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SpringBoot中Aware接口使用及原理解析

更新時(shí)間：2023年08月28日 10:14:47 作者：LBruse

在Spring中存在一個(gè)Aware接口,實(shí)現(xiàn)該接口可以讓我們的Bean獲取到Spring容器中特定的資源,但該接口只是個(gè)標(biāo)記接口,不存在任何方法,本文將給大家詳細(xì)介紹一下SpringBoot中Aware接口使用及原理,需要的朋友可以參考下

Aware接口

在Spring中存在一個(gè)Aware接口，實(shí)現(xiàn)該接口可以讓我們的Bean獲取到Spring容器中特定的資源，但該接口只是個(gè)標(biāo)記接口，不存在任何方法，因此我們還需要繼承Aware來(lái)做特定資源獲取的實(shí)現(xiàn)。

Spring中有不少繼承于Aware的接口的實(shí)現(xiàn)，比如當(dāng)前Bean想要獲取環(huán)境變量時(shí)，可以實(shí)現(xiàn)EnvironmentAware接口，想要獲取應(yīng)用上下文則可以實(shí)現(xiàn)ApplicationContextAware接口。

常用的Aware實(shí)現(xiàn)

接口	作用
BeanClassLoaderAware	獲得類加載器
BeanNameAware	獲取容器中Bean名稱
BeanFactoryAware	獲取bean創(chuàng)建工廠
EnvironmentAware	獲得環(huán)境變量
ResourceLoaderAware	獲取資源加載器
ApplicationEventPublisherAware	獲取應(yīng)用事件發(fā)布器
MessageSourceAware	獲取文本信息
ApplicationContextAware	獲取當(dāng)前應(yīng)用上下文

Aware示例

以下做一個(gè)代碼示例，實(shí)現(xiàn)EnvironmentAware接口，獲取到Environment并嘗試獲取并輸出自定義的屬性。除了Aware外，還涉及到之前提到的CommandLineRunner 和Property，可以點(diǎn)擊回顧。

創(chuàng)建一個(gè)AwareCommandLineRunner，實(shí)現(xiàn)EnvironmentAware接口，并嘗試獲取并輸出redis-host屬性

package geek.springboot.application.runner;
import lombok.extern.slf4j.Slf4j;
import org.springframework.boot.CommandLineRunner;
import org.springframework.context.EnvironmentAware;
import org.springframework.core.env.Environment;
import org.springframework.stereotype.Component;
@Slf4j
@Component
public class AwareCommandLineRunner implements CommandLineRunner, EnvironmentAware {
    @Override
    public void run(String... args) throws Exception {
        log.info("AwareCommandLineRunner running...");
    }
    @Override
    public void setEnvironment(Environment environment) {
        String redisHost = environment.getProperty("redis-host");
        log.info("redis-host is {}", redisHost);
    }
}

SpringApplication啟動(dòng)代碼如下

package geek.springboot.application;
import lombok.extern.slf4j.Slf4j;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import java.util.Properties;
@Slf4j
@SpringBootApplication
public class Application {
    public static void main(String[] args) {
        SpringApplication application = new SpringApplication(Application.class);
        // 添加redis-host配置  
        Properties properties = new Properties();
        properties.setProperty("redis-host", "127.0.0.1");
        application.setDefaultProperties(properties);
        application.run(args);
    }
}

啟動(dòng)輸出 2023-08-27 19:01:15.198 INFO 56188 --- [ main] g.s.a.runner.AwareCommandLineRunner : redis-host is 127.0.0.1

自定義Aware

新建一個(gè)RedisConfig配置類

package geek.springboot.application.configuration;
import lombok.Data;
import org.springframework.stereotype.Component;
@Data
@Component
public class RedisConfig {
    private String ip = "127.0.0.1";
    private Integer port = 6379;
    @Override
    public String toString() {
        return "RedisConfig{" +
                "ip='" + ip + ''' +
                ", port=" + port +
                '}';
    }
}

