1 /*
2 * Licensed to the Apache Software Foundation (ASF) under one
3 * or more contributor license agreements. See the NOTICE file
4 * distributed with this work for additional information
5 * regarding copyright ownership. The ASF licenses this file
6 * to you under the Apache License, Version 2.0 (the
7 * "License"); you may not use this file except in compliance
8 * with the License. You may obtain a copy of the License at
9 *
10 * http://www.apache.org/licenses/LICENSE-2.0
11 *
12 * Unless required by applicable law or agreed to in writing,
13 * software distributed under the License is distributed on an
14 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
15 * KIND, either express or implied. See the License for the
16 * specific language governing permissions and limitations
17 * under the License.
18 */
19 package org.apache.maven.api;
20
21 import java.util.Objects;
22 import java.util.function.Supplier;
23
24 import org.apache.maven.api.annotations.Experimental;
25 import org.apache.maven.api.annotations.Nonnull;
26 import org.apache.maven.api.annotations.Nullable;
27 import org.apache.maven.api.annotations.Provider;
28 import org.apache.maven.api.annotations.ThreadSafe;
29
30 /**
31 * A container for data that is specific to a session.
32 * All components may use this storage to associate arbitrary data with a session.
33 * <p>
34 * Unlike a cache, this session data is not subject to purging. For this same reason, session data should also not be
35 * abused as a cache (i.e. for storing values that can be re-calculated) to avoid memory exhaustion.
36 * <p>
37 * <strong>Note:</strong> Actual implementations must be thread-safe.
38 *
39 * @see Session#getData()
40 * @since 4.0.0
41 */
42 @Experimental
43 @ThreadSafe
44 @Provider
45 public interface SessionData {
46
47 /**
48 * Associates the specified session data with the given key.
49 *
50 * @param key the key under which to store the session data, must not be {@code null}
51 * @param value the data to associate with the key, may be {@code null} to remove the mapping
52 */
53 <T> void set(@Nonnull Key<T> key, @Nullable T value);
54
55 /**
56 * Associates the specified session data with the given key if the key is currently mapped to the given value. This
57 * method provides an atomic compare-and-update of some key's value.
58 *
59 * @param key the key under which to store the session data, must not be {@code null}
60 * @param oldValue the expected data currently associated with the key, may be {@code null}
61 * @param newValue the data to associate with the key, may be {@code null} to remove the mapping
62 * @return {@code true} if the key mapping was successfully updated from the old value to the new value,
63 * {@code false} if the current key mapping didn't match the expected value and was not updated.
64 */
65 <T> boolean replace(@Nonnull Key<T> key, @Nullable T oldValue, @Nullable T newValue);
66
67 /**
68 * Gets the session data associated with the specified key.
69 *
70 * @param key the key for which to retrieve the session data, must not be {@code null}
71 * @return the session data associated with the key or {@code null} if none
72 */
73 @Nullable
74 <T> T get(@Nonnull Key<T> key);
75
76 /**
77 * Retrieve of compute the data associated with the specified key.
78 *
79 * @param key the key for which to retrieve the session data, must not be {@code null}
80 * @param supplier the supplier will compute the new value
81 * @return the session data associated with the key
82 */
83 @Nullable
84 <T> T computeIfAbsent(@Nonnull Key<T> key, @Nonnull Supplier<T> supplier);
85
86 /**
87 * Create a key using the given class as an identifier and as the type of the object.
88 */
89 static <T> Key<T> key(Class<T> clazz) {
90 return new Key<>(clazz, clazz);
91 }
92
93 /**
94 * Create a key using the given class and id.
95 */
96 static <T> Key<T> key(Class<T> clazz, Object id) {
97 return new Key<>(clazz, id);
98 }
99
100 /**
101 * Key used to query the session data
102 * @param <T> the type of the object associated to this key
103 */
104 final class Key<T> {
105
106 private final Class<T> type;
107 private final Object id;
108
109 private Key(Class<T> type, Object id) {
110 this.type = type;
111 this.id = id;
112 }
113
114 public Class<T> type() {
115 return type;
116 }
117
118 @Override
119 public boolean equals(Object o) {
120 if (this == o) {
121 return true;
122 }
123 if (o == null || getClass() != o.getClass()) {
124 return false;
125 }
126 Key<?> key = (Key<?>) o;
127 return Objects.equals(id, key.id) && Objects.equals(type, key.type);
128 }
129
130 @Override
131 public int hashCode() {
132 return Objects.hash(id, type);
133 }
134 }
135 }