Loader API option 1; initial revision.

Signed-off-by: Laird Nelson <[email protected]>

.gitignore

@@ -5,6 +5,7 @@
 *.log
 
 # Editors
+*~
 .settings/
 .project
 .classpath

api/pom.xml

@@ -1,6 +1,6 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <!--
-    Copyright (c) 2021 Contributors to the Eclipse Foundation
+    Copyright (c) 2021, 2022 Contributors to the Eclipse Foundation
 
     See the NOTICE file(s) distributed with this work for additional
     information regarding copyright ownership.
@@ -49,4 +49,16 @@
         </dependency>
     </dependencies>
 
+    <build>
+        <plugins>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-javadoc-plugin</artifactId>
+                <configuration>
+                    <docfilessubdirs>true</docfilessubdirs>
+                </configuration>
+            </plugin>
+        </plugins>
+    </build>
+
 </project>

api/src/main/java/jakarta/config/ConfigException.java

@@ -0,0 +1,65 @@
+/*
+ * Copyright (c) 2022 Contributors to the Eclipse Foundation
+ *
+ * See the NOTICE file(s) distributed with this work for additional
+ * information regarding copyright ownership.
+ *
+ * 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 jakarta.config;
+
+/**
+ * A {@link RuntimeException} thrown when a problem is encountered in
+ * an implementation of the Jakarta Config specfication.
+ */
+public class ConfigException extends RuntimeException {
+
+    /**
+     * Creates a new {@link ConfigException}.
+     */
+    public ConfigException() {
+        super();
+    }
+
+    /**
+     * Creates a new {@link ConfigException}.
+     *
+     * @param message a detail message; may be {@code null}
+     */
+    public ConfigException(String message) {
+        super(message);
+    }
+
+    /**
+     * Creates a new {@link ConfigException}.
+     *
+     * @param cause the {@link Throwable} responsible for this {@link
+     * ConfigException}'s existence; may be {@code null}
+     */
+    public ConfigException(Throwable cause) {
+        super(cause);
+    }
+
+    /**
+     * Creates a new {@link ConfigException}.
+     *
+     * @param message a detail message; may be {@code null}
+     *
+     * @param cause the {@link Throwable} responsible for this {@link
+     * ConfigException}'s existence; may be {@code null}
+     */
+    public ConfigException(String message, Throwable cause) {
+        super(message, cause);
+    }
+
+}

