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hessian with dependency injection
Using Hessian with Dependency Injection pattern creates services which are simpler, protocol-independent and more easily tested. The Dependency Injection pattern (aka inversion of control) gives Resin the responsibility of configuring and assembling the service, protocol, and client.
GreetingAPI.java
package example;
public interface GreetingAPI {
public String hello();
}
Service ImplementationThe Greeting implementation is a plain Java class that implements the MatchService API. Making the service a plain class offers a number of advantages:
GreetingImpl.java
package example;
public class GreetingImpl implements GreetingAPI {
private String _greeting = "Hello, world";
public void setGreeting(String greeting)
{
_greeting = greeting;
}
public String greeting()
{
return _greeting;
}
}
Configuring the ServiceURL-based services can use the servlet configuration to define the service. The service class can use Resin IoC to inject its own dependencies. resin-web.xml
<web-app xmlns="http://caucho.com/ns/resin">
<servlet-mapping url-pattern="/hessian/greeting"
servlet-class="example.GreetingImpl">
<protocol type="hessian"/>
<init>
<greeting>Hello from resin-web.xml</greeting>
</init>
</servlet-mapping>
</web-app>
Configuring the client servlet with Dependency Injection allows for a simpler and more general client. The following client can use any proxy/stub which implements the GreetingAPI without change, for example:
Using the Dependency Injection pattern, the servlet doesn't care how the proxy is implemented, or how the greeting service is discovered. GreetingClientServlet.java
import javax.webbeans.In;
public class GreetingClientServlet extends GenericServlet {
@In private GreetingAPI _greeting;
public void service(ServletRequest req, ServletResponse res)
throws IOException, ServletException
{
PrintWriter out = res.getWriter();
out.println("Hello: " + _greeting.greeting());
}
}
Hessian Client using Dependency InjectionThe following code defines the client in the resin.web.xml.
The servlet defined above will inject the resin-web.xml
<web-app xmlns="http://caucho.com/ns/resin">
<web-service-client class="example.GreetingAPI"
url="hessian:${webApp.url}/hessian/greeting"/>
<servlet-mapping url-pattern="/client/greeting"
servlet-class="example.GreetingClientServlet"/>
</web-app>
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