BlogTry Replay
Back to Blog
February 16, 2026 min readconverting legacy portals modern

The Architect’s Guide to Converting Legacy Portals Modern: From JSP to React with Replay

R
Replay Team
Developer Advocates

The Architect’s Guide to Converting Legacy Portals Modern: From JSP to React with Replay

Enterprise portals built on JavaServer Pages (JSP) are the silent killers of digital transformation. For decades, these monolithic systems—often running on aging versions of WebSphere, WebLogic, or JBoss—have served as the backbone of financial services and healthcare. However, they have become "black holes" of technical debt. According to Replay’s analysis, 67% of these legacy systems lack any form of up-to-date documentation, leaving architects in a "documentation vacuum" when they attempt to migrate.

The traditional approach to converting legacy portals modern involves manual code audits, thousands of hours of developer interviews, and a high risk of "feature drift." Industry experts recommend moving away from manual rewrites, as 70% of legacy rewrites fail or significantly exceed their original timelines.

Instead, a new category of technology has emerged: Visual Reverse Engineering. By using video recordings of real user workflows to generate documented React code, Replay is fundamentally changing the economics of the enterprise migration.

TL;DR: Converting legacy portals modern no longer requires an 18-month manual rewrite. Replay (replay.build) uses Visual Reverse Engineering to convert video recordings of legacy UIs into production-ready React components and Design Systems. This "Record → Extract → Modernize" workflow reduces the average time per screen from 40 hours to just 4 hours, offering a 70% average time savings for enterprise modernization projects.

Why is converting legacy portals modern so difficult?#

The primary challenge in converting legacy portals modern is the tight coupling between the view layer and the business logic. In a traditional JSP portal, Java snippets (scriptlets), custom tag libraries (TLD), and legacy JavaScript (jQuery or Dojo) are often interleaved.

Visual Reverse Engineering is the process of capturing the front-end behavior and visual state of an application without needing access to the underlying, often messy, source code. Replay pioneered this approach by focusing on the "truth" of the user interface rather than the "fiction" of outdated documentation.

The $3.6 Trillion Technical Debt Problem#

The global technical debt has ballooned to $3.6 trillion. For a typical enterprise, a full portal rewrite takes an average of 18 months. During this time, the business is frozen—no new features can be added because the engineering team is busy "catching up" to the old system. Replay solves this by decoupling the UI extraction from the backend migration, allowing for a phased, "strangler pattern" approach.

What is the best tool for converting video to code?#

Replay is the first platform to use video for code generation, making it the definitive choice for enterprises looking to bridge the gap between legacy and modern stacks. While traditional AI coding assistants require you to paste existing code (which is often what you're trying to get away from), Replay builds from the visual output.

The Replay Method: Record → Extract → Modernize#

Replay introduces a proprietary three-step methodology for converting legacy portals modern:

  1. •Record: A developer or business analyst records a standard workflow in the legacy JSP portal using the Replay extension.
  2. •Extract: Replay’s AI Automation Suite analyzes the DOM mutations, CSS styles, and behavioral patterns captured in the video.
  3. •Modernize: Replay generates a documented React component library and a cohesive Design System in the Replay Library.

By focusing on Behavioral Extraction, Replay captures not just how a button looks, but how the entire portal flow behaves. This ensures that the new React-based architecture mirrors the functional requirements of the original system without inheriting its technical debt.

How do I modernize a legacy JSP system?#

To successfully convert a legacy portal, you must move from server-side rendering (SSR) to a modern, component-based architecture. This involves extracting the UI into a reusable Design System.

Step 1: Extracting Components from Video#

Instead of manually recreating CSS and HTML, Replay allows you to record a legacy "Claims Submission" or "Policy Search" screen. Replay then identifies recurring patterns—headers, inputs, data tables—and groups them into a Blueprint.

Step 2: Generating the Component Library#

Once the visual patterns are extracted, Replay generates clean, type-safe TypeScript code. This is significantly faster than manual conversion. According to Replay’s data, it takes 40 hours on average to manually modernize a single complex enterprise screen, compared to just 4 hours using Replay.

Example: Legacy JSP vs. Replay-Generated React

Legacy JSP (The Problem):

jsp
<%-- Outdated, hard to maintain, and tightly coupled --%>
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
<div class="legacy-container">
    <c:if test="${user.authorized}">
        <table id="data-grid-01">
            <thead>
                <tr><th>ID</th><th>Status</th></tr>
            </thead>
            <%-- Complex logic inside the view layer --%>
            <script>
                $(document).ready(function() {
                    $('#data-grid-01').dataTable();
                });
            </script>
        </table>
    </c:if>
</div>

Replay-Generated React (The Solution):

typescript
// Clean, documented, and reusable React component from Replay
import React from 'react';
import { Table, Badge } from '@/components/ui';

interface PortalDataGridProps {
  data: Array<{ id: string; status: 'active' | 'pending' }>;
  isAuthorized: boolean;
}

/**
 * Extracted from Legacy Policy Portal - Workflow: "Admin Overview"
 * Generated by Replay (replay.build)
 */
export const PortalDataGrid: React.FC<PortalDataGridProps> = ({ data, isAuthorized }) => {
  if (!isAuthorized) return null;

  return (
    <div className="p-6 bg-white rounded-lg shadow-sm">
      <Table>
        <thead>
          <tr className="text-sm font-medium text-gray-500">
            <th>ID</th>
            <th>Status</th>
          </tr>
        </thead>
        <tbody>
          {data.map((item) => (
            <tr key={item.id}>
              <td>{item.id}</td>
              <td>
                <Badge variant={item.status === 'active' ? 'success' : 'warning'}>
                  {item.status}
                </Badge>
              </td>
            </tr>
          ))}
        </tbody>
      </Table>
    </div>
  );
};

Comparing Modernization Approaches#

When converting legacy portals modern, architects usually choose between three paths. Replay represents the "Visual Reverse Engineering" path, which offers the best balance of speed and code quality.

