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               <h1>Dynamic Datasource</h1>
             </div>
           </div>
         </div>
         <div class="row">

             <div class="col-md-12">
                 <h1 id="_openejb_dynamic_datasource" class="sect0">OpenEJB dynamic datasource</h1>
 <div class="sect1">
 <h2 id="_goal">Goal</h2>
 <div class="sectionbody">
 <div class="paragraph">
 <p>The openejb dynamic datasource api aims to allow to use multiple data
 sources as one.</p>
 </div>
 <div class="paragraph">
 <p>It can be useful for technical reasons (load balancing for example) or
 functionnal reasons (filtering, aggregation, enriching&#8230;&#8203;).</p>
 </div>
 </div>
 </div>
 <div class="sect1">
 <h2 id="_the_api">The API</h2>
 <div class="sectionbody">
 <div class="paragraph">
 <p>The interface Router (<em>org.apache.openejb.resource.jdbc.Router</em>) have
 only one method to get the datasource to use:</p>
 </div>
 <div class="listingblock">
 <div class="content">
 <pre class="highlight"><code class="language-java" data-lang="java">Router.getDataSource()</code></pre>
 </div>
 </div>
 <div class="paragraph">
 <p>The <em>org.apache.openejb.resource.jdbc.RoutedDataSource</em> wraps a
 classical data source. It has to be used to declare your datasource.</p>
 </div>
 <div class="paragraph">
 <p>You can implement all the policy you want in your Router implementation.</p>
 </div>
 <div class="paragraph">
 <p>A class called <em>org.apache.openejb.resource.jdbc.AbstractRouter</em> is
 available to ease router development.</p>
 </div>
 </div>
 </div>
 <div class="sect1">
 <h2 id="_known_limitation_s">Known limitation(s)</h2>
 <div class="sectionbody">
 <div class="paragraph">
 <p>You have to use the same kind of databases (same version, same
 configuration&#8230;&#8203;).</p>
 </div>
 <div class="paragraph">
 <p>All database have to be created when you use the router. The way to do
 it automatically can depend of your JPA provider.</p>
 </div>
 <div class="sect2">
 <h3 id="_openjpa">OpenJPA</h3>
 <div class="paragraph">
 <p>OpenJPA initializes its database when the entitymanager is called for
 the first time so you need to initialize all your proxied datasource
 before using the other one. It can be done using an Init EJB doing a
 find() on each proxied datasource.</p>
 </div>
 </div>
 <div class="sect2">
 <h3 id="_hibernate">Hibernate</h3>
 <div class="paragraph">
 <p>Hibernate initializes the database when it starts so if you declare a
 persistence unit by database all databases will be initialized at the
 start up.</p>
 </div>
 </div>
 </div>
 </div>
 <div class="sect1">
 <h2 id="_example">Example</h2>
 <div class="sectionbody">
 <div class="sect2">
 <h3 id="_the_story_the_unit_test_example">The story (the unit test example)</h3>
 <div class="paragraph">
 <p>You want to use only one datasource in the code but you have a criteria
 to set to choose the real database to use between three.</p>
 </div>
 <div class="paragraph">
 <p>So in your code you want something like:</p>
 </div>
 <div class="listingblock">
 <div class="content">
 <pre class="highlight"><code class="language-java" data-lang="java">public class RoutedEJBBean {
     @PersistenceContext(unitName = "router")
     private EntityManager em;

     // this router is not automatic, we
     // need it to select the database to use
     @Resource(name = "My Router")
     private DeterminedRouter router;

     public void persist(int id, String name, String clientDatasource) {
         router.setDataSource(clientDatasource);
         em.persist(new Person(id, name));
     }
 }</code></pre>
 </div>
 </div>
 </div>
 </div>
 </div>
 <div class="sect1">
 <h2 id="_the_router_implementation">The router implementation</h2>
 <div class="sectionbody">
 <div class="paragraph">
 <p>The router will simply manage a map to store proxied datasources and a
 field to store the datasource used in the current thread (ThreadLocal).</p>
 </div>
 <div class="listingblock">
 <div class="content">
 <pre class="highlight"><code class="language-java" data-lang="java">public class DeterminedRouter implements Router {
     private String dataSourceNames; // used to store configuration (openejb.xml)
     private String defaultDataSourceName; // defautl data source name
     private Map&lt;String, DataSource&gt; dataSources = null; // proxied data sources
     private ThreadLocal&lt;DataSource&gt; currentDataSource = new ThreadLocal&lt;DataSource&gt;(); // the datasource to use or null