api/src/main/java/jakarta/config/Loader.java

@@ -0,0 +1,256 @@
+/*
+ * Copyright (c) 2022 Contributors to the Eclipse Foundation
+ *
+ * See the NOTICE file(s) distributed with this work for additional
+ * information regarding copyright ownership.
+ *
+ * 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 jakarta.config;
+
+import java.util.ServiceLoader;
+
+/**
+ * A loader of configuration-related objects.
+ *
+ * <p>Sample usage:</p>
+ *
+ * <blockquote><pre>{@linkplain Loader Loader} loader = {@linkplain Loader Loader}.{@linkplain Loader#bootstrap() bootstrap()};
+ *MyConfigurationRelatedObject object = null;
+ *try {
+ *  object = loader.{@linkplain #load(Class) load(MyConfigurationRelatedObject.class)};
+ *} catch ({@linkplain NoSuchObjectException} noSuchObjectException) {
+ *  // object is <a href="doc-files/terminology.html#absent">absent</a>
+ *} catch ({@linkplain ConfigException} configException) {
+ *  // a {@linkplain #load(Class) loading}-related error occurred
+ *}</pre></blockquote>
+ *
+ * @see #bootstrap()
+ *
+ * @see #bootstrap(ClassLoader)
+ *
+ * @see #load(Class)
+ *
+ * @see #load(TypeToken)
+ *
+ * @see <a href="doc-files/terminology.html">Terminology</a>
+ */
+public interface Loader {
+
+    /**
+     * Loads a configuration-related object of the supplied {@code
+     * type} and returns it.
+     *
+     * <p><strong>Note:</strong> The rules governing how it is
+     * determined whether any given configuration-related object is
+     * "of the supplied {@code type}" are currently wholly
+     * undefined.</p>
+     *
+     * <p>Implementations of this method must not return {@code
+     * null}.</p>
+     *
+     * <p>Implementations of this method must be idempotent.</p>
+     *
+     * <p>Implementations of this method must be safe for concurrent
+     * use by multiple threads.</p>
+     *
+     * <p>Implementations of this method may or may not return a <a
+     * href="doc-files/terminology.html#determinate">determinate</a>
+     * value.</p>
+     *
+     * @param <T> the type of object to load
+     *
+     * @param type the type of object to load; must not be {@code
+     * null}
+     *
+     * @return the loaded object; never {@code null}
+     *
+     * @exception NoSuchObjectException if the invocation was sound
+     * but the requested object was <a
+     * href="doc-files/terminology.html#absent">absent</a>
+     *
+     * @exception ConfigException if the invocation was sound but the
+     * object could not be loaded for any reason not related to <a
+     * href="doc-files/terminology.html#absent">absence</a>
+     *
+     * @exception IllegalArgumentException if the suplied {@code type}
+     * was invalid for any reason
+     *
+     * @exception NullPointerException if the supplied {@code type}
+     * was {@code null}
+     */
+    public <T> T load(Class<T> type);
+
+    /**
+     * Loads a configuration-related object of the supplied {@code
+     * type} and returns it.
+     *
+     * <p><strong>Note:</strong> The rules governing how it is
+     * determined whether any given configuration-related object is
+     * "of the supplied {@code type}" are currently wholly
+     * undefined.</p>
+     *
+     * <p>Implementations of this method must not return {@code
+     * null}.</p>
+     *
+     * <p>Implementations of this method must be idempotent.</p>
+     *
+     * <p>Implementations of this method must be safe for concurrent
+     * use by multiple threads.</p>
+     *
+     * <p>Implementations of this method may or may not return a <a
+     * href="doc-files/terminology.html#determinate">determinate</a>
+     * value.</p>
+     *
+     * @param <T> the type of object to load
+     *
+     * @param type the type of object to load; must not be {@code null}
+     *
+     * @return the loaded object; never {@code null}
+     *
+     * @exception NoSuchObjectException if the invocation was sound
+     * but the requested object was <a
+     * href="doc-files/terminology.html#absent">absent</a>
+     *
+     * @exception ConfigException if the invocation was sound but the
+     * object could not be loaded for any reason not related to <a
+     * href="doc-files/terminology.html#absent">absence</a>
+     *
+     * @exception IllegalArgumentException if the suplied {@code type}
+     * was invalid for any reason
+     *
+     * @exception NullPointerException if the supplied {@code type}
+     * was {@code null}
+     */
+    public <T> T load(TypeToken<T> type);
+
+    /**
+     * <em>{@linkplain #bootstrap(ClassLoader) Bootstraps}</em> a
+     * {@link Loader} instance for subsequent usage using the
+     * {@linkplain Thread#getContextClassLoader() context
