com.google.gerrit.server.PropertyMap Maven / Gradle / Ivy
// Copyright (C) 2020 The Android Open Source Project
//
// 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.gerrit.server;
import com.google.common.collect.ImmutableMap;
import java.util.Optional;
/**
* Immutable map that holds a collection of random objects allowing for a type-safe retrieval.
*
* Intended to be used in {@link CurrentUser} when the object is constructed during login and
* holds per-request state. This functionality allows plugins/extensions to contribute specific data
* to {@link CurrentUser} that is unknown to Gerrit core.
*/
public class PropertyMap {
/** Empty instance to be referenced once per JVM. */
public static final PropertyMap EMPTY = builder().build();
/**
* Typed key for {@link PropertyMap}. This class intentionally does not implement {@link
* Object#equals(Object)} and {@link Object#hashCode()} so that the same instance has to be used
* to retrieve a stored value.
*
*
We require the exact same key instance because {@link PropertyMap} is implemented in a
* type-safe fashion by using Java generics to guarantee the return type. The generic type can't
* be recovered at runtime, so there is no way to just use the type's full name as key - we'd have
* to pass additional arguments. At the same time, this is in-line with how we'd want callers to
* use {@link PropertyMap}: Instantiate a static, per-JVM key that is reused when setting and
* getting values.
*/
public static class Key {}
public static Key key() {
return new Key<>();
}
public static class Builder {
private ImmutableMap.Builder mutableMap;
private Builder() {
this.mutableMap = ImmutableMap.builder();
}
/** Adds the provided {@code value} to the {@link PropertyMap} that is being built. */
public Builder put(Key key, T value) {
mutableMap.put(key, value);
return this;
}
/** Builds and returns an immutable {@link PropertyMap}. */
public PropertyMap build() {
return new PropertyMap(mutableMap.build());
}
}
private final ImmutableMap map;
private PropertyMap(ImmutableMap map) {
this.map = map;
}
/** Returns a new {@link Builder} instance. */
public static Builder builder() {
return new Builder();
}
/** Returns the requested value wrapped as {@link Optional}. */
@SuppressWarnings("unchecked")
public Optional get(Key key) {
return Optional.ofNullable((T) map.get(key));
}
}