     /**
      * @param datasourceList datasource resource name, separator is a space
      */
     public void setDataSourceNames(String datasourceList) {
         dataSourceNames = datasourceList;
     }

     /**
      * lookup datasource in openejb resources
      */
     private void init() { // looking up datasources declared as proxied
         dataSources = new ConcurrentHashMap&lt;String, DataSource&gt;();
         for (String ds : dataSourceNames.split(" ")) {
             ContainerSystem containerSystem = SystemInstance.get().getComponent(ContainerSystem.class);

             Object o = null;
             Context ctx = containerSystem.getJNDIContext();
             try {
                 o = ctx.lookup("openejb:Resource/" + ds);
                 if (o instanceof DataSource) {
                     dataSources.put(ds, (DataSource) o);
                 }
             } catch (NamingException ignore) {
             }
         }
     }

     /**
      * @return the user selected data source if it is set
      *         or the default one
      *  @throws IllegalArgumentException if the data source is not found
      */
     public DataSource getDataSource() {
         // lazy init of routed datasources
         if (dataSources == null) {
             init();
         }

         // if no datasource is selected use the default one
         if (currentDataSource.get() == null) {
             if (dataSources.containsKey(defaultDataSourceName)) {
                 return dataSources.get(defaultDataSourceName);

             } else {
                 throw new IllegalArgumentException("you have to specify at least one datasource");
             }
         }

         // the developper set the datasource to use
         return currentDataSource.get();
     }

     /**
      *
      * @param datasourceName data source name
      */
     public void setDataSource(String datasourceName) {
         if (dataSources == null) {
             init();
         }
         if (!dataSources.containsKey(datasourceName)) {
             throw new IllegalArgumentException("data source called " + datasourceName + " can't be found.");
         }
         DataSource ds = dataSources.get(datasourceName);
         currentDataSource.set(ds);
     }

     public void setDefaultDataSourceName(String name) {
         this.defaultDataSourceName = name;
     }
 }</code></pre>
 </div>
 </div>
 </div>
 </div>
 <div class="sect1">
 <h2 id="_creation_of_the_service_provider_for_the_router">Creation of the service provider for the router</h2>
 <div class="sectionbody">
 <div class="paragraph">
 <p>To be able to use your router add a file called service-jar.xml under
 META-INF/. For example META-INF/org.router.</p>
 </div>
 <div class="paragraph">
 <p>This file will contain something like:</p>
 </div>
 <div class="listingblock">
 <div class="content">
 <pre class="highlight"><code class="language-xml" data-lang="xml">&lt;ServiceJar&gt;
   &lt;ServiceProvider id="DeterminedRouter" service="Resource"
            type="org.apache.openejb.resource.jdbc.Router" class-name="implementation class"&gt;
     Param defaultValue
     ParamWithNoDefaultValue
   &lt;/ServiceProvider&gt;
 &lt;/ServiceJar&gt;</code></pre>
 </div>
 </div>
 </div>
 </div>
 <div class="sect1">
 <h2 id="_openejb_xml">openejb.xml</h2>
 <div class="sectionbody">
 <div class="paragraph">
 <p>In the openejb.xml file, you have to declare your dynamic database and
 in our example it needs the proxied datasources too:</p>
 </div>
 <div class="listingblock">
 <div class="content">
 <pre class="highlight"><code class="language-xml" data-lang="xml">&lt;Resource id="router" type="&lt;your implementation&gt;" provider="&lt;your provider&gt;"&gt;
   Param value
 &lt;/Resource&gt;

 &lt;Resource id="route db" type="DataSource" provider="RoutedDataSource"&gt;
   Router router
 &lt;/Resource&gt;

 &lt;!–- real databases – for our example --&gt;
 &lt;Resource id="db1" type="DataSource"&gt;
   JdbcDriver org.hsqldb.jdbcDriver
   JdbcUrl jdbc:hsqldb:mem:db1
   UserName sa
   Password
   JtaManaged true
 &lt;/Resource&gt;
 &lt;Resource id="db2" type="DataSource"&gt;
   JdbcDriver org.hsqldb.jdbcDriver
   JdbcUrl jdbc:hsqldb:mem:db2
   UserName sa
   Password
   JtaManaged true
 &lt;/Resource&gt;
 &lt;Resource id="db3" type="DataSource"&gt;
   JdbcDriver org.hsqldb.jdbcDriver
   JdbcUrl jdbc:hsqldb:mem:db3
   UserName sa
   Password
   JtaManaged true
 &lt;/Resource&gt;</code></pre>
 </div>
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	<div id="main-block" class="container main-block">
	<div class="row title">
	<div class="col-md-12">
	<div class='page-header'>

