resourcemanager.java

java1.6众多例子参考

		while (parser.hasMoreTokens()) {
		    try {
			// System.out.println("loading");
			String className = parser.nextToken();
			Class c = helper.loadClass(className, loader);
			factories.add(new NamedWeakReference(c, className));
		    } catch (Exception e) {
			// ignore ClassNotFoundException, IllegalArgumentException
		    }
		}
		// System.out.println("adding to cache: " + factories);
		perLoaderCache.put(facProp, factories);
		return new FactoryEnumeration(factories, loader);
	    }
	}
    }

    /**
     * Retrieves a factory from a list of packages specified in a
     * property.
     * 
     * The property is gotten from the environment and the provider
     * resource file associated with the given context and concatenated.
     * classSuffix is added to the end of this list.
     * See getProperty(). The resulting property value is a list of package 
     * prefixes.
     *<p>
     * This method then constructs a list of class names by concatenating
     * each package prefix with classSuffix and attempts to load and 
     * instantiate the class until one succeeds.
     * Any class that cannot be loaded is ignored. 
     * The resulting object is then cached in a two-level hash table,
     * keyed first by the context class loader and then by the property's
     * value and classSuffix.
     * The next time threads of the same context class loader call this 
     * method, they use the cached factory.
     * If no factory can be loaded, NO_FACTORY is recorded in the table
     * so that next time it'll return quickly.
     *
     * @param propName	The non-null property name
     * @param env	The possibly null environment properties
     * @param ctx	The possibly null context
     * @param classSuffix The non-null class name
     *			(e.g. ".ldap.ldapURLContextFactory).
     * @param defaultPkgPrefix The non-null default package prefix.
     *        (e.g., "com.sun.jndi.url").
     * @return An factory object; null if none.
     * @exception NamingException If encounter problem while reading the provider
     * property file, or problem instantiating the factory.
     *
     * @see javax.naming.spi.NamingManager#getURLContext
     * @see javax.naming.spi.NamingManager#getURLObject
     */
    public static Object getFactory(String propName, Hashtable env, Context ctx,
	String classSuffix, String defaultPkgPrefix) throws NamingException {

	// Merge property with provider property and supplied default
	String facProp = getProperty(propName, env, ctx, true);
	if (facProp != null)
	    facProp += (":" + defaultPkgPrefix);
	else
	    facProp = defaultPkgPrefix;

	// Cache factory based on context class loader, class name, and
	// property val
	ClassLoader loader = helper.getContextClassLoader();
	String key = classSuffix + " " + facProp;

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

	synchronized (perLoaderCache) {
	    Object factory = null;

	    WeakReference factoryRef = (WeakReference) perLoaderCache.get(key);
	    if (factoryRef == NO_FACTORY) {
		return null;
	    } else if (factoryRef != null) {
		factory = factoryRef.get();
		if (factory != null) {	// check if weak ref has been cleared
		    return factory;
		}
	    }

	    // Not cached; find first factory and cache
	    StringTokenizer parser = new StringTokenizer(facProp, ":");
	    String className;
	    while (factory == null && parser.hasMoreTokens()) {
		className = parser.nextToken() + classSuffix;
		try {
		    // System.out.println("loading " + className);
		    factory = helper.loadClass(className, loader).newInstance();
		} catch (InstantiationException e) {
		    NamingException ne = 
			new NamingException("Cannot instantiate " + className);
		    ne.setRootCause(e);
		    throw ne;
		} catch (IllegalAccessException e) {
		    NamingException ne = 
			new NamingException("Cannot access " + className);
		    ne.setRootCause(e);
		    throw ne;
		} catch (Exception e) {
		    // ignore ClassNotFoundException, IllegalArgumentException,
		    // etc.
		}
	    }

	    // Cache it.
	    perLoaderCache.put(key, (factory != null)
					? new WeakReference(factory)
					: NO_FACTORY);
	    return factory;
	}
    }


