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    copied!<p>The portable approach for defining data sources is to use a <em><strong>resource reference</strong></em>. Resource references enable you to define the JNDI name for your data source, relative to your application naming context (<code>java:comp/env</code>), and then map that <em>logical reference</em> to the <em>physical resource</em> defined in the application server, whose JNDI name is <em>proprietary</em> to the application server vendor. This approach enables your code and assembly to be portable to any compliant application server.</p> <h1>Step 1: Declare and Lookup Resource Reference</h1> <h2>Option 1</h2> <p>This can be done by declaring a <code>resource-ref</code> in your web deployment descriptor (<code>WEB-INF/web.xml</code>):</p> <pre><code>&lt;resource-ref&gt; &lt;description&gt;My Data Source.&lt;/description&gt; &lt;res-ref-name&gt;jdbc/MyDataSource&lt;/res-ref-name&gt; &lt;res-type&gt;javax.sql.DataSource&lt;/res-type&gt; &lt;res-auth&gt;Container&lt;/res-auth&gt; &lt;/resource-ref&gt; </code></pre> <p>Within your code, you can then lookup this resource using the JNDI name <code>java:comp/env/jdbc/MyDataSource</code>:</p> <pre><code>dataSource = (DataSource) new InitialContext().lookup("java:comp/env/jdbc/MyDataSource"); </code></pre> <p>This JNDI name will not change regardless of the server where the application is deployed.</p> <h2>Option 2</h2> <p>Alternatively, starting in Java EE 5 (Servlet 2.5), this can be done even easier within your code using the <a href="http://download.oracle.com/javaee/5/api/javax/annotation/Resource.html" rel="noreferrer"><code>@Resource</code></a> annotation. This eliminates the need for configuring the resource-ref in your web deployment descriptor (web.xml) and prevents the need to perform an explicit JNDI lookup:</p> <pre><code>public class MyServlet extends HttpServlet { @Resource(name = "jdbc/MyDataSource") private DataSource dataSource; @Override protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { // dataSource may be accessed directly here since the container will automatically // inject an instance of the data source when the servlet is initialized } </code></pre> <p>This approach has the same results as the previous option, but cuts down on the boilerplate code and configuration in your assembly.</p> <h1>Step 2: Map Resource Reference to Data Source</h1> <p>Then, you will need to use your application server's proprietary approach for mapping the resource reference to the <em>physical data source</em> that you created on the server, for example, using JBoss's custom deployment descriptors (<code>WEB-INF/jboss-web.xml</code>):</p> <pre><code>&lt;?xml version="1.0" encoding="UTF-8"?&gt; &lt;jboss-web&gt; &lt;resource-ref&gt; &lt;res-ref-name&gt;jdbc/MyDataSource&lt;/res-ref-name&gt; &lt;res-type&gt;javax.sql.DataSource&lt;/res-type&gt; &lt;jndi-name&gt;java:/MyDataSource&lt;/jndi-name&gt; &lt;/resource-ref&gt; &lt;/jboss-web&gt; </code></pre> <p>Or, for example, using Tomcat's <code>context.xml</code>:</p> <pre><code>&lt;Resource name="jdbc/MyDataSource" . . . /&gt; </code></pre>
 

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