1.首先，什么是XML：
https://www.bilibili.com/video/BV19t4y1E7nR/?spm_id_from=333.337.search-card.all.click&vd_source=af888e4b9fbc70c4d5e7a445796ae8a1
2.理解控制反转：
https://blog.csdn.net/love_java_cc/article/details/78216228
3.理解属性注入：
https://blog.csdn.net/love_java_cc/article/details/78217700
4.构造器注入与XML配置：
https://blog.csdn.net/love_java_cc/article/details/78218176