spring boot 动态生成接口实现类的场景分析

在某些业务场景中，我们只需要业务代码中定义相应的接口或者相应的注解，并不需要实现对应的逻辑。

比如 mybatis和feign： 在 mybatis 中，我们只需要定义对应的mapper接口；在 feign 中，我们只需要定义对应业务系统中的接口即可。

那么在这种场景下，具体的业务逻辑时怎么执行的呢，其实原理都是动态代理。

我们这里不具体介绍动态代理，主要看一下它在springboot项目中的实际应用，下面我们模仿feign来实现一个调用三方接口的 httpclient。

一: 定义注解

package com.mysgk.blogdemo.annotation;

public @interface MyHttpClient {
}

二: 建立动态代理类

package com.mysgk.blogdemo.proxy;

import org.springframework.beans.factory.FactoryBean;

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

public class RibbonAopProxyFactory<T> implements FactoryBean<T>, InvocationHandler {

	private Class<T> interfaceClass;

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

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

	@Override
	public T getObject() throws Exception {
		return (T) Proxy.newProxyInstance(this.getClass().getClassLoader(), new Class[]{interfaceClass}, this);
	}

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

	@Override
	public boolean isSingleton() {
		return true;
	}

	/**
	 真正执行的方法
	 */
	@Override
	public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
		return "invoke " + proxy.getClass().getName() + "." + method.getName() + " , do anything ..";
	}
}

三: 注入spring容器

package com.mysgk.blogdemo.start;

import cn.hutool.core.util.ClassUtil;
import cn.hutool.core.util.StrUtil;
import com.mysgk.blogdemo.annotation.MyHttpClient;
import com.mysgk.blogdemo.proxy.RibbonAopProxyFactory;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
import org.springframework.beans.factory.support.BeanDefinitionBuilder;
import org.springframework.beans.factory.support.BeanDefinitionRegistry;
import org.springframework.beans.factory.support.BeanDefinitionRegistryPostProcessor;
import org.springframework.beans.factory.support.GenericBeanDefinition;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationContextAware;
import org.springframework.stereotype.Component;

import java.util.Set;

@Component
public class ScanHttpClients implements BeanDefinitionRegistryPostProcessor, ApplicationContextAware {

	private final Logger logger = LoggerFactory.getLogger(ScanHttpClients.class);

	private ApplicationContext ctx;

	public void run(BeanDefinitionRegistry registry) {

		Set<Class<?>> scanPackage = ClassUtil.scanPackageByAnnotation("com.mysgk", MyHttpClient.class);

		for (Class<?> cls : scanPackage) {

			BeanDefinitionBuilder builder = BeanDefinitionBuilder.genericBeanDefinition(cls);
			GenericBeanDefinition definition = (GenericBeanDefinition) builder.getRawBeanDefinition();
			definition.getPropertyValues().add("interfaceClass", definition.getBeanClassName());
			definition.setBeanClass(RibbonAopProxyFactory.class);
			definition.setAutowireMode(GenericBeanDefinition.AUTOWIRE_BY_TYPE);
			String beanName = StrUtil.removePreAndLowerFirst(cls.getSimpleName(), 0) + "RibbonClient";
			registry.registerBeanDefinition(beanName, definition);
		}

	}

	@Override
	public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) throws BeansException {
		run(registry);
	}

	@Override
	public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {

	}

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


}

四: 编写拦截器

package com.mysgk.blogdemo.aop;

import org.aspectj.lang.ProceedingJoinPoint;
import org.aspectj.lang.annotation.Around;
import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.annotation.Pointcut;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.http.HttpEntity;
import org.springframework.http.HttpMethod;
import org.springframework.http.ResponseEntity;
import org.springframework.stereotype.Component;
import org.springframework.web.client.RestTemplate;
@Component
@Aspect
public class InterceptAnnotation {

	@Autowired
	private RestTemplate ribbonLoadBalanced;

	@Pointcut("@annotation(com.mysgk.blogdemo.annotation.MyHttpClient)")
	public void execute() {

	}

	@Around("execute()")
	public Object interceptAnnotation(ProceedingJoinPoint joinPoint) throws Throwable {
		/**
		 * 此处省略 获取 url, httpMethod, requestEntity, responseType 等参数的处理过程
		 */
		ResponseEntity<?> exchange = ribbonLoadBalanced.exchange("url", HttpMethod.GET, HttpEntity.EMPTY, Object.class);
		return exchange.getBody();
	}

}

五: 新建测试类

package com.mysgk.blogdemo.client;

import com.mysgk.blogdemo.annotation.MyHttpClient;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RequestBody;

@MyHttpClient
public interface MyHttpClientTest {

	@PostMapping(value = "test/t1")
	Object test(String param);

}

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