Spring推荐使用构造器注入，我不推荐

Field injection:

++ less code to write
-- unsafe code
 - more complicated to test

Constructor injection:

++ safe code
 - more code to write (see the hint to Lombok)
 + easy to test

虽然官方推荐Constructor injection，个人更喜欢Field injection。原因如下： 更少的代码 约定优于配置，都用Field injection也很安全 用spring做单元测试field injection并不复杂