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<document><header><type>tutorial</type><tutorial-startpage>stateless</tutorial-startpage><title>Local Stateless Session Hello</title><description><p>Stateless sessions make database queries and updates robust bysetting transaction boundaries at each business method.This <var>stateless session</var> bean example annotates a singlebusiness method with a SUPPORTS transaction attribute, marking themethod as a read-only transaction boundary.</p><p>See also:</p><ul><li>The <a href="doc|resin-ejb.xtp">Resin-EJB</a> reference.</li></ul></description></header><body><localtoc/><s1><p>A Hello, World example for EJB 3.0 is much simpler than for earlierversions of EJB. To implement the EJB you need to implement:</p><ul><li>A local interface</li><li>The bean implementation</li></ul><p>To configure Resin to be a server for the EJB you need to:</p><ul><li>Configure the ejb-stateless-bean</li><li>Inject the bean into the application servlet</li></ul><p>In this tutorial, a simple "Hello" EJB is created anddeployed within Resin.</p></s1><s1 title="Files in this tutorial"><deftable><tr> <th>File</th> <th>Description</th></tr><tr> <td><viewfile-link file="WEB-INF/web.xml"/></td> <td>web.xml configuration</td></tr><tr> <td><viewfile-link file="WEB-INF/classes/example/Hello.java"/></td> <td>The local interface for the stateless session bean</td></tr><tr> <td><viewfile-link file="WEB-INF/classes/example/HelloBean.java"/></td> <td>The implementation for the stateless session bean</td></tr><tr> <td><viewfile-link file="WEB-INF/classes/example/HelloServlet.java"/></td> <td>The client for the stateless session bean</td></tr></deftable></s1><s1 title="Local Interface"><p>The remote interface defines the client view of the bean.It declares all the business methods. Ouronly business method is the <code>hello</code> method.</p><example title="Hello.java">package example;public interface Hello { public String hello();}</example></s1><s1 title="Bean Implementation"><p>The second class for EJBs is the bean implementation class. It implementsthe functionality provided by the remote interface.</p> <example title="HelloBean.java">package example;import javax.ejb.Stateless;import javax.ejb.TransactionAttribute;import static javax.ejb.TransactionAttributeType.SUPPORTS;import javax.webbeans.Named;@Statelesspublic class HelloBean implements Hello { @Named("greeting") private String _greeting; @TransactionAttribute(SUPPORTS) public String hello() { return _greeting; }}</example><s2 title="@Stateless"><p>The @Stateless annotation marks the bean as a stateless sessionbean. Resin will create a stub implementing <code>Hello</code> andstore it in the WebBeans directory with type <code>Hello</code> andname <code>@Named("HelloBean")</code>.</p><p>The @Stateless annotation can have an optional <code>name</code>value which overrides the default name of "HelloBean".</p></s2><s2 title="@Named"><p>The <a href="doc|webbeans-annotations.xtp#@Named">@javax.webbeans.Named</a>annotation tells Resin to lookup the greeting <code>String</code>in the WebBeans directory with the name binding "greeting" when thesession bean is created.</p><p>In this example, the greeting is configured with an <env-entry>in the web.xml.</p></s2><s2 title="Alternate Dependency Injection"><p>In some cases, it may be clearer to configure the session bean directly,rather than using WebBeans injection. Instead of creating a separate<env-entry>, you can configure the greeting value using XMLstraight from the resin-web.xml file.</p><example title="resin-web.xml"><web-app xmlns="http://caucho.com/ns/resin"> <ejb-stateless-bean class="qa.TestBean"> <init> <greeting>Hello, World from web.xml</greeting> </init> </ejb-stateless-bean></web-app></example></s2><s2 title="@TransactionAttribute"><p>Managing transactions is the primary purpose of statelesssession beans. Transactions are a more powerful version ofa <code>synchronized</code> lock used to protect database integrity.<a href="doc|ejb-annotations.xtp#@TransactionAttribute">@TransactionAttribute</a>marks the transaction boundary for each business method.</p><example>@javax.ejb.TransactionAttribute(SUPPORTS)public String hello()</example><p>The <code>hello()</code> business method uses SUPPORTS because it'sa read-only method. It doesn't need to start a new transaction on itsown, but will participate in any transaction that already exists.</p><p>The REQUIRED transaction value starts up a new transaction if nonealready exists. It's used when updating database values.</p><deftable><tr> <th>TransactionAttribute</th> <th>meaning</th></tr><tr> <td>REQUIRED</td> <td>Start a new transaction if necessary</td></tr><tr> <td>SUPPORTS</td> <td>Don't start a new transaction, but use one if it exists</td></tr></deftable></s2></s1><s1 title="Configuring the EJB stateless bean"><p><code><ejb-stateless-bean></code> configure the session beanfrom the resin-web.xml.The <ejb-stateless-bean> entry willlook at the bean's annotations to enhance the class.</p><example title="ejb-stateless-bean in web.xml"><web-app xmlns="http://caucho.com/ns/resin"> <env-entry env-entry-name="greeting" env-entry-type="java.lang.String" env-entry-value="Hello, World."/> <ejb-stateless-bean class="qa.TestBean"/></web-app></example><p>The <ejb-stateless-bean> can optionally configure the beandirectly with an <init> tag as described in the alternatedependency injection section.</p></s1><s1 title="Client"><example title="HelloServlet.java">import javax.webbeans.In;public class HelloServlet extends GenericServlet { @In private Hello _hello; public void service(HttpServletRequest req, HttpServletResponse res) throws IOException, ServletException { PrintWriter out = res.getWriter(); out.println(_hello.hello()); }}</example><s2 title="@EJB"><p>The <a href="doc|webbeans-annotations.xtp#@In">@In</a> annotation tellsResin to look for a <code>Hello</code> component in the WebBeans directory.</p><p>The servlet could also lookup the Hello bean with JNDI in the<code>init()</code> method or use an <init> configuration in theweb.xml:<example title="alternative configuration"><servlet servlet-name="hello" servlet-class="example.HelloServlet"> <init hello="${HelloBean}"/></servlet></example></p></s2></s1></body></document>⌨️ 快捷键说明
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