JSP Workflow Mapping: Visualizing Legacy Java Logic for React Reconstruction

The death of a legacy enterprise system usually happens in the dark. It’s not the lack of servers or the cost of maintenance that kills it—it’s the loss of tribal knowledge. When a JSP (JavaServer Pages) application has been running for fifteen years, the original architects are long gone, and the documentation is likely non-existent. You are left with a "black box" where business logic is inextricably tangled with UI tags and server-side scriptlets.

According to Replay’s analysis, 67% of legacy systems lack any form of up-to-date documentation, leaving modern engineering teams to guess how critical workflows actually function. This is where workflow mapping visualizing legacy logic becomes the difference between a successful migration and a $3.6 trillion addition to global technical debt.

To move from a monolithic JSP environment to a modern React architecture, you cannot simply "rewrite." You must decode. You need to see the invisible paths the data takes through the UI.

TL;DR: Manual JSP-to-React migrations fail because logic is hidden in server-side state. By using workflow mapping visualizing legacy processes through Replay, enterprises can reduce migration timelines from 18 months to a few weeks, achieving a 70% time saving by converting recorded user sessions directly into documented React components and design systems.

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The JSP Impasse: Why Traditional Migration Fails#

JSP was the gold standard for enterprise Java for decades, but its architectural pattern—mixing HTML, Java scriptlets, and Taglibs—is the antithesis of modern component-based development. In a JSP file, a single

statement might check a session variable, query a database via a DAO, and then decide which CSS class to apply to a .

When you attempt to migrate this to React, you face three primary hurdles:

1. •State Fragmentation: Logic is split between the client browser, the JSP container, and the Java Action classes.
2. •Hidden Workflows: Edge cases in user flows are buried in nested
   text

   <c:if>
   tags.
3. •The Documentation Gap: As noted, most systems have no blueprint.

Industry experts recommend that before a single line of React is written, a comprehensive audit of the "as-is" state must occur. However, manual auditing takes approximately 40 hours per screen. For an enterprise application with 500 screens, that’s 20,000 man-hours just for discovery.

Visual Reverse Engineering is the methodology of capturing runtime behavior to reconstruct source code and architectural intent without relying on outdated manual documentation.

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Workflow Mapping Visualizing Legacy Systems: The New Standard#

To bridge the gap, architects are turning to workflow mapping visualizing legacy behaviors. Instead of reading 100,000 lines of Java code, we record the application in action. By capturing every click, state change, and API call, we can generate a visual map of the application's DNA.

Replay automates this by recording real user workflows. It doesn't just take a video; it captures the metadata of the UI elements. This allows the platform to understand that a specific JSP

submission corresponds to a specific React state update.

The Comparison: Manual vs. Visual Reverse Engineering#

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Technical Implementation: From JSP Scriptlets to React Hooks#

The core challenge of workflow mapping visualizing legacy Java is translating the imperative nature of JSP into the declarative nature of React.

Consider a typical JSP snippet that handles a conditional discount display:

jsp
<%-- Legacy JSP Discount Logic --%>
<div class="container">
    <% 
        User user = (User) session.getAttribute("user");
        double discount = 0.0;
        if (user != null && user.getMembershipLevel().equals("GOLD")) {
            discount = 0.20;
    %>
        <p class="promo-text">Welcome Gold Member! You get 20% off.</p>
    <% } else { %>
        <p class="promo-text">Upgrade to Gold for exclusive discounts.</p>
    <% } %>
    <input type="hidden" id="discountValue" value="<%= discount %>" />
</div>

In this example, the logic is trapped on the server. To reconstruct this in React, Replay maps the visual output and the underlying data triggers to create a clean, functional component.

Video-to-code is the process of converting recorded user interface interactions and visual states into production-ready, documented frontend code.

