com.wealdtech.configuration.ConfigurationSource.java Source code

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Here is the source code for com.wealdtech.configuration.ConfigurationSource.java

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/*
 * Copyright 2012 - 2014 Weald Technology Trading Limited
 *
 * 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.wealdtech.configuration;

import java.io.BufferedReader;
import java.io.IOException;
import java.net.URISyntaxException;
import java.net.URL;
import java.nio.charset.Charset;
import java.nio.file.Files;
import java.nio.file.Paths;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import com.fasterxml.jackson.databind.ObjectMapper;
import com.wealdtech.DataError;
import com.wealdtech.jackson.ObjectMapperFactory;
import com.wealdtech.utils.ResourceLoader;

/**
 * A ConfigurationSource carries out the work to find, parse and
 * return a configuration object.
 *
 * Configurations allow for the creation of objects containing configuration
 * properties which can be accessed by real classes.  They provide
 * a single source for multiple different types of configuration information,
 * retaining the flexibility of file-based configuration with the strict checking
 * and validation available through object-based configuration.
 */
public class ConfigurationSource<T> {
    private static final Logger LOGGER = LoggerFactory.getLogger(ConfigurationSource.class);

    private static final String DEFAULTFILENAME = "config.json";

    public T getConfiguration(final Class<T> klazz) {
        return getConfiguration(DEFAULTFILENAME, klazz);
    }

    public T getConfiguration(final String filename, final Class<T> klazz) {
        final ObjectMapper mapper = ObjectMapperFactory.getDefaultMapper();
        try {
            return mapper.readValue(readFile(filename), klazz);
        } catch (IOException ioe) {
            LOGGER.error("Failed to parse JSON configuration file: {}", ioe.getLocalizedMessage(), ioe);
            throw new DataError("Failed to parse JSON configuration file", ioe);
        }
    }

    private static String readFile(final String filename) {
        final StringBuilder content = new StringBuilder();
        final String linefeed = System.getProperty("line.separator");
        try (BufferedReader reader = getReader(filename)) {
            if (reader == null) {
                throw new DataError("Failed to find resource \"" + filename + "\"");
            }
            String line;
            while ((line = reader.readLine()) != null) {
                content.append(line).append(linefeed);
            }
        } catch (IOException e) {
            LOGGER.warn("Failed to read file: {}", e.getLocalizedMessage());
            LOGGER.warn("Stack trace: {}", e);
            throw new DataError("Failed to read file: " + e.getLocalizedMessage(), e);
        }
        return content.toString();
    }

    private static BufferedReader getReader(final String filename) {
        final URL fileurl = ResourceLoader.getResource(filename);
        if (fileurl == null) {
            return null;
        }
        try {
            return Files.newBufferedReader(Paths.get(fileurl.toURI()), Charset.defaultCharset());
        } catch (IOException ioe) {
            LOGGER.warn("IO exception with {}: {}", fileurl, ioe);
            throw new DataError("Failed to access configuration file \"" + filename + "\"", ioe);
        } catch (URISyntaxException use) {
            LOGGER.warn("URI issue with {}: {}", fileurl, use);
            throw new DataError("Failed to access configuration file \"" + filename + "\"", use);
        }
    }
}