springBoot @Enable*注解的工作原理

Posted 2021-01-13 H.U.C-王子

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使用注解实现异步

RunnableDemo类

package com.boot.enable.bootenable;

import org.springframework.scheduling.annotation.Async;
import org.springframework.stereotype.Component;

import java.util.concurrent.TimeUnit;

@Component
public class RunnableDemo implements Runnable {

    @Async // 异步方式执行方法
    public void run() {
        for (int i = 0; i < 10; i++) {
            System.out.println("----------------"+ (i +1));
            try {
                TimeUnit.SECONDS.sleep(1);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }
}

测试类

package com.boot.enable.bootenable;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.ConfigurableApplicationContext;
import org.springframework.scheduling.annotation.EnableAsync;

@SpringBootApplication
@EnableAsync
public class BootEnableApplication {

    public static void main(String[] args) {
        ConfigurableApplicationContext context =
                SpringApplication.run(BootEnableApplication.class, args);
        Runnable bean = context.getBean(Runnable.class);
        System.out.println("-----------start-----------");
        bean.run();
        System.out.println("-----------end-----------");

        context.close();
    }
}

运行结果分析：

run方法打印的内容是异步进行的，是独立于主线程外的线程，所以-----------end-----------打印后，run方法依然再进行打印

几种装配方式

1.普通的方式

package com.boot.enable.imp.demo;

public class Book {
}

package com.boot.enable.imp.demo;

import org.springframework.stereotype.Component;

@Component
public class User {
}

package com.boot.enable.imp.demo;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.ConfigurableApplicationContext;
import org.springframework.context.annotation.Bean;

/**
 * 普通方式装配
 */
@SpringBootApplication
public class ImportApplication {

    @Bean
    public Book book() {
        return new Book();
    }

    public static void main(String[] args) {
        ConfigurableApplicationContext context =
                SpringApplication.run(ImportApplication.class, args);
        System.out.println(context.getBean(User.class));
        System.out.println(context.getBean(Book.class));

        context.close();
    }
}

使用@Import装配的第一种方式

package com.boot.enable.imp.demo1;

public class Book {
}

package com.boot.enable.imp.demo1;

public class User {
}

package com.boot.enable.imp.demo1;

import org.springframework.context.annotation.ImportSelector;
import org.springframework.core.type.AnnotationMetadata;

public class BeanImportSelector implements ImportSelector {//不需要注入其他属性时使用
    @Override
    public String[] selectImports(AnnotationMetadata importingClassMetadata) {
        return new String[]{"com.boot.enable.imp.demo1.Book"
                ,"com.boot.enable.imp.demo1.User"};
    }
}

package com.boot.enable.imp.demo1;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.ConfigurableApplicationContext;
import org.springframework.context.annotation.Import;

/**
 * 使用@Import方式装配
 */
@SpringBootApplication
// @Import({User.class, Book.class})
@Import(BeanImportSelector.class)
public class ImportApplication1 {

    public static void main(String[] args) {
        ConfigurableApplicationContext context =
                SpringApplication.run(ImportApplication1.class, args);
        System.out.println(context.getBean(User.class));
        System.out.println(context.getBean(Book.class));

        context.close();
    }
}

使用@Import装配第二种方式

package com.boot.enable.imp.demo2;

import org.springframework.beans.factory.config.BeanDefinition;
import org.springframework.beans.factory.support.BeanDefinitionBuilder;
import org.springframework.beans.factory.support.BeanDefinitionRegistry;
import org.springframework.context.annotation.ImportBeanDefinitionRegistrar;
import org.springframework.core.type.AnnotationMetadata;

public class MyBeanDefinitionRegistrar implements ImportBeanDefinitionRegistrar {//有属性注入时使用
    @Override
    public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {
        // 创建构建器对象
        BeanDefinitionBuilder bdb = BeanDefinitionBuilder.rootBeanDefinition(User.class);
        BeanDefinition beanDefinition = bdb.getBeanDefinition();
        registry.registerBeanDefinition("user", beanDefinition);