    // ---------- Private methods ----------

    /*
     * Returns the properties contained in the provider resource file
     * of an object's package.  Returns an empty hash table if the
     * object is null or the resource file cannot be found.  The
     * results are cached.
     *
     * @throws NamingException if an error occurs while reading the file.
     */
    private static Hashtable getProviderResource(Object obj)
	    throws NamingException
    {
	if (obj == null) {
	    return (new Hashtable(1));
	}
	synchronized (propertiesCache) {
	    Class c = obj.getClass();

	    Hashtable props = (Hashtable)propertiesCache.get(c);
	    if (props != null) {
		return props;
	    }
	    props = new Properties();

	    InputStream istream =
		helper.getResourceAsStream(c, PROVIDER_RESOURCE_FILE_NAME);

	    if (istream != null) {
		try {
		    ((Properties)props).load(istream);
		} catch (IOException e) {
		    NamingException ne = new ConfigurationException(
			    "Error reading provider resource file for " + c);
		    ne.setRootCause(e);
		    throw ne;
		}
	    }
	    propertiesCache.put(c, props);
	    return props;
	}
    }


    /*
     * Returns the Hashtable (never null) that results from merging
     * all application resource files available to this thread's
     * context class loader.  The properties file in <java.home>/lib
     * is also merged in.  The results are cached.
     *
     * SECURITY NOTES:
     * 1.  JNDI needs permission to read the application resource files.
     * 2.  Any class will be able to use JNDI to view the contents of
     * the application resource files in its own classpath.  Give
     * careful consideration to this before storing sensitive
     * information there.
     *
     * @throws NamingException if an error occurs while reading a resource
     *	file.
     */
    private static Hashtable getApplicationResources() throws NamingException {

	ClassLoader cl = helper.getContextClassLoader();

	synchronized (propertiesCache) {
	    Hashtable result = (Hashtable)propertiesCache.get(cl);
	    if (result != null) {
		return result;
	    }

	    try {
		NamingEnumeration resources =
		    helper.getResources(cl, APP_RESOURCE_FILE_NAME);
		while (resources.hasMore()) {
		    Properties props = new Properties();
		    props.load((InputStream)resources.next());

		    if (result == null) {
			result = props;
		    } else {
			mergeTables(result, props);
		    }
		}

		// Merge in properties from file in <java.home>/lib.
		InputStream istream =
		    helper.getJavaHomeLibStream(JRELIB_PROPERTY_FILE_NAME);
		if (istream != null) {
		    Properties props = new Properties();
		    props.load(istream);

		    if (result == null) {
			result = props;
		    } else {
			mergeTables(result, props);
		    }
		}
		
	    } catch (IOException e) {
		NamingException ne = new ConfigurationException(
			"Error reading application resource file");
		ne.setRootCause(e);
		throw ne;
	    }
	    if (result == null) {
		result = new Hashtable(11);
	    }
	    propertiesCache.put(cl, result);
	    return result;
	}
    }

    /*
     * Merge the properties from one hash table into another.  Each
     * property in props2 that is not in props1 is added to props1.
     * For each property in both hash tables that is one of the
     * standard JNDI properties that specify colon-separated lists,
     * the values are concatenated and stored in props1.
     */
    private static void mergeTables(Hashtable props1, Hashtable props2) {
	Enumeration keys = props2.keys();

	while (keys.hasMoreElements()) {
	    String prop = (String)keys.nextElement();
	    Object val1 = props1.get(prop);
	    if (val1 == null) {
		props1.put(prop, props2.get(prop));
	    } else if (isListProperty(prop)) {
		String val2 = (String)props2.get(prop);
		props1.put(prop, ((String)val1) + ":" + val2);
	    }
	}
    }

    /*
     * Is a property one of the standard JNDI properties that specify
     * colon-separated lists?
     */
    private static boolean isListProperty(String prop) {
	prop = prop.intern();
	for (int i = 0; i < listProperties.length; i++) {
	    if (prop == listProperties[i]) {
		return true;
	    }
	}
	return false;
    }
}