56 lines
1.7 KiB
Java
56 lines
1.7 KiB
Java
/*
|
|
* Copyright (C) 2017 Google Inc.
|
|
*
|
|
* 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 com.google.copybara;
|
|
|
|
import com.google.common.base.Preconditions;
|
|
import com.google.copybara.exception.RepoException;
|
|
import com.google.copybara.exception.ValidationException;
|
|
import com.google.copybara.util.console.Console;
|
|
import javax.annotation.Nullable;
|
|
|
|
/**
|
|
* Load a resource (repository, API client...) lazily to avoid side effects.
|
|
*/
|
|
public interface LazyResourceLoader<T> {
|
|
|
|
/**
|
|
* Load the resource.
|
|
*/
|
|
T load(@Nullable Console console) throws RepoException, ValidationException;
|
|
|
|
/**
|
|
* Constructs a {@link LazyResourceLoader} object that defers the loading of the resource
|
|
* until {@link #load(Console)} is called and after that always returns the same instance.
|
|
*/
|
|
static <T> LazyResourceLoader<T> memoized(LazyResourceLoader<T> delegate) {
|
|
|
|
return new LazyResourceLoader<T>() {
|
|
T resource;
|
|
|
|
/**
|
|
* @see LazyResourceLoader#load(Console)
|
|
*/
|
|
@Override
|
|
public T load(Console console) throws RepoException, ValidationException {
|
|
if (resource == null) {
|
|
resource = Preconditions.checkNotNull(delegate.load(console));
|
|
}
|
|
return resource;
|
|
}
|
|
};
|
|
}
|
|
}
|