io.helidon.integrations.oci.sdk.cdi.ConfigAccessor Maven / Gradle / Ivy
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* Copyright (c) 2024 Oracle and/or its affiliates.
*
* 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 io.helidon.integrations.oci.sdk.cdi;
import java.util.Objects;
import java.util.Optional;
/**
* A {@linkplain FunctionalInterface functional interface} whose implementations can {@linkplain #get(String) access
* known configuration values by name}.
*
* Note: This façade interface does not describe a general-purpose configuration
* system. It is deliberately minimal, deliberately dependency-free, deliberately suited only for the minimal
* requirements of classes and interfaces in this package, and deliberately generic only so that it can be
* backed for its restricted purposes by a variety of actual general-purpose configuration systems and libraries.
*
* @see #get(String)
*/
@FunctionalInterface
interface ConfigAccessor {
/**
* Returns an {@link Optional} {@linkplain Optional#get() housing} a {@link String}-typed configuration value
* suitable for the supplied configuration name, or an {@linkplain Optional#isEmpty() empty Optional}
* if such a value cannot be provided.
*
* Implementations of this method are not obligated to produce a determinate value and there are no additional
* semantics of any kind implied by this contract.
*
* @param name the configuration name; must not be {@code null}
*
* @return an {@link Optional} {@linkplain Optional#get() housing} a {@link String}-typed configuration value
* suitable for the supplied configuration name, or an {@linkplain Optional#isEmpty() empty Optional}
* if such a value cannot be provided; never {@code null}
*
* @exception NullPointerException if {@code name} is {@code null}
*/
Optional get(String name);
/**
* Returns a {@link ConfigAccessor} whose {@link #get(String)} method is implemented by first invoking this {@link
* ConfigAccessor}'s {@link #get(String)} method, or, if its return value {@linkplain Optional#isEmpty() is empty},
* invoking the {@link #get(String)} method of the supplied {@link ConfigAccessor}.
*
* @param ca a {@link ConfigAccessor}; must not be {@code null}
*
* @return a {@link ConfigAccessor} whose {@link #get(String)} method is implemented by first invoking this {@link
* ConfigAccessor}'s {@link #get(String)} method, or, if its return value {@linkplain Optional#isEmpty() is empty},
* invoking the {@link #get(String)} method of the supplied {@link ConfigAccessor}; never {@code null}
*
* @exception NullPointerException if {@code ca} is {@code null}
*/
default ConfigAccessor thenTry(ConfigAccessor ca) {
Objects.requireNonNull(ca, "ca");
return n -> get(n).or(() -> ca.get(n));
}
/**
* Returns a {@link ConfigAccessor} that returns an {@linkplain Optional#isEmpty() empty Optional} for
* every argument.
*
* @return a {@link ConfigAccessor} that returns an {@linkplain Optional#isEmpty() empty Optional} for
* every argument; never {@code null}
*/
static ConfigAccessor empty() {
return n -> Optional.empty();
}
/**
* Returns a {@link ConfigAccessor} backed by the {@link System#getenv(String)} method.
*
* @return a {@link ConfigAccessor} backed by the {@link System#getenv(String)} method; never {@code null}
*/
static ConfigAccessor environmentVariables() {
return n -> Optional.ofNullable(System.getenv(n));
}
/**
* Returns a {@link ConfigAccessor} backed by the {@link System#getProperty(String)} method.
*
* @return a {@link ConfigAccessor} backed by the {@link System#getProperty(String)} method; never {@code null}
*/
static ConfigAccessor systemProperties() {
return n -> Optional.ofNullable(System.getProperty(n));
}
}