
一、引出问题
自从小王被老王赶出家门后，老王就舒舒服服地住了几天，家里的书架上也买了不少纸质书。
[En]
Since Xiao Wang was driven out of the house by Lao Wang, Lao Wang has lived comfortably for a few days and bought a lot of paper books on the bookshelf at home.
一天，小王过着野蛮的生活回来了。小王也是个喜欢读书的人，但小王不喜欢纸质书，就让老王换成电子书。
[En]
One day, Xiao Wang came back from living a savage life. Xiao Wang is also a person who likes reading, but Xiao Wang doesn't like paper books, so he asks Lao Wang to replace them with electronic ones.
老王马上就不高兴了。我不知道设计这个书架花了多少个昼夜。用电子版取代它，不仅要花费我大量的精力来改变原有书架的结构，而且要找到我想读的书有多难。如果老李来了，想看纸质版，我是不是要改回去？
[En]
Lao Wang was unhappy immediately. I don't know how many days and nights it took to design the bookshelf. Replacing it with an electronic version will not only cost me a lot of energy to change the structure of the original bookshelf, but also how difficult it is to find the book I want to read. and what if Lao Li comes and wants to see the paper version, do I have to change it back?
老王满意地点了点头，你说得对，这其实就是结构设计模式中的适配器模式。
[En]
Lao Wang nodded with satisfaction, you are right, this is actually the adapter pattern in the structural design pattern.
二、概念与使用
引用Gof中对适配器设计模式的概念：将一个类的接口转化成客户希望的另一个接口，由于接口不兼容而不能一起工作的类可以一起工作。
很显然，在适配器设计模式中应该有三个角色。
目标类：Target，该角色把其他类转换为我们期望的接口，可以是一个抽象类或接口，也可以是具体类。
被适配者类（源）: Adaptee ，原有的接口，也是希望被适配的接口。