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| |
| <h1>Basics - Getting Things</h1> |
| </div> |
| </div> |
| </div> |
| <div class="row"> |
| |
| <div class="col-md-12"> |
| <h1 id="_getting_stuff_from_the_container" class="sect0">Getting Stuff from the Container</h1> |
| <div class="paragraph"> |
| <p>Generally speaking the only way to get a |
| <a href="container-managed-resource.html">Container-Managed Resource</a> is via |
| <em>dependency injection</em> or <em>lookup</em> from within a [Container-Managed |
| Component] .</p> |
| </div> |
| <div class="paragraph"> |
| <p>The <em>unbreakable rules</em>. Read these over and over again when things |
| don’t work.</p> |
| </div> |
| <div class="olist arabic"> |
| <ol class="arabic"> |
| <li> |
| <p>java:comp/env is the spec defined namespace for lookup of any |
| <a href="container-managed-resource.html">Container-Managed Resource</a></p> |
| </li> |
| <li> |
| <p>java:comp/env is <em>empty</em> by default</p> |
| </li> |
| <li> |
| <p>java:comp/env is <em>read-only</em> at runtime</p> |
| </li> |
| <li> |
| <p>java:comp/env is populated by <a href="declaring-references.html">Declaring |
| References</a> to [Container-Managed Resource] via xml or annotation</p> |
| </li> |
| <li> |
| <p>only <a href="container-managed-component.html">Container-Managed |
| Component</a> s, <em>not</em> their libraries, can [Declare References|Declaring |
| References] via xml or annotation</p> |
| </li> |
| <li> |
| <p>only <a href="container-managed-component.html">Container-Managed |
| Component</a> s, <em>not</em> their libraries, can get dependency injection of |
| [Container-Managed Resource] s</p> |
| </li> |
| <li> |
| <p>only <a href="container-managed-component.html">Container-Managed |
| Component</a> s, <em>and</em> their libraries, may lookup from java:comp/env</p> |
| </li> |
| <li> |
| <p>you <em>must</em> use the <em>no-arg</em> 'new InitialContext()' constructor to |
| lookup something from java:comp/env</p> |
| </li> |
| <li> |
| <p>the annotations and xml for <a href="declaring-references.html">Declaring |
| References</a> are <em>identical</em> in functionality, both <em>always</em> configure |
| lookup with <em>optional</em> dependency injection</p> |
| </li> |
| </ol> |
| </div> |
| <div class="sect1"> |
| <h2 id="_common_mistakes_misunderstandings_and_myths">Common mistakes, misunderstandings, and myths</h2> |
| <div class="sectionbody"> |
| <div class="ulist"> |
| <ul> |
| <li> |
| <p><em>"I tried it via annotation and it didn’t work, so I used xml and |
| then it did work"</em></p> |
| </li> |
| </ul> |
| </div> |
| <div class="paragraph"> |
| <p>See rule 9. If one form worked and the other didn’t, it means you simply |
| made a mistake in using one versus the other. Use what works for you, |
| but understand both annotations or xml will work for either lookup or |
| injection if used correctly.</p> |
| </div> |
| <div class="ulist"> |
| <ul> |
| <li> |
| <p><em>"I need to use lookups, so I can’t use the annotation"</em></p> |
| </li> |
| </ul> |
| </div> |
| <div class="paragraph"> |
| <p>See rule 9. Annotations are not just for injection, that is just how |
| they are typically used. Know that when you use an annotation for |
| injection, it will <em>always</em> create an entry in java:comp/env. As well |
| you can use the annotation at the <em>class level</em> and it will cause no |
| dependency injection and only the entry creation in java:comp/env.</p> |
| </div> |
| <div class="ulist"> |
| <ul> |
| <li> |
| <p><em>"I don’t want injection, so I can’t use the annotation"</em></p> |
| </li> |
| </ul> |
| </div> |
| <div class="paragraph"> |
| <p>See rule 9 and the above. You can use the annotation at the <em>class |
| level</em> and it will cause no dependency injection and only the entry |
| creation in java:comp/env.</p> |
| </div> |
| <div class="ulist"> |
| <ul> |
| <li> |
| <p><em>"I tried to list java:comp/env but it’s empty?!"</em></p> |
| </li> |
| </ul> |
| </div> |
| <div class="paragraph"> |
| <p>See rule 2 and rule 4. There will be nothing in java:comp/env unless you |
| <a href="declaring-references.html">Declare a Reference</a> to it. It does not |
| matter if is a DataSource configured at the server level, etc. Nothing |
| is bound into java:comp/env unless you explicitly declare a reference to |
| it. The Java EE 5 TCK (Technology Compatibility Kit) tests for this |
| extensively and is a rule we cannot break. Java EE 6 does finally offer |
| some new namesaces (java:global, java:app, and java:module) which will |
| offer some great new options for more global-style lookups.</p> |
| </div> |
| <div class="ulist"> |
| <ul> |
| <li> |
| <p><em>"I deployed the EJB but can’t look it up, it’s name is Foo"</em></p> |
| </li> |
| </ul> |
| </div> |
| <div class="paragraph"> |
| <p>See rule 2 and the above. Just creating an EJB doesn’t cause it to be |
| added to java:comp/env. If a |
| <a href="container-managed-component.html">Container-Managed Component</a> wants |
| to lookup the EJB they must [Declare a Reference|Declaring References] |
| to it via the <code>@EJB</code> annotionation or <ejb-local-ref> or <ejb-ref> in xml. |
| In Java EE 6, however, EJBs will be automatically bound to |
| "java:global[/<app-name>]/<module-name>/<bean-name>[!<fully-qualified-interface-name>]" |
| and can be looked up without declaring a reference first.</p> |
| </div> |
| <div class="ulist"> |
| <ul> |
| <li> |
| <p><em>"Which InitialContextFactory do I use for java:comp/env?"</em></p> |
| </li> |
| </ul> |
| </div> |
| <div class="paragraph"> |
| <p>See rule 8. You are not allowed to use an InitialContextFactory for |
| java:comp/env lookups. Setting an InitialContextFactory via |
| 'java.naming.factory.initial' in either System properties, |
| InitialContext properties, or a jndi.properties file is illegal and will |
| cause java:comp/env lookups to fail.</p> |
| </div> |
| <div class="ulist"> |
| <ul> |
| <li> |
| <p><em>"My Client can’t lookup the EJB from java:comp/env"</em></p> |
| </li> |
| </ul> |
| </div> |
| <div class="paragraph"> |
| <p>See rule 7. A plain, standalone, Java application cannot use |
| java:comp/env. There is the official concept of a Java EE Application |
| Client which can be packaged in an ear and deployed into the Container. |
| In practice, most people find them restrictive, cumbersome, and hard to |
| use and are therefore rarely employed in "real world" projects. Most |
| people opt to use the non-standard, vendor-specific, approach to looking |
| up EJBs from their plain java clients. In OpenEJB this can be done via |
| either the RemoteInitialContextFactory (for remote clients) or the |
| LocalInitialContextFactory (for local clients of an embedded container). |
| The JNDI names can be configured as <a href="jndi-names.html">shown here</a> .</p> |
| </div> |
| <div class="ulist"> |
| <ul> |
| <li> |
| <p><em>"I declared the reference, but still can’t look it up"</em></p> |
| </li> |
| </ul> |
| </div> |
| <div class="paragraph"> |
| <p>See all of the above and reread the rules a few times. Always check the |
| log output as well.</p> |
| </div> |
| </div> |
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