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  32 
  33   Provides a naming service for Java&nbsp;IDL.  The Object Request Broker Daemon
  34   (ORBD) also includes both a transient and persistent naming service.
  35 
  36 
  37   <P>
  38   The package and all its classes and interfaces
  39   were generated by running the tool <code>idlj</code> on the file
  40   <code>nameservice.idl</code>, which is a module written in OMG IDL.
  41 
  42   <H3>Package Specification</H3>
  43 
  44 <P>For a precise list of supported sections of official specifications with which
  45 the Java[tm] Platform, Standard Edition 6, ORB complies, see <A
  46 HREF="../CORBA/doc-files/compliance.html">Official Specifications for CORBA
  47 support in Java[tm] SE 6</A>.
  48 
  49   <H2>Interfaces</H2>
  50   The package <code>org.omg.CosNaming</code> contains two public interfaces
  51   and several auxiliary classes.
  52   <P>
  53   The interfaces are:
  54   <UL>
  55   <LI><code>NamingContext</code>
  56   <LI><code>BindingIterator</code>
  57   </UL>
  58   <P>
  59   These two interfaces provide the means to bind/unbind names and object
  60   references, to retrieve bound object references, and
  61   to iterate through a list of bindings.  The <code>NamingContext</code>
  62   interface supplies the main functionality for the naming service, and
  63   <code>BindingIterator</code> provides a means of iterating through a list
  64   of name/object reference bindings.
  65 
  66   <H2>Auxiliary Classes</H2>
  67   In order to map an OMG IDL interface to the Java programming language,
  68   the idlj compiler creates Java classes that can be thought of
  69   as auxiliary classes.
  70   Comments for the generated auxiliary classes
  71   used by the interfaces <code>NamingContext</code> and
  72   <code>BindingIterator</code> are included here.
  73 
  74   <H3>Classes Used by <code>NamingContext</code> and
  75   <code>BindingIterator</code></H3>
  76   The following are classes used by
  77   the naming service.  (Helper and  holder classes, which are
  78   generated for each of the classes listed here,  are discussed below.)
  79 
  80   <UL>
  81     <LI><code>public final class <B>NameComponent</B></code> --
  82     a building block for names.  (Names are bound to object references
  83     in a naming context.)
  84     <P>A name is an array of one or more <code>NameComponent</code> objects.
  85     A name with a single <code>NameComponent</code> is called
  86     a <I>simple name</I>; a name with multiple <code>NameComponent</code>
  87     objects is called a <I>compound name</I>.
  88     <P>
  89     A <code><B>NameComponent</B></code> object consists of two fields:
  90     <OL>
  91     <LI><code><B>id</B></code> -- a <code>String</code> used as an identifier
  92     <LI><code><B>kind</B></code> -- a <code>String</code> that can be used for any
  93     descriptive purpose.  Its importance is that it
  94     can be used to describe an object without affecting syntax.
  95     The C programming language, for example, uses the the syntactic convention
  96     of appending the extension ".c" to a file name to indicate that it is
  97     a source code file.  In a <code>NameComponent</code> object,
  98     the <code>kind</code> field can be used to describe the type of object
  99     rather than a file extension or some other syntactic convention.
 100     Examples of the value of the <code>kind</code> field include the strings
 101     <code>"c_source"</code>, <code>"object_code"</code>,
 102     <code>"executable"</code>,
 103     <code>"postscript"</code>, and <code>""</code>.  It is not unusual
 104     for the <code>kind</code> field to be the empty string.
 105     </OL>
 106     <P>
 107     In a name, each <code>NameComponent</code> object except the last denotes
 108     a <code>NamingContext</code> object; the last <code>NameComponent</code>
 109     object denotes the bound object reference.
 110     This is similar to a path name, in which the last name is the
 111     file name, and all names before it are directory names.
 112 
 113     <LI><code>public final class <B>Binding</B></code> --
 114     an object that associates a name with an object reference or a
 115     naming context.
 116     A <code>Binding</code> object has two fields:
 117     <OL>
 118     <LI><code><B>binding_name</B></code> - an array of one or more
 119     <code>NameComponent</code> objects that represents the bound name
 120     <LI><code><B>binding_type</B></code> - a <code>BindingType</code> object
 121     indicating whether the binding is between a name and an object
 122     reference or between a name and a naming context
 123     </OL>
 124     <P>
 125     The interface <code>NamingContext</code> has methods for
 126     binding/unbinding names with object references or naming contexts,
 127     for listing bindings,
 128     and for resolving bindings (given a name, the method
 129     <code>resolve</code> returns the object reference bound to it).
 130 
 131     <LI><code>public final class <B>BindingType</B></code> --
 132     an object that specifies whether the given <code>Binding</code>
 133     object is a binding between a name and an object reference (that is,
 134     not a naming context) or between a name and a naming context.
