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28 </head> |
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29 <body bgcolor="white"> |
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30 |
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31 Provides the classes and interfaces for accessing naming services. |
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32 |
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33 <p> |
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34 This package defines the naming operations of the Java Naming and |
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35 Directory Interface<font size=-2><sup>TM</sup></font> (JNDI). |
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36 JNDI provides naming and directory functionality to applications |
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37 written in the Java programming language. It is designed to be |
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38 independent of any specific naming or directory service |
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39 implementation. Thus a variety of services--new, emerging, and |
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40 already deployed ones--can be accessed in a common way. |
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41 |
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42 |
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43 <h4>Context</h4> |
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44 <p> |
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45 This package defines the notion of a <em>context</em>, represented |
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46 by the <tt>Context</tt> interface. |
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47 A context consists of a set of name-to-object <em>bindings</em>. |
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48 <tt>Context</tt> is the core interface for looking up, binding, unbinding, |
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49 and renaming objects, and for creating and destroying subcontexts. |
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50 <p> |
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51 <tt>lookup()</tt> is the most commonly used operation. |
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52 You supply <tt>lookup()</tt> |
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53 the name of the object you want |
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54 to look up, and it returns the object bound to that name. |
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55 For example, the following code fragment looks up |
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56 a printer and sends a document to the printer object |
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57 to be printed: |
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58 |
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59 <blockquote> |
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60 <pre> |
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61 Printer printer = (Printer)ctx.lookup("treekiller"); |
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62 printer.print(report); |
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63 </pre> |
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64 </blockquote> |
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65 |
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66 <h4>Names</h4> |
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67 <p> |
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68 Every naming method in the <tt>Context</tt> |
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69 interface has two |
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70 overloads: one that accepts a |
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71 <tt>Name</tt> argument and one that accepts a string name. |
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72 <tt>Name</tt> is an interface that represents a generic |
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73 name--an ordered sequence of zero of more components. |
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74 For these methods, <tt>Name</tt> can be used to represent a |
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75 <em>composite name</em> (<tt>CompositeName</tt>) |
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76 so that you can name an object using a name which spans multiple namespaces. |
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77 <p> |
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78 The overloads that accept <tt>Name</tt> |
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79 are useful for applications that need to manipulate names: composing |
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80 them, comparing components, and so on. |
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81 The overloads that accept string names are likely to be more useful |
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82 for simple applications, such as those that simply read in a name |
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83 and look up the corresponding object. |
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84 <p> |
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85 |
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86 <h4>Bindings</h4> |
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87 |
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88 The <tt>Binding</tt> class represents a name-to-object binding. |
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89 It is a tuple containing the name of the bound object, |
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90 the name of the object's class, and the object itself. |
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91 <p> |
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92 The <tt>Binding</tt> class is actually a subclass of |
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93 <tt>NameClassPair</tt>, which consists |
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94 simply of the object's name and the object's class name. |
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95 The <tt>NameClassPair</tt> is useful when you only want |
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96 information about the object's class and do not want to |
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97 pay the extra cost of getting the object. |
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98 |
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99 <h4>References</h4> |
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100 Objects are stored in naming and directory services in different ways. |
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101 If an object store supports storing Java objects, |
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102 it might support storing an object in its serialized form. |
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103 However, some naming and directory services do not support the |
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104 storing of Java objects. Furthermore, for some |
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105 objects in the directory, Java programs are but one group of applications |
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106 that access them. In this case, a serialized Java object might |
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107 not be the most appropriate representation. |
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108 JNDI defines a <em>reference</em>, represented by the <tt>Reference</tt> |
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109 class, which contains information on how to construct a copy of the object. |
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110 JNDI will attempt to turn references looked up from the directory |
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111 into the Java objects they represent, so that |
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112 JNDI clients have the illusion that what |
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113 is stored in the directory are Java objects. |
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114 |
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115 |
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116 <h4>The Initial Context</h4> |
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117 |
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118 In JNDI, all naming and directory operations are performed relative |
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119 to a context. There are no absolute roots. |
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120 Therefore JNDI defines an <em>initial context</em>, |
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121 <tt>InitialContext</tt>, |
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122 which provides a starting point for naming and directory operations. |
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123 Once you have an initial context, you can use it to |
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124 look up other contexts and objects. |
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125 |
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126 <h4>Exceptions</h4> |
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127 |
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128 JNDI defines a class hierarchy for exceptions that can be thrown in |
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129 the course of performing naming and directory operations. The root of |
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130 this class hierarchy is <tt>NamingException</tt>. |
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131 Programs interested in dealing with a particular exception |
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132 can catch the corresponding subclass of the exception. |
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133 Otherwise, programs should catch <tt>NamingException</tt>. |
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134 |
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135 |
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136 <h2>Package Specification</h2> |
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137 |
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138 The JNDI API Specification and related documents can be found in the |
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139 <a href="../../../technotes/guides/jndi/index.html">JNDI documentation</a>. |
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140 |
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141 @since 1.3 |
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142 |
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143 </body> |
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144 </html> |