Fix loading of the effective RecyclerFactoryConverter

log4j-layout-template-json-test/src/test/java/org/apache/logging/log4j/layout/template/json/resolver/MessageResolverTest.java

@@ -228,6 +228,8 @@ void test_MultiformatMessage() {
 
     private static final class TestMultiformatMessage implements MultiformatMessage {
 
+        private static final long serialVersionUID = 1L;
+
         @Override
         public String getFormattedMessage() {
             return "{\"foo\": \"bar\"}";

log4j-layout-template-json-test/src/test/java/org/apache/logging/log4j/layout/template/json/util/RecyclerFactoryConverterTest.java

@@ -0,0 +1,33 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to you 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.apache.logging.log4j.layout.template.json.util;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import org.apache.logging.log4j.layout.template.json.JsonTemplateLayoutDefaults;
+import org.junit.jupiter.api.Test;
+import org.junitpioneer.jupiter.SetSystemProperty;
+
+class RecyclerFactoryConverterTest {
+
+    @Test
+    @SetSystemProperty(key = "log4j.layout.jsonTemplate.recyclerFactory", value = RecyclerFactoryCustomConverter.NAME)
+    void custom_converter_should_be_effective() {
+        assertThat(JsonTemplateLayoutDefaults.getRecyclerFactory())
+                .isSameAs(RecyclerFactoryCustomConverter.RECYCLER_FACTORY);
+    }
+}

log4j-layout-template-json-test/src/test/java/org/apache/logging/log4j/layout/template/json/util/RecyclerFactoryCustomConverter.java

@@ -0,0 +1,63 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to you 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.apache.logging.log4j.layout.template.json.util;
+
+import java.util.function.Consumer;
+import java.util.function.Supplier;
+import org.apache.logging.log4j.core.config.plugins.Plugin;
+import org.apache.logging.log4j.core.config.plugins.convert.TypeConverter;
+import org.apache.logging.log4j.core.config.plugins.convert.TypeConverters;
+
+/**
+ * A custom {@link RecyclerFactory} type converter that always returns the same instance if the specification is {@value RecyclerFactoryCustomConverter#NAME}; otherwise, falls back to {@link RecyclerFactories#ofSpec(String) the default}.
+ */
+@SuppressWarnings("ComparableType")
+@Plugin(name = "RecyclerFactoryCustomConverter", category = TypeConverters.CATEGORY)
+public final class RecyclerFactoryCustomConverter
+        implements TypeConverter<RecyclerFactory>, Comparable<TypeConverter<RecyclerFactory>> {
+
+    static final String NAME = "魔法";
+
+    static final RecyclerFactory RECYCLER_FACTORY = new RecyclerFactory() {
+
+        @Override
+        public <V> Recycler<V> create(final Supplier<V> supplier, final Consumer<V> cleaner) {
+            return new Recycler<V>() {
+
+                @Override
+                public V acquire() {
+                    return supplier.get();
+                }
+
+                @Override
+                public void release(V value) {
+                    // Do nothing;
+                }
+            };
+        }
+    };
+
+    @Override
+    public int compareTo(TypeConverter<RecyclerFactory> typeConverter) {
+        return -1;
+    }
+
+    @Override
+    public RecyclerFactory convert(final String recyclerFactorySpec) {
+        return NAME.equals(recyclerFactorySpec) ? RECYCLER_FACTORY : RecyclerFactories.ofSpec(recyclerFactorySpec);
+    }
+}

log4j-layout-template-json/src/main/java/org/apache/logging/log4j/layout/template/json/JsonTemplateLayoutDefaults.java

@@ -22,7 +22,8 @@
 import java.nio.charset.StandardCharsets;
 import java.util.Locale;
 import java.util.TimeZone;
-import org.apache.logging.log4j.layout.template.json.util.RecyclerFactories;
+import org.apache.logging.log4j.core.config.plugins.convert.TypeConverter;
+import org.apache.logging.log4j.core.config.plugins.convert.TypeConverterRegistry;
 import org.apache.logging.log4j.layout.template.json.util.RecyclerFactory;
 import org.apache.logging.log4j.util.PropertiesUtil;
 
@@ -116,7 +117,34 @@ public static String getTruncatedStringSuffix() {
     }
 
     public static RecyclerFactory getRecyclerFactory() {
-        final String recyclerFactorySpec = PROPERTIES.getStringProperty("log4j.layout.jsonTemplate.recyclerFactory");
-        return RecyclerFactories.ofSpec(recyclerFactorySpec);
+
+        // Get the recycler factory specification
+        final String propertyName = "log4j.layout.jsonTemplate.recyclerFactory";
+        final String recyclerFactorySpec = PROPERTIES.getStringProperty(propertyName);
+
+        // Read the specification
+        @SuppressWarnings("unchecked")
+        final TypeConverter<RecyclerFactory> typeConverter = (TypeConverter<RecyclerFactory>)
+                TypeConverterRegistry.getInstance().findCompatibleConverter(RecyclerFactory.class);
+        final RecyclerFactory recyclerFactory;
+        try {
+            // Using `TypeConverter#convert()` instead of `TypeConverters.convert`.
+            // The latter doesn't pass the converter a null value, which is a valid input.
+            recyclerFactory = typeConverter.convert(recyclerFactorySpec);
+        } catch (final Exception error) {
+            final String message = String.format(
+                    "failed converting the recycler factory specified by the `%s` property: %s",
+                    propertyName, recyclerFactorySpec == null ? null : '`' + recyclerFactorySpec + '`');
+            throw new RuntimeException(message, error);
+        }
+
+        // Verify and return loaded recycler factory
+        if (recyclerFactory == null) {
+            final String message = String.format(
+                    "could not determine the recycler factory specified by the `%s` property: %s",
+                    propertyName, recyclerFactorySpec == null ? null : '`' + recyclerFactorySpec + '`');
+            throw new IllegalArgumentException(message);
+        }
+        return recyclerFactory;
     }
 }

log4j-layout-template-json/src/main/java/org/apache/logging/log4j/layout/template/json/util/RecyclerFactories.java

@@ -29,6 +29,10 @@
 import org.apache.logging.log4j.util.LoaderUtil;
 import org.jctools.queues.MpmcArrayQueue;
 
+/**
+ * @deprecated As of version {@code 2.25.0}, planned to be removed!
+ */
+@Deprecated
 public final class RecyclerFactories {
 
     private RecyclerFactories() {}

src/changelog/.2.x.x/3398_fix_JTL_RecyclerFactoryConverter.xml

@@ -0,0 +1,8 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<entry xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+       xmlns="https://logging.apache.org/xml/ns"
+       xsi:schemaLocation="https://logging.apache.org/xml/ns https://logging.apache.org/xml/ns/log4j-changelog-0.xsd"
+       type="fixed">
+    <issue id="3398" link="https://github.com/apache/logging-log4j2/pull/3398"/>
+    <description format="asciidoc">Fix loading of the effective `RecyclerFactoryConverter` in JSON Template Layout</description>
+</entry>