引入 guava 的 Beta 注解。

src/main/java/com/google/common/annotations/Beta.java

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+/*
+ * Copyright (C) 2010 The Guava Authors
+ *
+ * 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.common.annotations;
+
+import java.lang.annotation.Documented;
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+
+/**
+ * Signifies that a public API (public class, method or field) is subject to incompatible changes,
+ * or even removal, in a future release. An API bearing this annotation is exempt from any
+ * compatibility guarantees made by its containing library. Note that the presence of this
+ * annotation implies nothing about the quality or performance of the API in question, only the fact
+ * that it is not "API-frozen."
+ *
+ * <p>It is generally safe for <i>applications</i> to depend on beta APIs, at the cost of some extra
+ * work during upgrades. However it is generally inadvisable for <i>libraries</i> (which get
+ * included on users' CLASSPATHs, outside the library developers' control) to do so.
+ *
+ * @author Kevin Bourrillion
+ */
+@Retention(RetentionPolicy.CLASS)
+@Target({
+  ElementType.ANNOTATION_TYPE,
+  ElementType.CONSTRUCTOR,
+  ElementType.FIELD,
+  ElementType.METHOD,
+  ElementType.TYPE
+})
+@Documented
+@GwtCompatible
+public @interface Beta {}

src/main/java/com/google/common/annotations/GwtCompatible.java

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+/*
+ * Copyright (C) 2009 The Guava Authors
+ *
+ * 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.common.annotations;
+
+import java.lang.annotation.Documented;
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+
+/**
+ * The presence of this annotation on a type indicates that the type may be used with the <a
+ * href="http://code.google.com/webtoolkit/">Google Web Toolkit</a> (GWT). When applied to a method,
+ * the return type of the method is GWT compatible. It's useful to indicate that an instance created
+ * by factory methods has a GWT serializable type. In the following example,
+ *
+ * <pre>
+ * {@literal @}GwtCompatible
+ * class Lists {
+ *   ...
+ *   {@literal @}GwtCompatible(serializable = true)
+ *   {@literal static <E> List<E>} newArrayList(E... elements) {
+ *     ...
+ *   }
+ * }
+ * </pre>
+ *
+ * <p>The return value of {@code Lists.newArrayList(E[])} has GWT serializable type. It is also
+ * useful in specifying contracts of interface methods. In the following example,
+ *
+ * <pre>
+ * {@literal @}GwtCompatible
+ * interface ListFactory {
+ *   ...
+ *   {@literal @}GwtCompatible(serializable = true)
+ *   {@literal <E> List<E>} newArrayList(E... elements);
+ * }
+ * </pre>
+ *
+ * <p>The {@code newArrayList(E[])} method of all implementations of {@code ListFactory} is expected
+ * to return a value with a GWT serializable type.
+ *
+ * <p>Note that a {@code GwtCompatible} type may have some {@link GwtIncompatible} methods.
+ *
+ * @author Charles Fry
+ * @author Hayward Chan
+ */
+@Retention(RetentionPolicy.CLASS)
+@Target({ElementType.TYPE, ElementType.METHOD})
+@Documented
+@GwtCompatible
+public @interface GwtCompatible {
+
+  /**
+   * When {@code true}, the annotated type or the type of the method return value is GWT
+   * serializable.
+   *
+   * @see <a href=
+   *     "http://code.google.com/webtoolkit/doc/latest/DevGuideServerCommunication.html#DevGuideSerializableTypes">
+   *     Documentation about GWT serialization</a>
+   */
+  boolean serializable() default false;
+
+  /**
+   * When {@code true}, the annotated type is emulated in GWT. The emulated source (also known as
+   * super-source) is different from the implementation used by the JVM.
+   *
+   * @see <a href=
+   *     "http://code.google.com/webtoolkit/doc/latest/DevGuideOrganizingProjects.html#DevGuideModules">
+   *     Documentation about GWT emulated source</a>
+   */
+  boolean emulated() default false;
+}