code: @Override
      public void sawOpcode(int seen) {
          try {
              stack.precomputation(this);
  
              if (seen == Const.INVOKEINTERFACE) {
                  KeyType type = isKeyAccessMethod(seen);
                  if (type != null) {
                      int numParms = SignatureUtils.getNumParameters(getSigConstantOperand());
                      if (stack.getStackDepth() >= numParms) {
                          OpcodeStack.Item item = stack.getStackItem(numParms - 1);
                          String parmName = (String) item.getConstant();
                          if (parmName != null) {
                              String upperParmName = parmName.toUpperCase(Locale.getDefault());
                              Map<String, Map<String, List<SourceInfo>>> typeMap = parmInfo.get(KeyType.PARAMETER);
                              Map<String, List<SourceInfo>> parmCaseInfo = typeMap.get(upperParmName);
                              if (parmCaseInfo == null) {
                                  parmCaseInfo = new HashMap<>();
                                  typeMap.put(upperParmName, parmCaseInfo);
                              }
  
                              List<SourceInfo> annotations = parmCaseInfo.get(parmName);
                              if (annotations == null) {
                                  annotations = new ArrayList<>();
                                  parmCaseInfo.put(parmName, annotations);
                              }
  
                              annotations.add(new SourceInfo(getClassName(), getMethodName(), getMethodSig(), getMethod().isStatic(),
                                      SourceLineAnnotation.fromVisitedInstruction(getClassContext(), this, getPC())));
                          }
                      }
                  }
              }
          } finally {
              stack.sawOpcode(this, seen);
          }
      }
docs: implements the visitor to look for calls to HttpServletRequest.getParameter and collect what the name of the key is.
  
  @param seen
  the opcode of the currently parsed instruction