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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.shindig.gadgets.http;
import java.util.Map;
import java.util.SortedMap;
import com.google.common.collect.Maps;
/**
* Builds the cache key object.
*
* Takes extra care to build the cache keys that don't thrash persistent caches.
*/
public class CacheKeyBuilder {
private static final int NUM_LEGACY_PARAMS = 9;
private static final String DEFAULT_KEY_VALUE = "0";
private static final char KEY_SEPARATOR = ':';
/** The legacy parameters that need to appear in the cache key in a particular order. */
private Object[] legacyParams;
/** A sorted parameter map ensures an unique ordering of the hash keys */
private SortedMap paramMap;
public CacheKeyBuilder() {
this.paramMap = Maps.newTreeMap();
this.legacyParams = new Object[NUM_LEGACY_PARAMS];
}
private String getValueOrDefault(Object value) {
if (value == null) {
return DEFAULT_KEY_VALUE;
}
return String.valueOf(value);
}
/**
* Sets a legacy cache key parameter.
*
* The legacy cache key parameters have a fixed order. Since the cache key is not required
* to have all of the legacy parameters filled in, the index of the parameter must be given.
*
* @param index the index to place this parameter at; valid values are {@code 0} to
* {@link CacheKeyBuilder#NUM_LEGACY_PARAMS - 1}
* @param value the object that determines the legacy parameter
*/
public CacheKeyBuilder setLegacyParam(int index, Object value) {
legacyParams[index] = value;
return this;
}
/**
* Sets a cache key parameter.
*
*
Each parameter needs to be inserted in the cache key builder manually, so that
* the user has an option to select the parameters that need to become part of the key.
*
* @param name the parameter name; if null, the param will not be inserted
* @param value the object that determines the value of the parameter
*/
public CacheKeyBuilder setParam(String name, Object value) {
if (value != null) {
paramMap.put(name, String.valueOf(value));
}
return this;
}
/**
* Inserting the keys from the parameter map only if the keys are defined, prevents thrashing
* the existing persistent caches at rolling restart of high-traffic servers.
* The cache keys of all URIs that don't set these parameters must not change.
*
* TODO: String parameters that have KEY_SEPARATOR appearing as a part of a string param need
* to be escaped (e.g. with a backslash like so: ":" -> "\:") to prevent weird cache key
* collisions. Moreover the active character (backslash) needs to be escaped itself for similar
* reasons.
*/
public String build() {
StringBuilder keyBuilder = new StringBuilder(2 * String.valueOf(legacyParams[0]).length());
appendLegacyKeys(keyBuilder);
if (!paramMap.isEmpty()) {
for (Map.Entry mapEntry : paramMap.entrySet()) {
keyBuilder.append(KEY_SEPARATOR);
keyBuilder.append(String.format("%s=%s", mapEntry.getKey(), mapEntry.getValue()));
}
}
return keyBuilder.toString();
}
private void appendLegacyKeys(StringBuilder key) {
boolean first = true;
for (Object legacyParam : legacyParams) {
if (!first) {
key.append(KEY_SEPARATOR);
} else {
first = false;
}
key.append(getValueOrDefault(legacyParam));
}
}
}