JNDI(Java Naming and Directory Interface,Java命名和目录接口)是一组在Java应用中访问命名和目录服务的API。命名服务将名称和对象联系起来,使得我们可以用名称访问对象。
JNDI类似于JDBC一样,提供了一系列编程接口,用来规范命名服务中对象的创建和管理,通过JNDI可以实现对象的创建与托管,和对象的使用过程完全解耦.
比如:在application的底层创建对象,并将对象bind到特定的context中,对象的创建过程或者"查找"方式只有此底层模块支持,外部程序不可见.对于对象的使用者(调用者)只能通过JNDI的方式获取对象,对象使用者无法直接创建对象等.
在JDBC/JMS等程序开发时,我们通常将"JDBC/JMS"某些实例(或服务)的提供者交给"容器",这些容器可以为web server或者是spring容器;对于容器内的应用程序,可以简单的通过JNDI的方式来获取服务即可.而无需额外的关注它们创建的过程/托管的方式,甚至不能修改它们.
本实例简单的展示了JNDI SPI的实现,模拟一个"配置管理中心",通过web server或者spring容器的方式,向"配置管理中心"提交配置信息,应用程序可以通过JNDI的方式来查找相应的配置等.本实例中包括了:
1) ConfigInitialContextFactory.java : 它实现了 javax.naming.spi.InitialContextFactory接口,通过调用者传递的"环境参数"来创建Context查找点.应用程序(通常为客户端)使用.
2) ConfigContext.java : 实现了javax.naming.Context接口,它主要负责托管绑定在Context上的所有object,并提供了基于路径的查找方式.
3) ConfigObjectFactory.java : 实现了javax.naming.spi.ObjectFactory接口,用于容器(Container)来创建或者获取对象.
从JNDI中lookup得到的对象,是否线程安全?答:它和Context以及object的实现有关,如果从Context中每次lookup得到的都是新对象,且此对象不会在多线程环境中使用,这也就不会有线程安全的问题.此外,object如果支持并发操作,它也是线程安全的.
不同的JNDI SPI的实现不同,有可能每次lookup出来的对象都是不同的object..不过根据JNDI的规范要求,通过context.bind的对象,然后通过context.lookup,应该是同一个对象.
1. Config.java
"配置"信息,一个Config对象表示一条配置信息,普通的javabean,它实现了Reference接口.在JNDI Context中绑定的就是Config实例.
- import javax.naming.NamingException;
- import javax.naming.Reference;
- import javax.naming.Referenceable;
- import javax.naming.StringRefAddr;
- import java.io.Serializable;
- import java.util.HashSet;
- import java.util.Set;
- public class Config implements Referenceable, Serializable {
- private String name;
- private String sources;
- //配置文件中允许配置的"属性"
- protected static Set<String> properties = new HashSet<String>();
- static {
- properties.add("name");
- properties.add("sources");
- }
- protected Config() {
- }
- protected Config(String name) {
- this.name = name;
- }
- public String getName() {
- return name;
- }
- public void setName(String name) {
- this.name = name;
- }
- public String getSources() {
- return sources;
- }
- public void setSources(String sources) {
- this.sources = sources;
- }
- @Override
- public Reference getReference() throws NamingException {
- Reference reference = new Reference(Config.class.getName(),ConfigObjectFactory.class.getName(),null);
- reference.add(new StringRefAddr("name",this.name));
- reference.add(new StringRefAddr("sources",this.sources));
- return reference;
- }
- public static boolean contains(String property){
- return properties.contains(property);
- }
- }
2. ConfigContext.java
JNDI Context,用于维护Context中config对象实例,内部通过treeMap的方式保存了config实例与naming的关系,其中name类似于"jdbc/mysql"这种路径. 代码中有些方法没有实现,仅供参考.
