8202385: Annotation to mark serial-related fields and methods

Reviewed-by: rriggs, chegar, alanb

src/java.base/share/classes/java/io/Serial.java

@@ -0,0 +1,101 @@
+/*
+ * Copyright (c) 2018, 2019, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.  Oracle designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+package java.io;
+
+import java.lang.annotation.*;
+
+/**
+ * Indicates that an annotated field or method is part of the {@linkplain
+ * Serializable serialization mechanism} defined by the
+ * <cite>Java Object Serialization Specification</cite>. This
+ * annotation type is intended to allow compile-time checking of
+ * serialization-related declarations, analogous to the checking
+ * enabled by the {@link java.lang.Override} annotation type to
+ * validate method overriding. {@code Serializable} classes are encouraged to
+ * use <code>&#64;Serial</code> annotations to help a compiler catch
+ * mis-declared serialization-related fields and methods,
+ * mis-declarations that may otherwise be difficult to detect.
+ *
+ * <p>Specifically, annotations of this type should be
+ * applied to serialization-related methods and fields in classes
+ * declared to be {@code Serializable}. The five serialization-related
+ * methods are:
+ *
+ * <ul>
+ * <li>{@code private void writeObject(java.io.ObjectOutputStream stream) throws IOException}
+ * <li>{@code private void readObject(java.io.ObjectInputStream stream) throws IOException, ClassNotFoundException}
+ * <li>{@code private void readObjectNoData() throws ObjectStreamException}
+ * <li><i>ANY-ACCESS-MODIFIER</i> {@code Object writeReplace() throws ObjectStreamException}
+ * <li><i>ANY-ACCESS-MODIFIER</i> {@code Object readResolve() throws ObjectStreamException}
+ * </ul>
+ *
+ * The two serialization-related fields are:
+ *
+ * <ul>
+ * <li>{@code private static final ObjectStreamField[] serialPersistentFields}
+ * <li>{@code private static final long serialVersionUID}
+ * </ul>
+ *
+ * Compilers are encouraged to validate that a method or field marked with a
+ * <code>&#64;Serial</code> annotation is one of the defined serialization-related
+ * methods or fields declared in a meaningful context and issue a warning
+ * if that is not the case.
+ *
+ * <p>It is a semantic error to apply this annotation to other fields or methods, including:
+ * <ul>
+ * <li>fields or methods in a class that is not {@code Serializable}
+ *
+ * <li>fields or methods of the proper structural declaration, but in
+ * a type where they are ineffectual. For example, {@code enum} types
+ * are defined to have a {@code serialVersionUID} of {@code 0L} so a
+ * {@code serialVersionUID} field declared in an {@code enum} type is
+ * ignored. The five serialization-related methods identified above
+ * are likewise ignored for an {@code enum} type.
+ *
+ * <li>in a class that is {@code Externalizable}:
+ * <ul>
+ *   <li> method declarations of {@code writeObject}, {@code
+ *   readObject}, and {@code readObjectNoData}
+ *
+ *  <li>a field declaration for {@code serialPersistentFields}
+ * </ul>
+ *
+ * While the {@code Externalizable} interface extends {@code
+ * Serializable}, the three methods and one field above are
+ * <em>not</em> used for externalizable classes.
+ *
+ * </ul>
+ *
+ * Note that serialization mechanism accesses its designated fields
+ * and methods reflectively and those fields and methods may appear
+ * otherwise unused in a {@code Serializable} class.
+ *
+ * @see Serializable
+ * @see Externalizable
+ */
+@Target({ElementType.METHOD, ElementType.FIELD})
+@Retention(RetentionPolicy.SOURCE)
+public @interface Serial {}