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Diffstat (limited to 'qpid/java/common/src/main/java/org/apache/qpid/configuration/PropertyUtils.java')
| -rw-r--r-- | qpid/java/common/src/main/java/org/apache/qpid/configuration/PropertyUtils.java | 164 |
1 files changed, 164 insertions, 0 deletions
diff --git a/qpid/java/common/src/main/java/org/apache/qpid/configuration/PropertyUtils.java b/qpid/java/common/src/main/java/org/apache/qpid/configuration/PropertyUtils.java new file mode 100644 index 0000000000..6e2b25fb2c --- /dev/null +++ b/qpid/java/common/src/main/java/org/apache/qpid/configuration/PropertyUtils.java @@ -0,0 +1,164 @@ +/* + * + * 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)); + } + } +} |