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/*
*
* 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.qpid.configuration;
import java.util.ArrayList;
import java.util.Iterator;
/**
* PropertyUtils provides helper methods for dealing with Java properties.
*
* <p/><table id="crc"><caption>CRC Card</caption>
* <tr><th> Responsibilities <th> Collaborations
* <tr><td> Expand system properties into strings with named expansions.
* </table>
*
* @todo Make the lookup method generic by passing in the properties to use for the expansion, rather than hard coding
* as system properties. The expansion code has greater potential for re-use that way.
*
* @todo Some more property related code could be added to this utils class, which might more appropriately reside under
* org.apache.qpid.util. For example standardised code to load properties from a resource name, currently found in
* QpidProperties and possibly other places could be moved here.
*/
public class PropertyUtils
{
/**
* Given a string that contains substrings of the form <code>${xxx}</code>, looks up the valuea of 'xxx' as a
* system properties and substitutes tham back into the original string, to provide a property value expanded
* string.
*
* @param value The string to be scanned for property references. May be <code>null</code>, in which case this
* method returns immediately with no effect.
*
* @return The original string with the properties replaced, or <code>null</code> if the original string is
* <code>null</code>.
*
* @throws PropertyException If the string contains an opening <code>${</code> without a balancing <code>}</code>,
* or if the property to expand does not exist as a system property.
*/
public static String replaceProperties(String value) throws PropertyException
{
if (value == null)
{
return null;
}
ArrayList<String> fragments = new ArrayList<String>();
ArrayList<String> propertyRefs = new ArrayList<String>();
parsePropertyString(value, fragments, propertyRefs);
StringBuffer sb = new StringBuffer();
Iterator j = propertyRefs.iterator();
for (String fragment : fragments)
{
if (fragment == null)
{
String propertyName = (String) j.next();
// try to get it from the project or keys
// Backward compatibility
String replacement = System.getProperty(propertyName);
if (replacement == null)
{
throw new PropertyException("Property ${" + propertyName + "} has not been set", null);
}
fragment = replacement;
}
sb.append(fragment);
}
return sb.toString();
}
/**
* Parses the supplied value for properties which are specified using ${foo} syntax. $X is left as is, and $$
* specifies a single $.
*
* @param value The property string to parse.
* @param fragments Is populated with the string fragments. A null means "insert a property value here. The number
* of nulls in the list when populated is equal to the size of the propertyRefs list.
* @param propertyRefs Populated with the property names to be added into the final string.
*/
private static void parsePropertyString(String value, ArrayList<String> fragments, ArrayList<String> propertyRefs)
throws PropertyException
{
int prev = 0;
int pos;
// search for the next instance of $ from the 'prev' position
while ((pos = value.indexOf("$", prev)) >= 0)
{
// if there was any text before this, add it as a fragment
if (pos > 0)
{
fragments.add(value.substring(prev, pos));
}
// if we are at the end of the string, we tack on a $
// then move past it
if (pos == (value.length() - 1))
{
fragments.add("$");
prev = pos + 1;
}
else if (value.charAt(pos + 1) != '{')
{
// peek ahead to see if the next char is a property or not
// not a property: insert the char as a literal
if (value.charAt(pos + 1) == '$')
{
// two $ map to one $
fragments.add("$");
prev = pos + 2;
}
else
{
// $X maps to $X for all values of X!='$'
fragments.add(value.substring(pos, pos + 2));
prev = pos + 2;
}
}
else
{
// property found, extract its name or bail on a typo
int endName = value.indexOf('}', pos);
if (endName < 0)
{
throw new PropertyException("Syntax error in property: " + value, null);
}
String propertyName = value.substring(pos + 2, endName);
fragments.add(null);
propertyRefs.add(propertyName);
prev = endName + 1;
}
}
// no more $ signs found
// if there is any tail to the file, append it
if (prev < value.length())
{
fragments.add(value.substring(prev));
}
}
}
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