Hessian or Burlap in Spring via Http

       与RMI二进制JRMP私有协议不同，Hessian和Burlap是两种基于Http的轻量级远程服务解决方案。Hessian的消息内容是二进制的，因此在传输带宽上更有优势；Burlap的消息内容是XML，具有更强的可读性。

       与RMI类似，Hessian和Burlap都是基于代理的思想，所以理解起来非常容易。下面描述Spring是如何支持Hessian和Burlap远程调用的。

       一、准备工作，直接参见上一篇博客 RMI in Spring

       二、使用Hessian和Burlap发布服务

       HessianServiceExporter/BurlapServiceExporter对Hessian/Burlap服务所执行的功能与RmiServiceExporter对RMI服务所执行的功能是相同的：它将POJO的public方法发布成Hessian/Burlap服务方法。不过，其实现过程与RmiServiceExporter的绑定方式是不同的。HessianServiceExporter/BurlapServiceExporter是一个SpringMVC控制器，接受对Hessian/Burlap请求，并将这些请求翻译成对被导出POJO的方法调用。

        a.使用Hessian或Burlap发布服务的配置如下：

<!-- 在SpringMVC的配置文件中，当一个bean的name是以“/”开始的时候Spring会自动对它进行BeanNameUrlHandlerMapping。所以这里相当于是我们把“/hessianSpitter”映射到了HessianServiceExporter，根据上面的配置我们要请求这个远程服务的时候应该请求“/api/hessianSpitter”。 -->
	<!-- 注意这里是name属性，id属性服从XML命名规范不能以数字、符号打头 -->
	<bean name="/hessianSpitter"
		class="org.springframework.remoting.caucho.HessianServiceExporter">
		<property name="service" ref="splitterServiceS" />
		<property name="serviceInterface"
			value="com.alibaba.alimonitor.cloudconfig.common.SplitterService"></property>
	</bean></span>

	<!-- Burlap -->
	<bean id="burlapSpitter"
		class="org.springframework.remoting.caucho.BurlapServiceExporter">
		<property name="service" ref="splitterServiceS" />
		<property name="serviceInterface"
			value="com.alibaba.alimonitor.cloudconfig.common.SplitterService"></property>
	</bean></span>

      注意区别这两个bean，在配置的时候一个是name一个是id，主要是由于id命名要符合XML规范，name不需要，两者作用上是基本一样的，name可以看做id的补充吧（name与id的区别可以参见下一篇文章）。用name主要是为了用BeanNameUrlHandlerMapping映射，其实也可以用SimpleUrlHandlerMapping来做URL映射的，只是这里分别尝试不同的映射方式。

b.配置控制器

         前面说到Hessian和Burlap是采用控制器的方式将请求传递给服务Bean，那么现在就要配置映射关系，将请求URL映射到控制器上——这里就是“/hessianSpitter”或者“burlapSpitter”。

         首先配置前端控制器——DispatcherServlet。

<servlet>
		<servlet-name>appServlet</servlet-name>
		<servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
		<init-param>
			<param-name>contextConfigLocation</param-name>
			<param-value>classpath:spring-cloudconfig-all.xml</param-value>
		</init-param>
		<load-on-startup>1</load-on-startup>
	</servlet>
	<servlet-mapping>
		<servlet-name>appServlet</servlet-name>
		<url-pattern>/api/*</url-pattern>
	</servlet-mapping></span>

然后配置URL映射关系：

	<bean
		class="org.springframework.web.servlet.handler.BeanNameUrlHandlerMapping" /></span>

或者：

	<bean class="org.springframework.web.servlet.handler.SimpleUrlHandlerMapping">
		<property name="mappings">
			<value>/burlapSpitter=burlapSpitter</value>
		</property>
	</bean></span>

                 ps：BeanNameUrlHandlerMapping是默认生成的，所以也可以不显式配置。

                 这样就确定了两个bean发布后的访问路径分别为：

http://localhost:8080/api/hessianSpitter

或者：

http://localhost:8080/api/burlapSpitter

三、客户端远程调用Hessian和Burlap服务

       客户端的配置非常简单，与RMI类似，只需添加XML配置如下：

	<bean id="spitterService"
		class="org.springframework.remoting.caucho.HessianProxyFactoryBean">
		<property name="serviceUrl" value="http://localhost:8080/api/hessianSpitter" />
		<property name="serviceInterface"
			value="com.alibaba.alimonitor.cloudconfig.common.SplitterService" />
	</bean>

	<bean id="burlapSpitter"
		class="org.springframework.remoting.caucho.BurlapProxyFactoryBean">
		<property name="serviceUrl" value="http://localhost:8080/api/burlapSpitter" />
		<property name="serviceInterface"
			value="com.alibaba.alimonitor.cloudconfig.common.SplitterService" />
	</bean></span>

       注意配置中serviceUrl的路径是怎么拼的。

       客户端测试代码：

    public static void main(String[] args) {
        ApplicationContext context = new ClassPathXmlApplicationContext("rmi_test.xml");
        SplitterService splitterService = (SplitterService) context.getBean("moblieSplitterService");
        List<Author> authors = splitterService.getAuthors();
        System.out.println("rmi: \n" + JSON.toJSONString(authors));

        SplitterService spitterService = (SplitterService) context.getBean("spitterService");
        List<Author> authors2 = spitterService.getAuthors();
        System.out.println("hessian: \n" + JSON.toJSONString(authors2));

        SplitterService burlapSplitterService = (SplitterService) context.getBean("burlapSpitter");
        List<Author> authors3 = burlapSplitterService.getAuthors();
        System.out.println("burlap: \n" + JSON.toJSONString(authors3));

        SplitterService httpInvokerSplitterService = (SplitterService) context.getBean("httpInvokerSpitter");
        List<Author> authors4 = httpInvokerSplitterService.getAuthors();
        System.out.println("httpinvoker: \n" + JSON.toJSONString(authors4));
    }

输出结果：

rmi: 
[{"address":"杭州。浙江","age":25,"name":"程宁"},{"address":"成都。四川","age":24,"name":"亚如"}]
hessian: 
[{"address":"杭州。浙江","age":25,"name":"程宁"},{"address":"成都。四川","age":24,"name":"亚如"}]
burlap: 
[{"address":"杭州。浙江","age":25,"name":"程宁"},{"address":"成都。四川","age":24,"name":"亚如"}]
httpinvoker: 
[{"address":"杭州。浙江","age":25,"name":"程宁"},{"address":"成都。四川","age":24,"name":"亚如"}]

因为Hessian和Burlap是基于Http的，Http是公认支持的传输协议，这就解决了RMI防火墙阻隔的问题。