Create UserExcludedClassLoadersConfigurer; add documentation for otel…

….javaagent.exclude-classLoaders property

docs/advanced-configuration-options.md

@@ -18,6 +18,14 @@ which could have unknown side-effects.
 | ------------------------------ | ------------------------------ | -------------------------------------------------------------------------------------------------- |
 | otel.javaagent.exclude-classes | OTEL_JAVAAGENT_EXCLUDE_CLASSES | Suppresses all instrumentation for specific classes, format is "my.package.MyClass,my.package2.\*" |
 
+## Excluding specific classes loaders
+
+This can be used to Ignore the class loader specified and exclude it from being instrumented.
+
+| System property                | Environment variable                | Purpose                                                                         |
+| ------------------------------ |-------------------------------------|---------------------------------------------------------------------------------|
+| otel.javaagent.exclude-classLoaders | OTEL_JAVAAGENT_EXCLUDE_CLASSLOADERS | Ignore the specified class loaders, format is "my.package.MyClass,my.package2." |
+
 ## Running application with security manager
 
 This option can be used to let agent run with all privileges without being affected by security policy restricting some operations.

javaagent-tooling/src/main/java/io/opentelemetry/javaagent/tooling/ignore/UserExcludedClassLoadersConfigurer.java

@@ -0,0 +1,34 @@
+/*
+ * Copyright The OpenTelemetry Authors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package io.opentelemetry.javaagent.tooling.ignore;
+
+import static java.util.Collections.emptyList;
+
+import com.google.auto.service.AutoService;
+import io.opentelemetry.javaagent.extension.ignore.IgnoredTypesBuilder;
+import io.opentelemetry.javaagent.extension.ignore.IgnoredTypesConfigurer;
+import io.opentelemetry.sdk.autoconfigure.spi.ConfigProperties;
+import java.util.List;
+
+@AutoService(IgnoredTypesConfigurer.class)
+class UserExcludedClassLoadersConfigurer implements IgnoredTypesConfigurer {
+
+  // visible for tests
+  static final String EXCLUDED_CLASSLOADERS_CONFIG = "otel.javaagent.exclude-classLoaders";
+
+  @Override
+  public void configure(IgnoredTypesBuilder builder, ConfigProperties config) {
+    List<String> excludedClassLoaders = config.getList(EXCLUDED_CLASSLOADERS_CONFIG, emptyList());
+    for (String excludedClassLoader : excludedClassLoaders) {
+      excludedClassLoader = excludedClassLoader.trim();
+      // remove the trailing *
+      if (excludedClassLoader.endsWith("*")) {
+        excludedClassLoader = excludedClassLoader.substring(0, excludedClassLoader.length() - 1);
+      }
+      builder.ignoreClassLoader(excludedClassLoader);
+    }
+  }
+}