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// 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)); } }





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