/*
 * Copyright 2002-2019 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.core.env;

Environment implementation suitable for use in 'standard' (i.e. non-web) applications. 
In addition to the usual functions of a ConfigurableEnvironment such as property resolution and profile-related operations, this implementation configures two default property sources, to be searched in the following order: 

system properties 
system environment variables 
 That is, if the key "xyz" is present both in the JVM system properties as well as in the set of environment variables for the current process, the value of key "xyz" from system properties will return from a call to environment.getProperty("xyz"). This ordering is chosen by default because system properties are per-JVM, while environment variables may be the same across many JVMs on a given system. Giving system properties precedence allows for overriding of environment variables on a per-JVM basis. 
These default property sources may be removed, reordered, or replaced; and additional property sources may be added using the MutablePropertySources instance available from AbstractEnvironment.getPropertySources(). See ConfigurableEnvironment Javadoc for usage examples. 
See SystemEnvironmentPropertySource javadoc for details on special handling of property names in shell environments (e.g. Bash) that disallow period characters in variable names. 
Author:
Chris Beams
See Also:
ConfigurableEnvironment
SystemEnvironmentPropertySource
StandardServletEnvironment
Since:
3.1/**
 * {@link Environment} implementation suitable for use in 'standard' (i.e. non-web)
 * applications.
 *
 * <p>In addition to the usual functions of a {@link ConfigurableEnvironment} such as
 * property resolution and profile-related operations, this implementation configures two
 * default property sources, to be searched in the following order:
 * <ul>
 * <li>{@linkplain AbstractEnvironment#getSystemProperties() system properties}
 * <li>{@linkplain AbstractEnvironment#getSystemEnvironment() system environment variables}
 * </ul>
 *
 * That is, if the key "xyz" is present both in the JVM system properties as well as in
 * the set of environment variables for the current process, the value of key "xyz" from
 * system properties will return from a call to {@code environment.getProperty("xyz")}.
 * This ordering is chosen by default because system properties are per-JVM, while
 * environment variables may be the same across many JVMs on a given system.  Giving
 * system properties precedence allows for overriding of environment variables on a
 * per-JVM basis.
 *
 * <p>These default property sources may be removed, reordered, or replaced; and
 * additional property sources may be added using the {@link MutablePropertySources}
 * instance available from {@link #getPropertySources()}. See
 * {@link ConfigurableEnvironment} Javadoc for usage examples.
 *
 * <p>See {@link SystemEnvironmentPropertySource} javadoc for details on special handling
 * of property names in shell environments (e.g. Bash) that disallow period characters in
 * variable names.
 *
 * @author Chris Beams
 * @since 3.1
 * @see ConfigurableEnvironment
 * @see SystemEnvironmentPropertySource
 * @see org.springframework.web.context.support.StandardServletEnvironment
 */
public class StandardEnvironment extends AbstractEnvironment {

	
System environment property source name: "systemEnvironment". /** System environment property source name: {@value}. */
	public static final String SYSTEM_ENVIRONMENT_PROPERTY_SOURCE_NAME = "systemEnvironment";

	
JVM system properties property source name: "systemProperties". /** JVM system properties property source name: {@value}. */
	public static final String SYSTEM_PROPERTIES_PROPERTY_SOURCE_NAME = "systemProperties";


	
Customize the set of property sources with those appropriate for any standard
Java environment:

"systemProperties" 
"systemEnvironment" 
Properties present in "systemProperties" will take precedence over those in "systemEnvironment". 
See Also:
AbstractEnvironment.customizePropertySources(MutablePropertySources)
AbstractEnvironment.getSystemProperties()
AbstractEnvironment.getSystemEnvironment()/**
	 * Customize the set of property sources with those appropriate for any standard
	 * Java environment:
	 * <ul>
	 * <li>{@value #SYSTEM_PROPERTIES_PROPERTY_SOURCE_NAME}
	 * <li>{@value #SYSTEM_ENVIRONMENT_PROPERTY_SOURCE_NAME}
	 * </ul>
	 * <p>Properties present in {@value #SYSTEM_PROPERTIES_PROPERTY_SOURCE_NAME} will
	 * take precedence over those in {@value #SYSTEM_ENVIRONMENT_PROPERTY_SOURCE_NAME}.
	 * @see AbstractEnvironment#customizePropertySources(MutablePropertySources)
	 * @see #getSystemProperties()
	 * @see #getSystemEnvironment()
	 */
	@Override
	protected void customizePropertySources(MutablePropertySources propertySources) {
		propertySources.addLast(
				new PropertiesPropertySource(SYSTEM_PROPERTIES_PROPERTY_SOURCE_NAME, getSystemProperties()));
		propertySources.addLast(
				new SystemEnvironmentPropertySource(SYSTEM_ENVIRONMENT_PROPERTY_SOURCE_NAME, getSystemEnvironment()));
	}

}