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<HTML><HEAD><title>JNDI/DNS Service Provider</title></HEAD><BODY BGCOLOR="#FFFFFF" TEXT=#000000 LINK=#0000ff VLINK=#000077ALINK=#ff0000><hr SIZE=3 NOSHADE WIDTH="100%"><center><h1>DNS Service Provider for the <br>Java Naming Directory Interface<font size=4><sup>TM</sup></font> (JNDI)</h1></center><hr SIZE=3 NOSHADE WIDTH="100%"><P><FONT SIZE=-1>Please send feedback to<a href="mailto:jndi@java.sun.com">jndi@java.sun.com</a></FONT><P><P><I>Table of Contents</I><UL><LI><A HREF="#INTRO">Introduction</A></LI><LI> <A HREF="#CONF">Conformance</A></LI><LI><A HREF="#PROP">Environment Properties</A></LI><LI><A HREF="#TYPE">Mapping DNS Content to JNDI</A></LI><LI><A HREF="#URL">DNS Pseudo-URLs</A></LI><LI><A HREF="#API">API Mapping</A></LI><LI><A HREF="#USAGE">Usage Examples</A></LI><LI><A HREF="#SEC">Security Considerations</A></LI><li><A HREF="#FED">Federation</A></LI></UL><P><HR><P> <A NAME="INTRO"><H2>Introduction</H2><p>The DNS service provider allows JNDI applications to accessinformation stored in the internet Domain Name System.The provider presents the DNS namespace as a tree of JNDI directorycontexts, and DNS resource records as JNDI attributes.<p>This document describes the features of the DNS service provider,and contains details of how DNS is mapped onto JNDI.<p><hr><p><A NAME="CONF"><H2>Conformance</H2><p>The DNS service provider supports the Domain Name System as described in <a href=http://www.ietf.org/rfc/rfc1034.txt> RFC 1034</a> and<a href=http://www.ietf.org/rfc/rfc1035.txt> RFC 1035</a>.It currently supports the following resource record types and classes:<br><blockquote><table><tr valign=top><td> <table border> <tr><td> <em>Type</em> </td> <td> <em>Where Specified</em> </td></tr> <tr><td> A </td> <td align=center> RFC 1035 </td></tr> <tr><td> NS </td> <td align=center> RFC 1035 </td></tr> <tr><td> CNAME</td> <td align=center> RFC 1035 </td></tr> <tr><td> SOA </td> <td align=center> RFC 1035 </td></tr> <tr><td> PTR </td> <td align=center> RFC 1035 </td></tr> <tr><td> MX </td> <td align=center> RFC 1035 </td></tr> <tr><td> TXT </td> <td align=center> RFC 1035 </td></tr> <tr><td> HINFO</td> <td align=center> RFC 1035 </td></tr> <tr><td> AAAA </td> <td align=center> RFC 1886 </td></tr> <tr><td> NAPTR</td> <td align=center> RFC 2168 </td></tr> <tr><td> SRV </td> <td align=center> RFC 2782 </td></tr> </table></td><td> </td><td> <table border> <tr><td> <em>Class</em> </td> <td> <em>Where Specified</em> </td></tr> <tr><td> IN </td> <td align=center> RFC 1035 </td></tr> <tr><td> HS </td> <td align=center> RFC 1035 </td></tr> </table></td></tr></table></blockquote>Each lookup is initially performed using UDP. If the response is toolong to be returned in a UDP packet without being truncated, thelookup is repeated using TCP.<p><hr><p><A NAME="PROP"><H2>Environment Properties</H2><p>The following JNDI environment properties are relevant to the DNSservice provider. See the <a href=http://java.sun.com/j2se/1.3/docs/api/javax/naming/InitialContext.html#ENVIRONMENT>JNDI documentation</a>for a description of how properties are initialized using the initialcontext constructor, system properties, applet parameters, and resource files.<b><pre>java.naming.authoritative</pre></b><blockquote> This property is used to specify whether all responses must be authoritative. If its value is <tt>"true"</tt>, only authoritative responses are accepted from DNS servers; otherwise, all responses are accepted. If this property has not been set, the default is <tt>"false"</tt>. Here is an example that specifies that all responses must be authoritative.<blockquote><pre>env.put(Context.AUTHORITATIVE, "true");</pre></blockquote> Note that some information might be made unavailable when you request that only authoritative responses be returned because the DNS protocol does not provide a way to request authoritative information. For example, the DNS service provider might have retrieved nonauthoritative data as the result of a query and is subsequently forced to discard it because only authoritative data may be returned.</blockquote><b><pre>java.naming.factory.initial</pre></b><blockquote> This property is used to select the DNS service provider as the initial context. It is not used by the provider itself. It specifies the class name of the initial context factory for the provider, and may be set as in the following example:<blockquote><pre>env.put(Context.INITIAL_CONTEXT_FACTORY, "com.sun.jndi.dns.DnsContextFactory");</pre></blockquote></blockquote><b><pre>java.naming.factory.object</pre></b><blockquote> This property contains a colon-separated list of the fully-qualified class names of object factories for transforming objects read from DNS. This mechanism is used to transform objects into forms more useful to the application. See <a href="http://java.sun.com/j2se/1.3/docs/api/javax/naming/spi/DirectoryManager.html#getObjectInstance(java.lang.Object, javax.naming.Name, javax.naming.Context, java.util.Hashtable, javax.naming.directory.Attributes)"> <tt>DirectoryManager.getObjectInstance()</tt></a> for details.