/*
 * Copyright 2012-2020 the original author or authors.
 *
 * 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
 *
 *      https://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.springframework.boot.context;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

import org.springframework.boot.context.event.ApplicationEnvironmentPreparedEvent;
import org.springframework.context.ApplicationListener;
import org.springframework.core.Ordered;
import org.springframework.core.env.ConfigurableEnvironment;

An ApplicationListener that halts application startup if the system file encoding does not match an expected value set in the environment. By default has no effect, but if you set spring.mandatory_file_encoding (or some camelCase or UPPERCASE variant of that) to the name of a character encoding (e.g. "UTF-8") then this initializer throws an exception when the file.encoding System property does not equal it. 
 The System property file.encoding is normally set by the JVM in response to the LANG or LC_ALL environment variables. It is used (along with other platform-dependent variables keyed off those environment variables) to encode JVM arguments as well as file names and paths. In most cases you can override the file encoding System property on the command line (with standard JVM features), but also consider setting the LANG environment variable to an explicit character-encoding value (e.g. "en_GB.UTF-8"). 
Author:
Dave Syer, Madhura Bhave
Since:
1.0.0/**
 * An {@link ApplicationListener} that halts application startup if the system file
 * encoding does not match an expected value set in the environment. By default has no
 * effect, but if you set {@code spring.mandatory_file_encoding} (or some camelCase or
 * UPPERCASE variant of that) to the name of a character encoding (e.g. "UTF-8") then this
 * initializer throws an exception when the {@code file.encoding} System property does not
 * equal it.
 *
 * <p>
 * The System property {@code file.encoding} is normally set by the JVM in response to the
 * {@code LANG} or {@code LC_ALL} environment variables. It is used (along with other
 * platform-dependent variables keyed off those environment variables) to encode JVM
 * arguments as well as file names and paths. In most cases you can override the file
 * encoding System property on the command line (with standard JVM features), but also
 * consider setting the {@code LANG} environment variable to an explicit
 * character-encoding value (e.g. "en_GB.UTF-8").
 *
 * @author Dave Syer
 * @author Madhura Bhave
 * @since 1.0.0
 */
public class FileEncodingApplicationListener
		implements ApplicationListener<ApplicationEnvironmentPreparedEvent>, Ordered {

	private static final Log logger = LogFactory.getLog(FileEncodingApplicationListener.class);

	@Override
	public int getOrder() {
		return Ordered.LOWEST_PRECEDENCE;
	}

	@Override
	public void onApplicationEvent(ApplicationEnvironmentPreparedEvent event) {
		ConfigurableEnvironment environment = event.getEnvironment();
		String desired = environment.getProperty("spring.mandatory-file-encoding");
		if (desired == null) {
			return;
		}
		String encoding = System.getProperty("file.encoding");
		if (encoding != null && !desired.equalsIgnoreCase(encoding)) {
			if (logger.isErrorEnabled()) {
				logger.error("System property 'file.encoding' is currently '" + encoding + "'. It should be '" + desired
						+ "' (as defined in 'spring.mandatoryFileEncoding').");
				logger.error("Environment variable LANG is '" + System.getenv("LANG")
						+ "'. You could use a locale setting that matches encoding='" + desired + "'.");
				logger.error("Environment variable LC_ALL is '" + System.getenv("LC_ALL")
						+ "'. You could use a locale setting that matches encoding='" + desired + "'.");
			}
			throw new IllegalStateException("The Java Virtual Machine has not been configured to use the "
					+ "desired default character encoding (" + desired + ").");
		}
	}

}