Spring@PostConstruct注解和构造方法的调用顺序
先看下@PostConstruct的注解
* The PostConstruct annotation is used on a method that needs to be executed * after dependency injection is done to perform any initialization. This * method MUST be invoked before the class is put into service. This * annotation MUST be supported on all classes that support dependency * injection. The method annotated with PostConstruct MUST be invoked even * if the class does not request any resources to be injected. Only one * method can be annotated with this annotation. The method on which the * PostConstruct annotation is applied MUST fulfill all of the following * criteria -
自己翻译一下，意思是：
PostConstruct注解用于方法上，该方法在初始化的依赖注入操作之后被执行。这个方法必须在class被放到service之后被执行，这个注解所在的类必须支持依赖注入。
父类class，被@component注解修饰，说明会被spring扫描并创建。在默认构造方法里加上输出打印，init方法被@PostConstruct修饰
1 @Component
2 public class ParentBean implements InitializingBean{
3
4 public ParentBean() {
5 System.out.println("ParentBean construct");
6 }
7
8 @PostConstruct
9 public void init(){
10 System.out.println("ParentBean init");
11 }
12
13 public void afterPropertiesSet() throws Exception {
14 System.out.println("ParentBean afterPropertiesSet");
15 }
16
17 }
子类class，也被 @component注解修饰，其余配置和父类class一样
1 @Component
2 public class SonBean extends ParentBean{
3 public SonBean() {
4 System.out.println("SonBean construct");
5 }
6
7 @PostConstruct
8 public void init(){
9 System.out.println("SonBean init");
10 }
11 @Override
12 public void afterPropertiesSet() throws Exception {
13 System.out.println("SonBean afterPropertiesSet");
14 }
15
16 }
然后我们使用maven命令 jetty:run，控制台输出如下：
[INFO] Initializing Spring root WebApplicationContext ParentBean construct ParentBean init ParentBean afterPropertiesSet ParentBean construct SonBean construct SonBean init SonBean afterPropertiesSet [INFO] Set web app root system property: 'webapp.root' = [J:androidworkspacecomsrcmainwebapp] [INFO] Initializing log4j from [classpath:log4j.properties] [INFO] Started SelectChannelConnector@0.0.0.0:8088 [INFO] Started Jetty Server [INFO] Starting scanner at interval of 3 seconds.
可以看出优先执行依然是构造方法，这个是java的语言决定的，毕竟spring只是建立在java之上的框架。然后才是被PostConstruct修饰的方法，要注意的是这个方法在对象的初始化和依赖都完成之后才会执行，所以不必担心执行这个方法的时候有个别成员属性没有被初始化为null的情况发生。在init方法之后执行的才是afterPropertiesSet方法，这个方法必须实现InitializingBean接口，这个接口很多spring的bean都实现了他，从他的方法名就能看出在属性都被设置了之后执行，也属于springbean初始化方法。
其实spring提供了很多接口以供开发者在bean初始化后调用，可以在官网上查阅相关文档。