 135     <P>
 136     The class<code>BindingType</code> consists of two methods and
 137     four constants. Two of these constants are
 138     <code>BindingType</code> objects, and two are <code>int</code>s.
 139     <P>
 140     The <code>BindingType</code> objects
 141     can be passed to the constructor for the class
 142     <code>Binding</code> or used as parameters or return values.  These
 143     <code>BindingType</code> objects are:
 144     <UL>
 145     <LI><code>public static final BindingType <B>nobject</B></code> --
 146     to indicate that the binding is with an object reference
 147     <LI><code>public static final BindingType <B>ncontext</B></code> --
 148     to indicate that the binding is with a naming context
 149     </UL>
 150     <P>
 151     The <code>int</code> constants can be supplied to the method
 152     <code>from_int</code> to create  <code>BindingType</code> objects,
 153     or they can be return values for the method <code>value</code>.
 154     These constants are:
 155     <UL>
 156     <LI><code>public static final int <B>_nobject</B></code>
 157     <LI><code>public static final int <B>_ncontext</B></code>
 158     </UL>
 159     If the method <code>from_int</code> is supplied with anything other
 160     than <code>_nobject</code>
 161     or <code>_ncontext</code>, it will throw
 162     the exception <code>org.omg.CORBA.BAD_PARAM</code>.
 163     <P>Usage is as follows:
 164     <PRE>
 165        BindingType btObject = from_int(_nobject);
 166        BindingType btContext = from_int(_ncontext);
 167     </PRE>
 168     The variable <code>btObject</code> refers to a <code>BindingType</code>
 169     object initialized to represent a binding with an object reference.
 170     The variable <code>btContext</code> refers to a <code>BindingType</code>
 171     object initialized to represent a binding with a
 172     <code>NamingContex</code> object.
 173     <P>
 174     The method <code>value</code> returns either
 175     <code>_nobject</code> or <code>_ncontext</code>, so
 176     in the following line of code, the variable <code>bt</code>
 177     will contain <code>_nobject</code> or <code>_ncontext</code>:
 178     <PRE>
 179        int bt = BindingType.value();
 180     </PRE>
 181   </UL>
 182 
 183   <H3>Holder Classes</H3>
 184 
 185   OMG IDL uses OUT and INOUT parameters for returning values from operations.
 186   The mapping to the Java programming language, which does not have OUT
 187   and INOUT parameters, creates a special class for each type, called
 188   a holder class. 
 189   An instance of a holder class can be passed to a
 190   Java method as a parameter, and
 191   a value can be assigned to its <code>value</code> field.  This allows
 192   it to perform the function of an OUT or INOUT parameter.
 193   <P>The following holder classes are generated for the package
 194   <code>org.omg.CosNaming</code>:
 195   <UL>
 196   <LI><code>NamingContextHolder</code>
 197   <LI><code>BindingIteratorHolder</code>
 198   <LI><code>BindingHolder</code>
 199   <LI><code>BindingListHolder</code>
 200   <LI><code>BindingTypeHolder</code>
 201   <LI><code>NameComponentHolder</code>
 202   <LI><code>NameHolder</code>
 203   </UL>
 204   <P>
 205   Note that in the <code>org.omg.CORBA</code> package,
 206   there is a holder class for each of the basic Java types:
 207   <code>IntHolder</code>, <code>ShortHolder</code>,
 208   <code>StringHolder</code>, and so on.
 209   <P>
 210   Note also that there is a <code>NameHolder</code> class even though
 211   there is no <code>Name</code> class; similarly, there is a
 212   <code>BindingListHolder</code> class even though there is no
 213   <code>BindingList</code> class.  This is true because in the OMG IDL
 214   interface, <code>Name</code> and <code>BindingList</code> are
 215   <code>typedef</code>s.  There is no mapping from an IDL
 216   <code>typedef</code> to a Java construct, but holder classes
 217   are generated if the <code>typedef</code> is for a sequence or
 218   an array.  As mapped to the
 219   Java programming language, <code>Name</code> is an array of
 220   <code>NameComponent</code> objects, and a <code>BindingList</code>
 221   is an array of <code>Binding</code> objects.
 222   
 223   All holder classes have at least two constructors and one field:
 224   <UL>
 225   <LI><code><B>value</B></code> field -- an instance of the type being used as
 226     an OUT or INOUT parameter.  For example, the <code>value</code> field of a
 227     <code>NamingContextHolder</code> will be a <code>NamingContext</code>
 228     object.  
 229   <LI>default constructor -- a constructor that creates a new holder object
 230     initialized with the default value for the type.  For example, a new
 231     <code>BindingHolder</code> object created with the default constructor
 232     will have its <code>value</code> field set to <code>null</code> because
 233     that is the default value for an object.  Other defaults are
 234     <code>false</code> for  <code>boolean</code>,
 235     <code>0</code> for numeric and char types, and
 236     <code>null</code> for  object references.
