propertyplaceholderconfigurer.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.HashMap;
import java.util.HashSet;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Properties;
import java.util.Set;

import org.springframework.beans.BeansException;
import org.springframework.beans.MutablePropertyValues;
import org.springframework.beans.PropertyValue;
import org.springframework.beans.factory.BeanDefinitionStoreException;
import org.springframework.beans.factory.BeanFactory;
import org.springframework.beans.factory.BeanFactoryAware;
import org.springframework.beans.factory.BeanNameAware;
import org.springframework.core.Constants;
import org.springframework.util.ObjectUtils;

/**
 * A property resource configurer that resolves placeholders in bean property values of
 * context definitions. It <i>pulls</i> values from a properties file into bean definitions.
 *
 * <p>The default placeholder syntax follows the Ant / Log4J / JSP EL style:
 *
 * <pre>
 * ${...}</pre>
 *
 * <p>Example XML context definition:
 *
 * <pre>
 * &lt;bean id="dataSource" class="org.springframework.jdbc.datasource.DriverManagerDataSource"&gt;
 *   &lt;property name="driverClassName"&gt;&lt;value&gt;${driver}&lt;/value&gt;&lt;/property&gt;
 *   &lt;property name="url"&gt;&lt;value&gt;jdbc:${dbname}&lt;/value&gt;&lt;/property&gt;
 * &lt;/bean&gt;</pre>
 *
 * Example properties file:
 *
 * <pre>
 * driver=com.mysql.jdbc.Driver
 * dbname=mysql:mydb</pre>
 *
 * PropertyPlaceholderConfigurer checks simple property values, lists, maps,
 * props, and bean names in bean references. Furthermore, placeholder values can
 * also cross-reference other placeholders, like:
 *
 * <pre>
 * rootPath=myrootdir
 * subPath=${rootPath}/subdir</pre>
 *
 * In contrast to PropertyOverrideConfigurer, this configurer allows to fill in
 * explicit placeholders in context definitions. Therefore, the original definition
 * cannot specify any default values for such bean properties, and the placeholder
 * properties file is supposed to contain an entry for each defined placeholder.
 *
 * <p>If a configurer cannot resolve a placeholder, a BeanDefinitionStoreException
 * will be thrown. If you want to check against multiple properties files, specify
 * multiple resources via the "locations" setting. You can also define multiple
 * PropertyPlaceholderConfigurers, each with its <i>own</i> placeholder syntax.
 *
 * <p>Default property values can be defined via "properties", to make overriding
 * definitions in properties files optional. A configurer will also check against
 * system properties (e.g. "user.dir") if it cannot resolve a placeholder with any
 * of the specified properties. This can be customized via "systemPropertiesMode".
 *
 * <p>Note that the context definition <i>is</i> aware of being incomplete;
 * this is immediately obvious when looking at the XML definition file.
 *
 * <p>Property values can be converted after reading them in, through overriding
 * the <code>convertPropertyValue</code> method. For example, encrypted values
 * can be detected and decrypted accordingly before processing them.
 *
 * @author Juergen Hoeller
 * @since 02.10.2003
 * @see #setLocations
 * @see #setProperties
 * @see #setPlaceholderPrefix
 * @see #setPlaceholderSuffix
 * @see #setSystemPropertiesModeName
 * @see System#getProperty(String)
 * @see #convertPropertyValue
 * @see PropertyOverrideConfigurer
 */
public class PropertyPlaceholderConfigurer extends PropertyResourceConfigurer
    implements BeanNameAware, BeanFactoryAware {

	public static final String DEFAULT_PLACEHOLDER_PREFIX = "${";

	public static final String DEFAULT_PLACEHOLDER_SUFFIX = "}";


	/** Never check system properties. */
	public static final int SYSTEM_PROPERTIES_MODE_NEVER = 0;

	/**
	 * Check system properties if not resolvable in the specified properties.
	 * This is the default.
	 */
	public static final int SYSTEM_PROPERTIES_MODE_FALLBACK = 1;

