关键字：JNDI,J2EE,Java，命名和目录接口，Java Naming and Directory Interface
摘要：本文详细介绍了JNDI的目录相关内容，并以DNS Service Provider为例进行了示例代码的演示.本文为系列文章的第二篇，JNDI的基础内容请见本系列的第一篇
总述：
目录（Directory）可看作是对命名（Naming）的一个扩充，一个目录对象不仅像命名一样，而且还提供的对属性(Attributes)的操作.由API文档可知，javax.naming.directory.DirContext 类扩展自Context接口，同样，javax.naming.directory.InitialDirContext也扩展自 javax.naming.InitialContext,由此也可看出目录操作完全支持命名操作。下面给出一个DNS Service Provider例子以演示有关目录的一些操作：
<!-- Code creation by HtmlSave Eclipse Plug-in (C) 2005 Morten Moeller / eclipse.moelleryoung.com --> * Created on 2005-11-17 package com.sily.jndi; import java.util.Properties; /** * Description: * * @author shizy * @version 1.0 date:2005-11-17 */ public class TestDNSJndi { public static void main(String[] args) throws Exception { Properties env = new Properties(); env.put(Context.INITIAL_CONTEXT_FACTORY, "com.sun.jndi.dns.DnsContextFactory"); //此IP一定要为要访问的DNS服务器的IP,可通过网络设置查看 env.put(Context.PROVIDER_URL, "dns://10.17.45.239"); DirContext ctx = new InitialDirContext(env); System.out.println("a:" + ctx); DirContext ctx1 = (DirContext) ctx.lookup("www.sina.com"); System.out.println("b:" + ctx1); printAttributes("c:", ctx1.getAttributes("")); //从ctx.getAttributes("www.sina.com")与ctx1.getAttributes("")结果一样 printAttributes("d:", ctx.getAttributes("www.sina.com")); Attributes attrs1 = ctx.getAttributes("www.sina.com", new String[] { "a" }); Attributes attrs2 = ctx.getAttributes("www.163.com", new String[] { "a" }); Attributes attrs3 = ctx1.getAttributes("", new String[] { "a" }); Attributes attrs4 = ctx.getAttributes("www.baidu.com", new String[] { "a" }); printAttributes("e:", attrs1); printAttributes("f:", attrs2); printAttributes("g:", attrs3); printAttributes("attrs4:", attrs4); System.out.println("nameParse:"+ctx1.getNameInNamespace()); //list,此方法会导致程序lock //listEnumation("list:",ctx.list("")); //----------------------search Attributes matchAttrs = new BasicAttributes(true); matchAttrs.put(new BasicAttribute("a", "61.172.201.13")); NamingEnumeration answer = ctx1.search("www.sina.com", matchAttrs); printNamingEnumeration("search :", answer); } public static void printAttributes(String tag, Attributes attres) throws Exception { for (NamingEnumeration ae = attres.getAll(); ae.hasMore();) { Attribute attr = (Attribute) ae.next(); System.out .println(tag + "-----------------------------------------------\nattribute: " + attr.getID()); /* Print each value */ for (NamingEnumeration e = attr.getAll(); e.hasMore(); System.out .println("value: " + e.next())) ; } } public static void listEnumation(String tag, NamingEnumeration name) throws Exception { for (; name.hasMore();) { NameClassPair nameClass = (NameClassPair) name.next(); System.out .println(tag + "-----------------------------------------------\nattribute: " + nameClass.getName() + ":" + nameClass.getClassName()); } } public static void printNamingEnumeration(String tag, NamingEnumeration e) throws Exception { for (; e.hasMore();) { Attribute attr = (Attribute) e.next(); System.out .println(tag + "-----------------------------------------------\nattribute: " + attr.getID()); /* Print each value */ for (NamingEnumeration ve = attr.getAll(); ve.hasMore(); System.out .println("value: " + ve.next())) ; } } }
上例中，在jdk1.4中可运行通过。对于DNS Service Provider更详细的文档，大家可通过此URL下载：
上例一个可能运行结果如下：
a:javax.naming.directory.InitialDirContext@1bf216a
b:com.sun.jndi.dns.DnsContext@3a6727c:-----------------------------------------------attribute: CNAMEvalue: us.sina.com.cn.d:-----------------------------------------------attribute: CNAMEvalue: us.sina.com.cn.e:-----------------------------------------------attribute: Avalue: 218.30.66.67value: 218.30.66.68value: 218.30.66.69value: 218.30.66.70value: 218.30.66.71value: 218.30.66.56value: 218.30.66.57value: 218.30.66.58value: 218.30.66.59value: 218.30.66.60value: 218.30.66.61value: 218.30.66.62value: 218.30.66.63value: 218.30.66.64value: 218.30.66.65value: 218.30.66.66f:-----------------------------------------------attribute: Avalue: 220.181.28.42g:-----------------------------------------------attribute: Avalue: 218.30.66.68value: 218.30.66.69value: 218.30.66.70value: 218.30.66.71value: 218.30.66.56value: 218.30.66.57value: 218.30.66.58value: 218.30.66.59value: 218.30.66.60value: 218.30.66.61value: 218.30.66.62value: 218.30.66.63value: 218.30.66.64value: 218.30.66.65value: 218.30.66.66value: 218.30.66.67attrs4:-----------------------------------------------attribute: Avalue: 220.181.27.5nameParse:www.sina.com.Exception in thread "main" javax.naming.OperationNotSupportedExceptionat com.sun.jndi.dns.DnsContext.c_search(Unknown Source)at com.sun.jndi.toolkit.ctx.ComponentDirContext.p_search(Unknown Source)at com.sun.jndi.toolkit.ctx.PartialCompositeDirContext.search(Unknown Source)at com.sun.jndi.toolkit.ctx.PartialCompositeDirContext.search(Unknown Source)at com.sun.jndi.toolkit.ctx.PartialCompositeDirContext.search(Unknown Source)at com.sily.jndi.TestDNSJndi.main(TestDNSJndi.java:57)示例分析:通过分析代码，我们可以看出我们从DNS服务器获取了指定域名的IP地址,而且可以看出www.sina.com有多个IP.另外,可以看出从ctx.getAttributes("www.sina.com")得到的结果与ctx1.getAttributes("")结果一样,这便是目录操作的两种模式,这两种模式取得的结果是一样的,这点可以参考API文档():There are two basic models of what attributes should be associated with. First, attributes may be directly associated with a DirContext object. In this model, an attribute operation on the named object is roughly...另外,还有一点需要注意,从ctx.getAttributes()方法返回的Attributes中包含多个Attribute,每个Attribute包含多个values,其它详细内容请参考API文档
最后,代码NamingEnumeration answer = ctx1.search("www.sina.com", matchAttrs);试图对ctx1进行属性查找,但是抛出了异常,查看 DNS Service Provider 的文档可知,DNS Service Provider 没有提供对search方法的支持,大家可用其它的SP来测试此方法,如LDAP SP总结:
此例只是简单地演示的JNDI的目录操作,对于目录操作的其它高级主题如Search,Search Scope,Count Limit,Composite Names 等没有详细介绍,请参考其它相关文档.