org.ops4j.pax.runner.commons.properties.SystemPropertyUtils.java Source code

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Here is the source code for org.ops4j.pax.runner.commons.properties.SystemPropertyUtils.java

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/*
 * Copyright 2002-2007 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.ops4j.pax.runner.commons.properties;

import java.util.Properties;
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 <code>${...}</code> placeholders, to be resolved as
 * system properties: e.g. <code>${user.dir}</code>.
 *
 * @author Juergen Hoeller
 * @see #PLACEHOLDER_PREFIX
 * @see #PLACEHOLDER_SUFFIX
 * @see System#getProperty(String)
 * @since 1.2.5
 */
public abstract class SystemPropertyUtils {

    private static final Log LOGGER = LogFactory.getLog(SystemPropertyUtils.class);

    /**
     * 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(final String text) {
        return resolvePlaceholders(text, new Properties());
    }

    /**
     * Resolve ${...} placeholders in the given text, replacing them with corresponding property values or system
     * property values.
     *
     * @param text       the String to resolve
     * @param properties properties to be searched beside system properties
     *
     * @return the resolved String
     *
     * @see #PLACEHOLDER_PREFIX
     * @see #PLACEHOLDER_SUFFIX
     */
    public static String resolvePlaceholders(final String text, final Properties properties) {
        if (text == null) {
            return null;
        }
        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 = properties.getProperty(placeholder);
                    if (propVal == null) {
                        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 {
                        if (LOGGER.isWarnEnabled()) {
                            LOGGER.warn("Could not resolve placeholder '" + placeholder + "' in [" + text
                                    + "] as system property: neither system property nor environment variable found");
                        }
                    }
                } catch (Throwable ex) {
                    if (LOGGER.isWarnEnabled()) {
                        LOGGER.warn("Could not resolve placeholder '" + placeholder + "' in [" + text
                                + "] as system property: " + ex);
                    }
                }
                startIndex = buf.indexOf(PLACEHOLDER_PREFIX, nextIndex);
            } else {
                startIndex = -1;
            }
        }

        return buf.toString();
    }

}