resourcemanager.java

java1.6众多例子参考

/*
 * @(#)ResourceManager.java	1.14 05/11/17
 *
 * Copyright 2006 Sun Microsystems, Inc. All rights reserved.
 * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 */

package com.sun.naming.internal;

import java.applet.Applet;
import java.io.InputStream;
import java.io.IOException;
import java.net.URL;
import java.lang.ref.WeakReference;
import java.util.Enumeration;
import java.util.HashMap;
import java.util.Hashtable;
import java.util.Map;
import java.util.Properties;
import java.util.StringTokenizer;
import java.util.List;
import java.util.ArrayList;
import java.util.WeakHashMap;

import javax.naming.*;

/**
  * The ResourceManager class facilitates the reading of JNDI resource files.
  * 
  * @author Rosanna Lee
  * @author Scott Seligman
  * @version 1.14 05/11/17
  */

public final class ResourceManager {

    /*
     * Name of provider resource files (without the package-name prefix.)
     */
    private static final String PROVIDER_RESOURCE_FILE_NAME =
	    "jndiprovider.properties";

    /*
     * Name of application resource files.
     */
    private static final String APP_RESOURCE_FILE_NAME = "jndi.properties";

    /*
     * Name of properties file in <java.home>/lib.
     */
    private static final String JRELIB_PROPERTY_FILE_NAME = "jndi.properties";

    /*
     * The standard JNDI properties that specify colon-separated lists.
     */
    private static final String[] listProperties = {
	Context.OBJECT_FACTORIES,
	Context.URL_PKG_PREFIXES,
	Context.STATE_FACTORIES,
	// The following shouldn't create a runtime dependence on ldap package.
	javax.naming.ldap.LdapContext.CONTROL_FACTORIES
    };

    private static final VersionHelper helper =
	    VersionHelper.getVersionHelper();

    /*
     * A cache of the properties that have been constructed by
     * the ResourceManager.  A Hashtable from a provider resource
     * file is keyed on a class in the resource file's package.
     * One from application resource files is keyed on the thread's
     * context class loader.
     */
    private static final WeakHashMap propertiesCache = new WeakHashMap(11);

    /*
     * A cache of factory objects (ObjectFactory, StateFactory, ControlFactory).
     *
     * A two-level cache keyed first on context class loader and then
     * on propValue.  Value is a list of class or factory objects,
     * weakly referenced so as not to prevent GC of the class loader.
     * Used in getFactories().
     */
    private static final WeakHashMap factoryCache = new WeakHashMap(11);

    /*
     * A cache of URL factory objects (ObjectFactory).
     *
     * A two-level cache keyed first on context class loader and then
     * on classSuffix+propValue.  Value is the factory itself (weakly
     * referenced so as not to prevent GC of the class loader) or
     * NO_FACTORY if a previous search revealed no factory.  Used in
     * getFactory().
     */
    private static final WeakHashMap urlFactoryCache = new WeakHashMap(11);
    private static final WeakReference NO_FACTORY = new WeakReference(null);


    // There should be no instances of this class.
    private ResourceManager() {
    }


    // ---------- Public methods ----------

    /*
     * Given the environment parameter passed to the initial context
     * constructor, returns the full environment for that initial
     * context (never null).  This is based on the environment
     * parameter, the applet parameters (where appropriate), the
     * system properties, and all application resource files.
     *
     * <p> This method will modify <tt>env</tt> and save
     * a reference to it.  The caller may no longer modify it.
     *
     * @param env	environment passed to initial context constructor.
     *			Null indicates an empty environment.
     *
     * @throws NamingException if an error occurs while reading a
     *		resource file
     */
    public static Hashtable getInitialEnvironment(Hashtable env)
	    throws NamingException
    {
	String[] props = VersionHelper.PROPS;	// system/applet properties
	if (env == null) {
	    env = new Hashtable(11);
	}
	Applet applet = (Applet)env.get(Context.APPLET);

	// Merge property values from env param, applet params, and system
	// properties.  The first value wins:  there's no concatenation of
	// colon-separated lists.
	// Read system properties by first trying System.getProperties(),
	// and then trying System.getProperty() if that fails.  The former
	// is more efficient due to fewer permission checks.
	//
	String[] jndiSysProps = helper.getJndiProperties();
	for (int i = 0; i < props.length; i++) {
	    Object val = env.get(props[i]);
	    if (val == null) {
		if (applet != null) {
		    val = applet.getParameter(props[i]);
		}
		if (val == null) {
		    // Read system property.
		    val = (jndiSysProps != null)
			? jndiSysProps[i]
			: helper.getJndiProperty(i);
		}
		if (val != null) {
		    env.put(props[i], val);
		}
	    }
	}

