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<document> <header> <product>resin</product> <title>Hessian with Dependency Injection</title> <description> <p>Using Hessian with Dependency Injection patterncreates services which are simpler, protocol-independent and more easilytested. The Dependency Injection pattern (aka inversion of control)gives Resin the responsibility of configuring and assemblingthe service, protocol, and client.</p> </description> <type>tutorial</type> <tutorial-startpage>client/greeting</tutorial-startpage> </header> <body> <localtoc/><s1 title="Files in this tutorial"><deftable><tr> <td><viewfile-link file="WEB-INF/classes/example/GreetingAPI.java"/></td> <td>Interface for the greeting service.</td></tr><tr> <td><viewfile-link file="WEB-INF/classes/example/GreetingImpl.java"/></td> <td>The service implementation as a Java object</td></tr><tr> <td><viewfile-link file="WEB-INF/resin-web.xml"/></td> <td>Configures the environment</td></tr><tr> <td><viewfile-link file="WEB-INF/classes/example/GreetingClientServlet.java"/></td> <td>Client Servlet</td></tr></deftable></s1><s1 title="Service Implementation"><example title="GreetingAPI.java">package example;public interface GreetingAPI { public String hello();}</example><s2 title="Service Implementation"><p>The Greeting implementation is a plain Java class that implementsthe MatchService API. Making the service a plain class offers a number of advantages:</p><ul><li><b>Simplicity:</b> It can concentrate on its business logic because it doesn't need to implement any protocol-dependent code.</li><li><b>Independence:</b> It can be reused more easily because it isn't tied to a distributed framework (e.g. in contrast to EJB).</li><li><b>Testability:</b> It is more easily tested since the test harness doesn't need to implement the protocol or its stubs. The harness can just test the service as a plain old Java object.</li></ul><example title="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; }}</example></s2><s2 title="Configuring the Service"><p>URL-based services can use the servlet configuration to define theservice. The service class can use<a href="../../doc/resin-ioc.xtp">Resin IoC</a> to inject itsown dependencies.</p><example title="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></example></s2></s1><s1 title="Client"><p>Configuring the client servlet with Dependency Injectionallows for a simpler and more general client. The following clientcan use any proxy/stub which implements the GreetingAPI without change,for example:</p><ul> <li>Hessian proxy</li> <li>Burlap proxy</li> <li>EJB local object stub</li> <li>JMX proxy</li> <li>Java bean instance</li></ul><p>Using the Dependency Injection pattern, the servlet doesn't carehow the proxy is implemented, or how the greeting service isdiscovered.</p><example title="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()); }}</example><s2 title="Hessian Client using Dependency Injection"><p>The following code defines the client in the resin.web.xml.The servlet defined above will inject the <code>GreetingAPI</code>directly with the WebBeans <code>@In</code> annotation. Because the<code>GreetingAPI</code> is unique, there's no need to give it a name.</p><example title="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></example></s2><!--<s2 title="JMX Configuration"><p>The following JMX configuration shows the flexibility ofthe Dependency Injection pattern. With no changes to either theGreeting service or its client, the Greeting service can change toa JMX bean used by and the client to use a JMX proxy.</p><example title="resin-web.xml"><resource mbean-name="type=Greeting" mbean-interface="example.GreetingAPI" type="example.GreetingImpl"> <init> <greeting>Hello, web.xml</greeting> </init></resource><servlet-mapping url-pattern="/client/greeting" servlet-class="example.GreetingClientServlet"> <init> <name>JMX Client</name> <greeting>\${jndi("mbean:type=Greeting")}</greeting> </init></servlet-mapping></example></s2>--></s1> </body></document>⌨️ 快捷键说明
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