src/main/java/org/apache/sling/launchpad/base/shared/Util.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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.apache.sling.launchpad.base.shared;

import java.util.HashMap;
import java.util.Map;

/**
 * The <code>Util</code> class provides general shared utilities.
 */
public final class Util {

    // no instantiate
    private Util() {}

    // ---------- Property file variable substition support --------------------

    /**
     * The starting delimiter of variable names (value is "${").
     */
    private static final String DELIM_START = "${";

    /**
     * The ending delimiter of variable names (value is "}").
     */
    private static final String DELIM_STOP = "}";

    /**
     * This method performs property variable substitution on the specified
     * value. If the specified value contains the syntax
     * <tt>${&lt;prop-name&gt;}</tt>, where <tt>&lt;prop-name&gt;</tt>
     * refers to either a configuration property or a system property, then the
     * corresponding property value is substituted for the variable placeholder.
     * Multiple variable placeholders may exist in the specified value as well
     * as nested variable placeholders, which are substituted from inner most to
     * outer most. Configuration properties override system properties.
     *
     * @param val The string on which to perform property substitution.
     * @param currentKey The key of the property being evaluated used to detect
     *            cycles.
     * @param cycleMap Map of variable references used to detect nested cycles.
     * @param configProps Set of configuration properties.
     * @return The value of the specified string after system property
     *         substitution.
     * @throws IllegalArgumentException If there was a syntax error in the
     *             property placeholder syntax or a recursive variable
     *             reference.
     */
    public static String substVars(String val, String currentKey,
            Map<String, String> cycleMap, Map<String, String> configProps)
            throws IllegalArgumentException {

        /////////////////////////////////////////////////////////////////
        // This version copied from org.apache.felix.framework.util.Util, Rev. 1762242
        /////////////////////////////////////////////////////////////////

        // If there is currently no cycle map, then create
        // one for detecting cycles for this invocation.
        if (cycleMap == null) {
            cycleMap = new HashMap<>();
        }

        // Put the current key in the cycle map.
        cycleMap.put(currentKey, currentKey);

        // Assume we have a value that is something like:
        // "leading ${foo.${bar}} middle ${baz} trailing"

        // Find the first ending '}' variable delimiter, which
        // will correspond to the first deepest nested variable
        // placeholder.
        int stopDelim = -1;
        int startDelim = -1;

        do {
            stopDelim = val.indexOf(DELIM_STOP, stopDelim + 1);
            // If there is no stopping delimiter, then just return
            // the value since there is no variable declared.
            if (stopDelim < 0) {
                return val;
            }
            // Try to find the matching start delimiter by
            // looping until we find a start delimiter that is
            // greater than the stop delimiter we have found.
            startDelim = val.indexOf(DELIM_START);
            // If there is no starting delimiter, then just return
            // the value since there is no variable declared.
            if (startDelim < 0) {
                return val;
            }
            while (stopDelim >= 0) {
                int idx = val.indexOf(DELIM_START, startDelim + DELIM_START.length());
                if ((idx < 0) || (idx > stopDelim)) {
                    break;
                } else if (idx < stopDelim) {
                    startDelim = idx;
                }
            }
        } while ((startDelim > stopDelim) && (stopDelim >= 0));

        // At this point, we have found a variable placeholder so
        // we must perform a variable substitution on it.
        // Using the start and stop delimiter indices, extract
        // the first, deepest nested variable placeholder.
        String variable =
                val.substring(startDelim + DELIM_START.length(), stopDelim);

        // Verify that this is not a recursive variable reference.
        if (cycleMap.get(variable) != null) {
            throw new IllegalArgumentException(
                "recursive variable reference: " + variable);
        }

        // Get the value of the deepest nested variable placeholder.
        // Try to configuration properties first.
        String substValue = (configProps != null)
                ? configProps.get(variable)
                : null;
        if (substValue == null) {
            // Ignore unknown property values.
            substValue = System.getProperty(variable, "");
        }

        // Remove the found variable from the cycle map, since
        // it may appear more than once in the value and we don't
        // want such situations to appear as a recursive reference.
        cycleMap.remove(variable);

        // Append the leading characters, the substituted value of
        // the variable, and the trailing characters to get the new
        // value.
        val = val.substring(0, startDelim)
            + substValue
            + val.substring(stopDelim + DELIM_STOP.length(), val.length());

        // Now perform substitution again, since there could still
        // be substitutions to make.
        val = substVars(val, currentKey, cycleMap, configProps);

        // Return the value.
        return val;
    }

}