	// Merge the above with the values read from all application
	// resource files.  Colon-separated lists are concatenated.
	mergeTables(env, getApplicationResources());
	return env;
    }

    /**
      * Retrieves the property from the environment, or from the provider
      * resource file associated with the given context.  The environment
      * may in turn contain values that come from applet parameters,
      * system properties, or application resource files.
      *
      * If <tt>concat</tt> is true and both the environment and the provider
      * resource file contain the property, the two values are concatenated
      * (with a ':' separator).
      *
      * Returns null if no value is found.
      *
      * @param propName	The non-null property name
      * @param env	The possibly null environment properties
      * @param ctx	The possibly null context
      * @param concat	True if multiple values should be concatenated
      * @return the property value, or null is there is none.
      * @throws NamingException if an error occurs while reading the provider
      * resource file.
      */
    public static String getProperty(String propName, Hashtable env,
	Context ctx, boolean concat)
	    throws NamingException {

	String val1 = (env != null) ? (String)env.get(propName) : null;
	if ((ctx == null) ||
	    ((val1 != null) && !concat)) {
	    return val1;
	}
	String val2 = (String)getProviderResource(ctx).get(propName);
	if (val1 == null) {
	    return val2;
	} else if ((val2 == null) || !concat) {
	    return val1;
	} else {
	    return (val1 + ":" + val2);
	}
    }

    /**
     * Retrieves an enumeration of factory classes/object specified by a
     * property.
     * 
     * The property is gotten from the environment and the provider
     * resource file associated with the given context and concantenated.
     * See getProperty(). The resulting property value is a list of class names.
     *<p>
     * This method then loads each class using the current thread's context
     * class loader and keeps them in a list. Any class that cannot be loaded
     * is ignored. The resulting list is then cached in a two-level
     * hash table, keyed first by the context class loader and then by
     * the property's value.
     * The next time threads of the same context class loader call this 
     * method, they can use the cached list.
     *<p>
     * After obtaining the list either from the cache or by creating one from
     * the property value, this method then creates and returns a 
     * FactoryEnumeration using the list. As the FactoryEnumeration is 
     * traversed, the cached Class object in the list is instantiated and 
     * replaced by an instance of the factory object itself.  Both class
     * objects and factories are wrapped in weak references so as not to
     * prevent GC of the class loader.
     *<p>
     * Note that multiple threads can be accessing the same cached list
     * via FactoryEnumeration, which locks the list during each next().
     * The size of the list will not change,
     * but a cached Class object might be replaced by an instantiated factory
     * object.
     *
     * @param propName	The non-null property name
     * @param env	The possibly null environment properties
     * @param ctx	The possibly null context
     * @return An enumeration of factory classes/objects; null if none.
     * @exception NamingException If encounter problem while reading the provider
     * property file.
     * @see javax.naming.spi.NamingManager#getObjectInstance
     * @see javax.naming.spi.NamingManager#getStateToBind
     * @see javax.naming.spi.DirectoryManager#getObjectInstance
     * @see javax.naming.spi.DirectoryManager#getStateToBind
     * @see javax.naming.ldap.ControlFactory#getControlInstance
     */
    public static FactoryEnumeration getFactories(String propName, Hashtable env,
	Context ctx) throws NamingException {

	String facProp = getProperty(propName, env, ctx, true);
	if (facProp == null)
	    return null;  // no classes specified; return null

	// Cache is based on context class loader and property val
	ClassLoader loader = helper.getContextClassLoader();

	Map perLoaderCache = null;
	synchronized (factoryCache) {
	    perLoaderCache = (Map) factoryCache.get(loader);
	    if (perLoaderCache == null) {
		perLoaderCache = new HashMap(11);
		factoryCache.put(loader, perLoaderCache);
	    }
	}

	synchronized (perLoaderCache) {
	    List factories = (List) perLoaderCache.get(facProp);
	    if (factories != null) {
		// Cached list
		return factories.size() == 0 ? null 
		    : new FactoryEnumeration(factories, loader);
	    } else {
		// Populate list with classes named in facProp; skipping
		// those that we cannot load
		StringTokenizer parser = new StringTokenizer(facProp, ":");
		factories = new ArrayList(5);