spring HTTP invokers 实现远程调用

20.4 Exposing services using HTTP invokers

As opposed to Burlap and Hessian, which are both lightweight protocols using their own slim serialization mechanisms, Spring HTTP invokers use the standard Java serialization mechanism to expose services through HTTP. This has a huge advantage if your arguments
and return types are complex types that cannot be serialized using the serialization mechanisms Hessian and Burlap use (refer to the next section for more considerations when choosing a remoting technology).

Under the hood, Spring uses either the standard facilities provided by J2SE to perform HTTP calls or Commons

HttpClient

. Use the latter if you need more advanced and easy-to-use functionality. Refer to

jakarta.apache.org/commons/httpclient for more info.

//服务器端：

20.4.1 Exposing the service object

Setting up the HTTP invoker infrastructure for a service object resembles closely the way you would do the same using Hessian or Burlap. Just as Hessian support provides the

HessianServiceExporter

, Spring's HttpInvoker support provides the

org.springframework.remoting.httpinvoker.HttpInvokerServiceExporter

.

To expose the

AccountService

(mentioned above) within a Spring Web MVC

DispatcherServlet

, the following configuration needs to be in place in the dispatcher's application context:

<bean name="/AccountService" class="org.springframework.remoting.httpinvoker.HttpInvokerServiceExporter">
<property name="service" ref="accountService"/>
<property name="serviceInterface" value="example.AccountService"/>
</bean>

Such an exporter definition will be exposed through the

DispatcherServlet

's standard mapping facilities, as explained in the section on Hessian.

Alternatively, create an

HttpInvokerServiceExporter

in your root application context (e.g. in

'WEB-INF/applicationContext.xml'

):

<bean name="accountExporter" class="org.springframework.remoting.httpinvoker.HttpInvokerServiceExporter">
<property name="service" ref="accountService"/>
<property name="serviceInterface" value="example.AccountService"/>
</bean>

In addition, define a corresponding servlet for this exporter in

'web.xml'

, with the servlet name matching the bean name of the target exporter:

<servlet>
<servlet-name>accountExporter</servlet-name>
<servlet-class>org.springframework.web.context.support.HttpRequestHandlerServlet</servlet-class>
</servlet>

<servlet-mapping>
<servlet-name>accountExporter</servlet-name>
<url-pattern>/remoting/AccountService</url-pattern>
</servlet-mapping>

If you are running outside of a servlet container and are using Sun's Java 6, then you can use the built-in HTTP server implementation. You can configure the

SimpleHttpServerFactoryBean

together with a

SimpleHttpInvokerServiceExporter

as is shown in this example:

<bean name="accountExporter"
class="org.springframework.remoting.httpinvoker.SimpleHttpInvokerServiceExporter">
<property name="service" ref="accountService"/>
<property name="serviceInterface" value="example.AccountService"/>
</bean>

<bean id="httpServer"
class="org.springframework.remoting.support.SimpleHttpServerFactoryBean">
<property name="contexts">
<util:map>
<entry key="/remoting/AccountService" value-ref="accountExporter"/>
</util:map>
</property>
<property name="port" value="8080" />
</bean>

<property
name="port" value="8080" /> tomcat 服务器端口一致

//客服端代码

20.4.2 Linking in the service at the client

Again, linking in the service from the client much resembles the way you would do it when using Hessian or Burlap. Using a proxy, Spring will be able to translate your calls to HTTP POST requests to the URL pointing to the exported service.

<bean id="httpInvokerProxy" class="org.springframework.remoting.httpinvoker.HttpInvokerProxyFactoryBean">
<property name="serviceUrl" value="http://remotehost:8080/remoting/AccountService"/>
<property name="serviceInterface" value="example.AccountService"/>
</bean>

As mentioned before, you can choose what HTTP client you want to use. By default, the

HttpInvokerProxy

uses the J2SE HTTP functionality, but you can also use the Commons

HttpClient

by setting the

httpInvokerRequestExecutor

property:

<property name="httpInvokerRequestExecutor">
<bean class="org.springframework.remoting.httpinvoker.CommonsHttpInvokerRequestExecutor"/>
</property