reduce memory allocations

java/debugger/impl/src/com/intellij/debugger/jdi/MethodBytecodeUtil.java

@@ -82,11 +82,14 @@ public class MethodBytecodeUtil {
   private static void visit(Method method, byte[] bytecodes, MethodVisitor methodVisitor, boolean withLineNumbers) {
     ReferenceType type = method.declaringType();
     try {
-      try (ByteArrayOutputStream bos = new ByteArrayOutputStream(); DataOutputStream dos = new DataOutputStream(bos)) {
+      byte[] constantPool = getConstantPool(type);
+      try (ByteArrayBuilderOutputStream bos = new ByteArrayBuilderOutputStream(constantPool.length + 24);
+           DataOutputStream dos = new DataOutputStream(bos)) {
+
         dos.writeInt(0xCAFEBABE); // magic
         dos.writeInt(Opcodes.V1_8); // version
         dos.writeShort(type.constantPoolCount()); // constant_pool_count
-        dos.write(getConstantPool(type)); // constant_pool
+        dos.write(constantPool); // constant_pool
         dos.writeShort(0); //             access_flags;
         dos.writeShort(0); //             this_class;
         dos.writeShort(0); //             super_class;
@@ -95,7 +98,7 @@ public class MethodBytecodeUtil {
         dos.writeShort(0); //             methods_count;
         dos.writeShort(0); //             attributes_count;
 
-        ClassReader reader = new ClassReader(bos.toByteArray());
+        ClassReader reader = new ClassReader(bos.getBuffer());
         ClassWriter writer = new ClassWriter(reader, 0);
 
         String superName = null;
@@ -291,4 +294,15 @@ public class MethodBytecodeUtil {
     }
     return methodRef.get();
   }
+
+  private static class ByteArrayBuilderOutputStream extends ByteArrayOutputStream {
+    public ByteArrayBuilderOutputStream(int size) {
+      super(size);
+    }
+
+    byte[] getBuffer() {
+      assert buf.length == count : "Buffer is not fully filled";
+      return buf;
+    }
+  }
 }