De-duplicate a shortlist of very common strings found in class-files

Author: mcculls

class-match/src/main/java/datadog/instrument/classmatch/ClassFile.java

@@ -23,10 +23,17 @@
  */
 public final class ClassFile {
 
+  static final String JAVA_LANG_OBJECT = "java/lang/Object";
+  static final String STATIC_INITIALIZER = "<clinit>";
+  static final String CONSTRUCTOR = "<init>";
+  static final String SIMPLE_CALL = "()V";
+
   private static final String[] NO_INTERFACES = {};
   private static final FieldOutline[] NO_FIELDS = {};
   private static final MethodOutline[] NO_METHODS = {};
   private static final String[] NO_ANNOTATIONS = {};
+
+  private static final int ACC_INTERFACE = 0x0200;
   private static final int ACC_MODULE = 0x8000;
 
   // attribute header for annotations that are visible at runtime
@@ -171,7 +178,17 @@ private static ClassHeader parse(byte[] bytecode, boolean onlyHeader) {
     String className = utf(bytecode, cp[cp[u2(bytecode, cursor)]]);
     cursor += 2;
 
-    String superName = access != ACC_MODULE ? utf(bytecode, cp[cp[u2(bytecode, cursor)]]) : null;
+    String superName;
+    if ((access & ACC_INTERFACE) != 0) {
+      superName = JAVA_LANG_OBJECT;
+    } else if (access != ACC_MODULE) {
+      superName = utf(bytecode, cp[cp[u2(bytecode, cursor)]]);
+      if (JAVA_LANG_OBJECT.equals(superName)) {
+        superName = JAVA_LANG_OBJECT;
+      }
+    } else {
+      superName = null;
+    }
     cursor += 2;
 
     // optional list of implemented/extended interfaces
@@ -231,8 +248,14 @@ private static ClassHeader parse(byte[] bytecode, boolean onlyHeader) {
         int methodAccess = u2(bytecode, cursor);
         cursor += 2;
         String methodName = utf(bytecode, cp[u2(bytecode, cursor)]);
+        if (CONSTRUCTOR.equals(methodName)) {
+          methodName = CONSTRUCTOR;
+        }
         cursor += 2;
         String descriptor = utf(bytecode, cp[u2(bytecode, cursor)]);
+        if (SIMPLE_CALL.equals(descriptor)) {
+          descriptor = SIMPLE_CALL;
+        }
         cursor += 2;
         String[] annotations = NO_ANNOTATIONS;
         Map<UtfKey, String> ofInterest = annotationsOfInterest;

class-match/src/main/java/datadog/instrument/classmatch/MethodMatcher.java

@@ -6,6 +6,8 @@
 
 package datadog.instrument.classmatch;
 
+import static datadog.instrument.classmatch.ClassFile.CONSTRUCTOR;
+import static datadog.instrument.classmatch.ClassFile.STATIC_INITIALIZER;
 import static datadog.instrument.classmatch.InternalMatchers.ALL_METHODS;
 import static datadog.instrument.classmatch.InternalMatchers.declaresAnnotation;
 import static datadog.instrument.classmatch.InternalMatchers.declaresAnnotationOneOf;
@@ -58,7 +60,7 @@ static MethodMatcher method(Predicate<String> nameMatcher) {
    * @return matcher of constructor methods
    */
   static MethodMatcher constructor() {
-    return m -> "<init>".equals(m.methodName);
+    return m -> CONSTRUCTOR.equals(m.methodName);
   }
 
   /**
@@ -67,7 +69,7 @@ static MethodMatcher constructor() {
    * @return matcher of static-initializer methods
    */
   static MethodMatcher staticInitializer() {
-    return m -> "<clinit>".equals(m.methodName);
+    return m -> STATIC_INITIALIZER.equals(m.methodName);
   }
 
   /**