关于java:PostConstruct

以下述代码为例

TestController 中成员变量 testService 被 @Autowired 润饰
TestService 将会在 TestController 构造方法执行后注入

@Component
public class TestService {public TestService() {System.out.println("TestService construct");
    }
    public void init() {System.out.println("TestService init");
    }
}

@RestController
public class TestController {

    @Autowired
    private TestService testService;

    public TestController() {System.out.println("TestController construct");
        testService.init();}
}

此时启动 Spring 利用，则会呈现报错，其起因就是 testService 在执行 TestController 构造方法时并没有实现初始化和注入；
TestController 初始化时须要执行依赖中的办法时，这种写法就会引起问题；
此时就能够应用 @PostConstruct 来解决问题

Caused by: java.lang.NullPointerException: null
at com.example.demo.my.view.TestController.<init>(TestController.java:20) ~[classes/:na]
at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method) ~[na:na]
at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62) ~[na:na]
at java.base/jdk.internal.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45) ~[na:na]
at java.base/java.lang.reflect.Constructor.newInstance(Constructor.java:490) ~[na:na]

调整代码后

@RestController
public class TestController {

    @Autowired
    private TestService testService;

    public TestController() {System.out.println("TestController construct");
    }

    @PostConstruct
    public void initBeforeConstruct() {System.out.println("TestController PostConstruct");
        testService.init();}
}

此时启动输入后果

从中可见总体的执行程序

构造方法
@Autowird
@PostConstruct

@PostConstruct 是一种初始化形式