SimpleVipAddressResolver.java

/*
*
* Copyright 2013 Netflix, Inc.
*
* 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 com.netflix.client;

import java.util.regex.Matcher;
import java.util.regex.Pattern;

import com.netflix.client.config.IClientConfig;
import com.netflix.config.ConfigurationManager;

/**
 * A "VipAddress" in Ribbon terminology is a logical name used for a target
 * server farm. This class helps interpret and resolve a "macro" and obtain a
 * finalized vipAddress.
 * <p>
 * Ribbon supports a comma separated set of logcial addresses for a Ribbon
 * Client. Typical/default implementation uses the list of servers obtained from
 * the first of the comma separated list and progresses down the list only when
 * the priorr vipAddress contains no servers.
 * <p>
 * This class assumes that the vip address string may contain marcos in the format 
 * of ${foo}, where foo is a property in Archaius configuration, and tries to replace 
 * these macros with actual values.
 * 
 * <p>
 * e.g. vipAddress settings
 * 
 * <code>
 * ${foo}.bar:${port},${foobar}:80,localhost:8080
 * 
 * The above list will be resolved by this class as 
 * 
 * apple.bar:80,limebar:80,localhost:8080
 * 
 * provided that the Configuration library resolves the property foo=apple,port=80 and foobar=limebar
 * 
 * </code>
 * 
 * @author stonse
 * 
 */
public class SimpleVipAddressResolver implements VipAddressResolver {

    private static final Pattern VAR_PATTERN = Pattern.compile("\\$\\{(.*?)\\}");

    /**
     * Resolve the vip address by replacing macros with actual values in configuration. 
     * If there is no macro, the passed in string will be returned. If a macro is found but
     * there is no property defined in configuration, the same macro is returned as part of the
     * result.
     */
    @Override
    public String resolve(String vipAddressMacro, IClientConfig niwsClientConfig) {
        if (vipAddressMacro == null || vipAddressMacro.length() == 0) {
            return vipAddressMacro;
        }
        return replaceMacrosFromConfig(vipAddressMacro);
    }
    
    private static String replaceMacrosFromConfig(String macro) {
        String result = macro;
        Matcher matcher = VAR_PATTERN.matcher(result);
        while (matcher.find()) {
            String key = matcher.group(1);
            String value = ConfigurationManager.getConfigInstance().getString(key);
            if (value != null) {
                result = result.replaceAll("\\$\\{" + key + "\\}", value);
                matcher = VAR_PATTERN.matcher(result);
            }
        }        
        return result.trim();        
    }

}