JDK14/Java14源码在线阅读
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Provides the classes and interfaces for accessing naming services.
<p>
This package defines the naming operations of the Java Naming and
Directory Interface™ (JNDI).
JNDI provides naming and directory functionality to applications
written in the Java programming language. It is designed to be
independent of any specific naming or directory service
implementation. Thus a variety of services--new, emerging, and
already deployed ones--can be accessed in a common way.
<h2>Context</h2>
<p>
This package defines the notion of a <em>context</em>, represented
by the <code>Context</code> interface.
A context consists of a set of name-to-object <em>bindings</em>.
<code>Context</code> is the core interface for looking up, binding, unbinding,
and renaming objects, and for creating and destroying subcontexts.
<p>
<code>lookup()</code> is the most commonly used operation.
You supply <code>lookup()</code>
the name of the object you want
to look up, and it returns the object bound to that name.
For example, the following code fragment looks up
a printer and sends a document to the printer object
to be printed:
<blockquote>
<pre>
Printer printer = (Printer)ctx.lookup("treekiller");
printer.print(report);
</pre>
</blockquote>
<h2>Names</h2>
<p>
Every naming method in the <code>Context</code>
interface has two
overloads: one that accepts a
<code>Name</code> argument and one that accepts a string name.
<code>Name</code> is an interface that represents a generic
name--an ordered sequence of zero of more components.
For these methods, <code>Name</code> can be used to represent a
<em>composite name</em> (<code>CompositeName</code>)
so that you can name an object using a name which spans multiple namespaces.
<p>
The overloads that accept <code>Name</code>
are useful for applications that need to manipulate names: composing
them, comparing components, and so on.
The overloads that accept string names are likely to be more useful
for simple applications, such as those that simply read in a name
and look up the corresponding object.
<h2>Bindings</h2>
The <code>Binding</code> class represents a name-to-object binding.
It is a tuple containing the name of the bound object,
the name of the object's class, and the object itself.
<p>
The <code>Binding</code> class is actually a subclass of
<code>NameClassPair</code>, which consists
simply of the object's name and the object's class name.
The <code>NameClassPair</code> is useful when you only want
information about the object's class and do not want to
pay the extra cost of getting the object.
<h2>References</h2>
Objects are stored in naming and directory services in different ways.
If an object store supports storing Java objects,
it might support storing an object in its serialized form.
However, some naming and directory services do not support the
storing of Java objects. Furthermore, for some
objects in the directory, Java programs are but one group of applications
that access them. In this case, a serialized Java object might
not be the most appropriate representation.
JNDI defines a <em>reference</em>, represented by the <code>Reference</code>
class, which contains information on how to construct a copy of the object.
JNDI will attempt to turn references looked up from the directory
into the Java objects they represent, so that
JNDI clients have the illusion that what
is stored in the directory are Java objects.
<h2>The Initial Context</h2>
In JNDI, all naming and directory operations are performed relative
to a context. There are no absolute roots.
Therefore JNDI defines an <em>initial context</em>,
<code>InitialContext</code>,
which provides a starting point for naming and directory operations.
Once you have an initial context, you can use it to
look up other contexts and objects.
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