</blockquote><b><pre>java.naming.provider.url</pre></b><blockquote> This property specifies the host name and port of the DNS server used by the initial DNS context, as well the initial context's domain name. For details on the URL format see <a href="#URL">DNS Pseudo-URLs</a> below. <p> For example:<blockquote><pre>env.put(Context.PROVIDER_URL, "dns://server1.sun.com/java.sun.com");</pre></blockquote> will cause the provider to use the DNS server at server1.sun.com, and set the initial context's domain name to java.sun.com. If this property is not set, it defaults to "dns:" (all defaults as described in the <strong>DNS Pseudo-URLs</strong> section are used). <p> Multiple DNS servers may be specified by setting this property to a space-separated list of URLs. Each of the servers is contacted in turn until one of them responds. Since the initial context has only a single domain name, if multiple URLs are listed then each must contain the same domain part. For example:<blockquote><pre>env.put(Context.PROVIDER_URL, "dns://server1.sun.com/java.sun.com dns://server2.sun.com/java.sun.com");</pre></blockquote></blockquote><b><pre>com.sun.jndi.dns.lookup.attr</pre></b><blockquote> Before JNDI invokes an object factory on a DNS context, it by default reads and passes to the factory any internet TXT attributes of the context. This property, if set, names an alternate attribute identifier to use. See <a href=#TYPE> Mapping DNS Content to JNDI</a> below for information on the format of attribute identifiers.</blockquote><b><pre>com.sun.jndi.dns.recursion</pre></b><blockquote> This property is used to specify that recursion is disallowed on DNS queries. If this property has not been set or if it has been set to <tt>"true"</tt>, recursion is allowed; otherwise, recursion is disallowed. Here is an example that specifies that recursion on DNS queries is to be disallowed. <blockquote><pre>env.put("com.sun.jndi.dns.recursion", "false");</pre></blockquote></blockquote><hr><p><A NAME="TYPE"><H2>Mapping DNS Content to JNDI</H2>The DNS service provider maps DNS names, nodes, and resource records ontoJNDI data types as follows.<h4>Names</h4>DNS domain names are represented by JNDI compound <tt>Name</tt>objects with right-to-left, dot-separated syntax, and withbackslash (<tt>\</tt>) as the escape character. Names arecase-insensitive. They do not include trailing dots, with one exception:when an empty compound name is known to refer to the root domain, it may berepresented as "<tt>.</tt>".<h4>Nodes and Resource Records</h4>A DNS node is represented by a <tt>DirContext</tt> object.The resource records of the node are represented by attributes ofthe context. For example, if the DNS node sun.com contains an Arecord with the address 192.9.49.33 and an MX record with thedata "10 sun.com", the corresponding JNDI context will have an attributewith identifier "<tt>A</tt>" and string value "192.9.49.33" and an attributewith identifier "<tt>MX</tt>" and string value "10 sun.com".<p> Multiple records of the same type are represented as multi-valuedattributes. Records of unsupported types are represented byattributes with numeric identifiers and with byte arrays as values.<h4>Attribute Identifiers</h4><p> DNS resource record class and type names are mapped onto JNDIattribute identifiers. If a record is in the internet class,the corresponding attribute ID is simply the record's type name.If the type is an unsupported one, its integer value is used instead.If the record is not in the internet class, the class name (or integerclass value) is prepended to the attribute ID, separated by a space.For example, the attribute identifier "<tt>AAAA</tt>" represents an IPv6address record, and the attribute identifier "<tt>HS 97</tt>" represents aresource record of type 97 in the Hesiod class.<p> <em>Superclass</em> attribute identifiers are also defined.These may be useful when querying records using the<tt>DirContext.getAttributes()</tt> method. If an attribute namehas "<tt>*</tt>" in place of a type name (or class name), itrepresents records of any type (or class). For example, the attributeidentifier "<tt>IN *</tt>" may be passed to the<tt>getAttributes()</tt> method to find all internet class records.The attribute identifier "<tt>* *</tt>" representsrecords of any class or type.<p>Attribute identifiers are case-insensitive.