BeanDefinitionRegistryPostProcessor扩展

通过BeanDefinitionRegistryPostProcessor扩展能实现额外的很多功能，例如实现将一个接口动态代理，并将该代理对象在spring容器初始化完成前注册到spring容器中。实现可以通过@Autowired等注释或其他方法从spring容器中获取该代理对象。

import lombok.extern.slf4j.Slf4j;

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;

@Slf4j
public class HelloProxy implements InvocationHandler {

private Class<?> interfaceClass;

public Object bind(Class<?> cls) {
        this.interfaceClass = cls;
        return Proxy.newProxyInstance(cls.getClassLoader(), new Class[]{interfaceClass}, this);
    }

@Override
    public Object invoke(Object proxy, Method method, Object[] args) {
        log.info("调用代理方法, method: {}", method.getName());
        return "hello world";
    }

}

import org.springframework.beans.factory.FactoryBean;

public class ProxyBeanFactory<T> implements FactoryBean<T> {

private Class<T> interfaceClass;

public Class<T> getInterfaceClass() {
        return interfaceClass;
    }

public void setInterfaceClass(Class<T> interfaceClass) {
        this.interfaceClass = interfaceClass;
    }

@Override
    public T getObject() {
        return (T) new HelloProxy().bind(interfaceClass);
    }

@Override
    public Class<?> getObjectType() {
        return interfaceClass;
    }

@Override
    public boolean isSingleton() {
        // 单例模式
        return true;
    }

}

import com.wakzz.autowire.proxy.ProxyBeanFactory;
import org.springframework.beans.factory.annotation.AnnotatedBeanDefinition;
import org.springframework.beans.factory.config.BeanDefinitionHolder;
import org.springframework.beans.factory.support.BeanDefinitionBuilder;
import org.springframework.beans.factory.support.BeanDefinitionRegistry;
import org.springframework.beans.factory.support.GenericBeanDefinition;
import org.springframework.context.annotation.ClassPathBeanDefinitionScanner;
import org.springframework.core.type.classreading.MetadataReader;
import org.springframework.core.type.classreading.MetadataReaderFactory;
import org.springframework.core.type.filter.AnnotationTypeFilter;
import org.springframework.core.type.filter.TypeFilter;

import java.lang.annotation.Annotation;
import java.util.Set;

public class ClassPathReferenceScanner extends ClassPathBeanDefinitionScanner {

private BeanDefinitionRegistry registry;
    private Class<? extends Annotation> annotationClass;

public ClassPathReferenceScanner(BeanDefinitionRegistry registry) {
        super(registry, false);
        this.registry = registry;
    }

public void setAnnotationClass(Class<? extends Annotation> annotationClass) {
        this.annotationClass = annotationClass;
    }

/**
     * 只扫描出指定Annotation注解的类
     */
    public void registerFilters() {
        if (this.annotationClass != null) {
            addIncludeFilter(new AnnotationTypeFilter(this.annotationClass));
        }

// exclude package-info.java
        addExcludeFilter(new TypeFilter() {
            @Override
            public boolean match(MetadataReader metadataReader, MetadataReaderFactory metadataReaderFactory) {
                String className = metadataReader.getClassMetadata().getClassName();
                return className.endsWith("package-info");
            }
        });
    }

/**
     * 只扫描出接口类
     */
    @Override
    protected boolean isCandidateComponent(AnnotatedBeanDefinition beanDefinition) {
        return beanDefinition.getMetadata().isInterface() && beanDefinition.getMetadata().isIndependent();
    }

@Override
    public Set<BeanDefinitionHolder> doScan(String... basePackages) {
        Set<BeanDefinitionHolder> beanDefinitions = super.doScan(basePackages);
        processBeanDefinitions(beanDefinitions);
        return beanDefinitions;
    }

/**
     * 将扫描出的类实现代理类,并注册到spring中
     */
    private void processBeanDefinitions(Set<BeanDefinitionHolder> beanDefinitions) {
        for (BeanDefinitionHolder holder : beanDefinitions) {
            String className = holder.getBeanDefinition().getBeanClassName();

BeanDefinitionBuilder builder = BeanDefinitionBuilder.genericBeanDefinition(className);
            GenericBeanDefinition proxyDefinition = (GenericBeanDefinition) builder.getRawBeanDefinition();
            proxyDefinition.getPropertyValues().add("interfaceClass", className);
            proxyDefinition.setBeanClass(ProxyBeanFactory.class);
            proxyDefinition.setAutowireMode(GenericBeanDefinition.AUTOWIRE_BY_TYPE);
            this.registry.registerBeanDefinition(holder.getBeanName(), proxyDefinition);
        }
    }
}

import org.springframework.beans.factory.BeanNameAware;
import org.springframework.beans.factory.InitializingBean;
import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
import org.springframework.beans.factory.support.BeanDefinitionRegistry;
import org.springframework.beans.factory.support.BeanDefinitionRegistryPostProcessor;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationContextAware;

import java.lang.annotation.Annotation;

public class ReferenceRegistryPostProcessor implements BeanDefinitionRegistryPostProcessor, InitializingBean, ApplicationContextAware, BeanNameAware {

private String basePackage;

private Class<? extends Annotation> annotationClass;

private ApplicationContext applicationContext;

public void setBasePackage(String basePackage) {
        this.basePackage = basePackage;
    }

public void setAnnotationClass(Class<? extends Annotation> annotationClass) {
        this.annotationClass = annotationClass;
    }

@Override
    public void setApplicationContext(ApplicationContext applicationContext) {
        this.applicationContext = applicationContext;
    }

@Override
    public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) {
    }

@Override
    public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) {
        ClassPathReferenceScanner scanner = new ClassPathReferenceScanner(registry);
        scanner.setAnnotationClass(this.annotationClass);
        scanner.setResourceLoader(this.applicationContext);
        scanner.registerFilters();
        scanner.scan(basePackage);
    }

@Override
    public void afterPropertiesSet() {
    }

@Override
    public void setBeanName(String name) {
    }
}

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
public @interface Reference {
}

import com.wakzz.autowire.Reference;

@Reference
public interface TestService {

String sayHello();

}

import com.wakzz.autowire.Reference;
import org.springframework.beans.factory.support.BeanDefinitionRegistryPostProcessor;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration
public class ReferenceConfig {

@Bean
    public BeanDefinitionRegistryPostProcessor referenceRegistryPostProcessor() {
        ReferenceRegistryPostProcessor referenceRegistryPostProcessor = new ReferenceRegistryPostProcessor();
        referenceRegistryPostProcessor.setAnnotationClass(Reference.class);
        referenceRegistryPostProcessor.setBasePackage("com.wakzz.autowire");
        return referenceRegistryPostProcessor;
    }

}

ConfigurableApplicationContext applicationContext = new SpringApplicationBuilder()
		.sources(Application.class)
		.run(args);
TestService bean = applicationContext.getBean(TestService.class);
String response = bean.sayHello();
System.out.println(response);

最终输出如下:

2019-12-29 15:37:35.938  INFO 25336 --- [           main] com.wakzz.autowire.proxy.HelloProxy      : 调用代理方法, method: sayHello
hello world