/*
 * Copyright 2002-2020 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.core.env;

import org.springframework.lang.Nullable;

Interface for resolving properties against any underlying source.
Author:
Chris Beams, Juergen Hoeller
See Also:
Environment
PropertySourcesPropertyResolver
Since:
3.1/**
 * Interface for resolving properties against any underlying source.
 *
 * @author Chris Beams
 * @author Juergen Hoeller
 * @since 3.1
 * @see Environment
 * @see PropertySourcesPropertyResolver
 */
public interface PropertyResolver {

	
Return whether the given property key is available for resolution, i.e. if the value for the given key is not null. /**
	 * Return whether the given property key is available for resolution,
	 * i.e. if the value for the given key is not {@code null}.
	 */
	boolean containsProperty(String key);

	
Return the property value associated with the given key, or null if the key cannot be resolved. 
Params:
key – the property name to resolve
See Also:
getProperty(String, String)
getProperty(String, Class<Object>)
getRequiredProperty(String)/**
	 * Return the property value associated with the given key,
	 * or {@code null} if the key cannot be resolved.
	 * @param key the property name to resolve
	 * @see #getProperty(String, String)
	 * @see #getProperty(String, Class)
	 * @see #getRequiredProperty(String)
	 */
	@Nullable
	String getProperty(String key);

	
Return the property value associated with the given key, or defaultValue if the key cannot be resolved. 
Params:
key – the property name to resolve
defaultValue – the default value to return if no value is found
See Also:
getRequiredProperty(String)
getProperty(String, Class<Object>)/**
	 * Return the property value associated with the given key, or
	 * {@code defaultValue} if the key cannot be resolved.
	 * @param key the property name to resolve
	 * @param defaultValue the default value to return if no value is found
	 * @see #getRequiredProperty(String)
	 * @see #getProperty(String, Class)
	 */
	String getProperty(String key, String defaultValue);

	
Return the property value associated with the given key, or null if the key cannot be resolved. 
Params:
key – the property name to resolve
targetType – the expected type of the property value
See Also:
getRequiredProperty(String, Class<Object>)/**
	 * Return the property value associated with the given key,
	 * or {@code null} if the key cannot be resolved.
	 * @param key the property name to resolve
	 * @param targetType the expected type of the property value
	 * @see #getRequiredProperty(String, Class)
	 */
	@Nullable
	<T> T getProperty(String key, Class<T> targetType);

	
Return the property value associated with the given key, or defaultValue if the key cannot be resolved. 
Params:
key – the property name to resolve
targetType – the expected type of the property value
defaultValue – the default value to return if no value is found
See Also:
getRequiredProperty(String, Class<Object>)/**
	 * Return the property value associated with the given key,
	 * or {@code defaultValue} if the key cannot be resolved.
	 * @param key the property name to resolve
	 * @param targetType the expected type of the property value
	 * @param defaultValue the default value to return if no value is found
	 * @see #getRequiredProperty(String, Class)
	 */
	<T> T getProperty(String key, Class<T> targetType, T defaultValue);

	
Return the property value associated with the given key (never null). 
Throws:
IllegalStateException – if the key cannot be resolved
See Also:
getRequiredProperty(String, Class<Object>)/**
	 * Return the property value associated with the given key (never {@code null}).
	 * @throws IllegalStateException if the key cannot be resolved
	 * @see #getRequiredProperty(String, Class)
	 */
	String getRequiredProperty(String key) throws IllegalStateException;

	
Return the property value associated with the given key, converted to the given targetType (never null). 
Throws:
IllegalStateException – if the given key cannot be resolved/**
	 * Return the property value associated with the given key, converted to the given
	 * targetType (never {@code null}).
	 * @throws IllegalStateException if the given key cannot be resolved
	 */
	<T> T getRequiredProperty(String key, Class<T> targetType) throws IllegalStateException;

	
Resolve ${...} placeholders in the given text, replacing them with corresponding property values as resolved by getProperty. Unresolvable placeholders with no default value are ignored and passed through unchanged. 
Params:
text – the String to resolve
Throws:
IllegalArgumentException – if given text is null
See Also:
resolveRequiredPlaceholders
Returns:
the resolved String (never null)/**
	 * Resolve ${...} placeholders in the given text, replacing them with corresponding
	 * property values as resolved by {@link #getProperty}. Unresolvable placeholders with
	 * no default value are ignored and passed through unchanged.
	 * @param text the String to resolve
	 * @return the resolved String (never {@code null})
	 * @throws IllegalArgumentException if given text is {@code null}
	 * @see #resolveRequiredPlaceholders
	 */
	String resolvePlaceholders(String text);

	
Resolve ${...} placeholders in the given text, replacing them with corresponding property values as resolved by getProperty. Unresolvable placeholders with no default value will cause an IllegalArgumentException to be thrown. 
Throws:
IllegalArgumentException – if given text is null or if any placeholders are unresolvable
Returns:
the resolved String (never null)/**
	 * Resolve ${...} placeholders in the given text, replacing them with corresponding
	 * property values as resolved by {@link #getProperty}. Unresolvable placeholders with
	 * no default value will cause an IllegalArgumentException to be thrown.
	 * @return the resolved String (never {@code null})
	 * @throws IllegalArgumentException if given text is {@code null}
	 * or if any placeholders are unresolvable
	 */
	String resolveRequiredPlaceholders(String text) throws IllegalArgumentException;

}