第四讲、Spring之Bean后处理器

文章内容根据黑马程序员Spring视频教程所写！！！

视频地址：点击这里

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常见Bean后处理器

main方法

/*
    bean 后处理器的作用
 */
public class A04 {
    public static void main(String[] args) {
        // ⬇️GenericApplicationContext 是一个【干净】的容器
        GenericApplicationContext context = new GenericApplicationContext();

        // ⬇️用原始方法注册三个 bean
        context.registerBean("bean1", Bean1.class);
        context.registerBean("bean2", Bean2.class);
        context.registerBean("bean3", Bean3.class);

        context.getDefaultListableBeanFactory().setAutowireCandidateResolver(new ContextAnnotationAutowireCandidateResolver());
        context.registerBean(AutowiredAnnotationBeanPostProcessor.class); // @Autowired @Value

        context.registerBean(CommonAnnotationBeanPostProcessor.class); // @Resource @PostConstruct @PreDestroy
        // ⬇️初始化容器
        context.refresh(); // 执行beanFactory后处理器, 添加bean后处理器, 初始化所有单例
        System.out.println(context.getBean(Bean1.class));
        // ⬇️销毁容器
        context.close();

        /*
            学到了什么
                a. @Autowired 等注解的解析属于 bean 生命周期阶段(依赖注入, 初始化)的扩展功能
                b. 这些扩展功能由 bean 后处理器来完成
         */
    }
}

public class Bean1 {
    private static final Logger log = LoggerFactory.getLogger(Bean1.class);

    private Bean2 bean2;

    @Autowired
    public void setBean2(Bean2 bean2) {
        log.debug("@Autowired 生效: {}", bean2);
        this.bean2 = bean2;
    }

    @Autowired
    private Bean3 bean3;

    @Resource
    public void setBean3(Bean3 bean3) {
        log.debug("@Resource 生效: {}", bean3);
        this.bean3 = bean3;
    }

    private String home;

    @Autowired
    public void setHome(@Value("${JAVA_HOME}") String home) {
        log.debug("@Value 生效: {}", home);
        this.home = home;
    }

    @PostConstruct
    public void init() {
        log.debug("@PostConstruct 生效");
    }

    @PreDestroy
    public void destroy() {
        log.debug("@PreDestroy 生效");
    }

    @Override
    public String toString() {
        return "Bean1{" +
               "bean2=" + bean2 +
               ", bean3=" + bean3 +
               ", home='" + home + '\'' +
               '}';
    }
}

执行结果：

如果没有这段代码context.getDefaultListableBeanFactory().setAutowireCandidateResolver(new ContextAnnotationAutowireCandidateResolver());，则会报错，

context.registerBean("bean4", Bean4.class);
ConfigurationPropertiesBindingPostProcessor.register(context.getDefaultListableBeanFactory());
System.out.println(context.getBean(Bean4.class));

// 内置配置
@ConfigurationProperties(prefix = "java")
public class Bean4 {
    private String home;
    private String version;
    public String getHome() {
        return home;
    }
    public void setHome(String home) {
        this.home = home;
    }
    public String getVersion() {
        return version;
    }
    public void setVersion(String version) {
        this.version = version;
    }
    @Override
    public String toString() {
        return "Bean4{" +
               "home='" + home + '\'' +
               ", version='" + version + '\'' +
               '}';
    }
}

执行结果：