 237   <LI>constructor from an instance -- a constructor that creates a new
 238     holder object whose <code>value</code> field is
 239     initialized with the instance supplied
 240   </UL>
 241   <P>
 242   A holder class for a user-defined type (a Java class) has three more
 243   methods, but application developers do not use them directly.
 244  
 245   <H3>Helper Classes</H3>
 246   Helper classes, which are generated for all user-defined types
 247   in an OMG IDL interface, supply static methods needed to manipulate
 248   those types.
 249   <P>
 250   There is only one method in a helper class that an
 251   application programmer uses:  the
 252   method <code>narrow</code>.  Only Java interfaces mapped from IDL
 253   interfaces will have a helper class that includes a <code>narrow</code>
 254   method, so in the <code>CosNaming</code> package, only the classes
 255   <code>NamingContextHelper</code> and <code>BindingIteratorHelper</code>
 256   have a <code>narrow</code> method.
 257   <UL>
 258   <LI><code>public static NamingContext
 259   <B>narrow</B>(org.omg.CORBA.Object obj)</code> -- converts the given
 260    CORBA object to a <code>NamingContext</code> object
 261   <LI><code>public static BindingIterator
 262   <B>narrow</B>(org.omg.CORBA.Object obj)</code> -- converts the given
 263    CORBA object to a <code>BindingIterator</code> object
 264   </UL>
 265 <H2>Package <code>org.omg.CosNaming.NamingContextPackage</code></H2>
 266 This package supplies Helper and Holder classes for the exceptions used
 267 in the package <code>org.omg.CosNaming</code> and also for the class
 268 <code>NotFoundReason</code>, which supplies a reason for the exception
 269 <code>NotFound</code>.  
 270 <P>
 271 There are Helper and Holder classes for the following exceptions:
 272 <UL>
 273 <LI><code>AlreadyBound</code>
 274 <LI><code>CannotProceed</code>
 275 <LI><code>InvalidName</code>
 276 <LI><code>NotEmpty</code>
 277 <LI><code>NotFound</code>
 278 </UL>
 279 
 280 <h2>Naming Service Compatibility</h2>
 281 
 282 Sun's implementation of the <code>CosNaming</code> package complies
 283 with the OMG <code>COSNaming</code> specification.  In other words,
 284 the APIs in Sun's naming service are implemented according to the
 285 guidelines for a naming service provided by OMG.  Therefore, if a
 286 third-party vendor has implemented a naming service that is OMG
 287 compliant, it is possible to switch between Sun's implementation of
 288 <code>CosNaming</code> and the third-party vendor's implementation.
 289 However, it is important to understand that there can be minor
 290 variations in the way different vendors implement the naming service,
 291 such as differences in the exception strings.
 292 
 293 <h3>Instructions for Using a Third Party's Naming Service</h3>
 294 Although we encourage using an ORB and ORB services that are both
 295 from one vendor, it is possible to plug in a third party's
 296 <code>COSNaming</code> implementation with Sun's RMI-IIOP ORB.
 297 Here are the steps to follow:
 298 <OL>
 299   <LI>Create a properties file for the Bootstrap server and give it
 300       two entries.  For example, you could call this properties file
 301       <code>/tmp/services</code> and put the following in it:
 302       <code>NameService, &lt;Stringified IOR of the Root Naming Context&gt;</code>.
 303       <P>
 304       This associates <code>NameService</code> with the Root Naming
 305       Context of the <code>CosNaming</code> implementation that you
 306       want to use.
 307   <LI>Start the standalone Bootstrap server using the following command:
 308   <pre>
 309       <code>
 310       java -classpath $(CLASSPATH)
 311       com.sun.corba.ee.internal.CosNaming.BootstrapServer -InitialServicesFile
 312       "/tmp/services" [-ORBInitialPort port]
 313       </code>
 314   </pre>
 315   <P>
 316   Note that the square brackets at the end of the command indicate that
 317   specifying a port number is optional.
 318 </OL>
 319 <P>
 320 Now when an application calls the method
 321 <code>org.omg.CORBA.ORB.resolve_initial_references</code>, CORBA
 322 processes will contact the Bootstrap Server to get the Root Naming
 323 Context.
 324 
 325 <h2>Package Specification</h2>
 326 
 327 <ul>
 328  <li>Interoperable Naming Service (<a
 329 href="http://www.omg.org/cgi-bin/doc?ptc/00-08-07">ptc/00-08-07</a>)
 330 </ul>
 331 
 332 <h2>Related Documentation</h2>
 333 
 334 For an overview and examples of how to use the
 335 <code>CosNaming</code> API, please see:
 336 <ul>
 337   <li>{@extLink tnameserv NamingService}
 338 </ul>
 339 <p>
 340 For an overview of Java&nbsp;IDL, please see:
 341 <ul>
 342   <li>{@extLink idl_guides  Java&nbsp;IDL developer's home page}
 343 </ul>
 344 
 345 @since JDK1.3
 346 
 347 
 348 
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