Add wrappers for factories and register them in META-INF/services.

A side-effect of this work is the addition of `proj4j(…)` methods
as the reverse of `geoapi(…)` methods.

Author: desruisseaux

Diff for: geoapi/pom.xml

@@ -64,6 +64,7 @@
                     <links>
                         <link>https://www.geoapi.org/3.0/javadoc/</link>
                     </links>
+                    <excludePackageNames>org.locationtech.proj4j.geoapi.spi</excludePackageNames>
                 </configuration>
             </plugin>
         </plugins>

Diff for: geoapi/src/main/java/org/locationtech/proj4j/geoapi/AuthorityFactoryWrapper.java

@@ -0,0 +1,196 @@
+/*
+ * Copyright 2025, PROJ4J contributors
+ *
+ * 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 org.locationtech.proj4j.geoapi;
+
+import java.io.Serializable;
+import java.util.Set;
+import org.locationtech.proj4j.CRSFactory;
+import org.locationtech.proj4j.Proj4jException;
+import org.locationtech.proj4j.UnknownAuthorityCodeException;
+import org.opengis.metadata.citation.Citation;
+import org.opengis.referencing.IdentifiedObject;
+import org.opengis.referencing.NoSuchAuthorityCodeException;
+import org.opengis.referencing.crs.*;
+import org.opengis.util.FactoryException;
+import org.opengis.util.InternationalString;
+
+
+/**
+ * Wraps a PROJ4J implementation behind the equivalent GeoAPI interface.
+ *
+ * @author Martin Desruisseaux (Geomatys)
+ */
+@SuppressWarnings("serial")
+final class AuthorityFactoryWrapper extends Wrapper implements CRSAuthorityFactory, Serializable {
+    /**
+     * The wrapped PROJ4 implementation.
+     */
+    final CRSFactory impl;
+
+    /**
+     * Creates a new wrapper for the given PROJ4J implementation.
+     */
+    private AuthorityFactoryWrapper(final CRSFactory impl) {
+        this.impl = impl;
+    }
+
+    /**
+     * Wraps the given implementation.
+     *
+     * @param  impl the implementation to wrap, or {@code null}
+     * @return the wrapper, or {@code null} if the given implementation was null
+     */
+    static AuthorityFactoryWrapper wrap(final CRSFactory impl) {
+        return (impl != null) ? new AuthorityFactoryWrapper(impl) : null;
+    }
+
+    /**
+     * {@return the PROJ4J backing implementation}.
+     */
+    @Override
+    Object implementation() {
+        return impl;
+    }
+
+    /**
+     * {@return the factory name}.
+     */
+    @Override
+    public String getCode() {
+        return "PROJ4J";
+    }
+
+    /**
+     * {@return an identification of the softwware that provides the CRS definitions}.
+     * This is not the authority (EPSG, ESRI, <i>etc</i>).
+     */
+    @Override
+    public Citation getVendor() {
+        return SimpleCitation.PROJ4J;
+    }
+
+    /**
+     * Returns the name of the CRS for the given code. Usually, this method is for fetching the name without the
+     * cost of creating the full <abbr>CRS</abbr>. However, this implementation is inefficient in this regard.
+     */
+    @Override
+    public InternationalString getDescriptionText(String code) throws FactoryException {
+        return LocalizedString.wrap(createCoordinateReferenceSystem(code).getName().getCode());
+    }
+
+    /**
+     * Generic method defined in parent interface.
+     */
+    @Override
+    public IdentifiedObject createObject(String code) throws FactoryException {
+        return createCoordinateReferenceSystem(code);
+    }
+
+    /**
+     * Creates a CRS from a code in the {@code "AUTHORITY:CODE"} syntax.
+     * If the authority is unspecified, then {@code "EPSG"} is assumed.
+     *
+     * @param  code  the authority (optional) and code of the CRS to create
+     * @return the CRS for the given code
+     * @throws FactoryException if the CRS cannot be created
+     */
+    @Override
+    public CoordinateReferenceSystem createCoordinateReferenceSystem(String code) throws FactoryException {
+        try {
+            return AbstractCRS.wrap(impl.createFromName(code), false);
+        } catch (UnknownAuthorityCodeException e) {
+            final int s = code.indexOf(':');
