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：
* 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：http://java.sun.com/products/jndi/downloads/index.html
上例一个可能运行结果如下：
a:javax.naming.directory.InitialDirContext@1bf216a
b:com.sun.jndi.dns.DnsContext@3a6727
c:-----------------------------------------------
attribute: CNAME
value: us.sina.com.cn.
d:-----------------------------------------------
attribute: CNAME
value: us.sina.com.cn.
e:-----------------------------------------------
attribute: A
value: 218.30.66.67
value: 218.30.66.68
value: 218.30.66.69
value: 218.30.66.70
value: 218.30.66.71
value: 218.30.66.56
value: 218.30.66.57
value: 218.30.66.58
value: 218.30.66.59
value: 218.30.66.60
value: 218.30.66.61
value: 218.30.66.62
value: 218.30.66.63
value: 218.30.66.64
value: 218.30.66.65
value: 218.30.66.66
f:-----------------------------------------------
attribute: A
value: 220.181.28.42
g:-----------------------------------------------
attribute: A
value: 218.30.66.68
value: 218.30.66.69
value: 218.30.66.70
value: 218.30.66.71
value: 218.30.66.56
value: 218.30.66.57
value: 218.30.66.58
value: 218.30.66.59
value: 218.30.66.60
value: 218.30.66.61
value: 218.30.66.62
value: 218.30.66.63
value: 218.30.66.64
value: 218.30.66.65
value: 218.30.66.66
value: 218.30.66.67
attrs4:-----------------------------------------------
attribute: A
value: 220.181.27.5
nameParse:www.sina.com.
Exception in thread "main" javax.naming.OperationNotSupportedException
at 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(http://java.sun.com/j2se/1.5.0/docs/api/javax/naming/directory/DirContext.html):
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.
作者简介：
施祖阳，网名sylilzy,1979年生。
2002年起从事软件开发工作，主要研究JAVA、Linux及相关技术。
参考资料：