#87 : API: support SPI for net.cactusthorn.config.core.loader.Loader

README.md

@@ -393,6 +393,12 @@ FYI:
    - Custom loaders always have the highest priority: last added -> first used.
    - Custom loader implementation must be stateless and must have a default(no-argument) `public` constructor.
 
+### SPI
+[Service-provider loading facility](https://docs.oracle.com/javase/8/docs/api/java/util/ServiceLoader.html) (introduced in JDK 1.6) can be used to *automatically* add custom loader implementation to the `ConfigFactory`. Add file *META-INF\services\net.cactusthorn.config.core.loader.Loader* in the class path.   
+e.g.   
+- [core module](https://github.com/Gmugra/net.cactusthorn.config/blob/main/core/src/main/resources/META-INF/services/net.cactusthorn.config.core.loader.Loader)
+- [tests module](https://github.com/Gmugra/net.cactusthorn.config/blob/main/tests/src/main/resources/META-INF/services/net.cactusthorn.config.core.loader.Loader)
+
 ### System properties and/or environment variables in sources URIs
 Syntax: {*name*}
 e.g.

core/src/main/java/net/cactusthorn/config/core/ConfigFactory.java

@@ -29,8 +29,10 @@
 import java.net.URI;
 import java.util.ArrayDeque;
 import java.util.Collections;
+import java.util.Iterator;
 import java.util.LinkedHashSet;
 import java.util.Map;
+import java.util.ServiceLoader;
 import java.util.concurrent.ConcurrentHashMap;
 import java.util.function.Function;
 import java.util.stream.Collectors;
@@ -40,13 +42,6 @@
 import net.cactusthorn.config.core.loader.LoadStrategy;
 import net.cactusthorn.config.core.loader.Loader;
 import net.cactusthorn.config.core.loader.Loaders;
-import net.cactusthorn.config.core.loader.standard.ClasspathJarManifestLoader;
-import net.cactusthorn.config.core.loader.standard.ClasspathPropertiesLoader;
-import net.cactusthorn.config.core.loader.standard.ClasspathXMLLoader;
-import net.cactusthorn.config.core.loader.standard.SystemEnvLoader;
-import net.cactusthorn.config.core.loader.standard.SystemPropertiesLoader;
-import net.cactusthorn.config.core.loader.standard.UrlPropertiesLoader;
-import net.cactusthorn.config.core.loader.standard.UrlXMLLoader;
 import net.cactusthorn.config.core.util.ConfigBuilder;
 
 public final class ConfigFactory {
@@ -75,13 +70,10 @@ public static final class Builder {
         private LoadStrategy loadStrategy = LoadStrategy.MERGE;
 
         private Builder() {
-            loaders.add(new ClasspathPropertiesLoader());
-            loaders.add(new SystemPropertiesLoader());
-            loaders.add(new SystemEnvLoader());
-            loaders.add(new UrlPropertiesLoader());
-            loaders.add(new ClasspathXMLLoader());
-            loaders.add(new UrlXMLLoader());
-            loaders.add(new ClasspathJarManifestLoader());
+            ServiceLoader<Loader> serviceLoader = ServiceLoader.load(Loader.class);
+            for (Iterator<Loader> it = serviceLoader.iterator(); it.hasNext();) {
+                loaders.add(it.next());
+            }
         }
 
         public Builder addLoader(Loader loader) {

core/src/main/resources/META-INF/services/net.cactusthorn.config.core.loader.Loader

@@ -0,0 +1,7 @@
+net.cactusthorn.config.core.loader.standard.ClasspathJarManifestLoader
+net.cactusthorn.config.core.loader.standard.ClasspathPropertiesLoader
+net.cactusthorn.config.core.loader.standard.ClasspathXMLLoader
+net.cactusthorn.config.core.loader.standard.SystemEnvLoader
+net.cactusthorn.config.core.loader.standard.SystemPropertiesLoader
+net.cactusthorn.config.core.loader.standard.UrlPropertiesLoader
+net.cactusthorn.config.core.loader.standard.UrlXMLLoader

tests/src/main/java/net/cactusthorn/config/tests/loader/SinglePropertyLoader.java

@@ -0,0 +1,39 @@
+/*
+* Copyright (C) 2021, Alexei Khatskevich
+*
+* Licensed under the BSD 3-Clause license.
+* You may obtain a copy of the License at
+*
+* https://github.com/Gmugra/net.cactusthorn.config/blob/main/LICENSE
+*
+* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+* DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+* SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+* CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+*/
+package net.cactusthorn.config.tests.loader;
+
+import java.net.URI;
+import java.util.HashMap;
+import java.util.Map;
+
+import net.cactusthorn.config.core.loader.Loader;
+
+public class SinglePropertyLoader implements Loader {
+
+    @Override public boolean accept(URI uri) {
+        return uri.toString().equals("single:property");
+    }
+
+    @Override public Map<String, String> load(URI uri, ClassLoader classLoader) {
+        Map<String, String> result = new HashMap<>();
+        result.put("key", "value");
+        return result;
+    }
+}

tests/src/main/resources/META-INF/services/net.cactusthorn.config.core.loader.Loader

@@ -0,0 +1 @@
+net.cactusthorn.config.tests.loader.SinglePropertyLoader

tests/src/test/java/net/cactusthorn/config/tests/loader/SinglePropertyLoaderTest.java

@@ -0,0 +1,56 @@
+/*
+* Copyright (C) 2021, Alexei Khatskevich
+*
+* Licensed under the BSD 3-Clause license.
+* You may obtain a copy of the License at
+*
+* https://github.com/Gmugra/net.cactusthorn.config/blob/main/LICENSE
+*
+* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+* DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+* SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+* CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+*/
+package net.cactusthorn.config.tests.loader;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+import java.net.URI;
+import java.util.Map;
+
+import org.junit.jupiter.api.Test;
+
+import net.cactusthorn.config.core.ConfigFactory;
+import net.cactusthorn.config.core.loader.ConfigHolder;
+import net.cactusthorn.config.core.loader.Loader;
+
+public class SinglePropertyLoaderTest {
+
+    private static final Loader LOADER = new SinglePropertyLoader();
+    private static final ClassLoader CL = SinglePropertyLoaderTest.class.getClassLoader();
+    private static final URI SPURI = URI.create("single:property");
+
+    @Test public void accept() {
+        assertTrue(LOADER.accept(SPURI));
+    }
+
+    @Test public void notAccept() {
+        assertFalse(LOADER.accept(URI.create("classpath://a.properties")));
+    }
+
+    @Test public void load() {
+        Map<String, String> values = LOADER.load(SPURI, CL);
+        assertEquals("value", values.get("key"));
+    }
+
+    @Test public void loadFactory() {
+        ConfigHolder holder = ConfigFactory.builder().addSource("single:property").build().configHolder();
+        assertEquals("value", holder.getString("key"));
+    }
+}