	<h1>Dynamic Datasource</h1>
	</div>
	</div>
	</div>
	<div class="row">

	<div class="col-md-12">
	<h1 id="_openejb_dynamic_datasource" class="sect0">OpenEJB dynamic datasource</h1>
	<div class="sect1">
	<h2 id="_goal">Goal</h2>
	<div class="sectionbody">
	<div class="paragraph">
	<p>The openejb dynamic datasource api aims to allow to use multiple data
	sources as one.</p>
	</div>
	<div class="paragraph">
	<p>It can be useful for technical reasons (load balancing for example) or
	functionnal reasons (filtering, aggregation, enriching…).</p>
	</div>
	</div>
	</div>
	<div class="sect1">
	<h2 id="_the_api">The API</h2>
	<div class="sectionbody">
	<div class="paragraph">
	<p>The interface Router (<em>org.apache.openejb.resource.jdbc.Router</em>) have
	only one method to get the datasource to use:</p>
	</div>
	<div class="listingblock">
	<div class="content">
	<pre class="highlight"><code class="language-java" data-lang="java">Router.getDataSource()</code></pre>
	</div>
	</div>
	<div class="paragraph">
	<p>The <em>org.apache.openejb.resource.jdbc.RoutedDataSource</em> wraps a
	classical data source. It has to be used to declare your datasource.</p>
	</div>
	<div class="paragraph">
	<p>You can implement all the policy you want in your Router implementation.</p>
	</div>
	<div class="paragraph">
	<p>A class called <em>org.apache.openejb.resource.jdbc.AbstractRouter</em> is
	available to ease router development.</p>
	</div>
	</div>
	</div>
	<div class="sect1">
	<h2 id="_known_limitation_s">Known limitation(s)</h2>
	<div class="sectionbody">
	<div class="paragraph">
	<p>You have to use the same kind of databases (same version, same
	configuration…).</p>
	</div>
	<div class="paragraph">
	<p>All database have to be created when you use the router. The way to do
	it automatically can depend of your JPA provider.</p>
	</div>
	<div class="sect2">
	<h3 id="_openjpa">OpenJPA</h3>
	<div class="paragraph">
	<p>OpenJPA initializes its database when the entitymanager is called for
	the first time so you need to initialize all your proxied datasource
	before using the other one. It can be done using an Init EJB doing a
	find() on each proxied datasource.</p>
	</div>
	</div>
	<div class="sect2">
	<h3 id="_hibernate">Hibernate</h3>
	<div class="paragraph">
	<p>Hibernate initializes the database when it starts so if you declare a
	persistence unit by database all databases will be initialized at the
	start up.</p>
	</div>
	</div>
	</div>
	</div>
	<div class="sect1">
	<h2 id="_example">Example</h2>
	<div class="sectionbody">
	<div class="sect2">
	<h3 id="_the_story_the_unit_test_example">The story (the unit test example)</h3>
	<div class="paragraph">
	<p>You want to use only one datasource in the code but you have a criteria
	to set to choose the real database to use between three.</p>
	</div>
	<div class="paragraph">
	<p>So in your code you want something like:</p>
	</div>
	<div class="listingblock">
	<div class="content">
	<pre class="highlight"><code class="language-java" data-lang="java">public class RoutedEJBBean {
	@PersistenceContext(unitName = "router")
	private EntityManager em;

	// this router is not automatic, we
	// need it to select the database to use
	@Resource(name = "My Router")
	private DeterminedRouter router;

	public void persist(int id, String name, String clientDatasource) {
	router.setDataSource(clientDatasource);
	em.persist(new Person(id, name));
	}
	}</code></pre>
	</div>
	</div>
	</div>
	</div>
	</div>
	<div class="sect1">
	<h2 id="_the_router_implementation">The router implementation</h2>
	<div class="sectionbody">
	<div class="paragraph">
	<p>The router will simply manage a map to store proxied datasources and a
	field to store the datasource used in the current thread (ThreadLocal).</p>
	</div>
	<div class="listingblock">
	<div class="content">
	<pre class="highlight"><code class="language-java" data-lang="java">public class DeterminedRouter implements Router {
	private String dataSourceNames; // used to store configuration (openejb.xml)
	private String defaultDataSourceName; // defautl data source name
	private Map<String, DataSource> dataSources = null; // proxied data sources
	private ThreadLocal<DataSource> currentDataSource = new ThreadLocal<DataSource>(); // the datasource to use or null