<p><hr><p><A NAME="URL"><H2>DNS Pseudo-URLs</H2>A URL-like notation is used to represent a DNS server, port, and domain in the <tt>java.naming.provider.url</tt> property and in URL names passedto the initial context. The format of this pseudo-URL is:<pre> dns:[//host[:port]][/domain]</pre>The host and port indicate the DNS server to use.The host defaults to "localhost", and the port defaults to 53.The domain is the DNS domain name of the context, and is not necessarilyrelated to the domain of the server; it defaults to "." (the root domain).<p><hr><p><A NAME="API"><H2>API Mapping</H2>The DNS service provider implements the <tt>DirContext</tt> interface.Methods are mapped onto DNS operations as described below.Methods not listed are not supported.<b><pre>addToEnvironment()</pre></b> <blockquote> Adds a new property to the environment, or changes an existing property. </blockquote> <b><pre>close()</pre></b> <blockquote> Releases internal data structures. </blockquote> <b><pre>composeName()</pre></b> <blockquote> Composes two names. </blockquote> <b><pre>getAttributes()</pre></b> <blockquote> Returns attributes representing DNS resource records. </blockquote> <b><pre>getEnvironment()</pre></b> <blockquote> Returns the environment properties associated with this context. </blockquote><b><pre>getNameInNamespace()</pre></b> <blockquote> Returns the fully-qualified domain name of this node. </blockquote><b><pre>getNameParser()</pre></b> <blockquote> Returns a name parser for DNS domain names. </blockquote><b><pre>lookup()lookupLink()</pre></b> <blockquote> Returns a <tt>DirContext</tt> that represents the named node. The <tt>DirectoryManager.getObjectInstance()</tt> method is invoked on the object before it is returned, in case the application or user has supplied object factories. </blockquote><b><pre>list()listBindings()</pre></b> <blockquote> The listing of the DNS namespace is implemented using zone transfers, so these operations are potentially compute- and network-intensive, and they may not be supported by all DNS installations. The <tt>DirectoryManager.getObjectInstance()</tt> method is invoked on an object before it is returned, in case the application or user has supplied object factories; no attributes are passed in. </blockquote><b><pre>removeFromEnvironment()</pre></b> <blockquote> Removes a property from the environment. </blockquote><hr><p><A NAME="USAGE"><H2>Usage Examples</H2><h4>Example 1</h4>In this example we create an initial context representing the sun.com domain,then read the IP addresses (the A records) of two hosts in that domain.<blockquote><pre>Hashtable env = new Hashtable();env.put("java.naming.factory.initial", "com.sun.jndi.dns.DnsContextFactory");env.put("java.naming.provider.url", "dns://server1.sun.com/sun.com");DirContext ictx = new InitialDirContext(env);Attributes attrs1 = ictx.getAttributes("host1", new String[] {"A"});Attributes attrs2 = ictx.getAttributes("host2", new String[] {"A"});</pre></blockquote><h4>Example 2</h4>Instead of using the properties as above, we may pass a DNS pseudo-URLto the methods of the default initial context. In this example we read theMX record of a host in the sun.com domain.<blockquote><pre>DirContext ictx = new InitialDirContext();Attributes attrs3 = ictx.getAttributes("dns://server1.sun.com/host3.sun.com", new String[] {"MX"});</pre></blockquote><hr><p><A NAME="SEC"><h2>Security Considerations</h2>When a security manager has been installed,the DNS service provider and the application using it must both begranted the following permissions:<p><pre>permission java.net.SocketPermission "host[:port]", "connect,accept";</pre>for each host/port identified in the <tt>java.naming.provider.url</tt>property, in URL string names supplied to context methods, and inobject references.<p><hr><p><A NAME="FED"><H2>Federation</H2>The DNS service provider treats composite names as <em>strongly separated</em>.That is, it processes the first component of the composite name as a DNS domain name and the rest of the components as names in the <a href=http://java.sun.com/j2se/1.3/docs/guide/jndi/spec/spi/jndispi.fm.html#1003689>next naming system(s)</a> (<i>nns</i>). The implicit next naming system is determined dynamically.<p>For example, here is an example that liststhe root of the next naming system federated beyond a DNS context,and one that looks up a name using a multi-component composite name:<blockquote><pre>// List the root of the nns.// Note the use of a trailing slash to indicate traversal into the nns.NamingEnumeration enum = ctx.list("java.sun.com/");// A composite name lookup.Object obj = ctx.lookup("sun.com/some/x/y/z");</pre></blockquote> <p><HR SIZE=3 NOSHADE WIDTH=100%><br><i>Copyright © 2001 Sun Microsystems, Inc., All Rights Reserved.</i> </body></html>⌨️ 快捷键说明
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