/*
* Copyright 2002-2017 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}}. Using {@code PropertyPlaceholderHelper} 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<>(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} 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} 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}) or cause an exception ({@code false})
*/
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}} with the corresponding
* property from the supplied {@link Properties}.
* @param value the value containing the placeholders to be replaced
* @param properties the {@code Properties} to use for replacement
* @return the supplied value with placeholders replaced inline
*/
public String replacePlaceholders(String value, final Properties properties) {
Assert.notNull(properties, "'properties' must not be null");
return replacePlaceholders(value, new PlaceholderResolver() {
@Override
public String resolvePlaceholder(String placeholderName) {
return properties.getProperty(placeholderName);
}
});
}
/**
* Replaces all placeholders of format {@code ${name}} with the value returned
* from the supplied {@link PlaceholderResolver}.
* @param value the value containing the placeholders to be replaced
* @param placeholderResolver the {@code PlaceholderResolver} to use for replacement
* @return the supplied value with placeholders replaced inline
*/
public String replacePlaceholders(String value, PlaceholderResolver placeholderResolver) {
Assert.notNull(value, "'value' must not be null");
return parseStringValue(value, placeholderResolver, new HashSet<>());
}
protected String parseStringValue(
String value, PlaceholderResolver placeholderResolver, Set<String> visitedPlaceholders) {
StringBuilder result = new StringBuilder(value);
int startIndex = value.indexOf(this.placeholderPrefix);
while (startIndex != -1) {
int endIndex = findPlaceholderEndIndex(result, startIndex);
if (endIndex != -1) {
String placeholder = result.substring(startIndex + this.placeholderPrefix.length(), endIndex);
String originalPlaceholder = placeholder;
if (!visitedPlaceholders.add(originalPlaceholder)) {
throw new IllegalArgumentException(
"Circular placeholder reference '" + originalPlaceholder + "' 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);
result.replace(startIndex, endIndex + this.placeholderSuffix.length(), propVal);
if (logger.isTraceEnabled()) {
logger.trace("Resolved placeholder '" + placeholder + "'");
}
startIndex = result.indexOf(this.placeholderPrefix, startIndex + propVal.length());
}
else if (this.ignoreUnresolvablePlaceholders) {
// Proceed with unprocessed value.
startIndex = result.indexOf(this.placeholderPrefix, endIndex + this.placeholderSuffix.length());
}
else {
throw new IllegalArgumentException("Could not resolve placeholder '" +
placeholder + "'" + " in value \"" + value + "\"");
}
visitedPlaceholders.remove(originalPlaceholder);
}
else {
startIndex = -1;
}
}
return result.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.
*/
@FunctionalInterface
public interface PlaceholderResolver {
/**
* Resolve the supplied placeholder name to the replacement value.
* @param placeholderName the name of the placeholder to resolve
* @return the replacement value, or {@code null} if no replacement is to be made
*/
String resolvePlaceholder(String placeholderName);
}
}