vy commented on code in PR #2887:
URL: https://github.com/apache/logging-log4j2/pull/2887#discussion_r1731690092
##########
src/site/antora/modules/ROOT/pages/manual/plugins.adoc:
##########
@@ -281,3 +281,48 @@ See `@PluginElement("EventTemplateAdditionalField")` usage
in {project-github-ur
link:../javadoc/log4j-core/org/apache/logging/log4j/core/config/plugins/util/PluginUtil.html[`PluginUtil`],
which is a convenient wrapper around <<#plugin-discovery,`PluginManager`>>, to
discover and load plugins.
See
{project-github-url}/log4j-layout-template-json/src/main/java/org/apache/logging/log4j/layout/template/json/resolver/TemplateResolverFactories.java[`TemplateResolverFactories.java`]
for example usages.
+
+[#plugin-merge]
+== Merging plugin descriptors
+
+The plugin descriptor is located in a JAR file at the following fixed location:
+----
+META-INF/org/apache/logging/log4j/core/config/plugins/Log4j2Plugins.dat
+----
+
+Some deployment techniques like
+https://softwareengineering.stackexchange.com/questions/297276/what-is-a-shaded-java-dependency[shading]
+require multiple plugin descriptors to be merged into one.
+This can be done in multiple ways:
+
+* By using a resource transformer specialized in `Log4j2Plugins.dat` files.
+We are aware of the existence of the following resource transformers for
different Java build tools:
+
+https://maven.apache.org/plugins/maven-shade-plugin/[Maven Shade Plugin]:::
+You can use the
+https://logging.staged.apache.org/log4j/transform/log4j-transform-maven-shade-plugin-extensions.html#log4j-plugin-cache-transformer[Log4j
Plugin Descriptor Transformer].
+
+https://gradleup.com/shadow/[Gradle Shadow Plugin]:::
+You can use the
+https://github.com/GradleUp/shadow/blob/main/src/main/groovy/com/github/jengelman/gradle/plugins/shadow/transformers/Log4j2PluginsCacheFileTransformer.groovy[`Log4j2PluginsCacheFileTransformer`].
+
+* Since version `2.24.0` you can any resource transformer capable of
concatenating files using `\n` as separator.
Review Comment:
```suggestion
* Since version `2.24.0`, you can employ any resource transformer capable of
concatenating files using `\n` as separator.
```
##########
src/site/antora/modules/ROOT/pages/manual/plugins.adoc:
##########
@@ -281,3 +281,48 @@ See `@PluginElement("EventTemplateAdditionalField")` usage
in {project-github-ur
link:../javadoc/log4j-core/org/apache/logging/log4j/core/config/plugins/util/PluginUtil.html[`PluginUtil`],
which is a convenient wrapper around <<#plugin-discovery,`PluginManager`>>, to
discover and load plugins.
See
{project-github-url}/log4j-layout-template-json/src/main/java/org/apache/logging/log4j/layout/template/json/resolver/TemplateResolverFactories.java[`TemplateResolverFactories.java`]
for example usages.
+
+[#plugin-merge]
+== Merging plugin descriptors
+
+The plugin descriptor is located in a JAR file at the following fixed location:
+----
Review Comment:
```suggestion
[source]
----
```
##########
log4j-core-test/src/test/java/org/apache/logging/log4j/core/config/plugins/processor/PluginCacheTest.java:
##########
@@ -48,9 +42,51 @@ public void
testOutputIsReproducibleWhenInputOrderingChanges() throws IOExceptio
assertArrayEquals(cacheData(cacheA), cacheData(cacheB));
}
- private void createCategory(final PluginCache cache, final String
categoryName, final List<String> entryNames) {
+ @Test
+ void testDeserialize() throws IOException {
+ final PluginCache expected = createSampleCache();
+
+ final Map<String, Map<String, PluginEntry>> actual = new TreeMap<>();
+ PluginCache.loadInputStream(new
ByteArrayInputStream(cacheData(expected)), actual);
+
+ assertThat(actual).as("Deserialized plugin
cache").isEqualTo(expected.getAllCategories());
+ }
+
+ @Test
+ void testConcatenationOfCaches() throws IOException {
+ final ByteArrayOutputStream output = new ByteArrayOutputStream();
+ boolean first = true;
+ for (final String categoryName : Arrays.asList("one", "two")) {
+ final PluginCache cache = new PluginCache();
+ createCategory(cache, categoryName, Arrays.asList("alpha",
"bravo", "charlie"));
+ cache.writeCache(output);
+ if (first) {
+ output.write('\n');
+ first = false;
+ }
+ }
+
+ final Map<String, Map<String, PluginEntry>> actual = new TreeMap<>();
+ PluginCache.loadInputStream(new
ByteArrayInputStream(output.toByteArray()), actual);
+
+ assertThat(actual)
+ .as("Deserialized plugin cache")
+ .isEqualTo(createSampleCache().getAllCategories());
Review Comment:
_Nit:_ I'd prefer `createSampleCache()` accept categories and entries,
instead of assuming hardcoded values will be identical in multiple places.
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