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Microsoft JDBC Driver for SQL Server.
There is a newer version: 12.8.1.jre11
/*
 * Microsoft JDBC Driver for SQL Server
 * 
 * Copyright(c) Microsoft Corporation All rights reserved.
 * 
 * This program is made available under the terms of the MIT License. See the LICENSE file in the project root for more information.
 */

package com.microsoft.sqlserver.jdbc;

import java.util.HashMap;
import java.util.logging.Level;

final class FailoverMapSingleton {
    private static int INITIALHASHMAPSIZE = 5;
    private static HashMap failoverMap = new HashMap(INITIALHASHMAPSIZE);

    private FailoverMapSingleton() {
        /* hide the constructor to stop the instantiation of this class. */}

    private static String concatPrimaryDatabase(String primary,
            String instance,
            String database) {
        StringBuilder buf = new StringBuilder();
        buf.append(primary);
        if (null != instance) {
            buf.append("\\");
            buf.append(instance);
        }
        buf.append(";");
        buf.append(database);
        return buf.toString();
    }

    static FailoverInfo getFailoverInfo(SQLServerConnection connection,
            String primaryServer,
            String instance,
            String database) {
        synchronized (FailoverMapSingleton.class) {
            if (true == failoverMap.isEmpty()) {
                return null;
            }
            else {
                String mapKey = concatPrimaryDatabase(primaryServer, instance, database);
                if (connection.getConnectionLogger().isLoggable(Level.FINER))
                    connection.getConnectionLogger().finer(connection.toString() + " Looking up info in the map using key: " + mapKey);
                FailoverInfo fo = failoverMap.get(mapKey);
                if (null != fo)
                    fo.log(connection);
                return fo;
            }
        }
    }

    // The map is populated with primary server, instance name and db as the key (always user info) value is the failover server name provided
    // by the server. The map is only populated if the server sends failover info.
    static void putFailoverInfo(SQLServerConnection connection,
            String primaryServer,
            String instance,
            String database,
            FailoverInfo actualFailoverInfo,
            boolean actualuseFailover,
            String failoverPartner) throws SQLServerException {
        FailoverInfo fo;

        synchronized (FailoverMapSingleton.class) {
            // one more check to make sure someone already did not do this
            if (null == (fo = getFailoverInfo(connection, primaryServer, instance, database))) {
                if (connection.getConnectionLogger().isLoggable(Level.FINE))
                    connection.getConnectionLogger().fine(connection.toString() + " Failover map add server: " + primaryServer + "; database:"
                            + database + "; Mirror:" + failoverPartner);
                failoverMap.put(concatPrimaryDatabase(primaryServer, instance, database), actualFailoverInfo);
            }
            else
                // if the class exists make sure the latest info is updated
                fo.failoverAdd(connection, actualuseFailover, failoverPartner);
        }
    }
}