- import javax.naming.*;
- import javax.naming.spi.NamingManager;
- import java.util.*;
- import java.util.concurrent.ConcurrentHashMap;
- public class ConfigContext implements Context {
- //private Map<String, Config> bindings = new ConcurrentHashMap<String, Config>();
- protected static final NameParser PARSER = new NameParserImpl();
- private Hashtable environment = new Hashtable();
- protected static final String SCHEMA = "config:";
- static class NameParserImpl implements NameParser {
- public Name parse(String name) throws NamingException {
- return new CompositeName(name);
- }
- }
- private SortedMap<String,Config> bindings = new TreeMap<String, Config>();
- private String prefix = "";
- public ConfigContext(){}
- public ConfigContext(Hashtable environment){
- this.environment = environment;
- }
- protected ConfigContext(String prefix){
- this.prefix = prefix;
- }
- protected ConfigContext(String prefix,SortedMap<String,Config> bindings){
- this.prefix = prefix;
- this.bindings = bindings;
- }
- public Object lookup(Name name) throws NamingException {
- return lookup(name.toString()) ;
- }
- public Object lookup(String name) throws NamingException {
- String currentPath = null;
- if(!name.startsWith("/")){
- currentPath = prefix + "/" + name;
- } else{
- currentPath = prefix + name;
- }
- Config config = bindings.get(currentPath);
- //如果节点存在,则直接返回
- if(config != null){
- return config;
- }
- SortedMap<String,Config> tailMap = bindings.tailMap(currentPath);
- if(!tailMap.isEmpty()){
- //copy
- SortedMap<String,Config> subBindings = new TreeMap<String, Config>();
- Iterator<String> it = tailMap.keySet().iterator();
- for(Map.Entry<String,Config> entry : tailMap.entrySet()){
- String path = entry.getKey();
- if(path.startsWith(currentPath)){
- subBindings.put(path,entry.getValue()) ;
- }
- }
- if(!subBindings.isEmpty()){
- return new ConfigContext(currentPath,subBindings);
- }
- }
- //other ,proxy
- int pos = name.indexOf(':');
- if (pos > 0) {
- String scheme = name.substring(0, pos);
- Context ctx = NamingManager.getURLContext(scheme, environment);
- if (ctx != null) {
- return ctx.lookup(name);
- }
- }
- return null;
- }
- public void bind(Name name, Object obj) throws NamingException {
- bind(name.toString(),obj);
- }
- public void bind(String name, Object obj) throws NamingException {
- if(!(obj instanceof Config)){
- return;
- }
- String currentPath = null;
- if(!name.startsWith("/")){
- currentPath = prefix + "/" + name;
- } else{
- currentPath = prefix + name;
- }
- bindings.put(currentPath,(Config)obj);
- }
- public void rebind(Name name, Object obj) throws NamingException {
- bind(name,obj);
- }
- public void rebind(String name, Object obj) throws NamingException {
- bind(name,obj);
- }
- public void unbind(Name name) throws NamingException {
- unbind(name.toString());
- }
- public void unbind(String name) throws NamingException {
- bindings.remove(name);
- }
- public void rename(Name oldName, Name newName) throws NamingException {
- rename(oldName.toString(), newName.toString());
- }
- public void rename(String oldName, String newName) throws NamingException {
- if(!bindings.containsKey(oldName)){
- throw new NamingException("Name of " + oldName +" don't exist") ;
- }
- if(bindings.containsKey(newName)){
- throw new NamingException("Name of " + newName + " has already exist.");
- }
- Config value = bindings.remove(oldName);
- bindings.put(newName,value);
- }
- public NameParser getNameParser(String name) throws NamingException {
- return PARSER;
- }
- public Name composeName(Name name, Name prefix) throws NamingException {
- Name result = (Name)prefix.clone();
- result.addAll(name);
- return result;
- }
- public String composeName(String name, String prefix) throws NamingException {
- CompositeName result = new CompositeName(prefix);
- result.addAll(new CompositeName(name));
- return result.toString();
- }
- public Object addToEnvironment(String propName, Object propVal) throws NamingException {
- return this.environment.put(propName,propName.toString());
- }
- public Object removeFromEnvironment(String propName) throws NamingException {
- return this.environment.remove(propName);
- }
- public String getNameInNamespace() throws NamingException {
- return "";
- }
- }
3. ConfigInitialContextFactory.java
实例化ConfigContext,应用程序就可以使用Context中绑定的对象.
- import javax.naming.*;
- import javax.naming.spi.InitialContextFactory;
- import java.util.HashMap;
- import java.util.Hashtable;
- import java.util.Map;
- import java.util.Properties;
- /**
- *
- */
- public class ConfigInitialContextFactory implements InitialContextFactory {
- protected static final String PREFIX = "config.";
- protected static final String NAME_SUFFIX = ".name";
- protected static final String SOURCES_SUFFIX = ".sources";
- public Context getInitialContext(Hashtable<?, ?> environment) throws NamingException {
- //environment中包括了当前application中所有的JNDI配置信息
- //在实例化context时需要有选择性的操作.
- //比如,当前应用中有JMS的JNDI配置,那么此environment也包括这些信息.
- if (environment == null) {
- return new ConfigContext();
- }
- Map<String, Map<String, String>> configs = new HashMap<String, Map<String, String>>();
- Properties innerEnv = new Properties();
- for (Map.Entry entry : environment.entrySet()) {
- String key = (String) entry.getKey();
- if (!key.startsWith(PREFIX)) {
- continue;
- }
- int begin = key.indexOf(".");
- int end = key.lastIndexOf(".");
- if (begin == end) {
- continue;
- }
- String property = key.substring(end + 1);
- if(!Config.contains(property)){
- continue;
- }
- //将naming表示为类似于目录的路径,其实它可以为任意字符串.
