Java tutorial
/* * Copyright 2002-2005 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.util; import org.apache.commons.logging.Log; import org.apache.commons.logging.LogFactory; /** * Helper class for resolving placeholders in texts. * Usually applied to file paths. * * <p>A text may contain ${...} placeholders, to be resolved as * system properties: e.g. ${user.dir}. * * @author Juergen Hoeller * @since 1.2.5 * @see #PLACEHOLDER_PREFIX * @see #PLACEHOLDER_SUFFIX * @see System#getProperty(String) */ public abstract class SystemPropertyUtils { /** Prefix for system property placeholders: "${" */ public static final String PLACEHOLDER_PREFIX = "${"; /** Suffix for system property placeholders: "}" */ public static final String PLACEHOLDER_SUFFIX = "}"; private static final Log logger = LogFactory.getLog(SystemPropertyUtils.class); /** * Resolve ${...} placeholders in the given text, * replacing them with corresponding system property values. * @param text the String to resolve * @return the resolved String * @see #PLACEHOLDER_PREFIX * @see #PLACEHOLDER_SUFFIX */ public static String resolvePlaceholders(String text) { StringBuffer buf = new StringBuffer(text); // The following code does not use JDK 1.4's StringBuffer.indexOf(String) // method to retain JDK 1.3 compatibility. The slight loss in performance // is not really relevant, as this code will typically just run on startup. int startIndex = text.indexOf(PLACEHOLDER_PREFIX); while (startIndex != -1) { int endIndex = buf.toString().indexOf(PLACEHOLDER_SUFFIX, startIndex + PLACEHOLDER_PREFIX.length()); if (endIndex != -1) { String placeholder = buf.substring(startIndex + PLACEHOLDER_PREFIX.length(), endIndex); String propVal = System.getProperty(placeholder); if (propVal != null) { buf.replace(startIndex, endIndex + PLACEHOLDER_SUFFIX.length(), propVal); startIndex = buf.toString().indexOf(PLACEHOLDER_PREFIX, startIndex + propVal.length()); } else { if (logger.isWarnEnabled()) { logger.warn("Could not resolve placeholder '" + placeholder + "' in [" + text + "] as system property"); } startIndex = buf.toString().indexOf(PLACEHOLDER_PREFIX, endIndex + PLACEHOLDER_SUFFIX.length()); } } else { startIndex = -1; } } return buf.toString(); } }