preferencesplaceholderconfigurer.java

一个关于Spring框架的示例应用程序,简单使用,可以参考.

/*
 * Copyright 2002-2004 the original author or authors.
 * 
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 * 
 *      http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */ 

package org.springframework.beans.factory.config;

import java.util.Properties;
import java.util.prefs.Preferences;

import org.springframework.beans.factory.InitializingBean;

/**
 * Subclass of PropertyPlaceholderConfigurer that supports J2SE 1.4's
 * Preferences API (java.util.prefs).
 *
 * <p>Tries to resolve placeholders as keys first in the user preferences,
 * then in the system preferences, then in this configurer's properties.
 * Thus, behaves like PropertyPlaceholderConfigurer if no corresponding
 * preferences defined.
 *
 * <p>Supports custom paths for the system and user preferences trees.
 * Uses the respective root nodes if not specified.
 *
 * @author Juergen Hoeller
 * @since 16.02.2004
 * @see #setSystemTreePath
 * @see #setUserTreePath
 * @see java.util.prefs.Preferences
 */
public class PreferencesPlaceholderConfigurer extends PropertyPlaceholderConfigurer implements InitializingBean {

	private String systemTreePath;

	private String userTreePath;

	private Preferences systemPrefs;

	private Preferences userPrefs;

	/**
	 * Set the path in the system preferences tree to use for resolving
	 * placeholders. Uses the root node by default.
	 */
	public void setSystemTreePath(String systemTreePath) {
		this.systemTreePath = systemTreePath;
	}

	/**
	 * Set the path in the system preferences tree to use for resolving
	 * placeholders. Uses the root node by default.
	 */
	public void setUserTreePath(String userTreePath) {
		this.userTreePath = userTreePath;
	}

	/**
	 * This implementation eagerly fetches the Preferences instances
	 * for the required system and user tree nodes.
	 */
	public void afterPropertiesSet() {
		this.systemPrefs = (this.systemTreePath != null) ?
		    Preferences.systemRoot().node(this.systemTreePath) : Preferences.systemRoot();
		this.userPrefs = (this.userTreePath != null) ?
		    Preferences.userRoot().node(this.userTreePath) : Preferences.userRoot();
	}

	/**
	 * This implementation tries to resolve placeholders as keys first
	 * in the user preferences, then in the system preferences, then in
	 * the passed-in properties.
	 */
	protected String resolvePlaceholder(String placeholder, Properties props) {
		String value = this.userPrefs.get(placeholder, null);
		if (value == null) {
			value = this.systemPrefs.get(placeholder, null);
			if (value == null) {
				value = props.getProperty(placeholder);
			}
		}
		return value;
	}

}