DefaultPropertyPlaceholderConfigurer.java

package com.baidu.disconf.client.addons.properties;

import java.util.Properties;

import org.springframework.beans.factory.config.PropertyPlaceholderConfigurer;

/**
 * A property resource configurer that resolves placeholders with defaults in bean property values of
 * context definitions. It <i>pulls</i> values from a properties file into bean definitions,
 * using the default value if no value is given in the properties file.
 * <p/>
 * <p>The default syntax uses an equals sign ('=') to separate the placeholder name from the default value.
 * This syntax mimicks the syntax which would be used in a property file.
 * <p/>
 * <p>Example:
 * <pre>
 * <bean id="dataSource" class="org.springframework.jdbc.datasource.DriverManagerDataSource">
 *   <property name="driverClassName" value="${driver=com.mysql.jdbc.Driver}"/>
 *   <property name="url" value="jdbc:${dbname=mysql:mydb}"/>
 * </bean></pre>
 *
 * <p>Having a default value directly inside the bean definition file, at the place where the property
 * is set, avoids redundantly listing the placeholder names. It is most useful for properties that usually
 * keep their default value and are rarely customized outside the bean definition file.
 *
 * <p>The lookup order for properties and locations is exactly as described in {@link PropertyPlaceholderConfigurer}.
 * The default value is only used if none of the specified properties and locations contains a value for
 * the placeholder.  If no default value is specified, this class behaves exactly the same as its superclass.
 *
 * @see PropertyPlaceholderConfigurer
 * @see #setDefaultSeparator
 */
public class DefaultPropertyPlaceholderConfigurer extends PropertyPlaceholderConfigurer {
    /**
     *
     */
    public static final String DEFAULT_DEFAULT_SEPARATOR = "=";

    /**
     *
     */
    private String defaultSeparator = DEFAULT_DEFAULT_SEPARATOR;

    /**
     * Set the string that separates a placeholder name from the default value.
     * The default is "=".
     *
     * @param def separator
     *
     * @see #DEFAULT_DEFAULT_SEPARATOR
     */
    public final void setDefaultSeparator(final String def) {
        this.defaultSeparator = def;
    }

    /**
     * @param placeholderWithDefault default placeholder
     * @param props                  properties instance
     * @param systemPropertiesMode   system properties mode
     *
     * @return the resolved placeholder
     */
    protected final String resolvePlaceholder(final String placeholderWithDefault, final Properties props,
                                              final int systemPropertiesMode) {
        String placeholder = getPlaceholder(placeholderWithDefault);
        String resolved = super.resolvePlaceholder(placeholder, props, systemPropertiesMode);
        if (resolved == null) {
            resolved = getDefault(placeholderWithDefault);
        }
        return resolved;
    }

    /**
     * extract the placeholder name from the complete placeholder string (between prefix and separator,
     * or complete placeholder if no separator is found).
     *
     * @param placeholderWithDefault default placeholder
     *
     * @return the placeholder
     *
     * @see #setPlaceholderPrefix
     * @see #setDefaultSeparator
     * @see #setPlaceholderSuffix
     */
    protected final String getPlaceholder(final String placeholderWithDefault) {
        int separatorIdx = placeholderWithDefault.indexOf(defaultSeparator);
        if (separatorIdx == -1) {
            return placeholderWithDefault;
        }
        return placeholderWithDefault.substring(0, separatorIdx);
    }

    /**
     * extract the default value from the complete placeholder (the part between separator and suffix).
     *
     * @param placeholderWithDefault
     *
     * @return the default value, or null if none is given.
     *
     * @see #setPlaceholderPrefix
     * @see #setDefaultSeparator
     * @see #setPlaceholderSuffix
     */
    protected final String getDefault(final String placeholderWithDefault) {
        int separatorIdx = placeholderWithDefault.indexOf(defaultSeparator);
        if (separatorIdx == -1) {
            return null;
        } else {
            return placeholderWithDefault.substring(separatorIdx + 1);
        }
    }
}