simplify the provider lookup, add logging

Signed-off-by: Lukas Jungmann <lukas.jungmann@oracle.com>

api/src/main/java/jakarta/json/spi/JsonProvider.java

diff --git a/api/src/main/java/jakarta/json/spi/JsonProvider.java b/api/src/main/java/jakarta/json/spi/JsonProvider.java
index 13f89db..02ca904 100644
--- a/api/src/main/java/jakarta/json/spi/JsonProvider.java
+++ b/api/src/main/java/jakarta/json/spi/JsonProvider.java
@@ -23,11 +23,15 @@
 import java.lang.reflect.Method;
 import java.math.BigDecimal;
 import java.math.BigInteger;
+import java.security.AccessController;
+import java.security.PrivilegedAction;
 import java.util.Collection;
 import java.util.Iterator;
 import java.util.Map;
 import java.util.Optional;
 import java.util.ServiceLoader;
+import java.util.logging.Level;
+import java.util.logging.Logger;
 
 import jakarta.json.JsonArray;
 import jakarta.json.JsonArrayBuilder;
@@ -74,6 +78,9 @@
     private static final String DEFAULT_PROVIDER
             = "org.eclipse.parsson.JsonProviderImpl";
 
+    /** A logger */
+    private static final Logger LOG = Logger.getLogger(JsonProvider.class.getName());
+
     /**
      * Default constructor.
      */
@@ -100,26 +107,55 @@
      * @return a JSON provider
      */
     public static JsonProvider provider() {
-        if (LazyFactoryLoader.JSON_PROVIDER != null) {
-            return newInstance(LazyFactoryLoader.JSON_PROVIDER);
+        LOG.log(Level.FINE, "Checking system property {0}", JSONP_PROVIDER_FACTORY);
+        final String factoryClassName = System.getSecurityManager() != null
+                ? AccessController.doPrivileged((PrivilegedAction<String>) () -> System.getProperty(JSONP_PROVIDER_FACTORY))
+                : System.getProperty(JSONP_PROVIDER_FACTORY);
+        if (factoryClassName != null) {
+            JsonProvider provider = newInstance(factoryClassName);
+            LOG.log(Level.FINE, "System property used; returning object [{0}]",
+                    provider.getClass().getName());
+            return provider;
         }
+
+        LOG.log(Level.FINE, "Checking ServiceLoader");
         ServiceLoader<JsonProvider> loader = ServiceLoader.load(JsonProvider.class);
         Iterator<JsonProvider> it = loader.iterator();
         if (it.hasNext()) {
-            return it.next();
+            JsonProvider provider = it.next();
+            LOG.log(Level.FINE, "ServiceLoader loading Facility used; returning object [{0}]",
+                    provider.getClass().getName());
+            return provider;
         }
 
         // handling OSGi (specific default)
         if (isOsgi()) {
-            JsonProvider result = lookupUsingOSGiServiceLoader(JsonProvider.class);
-            if (result != null) {
-                return result;
+            LOG.log(Level.FINE, "Checking OSGi");
+            JsonProvider provider = lookupUsingOSGiServiceLoader(JsonProvider.class);
+            if (provider != null) {
+                LOG.log(Level.FINE, "OSGi loading facility used; returning object [{0}].",
+                        provider.getClass().getName());
+                return provider;
             }
         }
 
+        // else no provider found
+        LOG.fine("Trying to create the platform default provider");
+        return newInstance(DEFAULT_PROVIDER);
+    }
+
+    /**
+     * Creates a new instance from the specified class
+     * @param className class to instantiate
+     * @return the JsonProvider instance
+     * @throws IllegalArgumentException for reflection issues
+     */
+    private static JsonProvider newInstance(String className) {
         try {
-            Class<?> clazz = Class.forName(DEFAULT_PROVIDER);
-            return (JsonProvider) clazz.getConstructor().newInstance();
+            checkPackageAccess(className);
+            @SuppressWarnings({"unchecked"})
+            Class<JsonProvider> clazz = (Class<JsonProvider>) Class.forName(className);
+            return clazz.getConstructor().newInstance();
         } catch (ClassNotFoundException x) {
             throw new JsonException(
                     "Provider " + DEFAULT_PROVIDER + " not found", x);
@@ -131,21 +167,6 @@
     }
 
     /**
-     * Creates a new instance from the specified class
-     * @param clazz class to instance
-     * @return the JsonProvider instance
-     * @throws IllegalArgumentException for reflection issues
-     */
-    private static JsonProvider newInstance(Class<? extends JsonProvider> clazz) {
-        checkPackageAccess(clazz.getName());
-        try {
-            return clazz.getConstructor().newInstance();
-        } catch (ReflectiveOperationException e) {
-            throw new IllegalArgumentException("Unable to create " + clazz.getName(), e);
-        }
-    }
-
-    /**
      * Make sure that the current thread has an access to the package of the given name.
      * @param className The class name to check.
      */
@@ -617,37 +638,10 @@
             @SuppressWarnings({"unchecked"})
             Iterator<? extends T> iter = ((Iterable<? extends T>) m.invoke(null, (Object[]) args)).iterator();
             return iter.hasNext() ? iter.next() : null;
-        } catch (Exception ignored) {
-            // log and continue
+        } catch (Exception ex) {
+            LOG.log(Level.FINE, "Unable to find from OSGi: [" + serviceClass.getName() + "]", ex);
             return null;
         }
     }
 
-    /**
-     * Lazy loads the class specified in System property with the key JSONP_PROVIDER_FACTORY.
-     * If no property is set, the value of {@link #JSON_PROVIDER} will be null.
-     * In case of errors an IllegalStateException is thrown.
-     *
-     */
-    @SuppressWarnings("unchecked")
-    private static class LazyFactoryLoader {
-
-        /**
-         * JSON provider class
-         */
-        private static final Class<? extends JsonProvider> JSON_PROVIDER;
-
-        static {
-            String className = System.getProperty(JSONP_PROVIDER_FACTORY);
-            if (className != null) {
-                try {
-                    JSON_PROVIDER = (Class<? extends JsonProvider>) Class.forName(className);
-                } catch (ReflectiveOperationException e) {
-                    throw new IllegalStateException("Unable to create " + className, e);
-                }
-            } else {
-                JSON_PROVIDER = null;
-            }
-        }
-    }
 }

api/src/main/java/module-info.java

diff --git a/api/src/main/java/module-info.java b/api/src/main/java/module-info.java
index 12cd6ba..4ff532f 100644
--- a/api/src/main/java/module-info.java
+++ b/api/src/main/java/module-info.java
@@ -18,6 +18,7 @@
  * Jakarta JSON Processing API.
  */
 module jakarta.json {
+    requires java.logging;
     exports jakarta.json;
     exports jakarta.json.spi;
     exports jakarta.json.stream;