# FilePropertyLoader.java

    /*
     * Copyright (c) 2019, WSO2 Inc. (http://www.wso2.org) All Rights Reserved.
     *
     * 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.apache.synapse.commons.util;

    import com.google.common.util.concurrent.ThreadFactoryBuilder;
    import org.apache.commons.lang.StringUtils;
    import org.apache.commons.logging.Log;
    import org.apache.commons.logging.LogFactory;
    import org.apache.synapse.commons.SynapseCommonsException;

    import java.io.File;
    import java.io.FileInputStream;
    import java.io.InputStream;
    import java.io.IOException;
    import java.util.HashMap;
    import java.util.Map;
    import java.util.Objects;
    import java.util.Properties;
    import java.util.concurrent.Executors;
    import java.util.concurrent.TimeUnit;

    /**
     * File Property loader can be used to load the file property variables.
     */
    public class FilePropertyLoader {

        private static final Log LOG = LogFactory.getLog(FilePropertyLoader.class);
        private static final String CONF_LOCATION = "conf.location";
        private static final String FILE_PROPERTY_PATH = "properties.file.path";
        private static final String DEFAULT_PROPERTY_FILE = "file.properties";
        private static final String FILE_SYNC_INTERVAL = "file.properties.sync.interval";
        private static final String FILE_CANNOT_BE_FOUND_ERROR = "File cannot found in ";
        private String propertiesFilePath;
        private long lastModifiedTimestamp;
        private Map<String, String> propertyMap;

        private static FilePropertyLoader fileLoaderInstance;

        private FilePropertyLoader() {
            init();
            loadPropertiesFile();
            String fileSyncIntervalString = System.getProperty(FILE_SYNC_INTERVAL);
            if (StringUtils.isNotEmpty(fileSyncIntervalString)) {
                try {
                    int syncInterval = Integer.parseInt(fileSyncIntervalString);
                    if (syncInterval > 0) {
                        if (LOG.isDebugEnabled()) {
                            LOG.debug("File syncing enabled with interval " + syncInterval);
                        }
                        Executors.newSingleThreadScheduledExecutor(
                                new ThreadFactoryBuilder().setNameFormat("FilePropertySyncTask-%d").build())
                                .scheduleAtFixedRate(
                                        () -> {
                                            try {
                                                loadPropertiesFile();
                                                if (LOG.isDebugEnabled()) {
                                                    LOG.debug("File property sync task completed");
                                                }
                                            } catch (Exception e) {
                                                LOG.error("Error while syncing properties file ", e);
                                            }
                                        }, syncInterval, syncInterval, TimeUnit.SECONDS);
                    }
                } catch (NumberFormatException e) {
                    LOG.warn("Dropping system property " + FILE_SYNC_INTERVAL + " with incorrect value specified. File "
                             + "property syncing will be disabled. ");
                }
            }
        }

        public static FilePropertyLoader getInstance() {
            if (Objects.nonNull(fileLoaderInstance)) {
                return fileLoaderInstance;
            }
            synchronized (FilePropertyLoader.class) {
                if (Objects.isNull(fileLoaderInstance)) {
                    fileLoaderInstance = new FilePropertyLoader();
                }
                return fileLoaderInstance;
            }
        }

        public String getValue(String input) {
            return propertyMap.get(input);
        }

        private void loadPropertiesFile() throws SynapseCommonsException {
            File file = new File(propertiesFilePath);
            if (file.exists()) {
                if (file.lastModified() > lastModifiedTimestamp) {
                    try (InputStream in = new FileInputStream(propertiesFilePath)) {
                        Properties rawProps = new Properties();
                        Map<String, String> tempPropertyMap = new HashMap<>();
                        rawProps.load(in);
                        for (Map.Entry<Object, Object> propertyEntry : rawProps.entrySet()) {
                            String strValue = (String) propertyEntry.getValue();
                            tempPropertyMap.put((String) propertyEntry.getKey(), strValue);
                        }
                        propertyMap = tempPropertyMap;
                        lastModifiedTimestamp = file.lastModified();
                        if (LOG.isDebugEnabled()) {
                            LOG.debug("Synced properties from " + propertiesFilePath);
                        }
                    } catch (IOException ex) {
                        throw new SynapseCommonsException("Failed to read " + propertiesFilePath, ex);
                    }
                }
            } else {
                throw new SynapseCommonsException(FILE_CANNOT_BE_FOUND_ERROR + propertiesFilePath);
            }
        }

        private void init() {
            String filePath = System.getProperty(FILE_PROPERTY_PATH);

            if (null == filePath || filePath.isEmpty()) {
                throw new SynapseCommonsException(FILE_PROPERTY_PATH + " is empty or null");
            }
            if (("default").equals(filePath)) {
                propertiesFilePath = System.getProperty(CONF_LOCATION) + File.separator + DEFAULT_PROPERTY_FILE;
            } else {
                propertiesFilePath = filePath;
            }

            File file = new File(propertiesFilePath);
            if (!file.exists()) {
                throw new SynapseCommonsException(FILE_CANNOT_BE_FOUND_ERROR + filePath);
            }
            propertyMap = new HashMap<>();
        }
    }