Optimize ClassNameReader.getClassName via direct ASM API

getClassName now calls ClassReader.getClassName() directly instead
of routing through the visitor-based getClassInfo. Previously, it
allocated a List and a ClassVisitor and decoded super_class and
every interface name only to discard all but the first element.

The method is on the hot path of every CGLIB proxy class definition,
so this change significantly lowers its per-call processing cost.

Signed-off-by: cookie-meringue <daehyeon3351@gmail.com>

Author: cookie-meringue

spring-core/src/jmh/java/org/springframework/cglib/core/ClassNameReaderBenchmark.java

@@ -0,0 +1,133 @@
+/*
+ * Copyright 2002-present the original author or authors.
+ *
+ * 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
+ *
+ *      https://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.springframework.cglib.core;
+
+import java.util.concurrent.TimeUnit;
+
+import org.openjdk.jmh.annotations.Benchmark;
+import org.openjdk.jmh.annotations.BenchmarkMode;
+import org.openjdk.jmh.annotations.Level;
+import org.openjdk.jmh.annotations.Measurement;
+import org.openjdk.jmh.annotations.Mode;
+import org.openjdk.jmh.annotations.OutputTimeUnit;
+import org.openjdk.jmh.annotations.Scope;
+import org.openjdk.jmh.annotations.Setup;
+import org.openjdk.jmh.annotations.State;
+import org.openjdk.jmh.annotations.Warmup;
+
+import org.springframework.asm.ClassReader;
+import org.springframework.cglib.proxy.Enhancer;
+import org.springframework.cglib.proxy.MethodInterceptor;
+
+/**
+ * Benchmarks for {@link ClassNameReader#getClassName(ClassReader)}.
+ * Comparing the legacy {@code getClassInfo(r)[0]} delegation against a direct {@code ClassReader.getClassName()} call.
+ *
+ * @author Daehyeon Kim
+ */
+public class ClassNameReaderBenchmark {
+
+	@BenchmarkMode(Mode.AverageTime)
+	@OutputTimeUnit(TimeUnit.NANOSECONDS)
+	@Warmup(iterations = 5, time = 2)
+	@Measurement(iterations = 5, time = 2)
+	public static class WithoutInterfaces {
+
+		@State(Scope.Benchmark)
+		public static class BenchmarkState {
+
+			public ClassReader classReader;
+
+			@Setup(Level.Trial)
+			public void setup() {
+				this.classReader = generateProxyReader(new Class<?>[0]);
+			}
+		}
+
+		@Benchmark
+		public String viaGetClassInfo(BenchmarkState state) {
+			return ClassNameReader.getClassInfo(state.classReader)[0];
+		}
+
+		@Benchmark
+		public String viaGetClassName(BenchmarkState state) {
+			return state.classReader.getClassName().replace('/', '.');
+		}
+	}
+
+	@BenchmarkMode(Mode.AverageTime)
+	@OutputTimeUnit(TimeUnit.NANOSECONDS)
+	@Warmup(iterations = 5, time = 2)
+	@Measurement(iterations = 5, time = 2)
+	public static class WithInterfaces {
+
+		@State(Scope.Benchmark)
+		public static class BenchmarkState {
+
+			public ClassReader classReader;
+
+			@Setup(Level.Trial)
+			public void setup() {
+				this.classReader = generateProxyReader(
+						new Class<?>[]{Cloneable.class, Comparable.class, Runnable.class}
+				);
+			}
+		}
+
+		@Benchmark
+		public String viaGetClassInfo(BenchmarkState state) {
+			return ClassNameReader.getClassInfo(state.classReader)[0];
+		}
+
+		@Benchmark
+		public String viaGetClassName(BenchmarkState state) {
+			return state.classReader.getClassName().replace('/', '.');
+		}
+	}
+
+	private static ClassReader generateProxyReader(Class<?>[] interfaces) {
+		CapturingGeneratorStrategy strategy = new CapturingGeneratorStrategy();
+		Enhancer enhancer = new Enhancer();
+		enhancer.setSuperclass(ProxyTarget.class);
+		enhancer.setCallbackType(MethodInterceptor.class);
+		enhancer.setUseCache(false);
+		enhancer.setInterfaces(interfaces);
+		enhancer.setStrategy(strategy);
+		enhancer.createClass();
+		return strategy.createClassReader();
+	}
+
+	public static class ProxyTarget {
+	}
+
+	private static class CapturingGeneratorStrategy implements GeneratorStrategy {
+
+		private static final GeneratorStrategy delegate = DefaultGeneratorStrategy.INSTANCE;
+
+		private byte[] captured;
+
+		@Override
+		public byte[] generate(ClassGenerator cg) throws Exception {
+			this.captured = delegate.generate(cg);
+			return this.captured;
+		}
+
+		private ClassReader createClassReader() {
+			return new ClassReader(this.captured);
+		}
+	}
+}

spring-core/src/main/java/org/springframework/cglib/core/ClassNameReader.java

@@ -34,9 +34,11 @@ private ClassNameReader() {
 	private static class EarlyExitException extends RuntimeException {
 	}
 
+	// SPRING PATCH BEGIN
 	public static String getClassName(ClassReader r) {
-		return getClassInfo(r)[0];
+		return r.getClassName().replace('/', '.');
 	}
+	// SPRING PATCH END
 
     public static String[] getClassInfo(ClassReader r) {
         final List<String> array = new ArrayList<>();