創(chuàng)建一個(gè)RedisAware接口，Bean實(shí)現(xiàn)該接口即可獲取RedisConfig

package geek.springboot.application.aware;
import geek.springboot.application.configuration.RedisConfig;
import org.springframework.beans.factory.Aware;
/**
 * 自定義Aware
 *
 * @author Bruse
 */
public interface RedisAware extends Aware {
    void setRedisConfig(RedisConfig config);
}

創(chuàng)建一個(gè)RedisAwareProcessor，實(shí)現(xiàn)BeanPostProcessor接口，由它具體負(fù)責(zé)將RedisConfig注入實(shí)現(xiàn)了RedisAware接口的Bean。為什么要實(shí)現(xiàn)BeanPostProcessor后邊的原理分析會(huì)提及。

package geek.springboot.application.aware;
import geek.springboot.application.configuration.RedisConfig;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.config.BeanPostProcessor;
import org.springframework.context.ApplicationContext;
import org.springframework.stereotype.Component;
/**
 * 自定義RedisAwareProcessor
 *
 * @author Bruse
 */
@Component
public class RedisAwareProcessor implements BeanPostProcessor {
    @Autowired
    private ApplicationContext context;
    @Override
    public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
        // 判斷當(dāng)前Bean是否實(shí)現(xiàn)RedisAware
        if (bean instanceof RedisAware) {
            // 強(qiáng)轉(zhuǎn),調(diào)用setRedisConfig方法注入RedisConfig
            ((RedisAware) bean).setRedisConfig(context.getBean(RedisConfig.class));
        }
        return bean;
    }
}

AwareCommandLineRunner實(shí)現(xiàn)RedisAware接口

package geek.springboot.application.runner;
import geek.springboot.application.aware.RedisAware;
import geek.springboot.application.configuration.RedisConfig;
import lombok.extern.slf4j.Slf4j;
import org.springframework.boot.CommandLineRunner;
import org.springframework.context.EnvironmentAware;
import org.springframework.core.env.Environment;
import org.springframework.stereotype.Component;
@Slf4j
@Component
public class AwareCommandLineRunner implements CommandLineRunner, EnvironmentAware, RedisAware {
    @Override
    public void run(String... args) throws Exception {
        log.info("AwareCommandLineRunner running...");
    }
    @Override
    public void setEnvironment(Environment environment) {
        String redisHost = environment.getProperty("redis-host");
        log.info("redis-host is {}", redisHost);
    }
    @Override
    public void setRedisConfig(RedisConfig config) {
        log.info("redis config: {}", config.toString());
    }
}

啟動(dòng)SpringApplication，輸出如下

2023-08-27 19:08:36.641 INFO 79920 --- [ main] g.s.a.runner.AwareCommandLineRunner : redis config: RedisConfig{ip='127.0.0.1', port=6379}

Aware原理

在AwareCommandLineRunner的setEnvironment方法打上斷點(diǎn)，根據(jù)調(diào)用?？梢钥吹绞窃?code>ApplicationContextAwareProcessor的invokeAwareInterfaces()方法中調(diào)用setEnvironment()方法進(jìn)Environment注入的

接著再往上查找，可以看到invokeAwareInterfaces()方法又是在postProcessBeforeInitialization()中調(diào)用的

而ApplicationContextAwareProcessor正好實(shí)現(xiàn)了BeanPostProcessor接口。這也就是為什么上邊自定義Aware實(shí)現(xiàn)時(shí)，需要?jiǎng)?chuàng)建一個(gè)RedisAwareProcessor并實(shí)現(xiàn)BeanPostProcessor的原因

再往上查看調(diào)用棧的話，可以理清完整的從上到下Aware調(diào)用鏈路

調(diào)用AbstractAutowireCapableBeanFactory的doCreateBean()方法
調(diào)用AbstractAutowireCapableBeanFactory的initializeBean()方法
調(diào)用AbstractAutowireCapableBeanFactory的applyBeanPostProcessorsBeforeInitialization()方法
調(diào)用ApplicationContextAwareProcessor的postProcessBeforeInitialization()方法
調(diào)用ApplicationContextAwareProcessor的invokeAwareInterfaces()方法
調(diào)用Aware接口實(shí)現(xiàn)的方法