        BeanDefinitionBuilder bdb1 = BeanDefinitionBuilder.rootBeanDefinition(Book.class);
        BeanDefinition beanDefinition1 = bdb1.getBeanDefinition();
        registry.registerBeanDefinition("book", beanDefinition1);
    }
}

package com.boot.enable.imp.demo2;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.ConfigurableApplicationContext;
import org.springframework.context.annotation.Import;

/**
 * 使用@Import方式装配
 */
@SpringBootApplication
@Import(MyBeanDefinitionRegistrar.class)
public class ImportApplication1 {

    public static void main(String[] args) {
        ConfigurableApplicationContext context =
                SpringApplication.run(ImportApplication1.class, args);
        System.out.println(context.getBean("user",User.class));
        System.out.println(context.getBean(Book.class));

        context.close();
    }
}

实例演示：注解注册监控器实现

实体类准备：

package com.boot.enable.sample.bean;

import org.springframework.stereotype.Component;

@Component
public class Person {
}

public class Person1 {
}

package com.boot.enable.sample.bean;

import org.springframework.stereotype.Component;

@Component
public class Person2 {
}

package com.boot.enable.sample.vo;

import org.springframework.stereotype.Component;

@Component
public class UserVO {
}

自定义一个注解（借用@Import机制）

package com.boot.enable.sample;

import org.springframework.context.annotation.Import;

import java.lang.annotation.*;

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Import(ScannerPackageRegistrar.class)
public @interface EnableScanner {
    String[] packages();
}

package com.boot.enable.sample;

import org.springframework.beans.factory.support.BeanDefinitionBuilder;
import org.springframework.beans.factory.support.BeanDefinitionRegistry;
import org.springframework.context.annotation.ImportBeanDefinitionRegistrar;
import org.springframework.core.type.AnnotationMetadata;

import java.util.Arrays;
import java.util.List;

public class ScannerPackageRegistrar implements ImportBeanDefinitionRegistrar {
    @Override
    public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata,
                                        BeanDefinitionRegistry registry) {
        String[] attrs = (String[]) importingClassMetadata
                .getAnnotationAttributes(EnableScanner.class.getName())
                .get("packages");//获取到注解的packages属性
        List<String> packages = Arrays.asList(attrs);
        System.out.println(packages);
        BeanDefinitionBuilder bdb = BeanDefinitionBuilder.rootBeanDefinition(MyBeanDefinitionProcessor.class);
        bdb.addPropertyValue("packages", packages);//注入属性

        registry.registerBeanDefinition(MyBeanDefinitionProcessor.class.getName(), bdb.getBeanDefinition());//装配到Spring容器中

    }
}

package com.boot.enable.sample;

import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.BeanPostProcessor;

import java.util.List;

public class MyBeanDefinitionProcessor implements BeanPostProcessor {

    private List<String> packages;

    public List<String> getPackages() {
        return packages;
    }

    public void setPackages(List<String> packages) {
        this.packages = packages;
    }

    @Override//扫描出装配到容器中的类并打印出对应实例
    public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
        for (String pack : packages) {

            if (bean.getClass().getName().startsWith(pack)) {
                System.out.println("instance bean:"+bean.getClass().getName());
            }
        }
        return bean;
    }
}

测试类

package com.boot.enable.sample;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.ConfigurableApplicationContext;

/**
 * 普通方式装配
 */
@SpringBootApplication
@EnableScanner(packages ={"com.boot.enable.sample.bean","com.boot.enable.sample.vo"}) // 启用监控扫描类的注解
public class ScannerPackageApplication {

    public static void main(String[] args) {
        ConfigurableApplicationContext context =
                SpringApplication.run(ScannerPackageApplication.class, args);
        context.close();

        new ScannerPackageApplication().callFunction(new FunctionImpl());//回调演示
    }


    interface Function {
        void hello();
    }

    static class FunctionImpl implements Function {

        @Override
        public void hello() {
            System.out.println("调用了FunctionImpl->Hello方法");
        }
    }

    public void callFunction(Function fun) {
　　　　　//处理其他事　
        fun.hello();  //回调
　　　　 //处理其他事
    }
}

打印结果（打印出注入到Spring容器中的实例，Person1未加注解，所以未打印）

监控器流程图解

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