+     * classloader}.
+     *
+     * <p>This method never returns {@code null}.</p>
+     *
+     * <p>This method is idempotent.</p>
+     *
+     * <p>This method is safe for concurrent use by multiple
+     * threads.</p>
+     *
+     * <p>This method may or may not return a <a
+     * href="doc-files/terminology.html#determinate">determinate</a>
+     * value. See {@link #bootstrap(ClassLoader)} for details.</p>
+     *
+     * <p>Except as possibly noted above, the observable behavior of
+     * this method is specified to be identical to that of the {@link
+     * #bootstrap(ClassLoader)} method.</p>
+     *
+     * @return a {@link Loader}; never {@code null}
+     *
+     * @exception java.util.ServiceConfigurationError if bootstrapping
+     * failed because of a {@link ServiceLoader#load(Class,
+     * ClassLoader)} or {@link ServiceLoader#findFirst()} problem
+     *
+     * @exception ConfigException if bootstrapping failed because of a
+     * {@link Loader#load(Class)} problem
+     *
+     * @see #bootstrap(ClassLoader)
+     */
+    public static Loader bootstrap() {
+        return bootstrap(Thread.currentThread().getContextClassLoader());
+    }
+
+    /**
+     * <em>Bootstraps</em> a {@link Loader} instance for subsequent
+     * usage.
+     *
+     * <p>The bootstrap process proceeds as follows:</p>
+     *
+     * <ol>
+     *
+     * <li>A <em>primordial {@link Loader}</em> is located with
+     * observable effects equal to those resulting from executing the
+     * following code:
+     *
+     * <blockquote><pre>{@linkplain Loader} loader = {@linkplain ServiceLoader}.{@linkplain ServiceLoader#load(Class, ClassLoader) load(Loader.class, classLoader)}
+     *  .{@linkplain java.util.ServiceLoader#findFirst() findFirst()}
+     *  .{@linkplain java.util.Optional#orElseThrow() orElseThrow}({@linkplain NoSuchObjectException#NoSuchObjectException() NoSuchObjectException::new});</pre></blockquote></li>
+     *
+     * <li>The {@link #load(Class)} method is invoked on the resulting
+     * {@link Loader} with {@link Loader Loader.class} as its sole
+     * argument.
+     *
+     * <ul>
+     *
+     * <li>If the invocation throws a {@link NoSuchObjectException},
+     * the primordial {@link Loader} is returned.</li>
+     *
+     * <li>If the invocation returns a {@link Loader}, that {@link
+     * Loader} is returned.</li>
+     *
+     * </ul>
+     *
+     * </li>
+     *
+     * </ol>
+     *
+     * <p>This method never returns {@code null}.</p>
+     *
+     * <p>This method is idempotent.</p>
+     *
+     * <p>This method is safe for concurrent use by multiple
+     * threads.</p>
+     *
+     * <p>This method may or may not return a <a
+     * href="doc-files/terminology.html#determinate">determinate</a>
+     * value depending on the implementation of the {@link Loader}
+     * loaded in step 2 above.</p>
+     *
+     * <p><strong>Note:</strong> The implementation of this method may
+     * change without notice between any two versions of this
+     * specification.  The requirements described above, however, will
+     * be honored in any minor version of this specification within a
+     * given major version.</p>
+     *
+     * @param classLoader the {@link ClassLoader} used to {@linkplain
+     * ServiceLoader#load(Class, ClassLoader) locate service provider
+     * files}; may be {@code null} to indicate the system classloader
+     * (or bootstrap class loader) in accordance with the contract of
+     * the {@link ServiceLoader#load(Class, ClassLoader)} method;
+     * often is the return value of an invocation of {@link
+     * Thread#getContextClassLoader()
+     * Thread.currentThread().getContextClassLoader()}
+     *
+     * @return a {@link Loader}; never {@code null}
+     *
+     * @exception java.util.ServiceConfigurationError if bootstrapping
+     * failed because of a {@link ServiceLoader#load(Class,
+     * ClassLoader)} or {@link ServiceLoader#findFirst()} problem
+     *
+     * @exception ConfigException if bootstrapping failed because of a
+     * {@link Loader#load(Class)} problem
+     */
+    public static Loader bootstrap(ClassLoader classLoader) {
+        Loader loader = ServiceLoader.load(Loader.class, classLoader)
+            .findFirst()
+            .orElseThrow(NoSuchObjectException::new);
+        try {
+            return loader.load(Loader.class);
+        } catch (NoSuchObjectException absentValueException) {
+            System.getLogger(Loader.class.getName())
+                .log(System.Logger.Level.DEBUG, absentValueException::getMessage, absentValueException);
+            return loader;
+        }
+    }
+
+}