	/**
	* @param datasourceList datasource resource name, separator is a space
	*/
	public void setDataSourceNames(String datasourceList) {
	dataSourceNames = datasourceList;
	}

	/**
	* lookup datasource in openejb resources
	*/
	private void init() { // looking up datasources declared as proxied
	dataSources = new ConcurrentHashMap<String, DataSource>();
	for (String ds : dataSourceNames.split(" ")) {
	ContainerSystem containerSystem = SystemInstance.get().getComponent(ContainerSystem.class);

	Object o = null;
	Context ctx = containerSystem.getJNDIContext();
	try {
	o = ctx.lookup("openejb:Resource/" + ds);
	if (o instanceof DataSource) {
	dataSources.put(ds, (DataSource) o);
	}
	} catch (NamingException ignore) {
	}
	}
	}

	/**
	* @return the user selected data source if it is set
	* or the default one
	* @throws IllegalArgumentException if the data source is not found
	*/
	public DataSource getDataSource() {
	// lazy init of routed datasources
	if (dataSources == null) {
	init();
	}

	// if no datasource is selected use the default one
	if (currentDataSource.get() == null) {
	if (dataSources.containsKey(defaultDataSourceName)) {
	return dataSources.get(defaultDataSourceName);

	} else {
	throw new IllegalArgumentException("you have to specify at least one datasource");
	}
	}

	// the developper set the datasource to use
	return currentDataSource.get();
	}

	/**
	*
	* @param datasourceName data source name
	*/
	public void setDataSource(String datasourceName) {
	if (dataSources == null) {
	init();
	}
	if (!dataSources.containsKey(datasourceName)) {
	throw new IllegalArgumentException("data source called " + datasourceName + " can't be found.");
	}
	DataSource ds = dataSources.get(datasourceName);
	currentDataSource.set(ds);
	}

	public void setDefaultDataSourceName(String name) {
	this.defaultDataSourceName = name;
	}
	}</code></pre>
	</div>
	</div>
	</div>
	</div>
	<div class="sect1">
	<h2 id="_creation_of_the_service_provider_for_the_router">Creation of the service provider for the router</h2>
	<div class="sectionbody">
	<div class="paragraph">
	<p>To be able to use your router add a file called service-jar.xml under
	META-INF/. For example META-INF/org.router.</p>
	</div>
	<div class="paragraph">
	<p>This file will contain something like:</p>
	</div>
	<div class="listingblock">
	<div class="content">
	<pre class="highlight"><code class="language-xml" data-lang="xml"><ServiceJar>
	<ServiceProvider id="DeterminedRouter" service="Resource"
	type="org.apache.openejb.resource.jdbc.Router" class-name="implementation class">
	Param defaultValue
	ParamWithNoDefaultValue
	</ServiceProvider>
	</ServiceJar></code></pre>
	</div>
	</div>
	</div>
	</div>
	<div class="sect1">
	<h2 id="_openejb_xml">openejb.xml</h2>
	<div class="sectionbody">
	<div class="paragraph">
	<p>In the openejb.xml file, you have to declare your dynamic database and
	in our example it needs the proxied datasources too:</p>
	</div>
	<div class="listingblock">
	<div class="content">
	<pre class="highlight"><code class="language-xml" data-lang="xml"><Resource id="router" type="<your implementation>" provider="<your provider>">
	Param value
	</Resource>

	<Resource id="route db" type="DataSource" provider="RoutedDataSource">
	Router router
	</Resource>

	<!–- real databases – for our example -->
	<Resource id="db1" type="DataSource">
	JdbcDriver org.hsqldb.jdbcDriver
	JdbcUrl jdbc:hsqldb:mem:db1
	UserName sa
	Password
	JtaManaged true
	</Resource>
	<Resource id="db2" type="DataSource">
	JdbcDriver org.hsqldb.jdbcDriver
	JdbcUrl jdbc:hsqldb:mem:db2
	UserName sa
	Password
	JtaManaged true
	</Resource>
	<Resource id="db3" type="DataSource">
	JdbcDriver org.hsqldb.jdbcDriver
	JdbcUrl jdbc:hsqldb:mem:db3
	UserName sa
	Password
	JtaManaged true
	</Resource></code></pre>
	</div>
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