重学 Java 设计模式：实战代理模式「模拟 mybatis-spring 中定义 DAO 接口，使用代理类方式操作数据库原理实现场景」

itstack-demo-design-12-00
└── src
    ├── main
    │   ├── java
    │   │   └── org.itstack.demo.design
    │   │       ├── agent
    │   │       │	├── MapperFactoryBean.java
    │   │       │	├── RegisterBeanFactory.java
    │   │       │	└── Select.java
    │   │       └── IUserDao.java
    │   └── resources	
    │       └── spring-config.xml
    └── test
        └── java
            └── org.itstack.demo.test
                └── ApiTest.java

@Documented
@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.METHOD})
public @interface Select {
    String value() default "";  // sql语句
}

public interface IUserDao {
    @Select("select userName from user where id = #{uId}")
    String queryUserInfo(String uId);
}

public class MapperFactoryBean<T> implements FactoryBean<T> {
    private Logger logger = LoggerFactory.getLogger(MapperFactoryBean.class);
    private Class<T> mapperInterface;
    public MapperFactoryBean(Class<T> mapperInterface) {
        this.mapperInterface = mapperInterface;
    }
    @Override
    public T getObject() throws Exception {
        InvocationHandler handler = (proxy, method, args) -> {
            Select select = method.getAnnotation(Select.class);
            logger.info("SQL：{}", select.value().replace("#{uId}", args[0].toString()));
            return args[0] + ",小傅哥,bugstack.cn - 沉淀、分享、成长，让自己和他人都能有所收获！";
        };
        return (T) Proxy.newProxyInstance(this.getClass().getClassLoader(), new Class[]{mapperInterface}, handler);
    }
    @Override
    public Class<?> getObjectType() {
        return mapperInterface;
    }
    @Override
    public boolean isSingleton() {
        return true;
    }
}

public class RegisterBeanFactory implements BeanDefinitionRegistryPostProcessor {
    
    @Override
    public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) throws BeansException {
        
        GenericBeanDefinition beanDefinition = new GenericBeanDefinition();
        beanDefinition.setBeanClass(MapperFactoryBean.class);
        beanDefinition.setScope("singleton");
        beanDefinition.getConstructorArgumentValues().addGenericArgumentValue(IUserDao.class);
        BeanDefinitionHolder definitionHolder = new BeanDefinitionHolder(beanDefinition, "userDao");
        BeanDefinitionReaderUtils.registerBeanDefinition(definitionHolder, registry);
    }
    @Override
    public void postProcessBeanFactory(ConfigurableListableBeanFactory configurableListableBeanFactory) throws BeansException {
        // left intentionally blank
    }
}

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.0.xsd"
       default-autowire="byName">
    <bean id="userDao" class="org.itstack.demo.design.agent.RegisterBeanFactory"/>
</beans>

@Test
public void test_IUserDao() {
    BeanFactory beanFactory = new ClassPathXmlApplicationContext("spring-config.xml");
    IUserDao userDao = beanFactory.getBean("userDao", IUserDao.class);
    String res = userDao.queryUserInfo("100001");
    logger.info("测试结果：{}", res);
}

23:21:57.551 [main] DEBUG o.s.core.env.StandardEnvironment - Adding PropertySource 'systemProperties' with lowest search precedence
...
23:21:57.858 [main] DEBUG o.s.c.s.ClassPathXmlApplicationContext - Unable to locate LifecycleProcessor with name 'lifecycleProcessor': using default [org.springframework.context.support.DefaultLifecycleProcessor@7bc1a03d]
23:21:57.859 [main] DEBUG o.s.b.f.s.DefaultListableBeanFactory - Returning cached instance of singleton bean 'lifecycleProcessor'
23:21:57.860 [main] DEBUG o.s.c.e.PropertySourcesPropertyResolver - Could not find key 'spring.liveBeansView.mbeanDomain' in any property source
23:21:57.861 [main] DEBUG o.s.b.f.s.DefaultListableBeanFactory - Returning cached instance of singleton bean 'userDao'
23:21:57.915 [main] INFO  o.i.d.design.agent.MapperFactoryBean - SQL：select userName from user where id = 100001
23:21:57.915 [main] INFO  org.itstack.demo.design.test.ApiTest - 测试结果：100001,小傅哥,bugstack.cn - 沉淀、分享、成长，让自己和他人都能有所收获！
Process finished with exit code 0