docs/service-locator.adoc

= Service Locator
:index-group: Unrevised
:jbake-date: 2018-12-05
:jbake-type: page
:jbake-status: published

The functionality of the
link:jndi-names.html[openejb.jndiname.format] allows for writing some
really fun service locator code. Creating the exact layout you want
using the exact data you want means you can create robust libraries for
pulling things out of JNDI.

= Lookup examples

To get the creative juices flowing here are a few examples of lookup
methods you could create for your service locator, the jndi name formats
that would work with those lookups, and examples of client code using
the service locator. For simplicity, we'll assume all the lookup
examples start with this basic class that has a built-in lookup allowing
for a common prefix to be optionally applied to the beginning of all
lookup strings.

[source,java]
----
public class MyLocator {
    private final Context context;

    public MyLocator() throws NamingException {
        this(null);
    }

    public MyLocator(String commonPrefix) throws NamingException {
        Properties properties = new Properties();
        properties.put(Context.INITIAL_CONTEXT_FACTORY, "org.apache.openejb.client.RemoteInitialContextFactory");
        properties.put(Context.PROVIDER_URL, "ejbd://localhost:4201/");
        this.context = new InitialContext(properties);
    }

    public Object lookup(String name) {
        try {
            if (commonPrefix != null) name = commonPrefix + "/" +name;
            return context.lookup(name);
        } catch (NamingException e) {
            throw new IllegalArgumentException(e);
        }
    }
}
----

== Just the interface Usable with JNDI name formats ending in the full
class name of the interface such as: - \{interfaceClass}

[source,java]
----
public <T> T lookup(Class<T> type) {
    return (T) lookup(type.getName());
}



MyLocator locator = new MyLocator();
Widget widget = locator.lookup(Widget.class);   
----

Or with a common prefix or with a common prefix supplied in constructor
such as: - \{moduleId}/\{interfaceClass} -
ejb/\{moduleId}/\{interfaceClass}

[source,java]
----
MyLocator locator = new MyLocator("ejb/superbiz");
Widget widget = locator.lookup(Widget.class);   
Store store = locator.lookup(Store.class);
----

== Interface class and a prefix

Usable with JNDI name formats including a varying prefix such as ejbName
or deploymentID and ending in the full class name of the interface

* \{ejbName}/\{interfaceClass}
* \{deploymentId}/\{interfaceClass}
+
public T lookup(String prefix, Class type) \{ return (T) lookup(prefix +
"/" + type.getName()); }
+
MyLocator locator = new MyLocator(); Widget redWidget =
locator.lookup("RedWidgetBean", Widget.class); +
Widget blueWidget = locator.lookup("BlueWidgetBean", Widget.class);

Or with a common prefix or with a common prefix supplied in constructor
such as: - \{moduleId}/\{ejbName}/\{interfaceClass} -
ejb/\{moduleId}/\{deploymentId}/\{interfaceClass}

[source,java]
----
MyLocator locator = new MyLocator("accountingApp");
Widget widget = locator.lookup("RedWidgetBean", Widget.class);   
Store store = locator.lookup("StoreBean", Store.class);
----

== Interface class and ejb class

Usable with JNDI name formats comprised of the interfaceClass and
ejbClass

For variation, the interface class is the prefix and the ejb class is
the suffix. This is neat as the the prefix (the interface class name)
becomes a jndi context with one binding in it for each implementing ejb
class.

Works with: - \{interfaceClass}/\{ejbClass}

[source,java]
----
public <T> T lookup(Class<T> type, Class ejbClass) {
    return (T) lookup(type.getName() + "/" + ejbClass.getName());
}



MyLocator locator = new MyLocator();
Widget widget = locator.lookup(Widget.class, BlueWidgetBean.class);   
----

Or with a common prefix or with a common prefix supplied in constructor
such as: - \{moduleId}/\{interfaceClass}/\{ejbClass} -
ejb/\{moduleId}/\{interfaceClass}/\{ejbClass}

[source,java]
----
MyLocator locator = new MyLocator("ejb/purchasingApp");
Widget widget = locator.lookup(Widget.class, RedWidgetBean.class);
Store store = locator.lookup(Store.class, StoreBean.class);
----

== Interface class and ejb class with simple names

Similar to the above example but using the simple name of the classes
resulting in a JNDI tree that's a bit more human readable. -
\{ejbClass.simpleName}/\{interfaceClass.simpleName}

[source,java]
----
public <T> T lookup(Class ejbClass, Class<T> type) {
    return (T) lookup(ejbClass.getSimpleName() + "" + type.getSimpleName());
}
----

and

[source,java]
----
MyLocator locator = new MyLocator();
Widget widget = locator.lookup(RedWidgetBean.class, Widget.class);   
----

Or with a common prefix or with a common prefix supplied in constructor
such as: -
\{moduleId}/\{ejbClass.simpleName}/\{interfaceClass.simpleName} -
ejb/\{moduleId}/\{ejbClass.simpleName}/\{interfaceClass.simpleName}

[source,java]
----
MyLocator locator = new MyLocator("shippingApp");
Widget widget = locator.lookup(GreenWidgetBean.class, Widget.class);   
Store store = locator.lookup(SuperStoreBean.class, Store.class);
----