/*
* Copyright 2002-2010 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;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Map;
import java.util.Properties;
import java.util.Set;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
/**
* Utility class for working with Strings that have placeholder values in them. A placeholder takes the form
* <code>${name}</code>. Using <code>PropertyPlaceholderHelper</code> these placeholders can be substituted for
* user-supplied values. <p> Values for substitution can be supplied using a {@link Properties} instance or
* using a {@link PlaceholderResolver}.
*
* @author Juergen Hoeller
* @author Rob Harrop
* @since 3.0
*/
public class PropertyPlaceholderHelper {
private static final Log logger = LogFactory.getLog(PropertyPlaceholderHelper.class);
private static final Map<String, String> wellKnownSimplePrefixes = new HashMap<String, String>(4);
static {
wellKnownSimplePrefixes.put("}", "{");
wellKnownSimplePrefixes.put("]", "[");
wellKnownSimplePrefixes.put(")", "(");
}
private final String placeholderPrefix;
private final String placeholderSuffix;
private final String simplePrefix;
private final String valueSeparator;
private final boolean ignoreUnresolvablePlaceholders;
/**
* Creates a new <code>PropertyPlaceholderHelper</code> that uses the supplied prefix and suffix.
* Unresolvable placeholders are ignored.
* @param placeholderPrefix the prefix that denotes the start of a placeholder.
* @param placeholderSuffix the suffix that denotes the end of a placeholder.
*/
public PropertyPlaceholderHelper(String placeholderPrefix, String placeholderSuffix) {
this(placeholderPrefix, placeholderSuffix, null, true);
}
/**
* Creates a new <code>PropertyPlaceholderHelper</code> that uses the supplied prefix and suffix.
* @param placeholderPrefix the prefix that denotes the start of a placeholder
* @param placeholderSuffix the suffix that denotes the end of a placeholder
* @param valueSeparator the separating character between the placeholder variable
* and the associated default value, if any
* @param ignoreUnresolvablePlaceholders indicates whether unresolvable placeholders should be ignored
* (<code>true</code>) or cause an exception (<code>false</code>).
*/
public PropertyPlaceholderHelper(String placeholderPrefix, String placeholderSuffix,
String valueSeparator, boolean ignoreUnresolvablePlaceholders) {
Assert.notNull(placeholderPrefix, "placeholderPrefix must not be null");
Assert.notNull(placeholderSuffix, "placeholderSuffix must not be null");
this.placeholderPrefix = placeholderPrefix;
this.placeholderSuffix = placeholderSuffix;
String simplePrefixForSuffix = wellKnownSimplePrefixes.get(this.placeholderSuffix);
if (simplePrefixForSuffix != null && this.placeholderPrefix.endsWith(simplePrefixForSuffix)) {
this.simplePrefix = simplePrefixForSuffix;
}
else {
this.simplePrefix = this.placeholderPrefix;
}
this.valueSeparator = valueSeparator;
this.ignoreUnresolvablePlaceholders = ignoreUnresolvablePlaceholders;
}
/**
* Replaces all placeholders of format <code>${name}</code> with the corresponding property
* from the supplied {@link Properties}.
* @param value the value containing the placeholders to be replaced.
* @param properties the <code>Properties</code> to use for replacement.
* @return the supplied value with placeholders replaced inline.
*/
public String replacePlaceholders(String value, final Properties properties) {
Assert.notNull(properties, "Argument 'properties' must not be null.");
return replacePlaceholders(value, new PlaceholderResolver() {
public String resolvePlaceholder(String placeholderName) {
return properties.getProperty(placeholderName);
}
});
}
/**
* Replaces all placeholders of format <code>${name}</code> with the value returned from the supplied
* {@link PlaceholderResolver}.
* @param value the value containing the placeholders to be replaced.
* @param placeholderResolver the <code>PlaceholderResolver</code> to use for replacement.
* @return the supplied value with placeholders replaced inline.
*/
public String replacePlaceholders(String value, PlaceholderResolver placeholderResolver) {
Assert.notNull(value, "Argument 'value' must not be null.");
return parseStringValue(value, placeholderResolver, new HashSet<String>());
}
protected String parseStringValue(
String strVal, PlaceholderResolver placeholderResolver, Set<String> visitedPlaceholders) {
StringBuilder buf = new StringBuilder(strVal);
int startIndex = strVal.indexOf(this.placeholderPrefix);
while (startIndex != -1) {
int endIndex = findPlaceholderEndIndex(buf, startIndex);
if (endIndex != -1) {
String placeholder = buf.substring(startIndex + this.placeholderPrefix.length(), endIndex);
if (!visitedPlaceholders.add(placeholder)) {
throw new IllegalArgumentException(
"Circular placeholder reference '" + placeholder + "' in property definitions");
}
// Recursive invocation, parsing placeholders contained in the placeholder key.
placeholder = parseStringValue(placeholder, placeholderResolver, visitedPlaceholders);
// Now obtain the value for the fully resolved key...
String propVal = placeholderResolver.resolvePlaceholder(placeholder);
if (propVal == null && this.valueSeparator != null) {
int separatorIndex = placeholder.indexOf(this.valueSeparator);
if (separatorIndex != -1) {
String actualPlaceholder = placeholder.substring(0, separatorIndex);
String defaultValue = placeholder.substring(separatorIndex + this.valueSeparator.length());
propVal = placeholderResolver.resolvePlaceholder(actualPlaceholder);
if (propVal == null) {
propVal = defaultValue;
}
}
}
if (propVal != null) {
// Recursive invocation, parsing placeholders contained in the
// previously resolved placeholder value.
propVal = parseStringValue(propVal, placeholderResolver, visitedPlaceholders);
buf.replace(startIndex, endIndex + this.placeholderSuffix.length(), propVal);
if (logger.isTraceEnabled()) {
logger.trace("Resolved placeholder '" + placeholder + "'");
}
startIndex = buf.indexOf(this.placeholderPrefix, startIndex + propVal.length());
}
else if (this.ignoreUnresolvablePlaceholders) {
// Proceed with unprocessed value.
startIndex = buf.indexOf(this.placeholderPrefix, endIndex + this.placeholderSuffix.length());
}
else {
throw new IllegalArgumentException("Could not resolve placeholder '" + placeholder + "'");
}
visitedPlaceholders.remove(placeholder);
}
else {
startIndex = -1;
}
}
return buf.toString();
}
private int findPlaceholderEndIndex(CharSequence buf, int startIndex) {
int index = startIndex + this.placeholderPrefix.length();
int withinNestedPlaceholder = 0;
while (index < buf.length()) {
if (StringUtils.substringMatch(buf, index, this.placeholderSuffix)) {
if (withinNestedPlaceholder > 0) {
withinNestedPlaceholder--;
index = index + this.placeholderSuffix.length();
}
else {
return index;
}
}
else if (StringUtils.substringMatch(buf, index, this.simplePrefix)) {
withinNestedPlaceholder++;
index = index + this.simplePrefix.length();
}
else {
index++;
}
}
return -1;
}
/**
* Strategy interface used to resolve replacement values for placeholders contained in Strings.
* @see PropertyPlaceholderHelper
*/
public static interface PlaceholderResolver {
/**
* Resolves the supplied placeholder name into the replacement value.
* @param placeholderName the name of the placeholder to resolve.
* @return the replacement value or <code>null</code> if no replacement is to be made.
*/
String resolvePlaceholder(String placeholderName);
}
}
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