- String name = key.substring(begin + 1, end).replaceAll("\\.", "/");
- Map<String, String> properties = configs.get(name);
- if (properties == null) {
- properties = new HashMap<String, String>();
- configs.put(name, properties);
- }
- String content = "";
- if (entry.getValue() != null) {
- content = entry.getValue().toString();
- }
- properties.put(property, content);
- innerEnv.put(name + "/" + property,content);
- }
- Context context = new ConfigContext();
- for (Map.Entry<String, Map<String, String>> entry : configs.entrySet()){
- String name = entry.getKey();
- Config config = createConfig(name, entry.getValue());
- context.bind(name, config);
- }
- return context;
- }
- private Config createConfig(String name, Map<String, String> properties) {
- if (name == null) {
- throw new RuntimeException("config name cant be empty..");
- }
- Config config = new Config(name);
- String sources = properties.get("sources");
- if (sources != null) {
- config.setSources(sources);
- }
- //more properties setting..
- return config;
- }
- public static void main(String[] args) throws Exception {
- Properties env = new Properties();
- env.put(Context.INITIAL_CONTEXT_FACTORY, "com.demo.config.jndi.ConfigInitialContextFactory");
- env.put("config.database.mysql.name", "mysql-jdbc");
- env.put("config.database.mysql.sources", "192.168.0.122:3306");
- Context context = new InitialContext(env);
- Config config = (Config) context.lookup("database/mysql");
- if (config != null) {
- System.out.println(config.getName() + "," + config.getSources());
- }
- Name name = new CompositeName("database/mysql");
- config = (Config) context.lookup(name);
- if (config != null) {
- System.out.println(config.getName() + "," + config.getSources());
- }
- Context subContext = (Context)context.lookup("database");
- config = (Config) subContext.lookup("mysql");
- if (config != null) {
- System.out.println(config.getName() + "," + config.getSources());
- }
- }
- }
4. ConfigObjectFactory.java
应用程序或者外部容器,创建对象的工厂.
- import javax.naming.*;
- import javax.naming.spi.ObjectFactory;
- import java.util.*;
- /**
- * Created with IntelliJ IDEA.
- * User: guanqing-liu
- * Date: 13-11-5
- * Time: 下午2:58
- * To change this template use File | Settings | File Templates.
- */
- public class ConfigObjectFactory implements ObjectFactory {
- public Object getObjectInstance(Object obj, Name name, Context nameCtx, Hashtable<?, ?> environment) throws Exception {
- // // you should be very careful;
- // if (nameCtx != null && name != null) {
- // Object result = nameCtx.lookup(name);
- // if (result != null && (result instanceof Config)) {
- // return result;
- // }
- // }
- // if (name != null && environment != null) {
- // Context context = new InitialContext(environment);
- // Object result = context.lookup(name);
- // if (result != null && (result instanceof Config)) {
- // return result;
- // }
- // }
- //rebuild object from reference
- //
- if (!(obj instanceof Reference)) {
- return null;
- }
- Reference reference = (Reference) obj;
- //类型检测
- if (!Config.class.getName().equalsIgnoreCase(reference.getClassName())) {
- return null;
- }
- Map<String, String> properties = new HashMap<String, String>();
- for (String property : Config.properties) {
- StringRefAddr addr = (StringRefAddr) reference.get(property);
- if (addr != null) {
- properties.put(property, addr.getContent().toString());
- }
- }
- //build
- Config config = new Config();
- config.setName(properties.get("name"));
- config.setSources(properties.get("sources"));
- return config;
- }
- public static void main(String[] args) throws Exception {
- Reference reference = new Reference(Config.class.getName(), ConfigObjectFactory.class.getName(), null);
- reference.add(new StringRefAddr("name", "mysql-jdbc"));
- reference.add(new StringRefAddr("sources", "192.168.0.122:3306"));
- Config config = (Config) new ConfigObjectFactory().getObjectInstance(reference, null, null, null);
- System.out.println(config.getName() + "<>" + config.getSources());
- }
- }
5. spring配置
1) config-jndi.properties文件
- //config-jndi.properties文件
- java.naming.factory.initial=com.demo.config.jndi.ConfigInitialContextFactory
- java.naming.factory.object=com.demo.config.jndi.ConfigObjectFactory
- config.server.zookeeper.name=zookeeper
- config.server.zookeeper.sources=192.168.0.15:2181
- config.server.mysql.name=mysql
- config.server.mysql.sources=192.168.0.15:3306
2) spring.xml配置
- <bean id="configEnv" class="org.springframework.beans.factory.config.PropertiesFactoryBean">
- <property name="locations" value="classpath:config-jndi.properties"/>
- </bean>
- <bean id="jndiTemplate" class="org.springframework.jndi.JndiTemplate">
- <property name="environment" ref="configEnv"/>
- </bean>
- <bean id="zookeeperConfig" class="org.springframework.jndi.JndiObjectFactoryBean">
- <property name="jndiName" value="server/zookeeper"/>
- </bean>
- <bean id="mysqlConfig" class="org.springframework.jndi.JndiObjectFactoryBean">
- <property name="jndiName" value="server/mysql"/>
- </bean>
3) 测试类
- public class JNDISpringMain {
- public static void main(String[] args){
- ApplicationContext context = new ClassPathXmlApplicationContext("spring-context.xml");
- Config config = (Config)context.getBean("zookeeperConfig");
- System.out.println(config.getName() + "<>" + config.getSources());
- }
- }