通过注解自动暴露Hessian服务

一、Hessian与spring集成

Hessian可以与spring完美无缝的集成，我们先来看一下如何集成：

服务端服务暴露

@Autowired
private HelloService helloService;

@Bean(name = "/helloService")
public HessianServiceExporter exportHelloService() {
    HessianServiceExporter exporter = new HessianServiceExporter();
    exporter.setService(helloService);
    exporter.setServiceInterface(HelloService .class);
    return exporter;
}

以上使用spring在代码配置声明bean的方式暴露了一个hession服务：http://localhost:8080/Hello/helloService

客户端声明与调用
声明

<bean id="studentService" class="org.springframework.remoting.caucho.HessianProxyFactoryBean">
        <!-- 请求代理Servlet路径 -->
        <property name="serviceUrl">
            <value>http://localhost:8080/Hello/helloService</value>
        </property>
        <!-- 接口定义 -->
        <property name="serviceInterface">
            <value>com.test.hello.service.HelloService</value>
        </property>
</bean>

调用

ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext("classpath:/spring/ApplicationContext.xml");
HelloService helloService = (HelloService) context.getBean("helloService");
helloService.sayHi("hi, i am client");

二、存在的问题

上述的方法是最常用的集成方式，但存在一个问题，如果我们现在要在服务端暴露另外一个服务，那么需要添加如下代码：

@Autowired
private AnotherService1 anotherService;

@Bean(name = "/anotherService")
public HessianServiceExporter exportAnotherService() {
    HessianServiceExporter exporter = new HessianServiceExporter();
    exporter.setService(anotherService);
    exporter.setServiceInterface(AnotherService .class);
    return exporter;
}

如果再来一个服务呢，那我们就再添加类似的代码，能不能不重复添加这些类似的暴露代码呢？

三、使用注解自动暴露服务

首先，新建一个叫HessianService的注解类，注意这个注解类包含了spring的Service注解

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

import org.springframework.stereotype.Service;

@Target({ java.lang.annotation.ElementType.TYPE })
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Service
public @interface HessianService {
    public abstract String value() default "";
}

接着，我们把原先用@Service注解的服务类换成@HessianService

@HessianService
public class HelloServiceImpl implements HelloService {
    ...
    ...
}

然后，我们使用spring的BeanFactoryPostProcessor机制，动态暴露hessian服务

@Component
public class HessianServiceScanner implements BeanFactoryPostProcessor {

    public void postProcessBeanFactory(
            ConfigurableListableBeanFactory beanFactory) throws BeansException {
        String[] beanNames = beanFactory
                .getBeanNamesForAnnotation(HessianService.class);
        for (String beanName : beanNames) {
            String className = beanFactory.getBeanDefinition(beanName)
                    .getBeanClassName();
            Class<?> clasz = null;
            try {
                clasz = Class.forName(className);
            } catch (ClassNotFoundException e) {
                throw new BeanInitializationException(e.getMessage(), e);
            }
            String hessianServiceBeanName = "/" + beanName.replace("Impl", "");

            BeanDefinitionBuilder builder = BeanDefinitionBuilder
                    .rootBeanDefinition(HessianServiceExporter.class);
            builder.addPropertyReference("service", beanName);
            builder.addPropertyValue("serviceInterface",
                    clasz.getInterfaces()[0].getName());
            ((BeanDefinitionRegistry) beanFactory).registerBeanDefinition(
                    hessianServiceBeanName, builder.getBeanDefinition());
        }
    }

}