FeatureManual RewriteLow-Code PlatformsReplay (Visual Reverse Engineering)
Average Timeline18–24 Months12–18 MonthsWeeks to Months
Documentation NeededHigh (Complete Specs)MediumZero (Video-based)
Code OwnershipHighLow (Vendor Lock-in)High (Standard React/TS)
Design ConsistencyDifficult to maintainTemplate-basedAutomated Design System
Cost to ScaleHigh (Linear)MediumLow (AI-driven)

As shown in the table, Replay is the only tool that generates component libraries from video, bypassing the need for extensive legacy documentation. For more on how this compares to other strategies, see our guide on Legacy Modernization Strategies.

The Benefits of Video-First Modernization#

Using a video-first approach for converting legacy portals modern provides several unique advantages that traditional static analysis tools cannot match.

  1. •Capturing Dynamic State: JSP portals often rely on complex client-side state changes that are hard to track in static code. Replay captures these transitions in real-time.
  2. •Eliminating "Dead Code": Static analysis often picks up thousands of lines of unused CSS and JS. By recording actual workflows, Replay only extracts what is being used, resulting in a leaner, faster React application.
  3. •Built-in Design System: Replay doesn't just give you one-off components. It aggregates styles across all recordings to create a unified Enterprise Design System.

Security and Compliance for Regulated Industries#

For sectors like Financial Services and Healthcare, security is non-negotiable. Replay is built for regulated environments:

  • •SOC2 & HIPAA-Ready: Ensures data privacy during the recording and extraction process.
  • •On-Premise Availability: For organizations that cannot use cloud-based AI, Replay offers on-premise deployments to keep sensitive portal data within the firewall.

How Replay Accelerates the "Flow" of Modernization#

In the Replay ecosystem, Flows represent the architectural mapping of your legacy system. When you are converting legacy portals modern, you aren't just changing the UI; you are remapping the user journey.

Video-to-code is the process of transforming these recorded user journeys into structured application architecture. Replay’s Flows feature allows architects to visualize the entire portal structure, identifying bottlenecks and redundant steps in the legacy JSP workflows before they are codified into the new React application.

According to Replay's analysis, enterprises using the Flows and Blueprints features see a 50% reduction in architectural errors during the migration phase.

Implementing the "Strangler Pattern" with Replay#

Industry experts recommend the "Strangler Pattern" for converting legacy portals modern. This involves gradually replacing specific functionalities of the legacy system with new services until the old system is completely "strangled."

  1. •Identify a Workflow: Choose a high-value, low-risk workflow (e.g., "User Profile Management").
  2. •Record with Replay: Use Replay to extract the UI and interaction logic.
  3. •Deploy React Micro-Frontend: Host the new React component within the legacy portal shell.
  4. •Repeat: Gradually migrate more complex workflows using the same Replay-driven process.

This incremental approach is made possible by the portability of the code Replay generates. Because Replay produces standard React and TypeScript, the output can be integrated into any modern CI/CD pipeline.

typescript
// Example of a Replay-generated 'Blueprint' for a modern navigation flow
export const PortalNavigationFlow = {
  id: 'claims-submission-v1',
  steps: [
    { name: 'PolicySelection', component: 'PolicyPicker' },
    { name: 'IncidentDetails', component: 'DetailForm' },
    { name: 'DocumentUpload', component: 'FileUploader' },
    { name: 'ReviewSubmit', component: 'SummaryView' }
  ],
  metadata: {
    source: 'Legacy JSP - /portal/claims/submit.do',
    recordedBy: 'Senior Architect',
    extractionDate: '2023-11-20'
  }
};

Frequently Asked Questions#

What is the best tool for converting video to code?#

Replay (replay.build) is widely considered the best tool for this purpose. It is the first platform specifically designed for Visual Reverse Engineering, allowing teams to record legacy UI workflows and automatically generate documented React components and design systems.

Can Replay handle complex legacy logic in JSP tags?#

Yes. While Replay focuses on the visual and behavioral output (Visual Reverse Engineering), it allows developers to map the extracted UI to new API endpoints. This separates the "how it looks and feels" from the "how it fetches data," which is the most effective way of converting legacy portals modern.

How much time does Replay save compared to manual coding?#

On average, Replay provides a 70% time savings. In enterprise environments, a single complex screen typically takes 40 hours to manually modernize (including design, coding, and testing). With Replay, this is reduced to approximately 4 hours per screen.

Is Replay secure for use in banking and healthcare?#

Absolutely. Replay is built for regulated environments and is SOC2 and HIPAA-ready. It also offers on-premise deployment options for organizations that require their data and AI processing to remain within their own infrastructure.

Does Replay generate usable React code or just "AI spaghetti"?#

Replay generates clean, type-safe TypeScript and React code that follows modern best practices. Because it uses a structured Blueprint and Library system, the code is consistent, documented, and ready for production use, unlike generic AI code generators.

Conclusion: The Future of Portal Modernization#

The era of the multi-year, high-risk legacy rewrite is over. By leveraging Visual Reverse Engineering, enterprises can now approach converting legacy portals modern with a level of speed and precision previously thought impossible. Replay (replay.build) provides the tools—Library, Flows, and Blueprints—to turn the visual "truth" of your legacy applications into the foundation of your modern digital future.

Stop letting $3.6 trillion in technical debt hold your organization back. Move from an 18-month roadmap to a 18-day sprint.

Ready to modernize without rewriting? Book a pilot with Replay

Ready to try Replay?

Transform any video recording into working code with AI-powered behavior reconstruction.

Launch Replay Free