+            throw (NoSuchAuthorityCodeException) new NoSuchAuthorityCodeException(
+                    "No registered CRS for \"" + code + "\".",
+                    (s >= 0) ? code.substring(0, s).trim() : null,
+                    (s >= 0) ? code.substring(s).trim() : code, code).initCause(e);
+        } catch (Proj4jException e) {
+            throw new FactoryException("Cannot create a CRS for \"" + code + "\".", e);
+        }
+    }
+
+    /**
+     * Creates the CRS from the specified code and cast to a geographic CRS.
+     *
+     * @param  code  the authority (optional) and code of the CRS to create
+     * @return the CRS for the given code
+     * @throws FactoryException if the CRS cannot be created or is not geographic
+     */
+    @Override
+    public GeographicCRS createGeographicCRS(String code) throws FactoryException {
+        try {
+            return (GeographicCRS) createCoordinateReferenceSystem(code);
+        } catch (ClassCastException e) {
+            throw new FactoryException("The CRS identified by \"" + code + "\" is not geographic.", e);
+        }
+    }
+
+    /**
+     * Creates the CRS from the specified code and cast to a projected CRS.
+     *
+     * @param  code  the authority (optional) and code of the CRS to create
+     * @return the CRS for the given code
+     * @throws FactoryException if the CRS cannot be created or is not projected
+     */
+    @Override
+    public ProjectedCRS createProjectedCRS(String code) throws FactoryException {
+        try {
+            return (ProjectedCRS) createCoordinateReferenceSystem(code);
+        } catch (ClassCastException e) {
+            throw new FactoryException("The CRS identified by \"" + code + "\" is not projected.", e);
+        }
+    }
+
+    @Override
+    public GeocentricCRS createGeocentricCRS(String code) throws NoSuchAuthorityCodeException, FactoryException {
+        throw new FactoryException("Not implemented.");
+    }
+
+    @Override
+    public VerticalCRS createVerticalCRS(String code) throws NoSuchAuthorityCodeException, FactoryException {
+        throw new FactoryException("Not implemented.");
+    }
+
+    @Override
+    public TemporalCRS createTemporalCRS(String code) throws NoSuchAuthorityCodeException, FactoryException {
+        throw new FactoryException("Not implemented.");
+    }
+
+    @Override
+    public EngineeringCRS createEngineeringCRS(String code) throws NoSuchAuthorityCodeException, FactoryException {
+        throw new FactoryException("Not implemented.");
+    }
+
+    @Override
+    public ImageCRS createImageCRS(String code) throws NoSuchAuthorityCodeException, FactoryException {
+        throw new FactoryException("Not implemented.");
+    }
+
+    @Override
+    public DerivedCRS createDerivedCRS(String code) throws NoSuchAuthorityCodeException, FactoryException {
+        throw new FactoryException("Not implemented.");
+    }
+
+    @Override
+    public CompoundCRS createCompoundCRS(String code) throws FactoryException {
+        throw new FactoryException("Not implemented.");
+    }
+
+    @Override
+    public Set<String> getAuthorityCodes(Class<? extends IdentifiedObject> type) throws FactoryException {
+        throw new FactoryException("Not implemented.");
+    }
+}

Diff for: geoapi/src/main/java/org/locationtech/proj4j/geoapi/DatumWrapper.java

@@ -36,7 +36,7 @@ final class DatumWrapper extends Wrapper implements GeodeticDatum, Serializable
     /**
      * The wrapped PROJ4 implementation.
      */
-    private final org.locationtech.proj4j.datum.Datum impl;
+    final org.locationtech.proj4j.datum.Datum impl;
 
     /**
      * The prime meridian, or {@code null} for Greenwich

Diff for: geoapi/src/main/java/org/locationtech/proj4j/geoapi/EllipsoidWrapper.java

@@ -33,7 +33,7 @@ final class EllipsoidWrapper extends Wrapper implements Ellipsoid, Serializable
     /**
      * The wrapped PROJ4 implementation.
      */
-    private final org.locationtech.proj4j.datum.Ellipsoid impl;
+    final org.locationtech.proj4j.datum.Ellipsoid impl;
 
     /**
      * Creates a new wrapper for the given PROJ4J implementation.