	/**
	 * Check system properties first, before trying the specified properties.
	 * This allows system properties to override any other property source.
	 */
	public static final int SYSTEM_PROPERTIES_MODE_OVERRIDE = 2;


	private static final Constants constants = new Constants(PropertyPlaceholderConfigurer.class);

	private String placeholderPrefix = DEFAULT_PLACEHOLDER_PREFIX;

	private String placeholderSuffix = DEFAULT_PLACEHOLDER_SUFFIX;

	private int systemPropertiesMode = SYSTEM_PROPERTIES_MODE_FALLBACK;

	private boolean ignoreUnresolvablePlaceholders = false;

	private String beanName;

	private BeanFactory beanFactory;


	/**
	 * Set the prefix that a placeholder string starts with.
	 * The default is "${".
	 * @see #DEFAULT_PLACEHOLDER_PREFIX
	 */
	public void setPlaceholderPrefix(String placeholderPrefix) {
		this.placeholderPrefix = placeholderPrefix;
	}

	/**
	 * Set the suffix that a placeholder string ends with.
	 * The default is "}".
	 * @see #DEFAULT_PLACEHOLDER_SUFFIX
	 */
	public void setPlaceholderSuffix(String placeholderSuffix) {
		this.placeholderSuffix = placeholderSuffix;
	}

	/**
	 * Set the system property mode by the name of the corresponding constant,
	 * e.g. "SYSTEM_PROPERTIES_MODE_OVERRIDE".
	 * @param constantName name of the constant
	 * @throws java.lang.IllegalArgumentException if an invalid constant was specified
	 * @see #setSystemPropertiesMode
	 */
	public void setSystemPropertiesModeName(String constantName) throws IllegalArgumentException {
		this.systemPropertiesMode = constants.asNumber(constantName).intValue();
	}

	/**
	 * Set how to check system properties: as fallback, as override, or never.
	 * For example, will resolve ${user.dir} to the "user.dir" system property.
	 * <p>The default is "fallback": If not being able to resolve a placeholder
	 * with the specified properties, a system property will be tried.
	 * "override" will check for a system property first, before trying the
	 * specified properties. "never" will not check system properties at all.
	 * @see #SYSTEM_PROPERTIES_MODE_NEVER
	 * @see #SYSTEM_PROPERTIES_MODE_FALLBACK
	 * @see #SYSTEM_PROPERTIES_MODE_OVERRIDE
	 * @see #setSystemPropertiesModeName
	 */
	public void setSystemPropertiesMode(int systemPropertiesMode) {
		this.systemPropertiesMode = systemPropertiesMode;
	}

	/**
	 * Set whether to ignore unresolvable placeholders. Default is false:
	 * An exception will be thrown if a placeholder cannot not be resolved.
	 */
	public void setIgnoreUnresolvablePlaceholders(boolean ignoreUnresolvablePlaceholders) {
		this.ignoreUnresolvablePlaceholders = ignoreUnresolvablePlaceholders;
	}

	/**
	 * Only necessary to check that we're not parsing our own bean definition,
	 * to avoid failing on unresolvable placeholders in properties file locations.
	 * The latter case can happen with placeholders for system properties in
	 * resource locations.
	 * @see #setLocations
	 * @see org.springframework.core.io.ResourceEditor
	 */
	public void setBeanName(String beanName) {
		this.beanName = beanName;
	}

	/**
	 * Only necessary to check that we're not parsing our own bean definition,
	 * to avoid failing on unresolvable placeholders in properties file locations.
	 * The latter case can happen with placeholders for system properties in
	 * resource locations.
	 * @see #setLocations
	 * @see org.springframework.core.io.ResourceEditor
	 */
	public void setBeanFactory(BeanFactory beanFactory) {
		this.beanFactory = beanFactory;
	}


	protected void processProperties(ConfigurableListableBeanFactory beanFactoryToProcess, Properties props)
			throws BeansException {
		String[] beanNames = beanFactoryToProcess.getBeanDefinitionNames();
		for (int i = 0; i < beanNames.length; i++) {
			// Check that we're not parsing our own bean definition,
			// to avoid failing on unresolvable placeholders in properties file locations.
			if (!(beanNames[i].equals(this.beanName) && beanFactoryToProcess.equals(this.beanFactory))) {
				BeanDefinition bd = beanFactoryToProcess.getBeanDefinition(beanNames[i]);
				try {
					parseBeanDefinition(props, bd);
				}
				catch (BeanDefinitionStoreException ex) {
					throw new BeanDefinitionStoreException(bd.getResourceDescription(), beanNames[i], ex.getMessage());
				}
			}
		}
	}