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spring ide_2.3.0 » org » springframework » util » SystemPropertyUtils.java
/*
 * Copyright 2002-2008 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;

/**
 * Helper class for resolving placeholders in texts. Usually applied to file paths.
 *
 * <p>A text may contain <code>${...}</code> placeholders, to be resolved as
 * system properties: e.g. <code>${user.dir}</code>.
 *
 * @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 = "}";


  /**
   * 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);

    int startIndex = buf.indexOf(PLACEHOLDER_PREFIX);
    while (startIndex != -1) {
      int endIndex = buf.indexOf(PLACEHOLDER_SUFFIX, startIndex + PLACEHOLDER_PREFIX.length());
      if (endIndex != -1) {
        String placeholder = buf.substring(startIndex + PLACEHOLDER_PREFIX.length(), endIndex);
        int nextIndex = endIndex + PLACEHOLDER_SUFFIX.length();
        try {
          String propVal = System.getProperty(placeholder);
          if (propVal == null) {
            // Fall back to searching the system environment.
            propVal = System.getenv(placeholder);
          }
          if (propVal != null) {
            buf.replace(startIndex, endIndex + PLACEHOLDER_SUFFIX.length(), propVal);
            nextIndex = startIndex + propVal.length();
          }
          else {
            System.err.println("Could not resolve placeholder '" + placeholder + "' in [" + text +
                "] as system property: neither system property nor environment variable found");
          }
        }
        catch (Throwable ex) {
          System.err.println("Could not resolve placeholder '" + placeholder + "' in [" + text +
              "] as system property: " + ex);
        }
        startIndex = buf.indexOf(PLACEHOLDER_PREFIX, nextIndex);
      }
      else {
        startIndex = -1;
      }
    }

    return buf.toString();
  }

}
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