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Apache Commons Text is a library focused on algorithms working on strings.
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You 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.commons.text.lookup;
import org.apache.commons.text.StringSubstitutor;
/**
* Looks up keys from environment variables.
*
* Using a {@link StringLookup} from the {@link StringLookupFactory}:
*
*
*
* StringLookupFactory.INSTANCE.dateStringLookup().lookup("USER");
*
*
* Using a {@link StringSubstitutor}:
*
*
*
* StringSubstitutor.createInterpolator().replace("... ${env:USER} ..."));
*
*
* The above examples convert (on Linux) {@code "USER"} to the current user name. On Windows 10, you would use
* {@code "USERNAME"} to the same effect.
*
*
* @since 1.3
*/
final class EnvironmentVariableStringLookup extends AbstractStringLookup {
/**
* Defines the singleton for this class.
*/
static final EnvironmentVariableStringLookup INSTANCE = new EnvironmentVariableStringLookup();
/**
* No need to build instances for now.
*/
private EnvironmentVariableStringLookup() {
// empty
}
/**
* Looks up the value of the given environment variable.
*
* @param key the key to be looked up, may be null
* @return The value of the environment variable.
* @see System#getenv(String)
*/
@Override
public String lookup(final String key) {
// getenv throws NullPointerException if name
is null
return key != null ? System.getenv(key) : null;
}
}