The Reconstructed React Component#

Using the insights from the workflow mapping, Replay generates a TypeScript/React component that separates the concerns:

typescript
import React from 'react';

interface PromoDisplayProps {
  membershipLevel: 'GOLD' | 'SILVER' | 'BRONZE' | 'NONE';
}

/**
 * Reconstructed from Legacy Order Management Flow
 * Mapping: JSP Session Attribute 'user' -> React Prop 'membershipLevel'
 */
export const PromoDisplay: React.FC<PromoDisplayProps> = ({ membershipLevel }) => {
  const isGold = membershipLevel === 'GOLD';
  const discount = isGold ? 0.20 : 0.0;

  return (
    <div className="p-4 border rounded-md shadow-sm">
      {isGold ? (
        <p className="text-gold-600 font-bold">
          Welcome Gold Member! You get {discount * 100}% off.
        </p>
      ) : (
        <p className="text-gray-500">
          Upgrade to Gold for exclusive discounts.
        </p>
      )}
      <input type="hidden" value={discount} />
    </div>
  );
};

By workflow mapping visualizing legacy logic, Replay identifies that

is a critical state variable. It then generates the corresponding TypeScript interfaces, ensuring type safety—something JSP completely lacks.

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The Role of "Flows" in Architecture Reconstruction#

In the Replay ecosystem, "Flows" represent the architectural visualization of the legacy system. When you record a session—say, a user navigating through a complex insurance claim submission—Replay breaks down that recording into a sequence of states.

1. •Entry Point: The JSP URL and initial session state.
2. •Interaction Nodes: Every button click or form input.
3. •Side Effects: API calls or page redirects.
4. •Exit Point: The final success or error state.

This visualization is crucial for Modernizing Legacy Systems because it allows architects to see the "hidden" paths. Often, JSP apps have dead code—pages that exist but are never reached, or logic branches that are no longer valid. Replay identifies what is actually used, allowing you to prune the technical debt during the migration.

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Accelerating the Design System Transition#

One of the biggest hurdles in moving from JSP to React is the lack of a Design System. Legacy Java apps usually rely on a hodgepodge of global CSS, inline styles, and deprecated HTML tags like

or .

According to Replay's analysis, manual creation of a component library for a legacy app takes months of design-to-dev handoffs. Replay’s Library feature automates this. As it performs workflow mapping visualizing legacy UIs, it identifies recurring patterns. If it sees a specific button style used across 50 JSP pages, it automatically extracts that as a reusable React component in your new Design System.

Example: Mapping a Legacy Table to a Modern Data Grid#

Legacy JSP tables are often hard-coded with complex loops. Replay maps the visual data structure to a modern, accessible React table.

typescript
// Modernized Data Table generated from Legacy JSP 'results.jsp'
import { useTable } from 'react-table';

const LegacyDataGrid = ({ data }) => {
  const columns = React.useMemo(
    () => [
      { Header: 'Order ID', accessor: 'orderId' },
      { Header: 'Customer', accessor: 'customerName' },
      { Header: 'Status', accessor: 'status' },
      { Header: 'Total', accessor: 'totalAmount' },
    ],
    []
  );

  return (
    <div className="overflow-x-auto">
      <table className="min-w-full divide-y divide-gray-200">
        {/* Replay-generated accessible table structure */}
        <thead>{/* ... */}</thead>
        <tbody>{/* ... */}</tbody>
      </table>
    </div>
  );
};

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Why Regulated Industries Choose Visual Reverse Engineering#

For Financial Services, Healthcare, and Government sectors, "moving fast and breaking things" isn't an option. These industries are tethered to legacy Java because the risk of losing business logic is too high.

Workflow mapping visualizing legacy logic provides an audit trail. Because Replay is built for regulated environments—offering SOC2 compliance, HIPAA readiness, and On-Premise deployment—it allows these organizations to modernize without exposing sensitive data.

The $3.6 trillion global technical debt isn't just a number; it's a barrier to innovation. By using Replay to map these workflows, a bank can move its core banking portal from JSP to React in weeks rather than years, ensuring that every regulatory check and balance is preserved in the new code.

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Implementing the Replay Blueprint#

The Blueprint in Replay acts as the bridge. It is an interactive editor where architects can refine the AI-generated React code.

1. •Record: A subject matter expert records the standard operating procedures in the legacy JSP app.
2. •Map: Replay performs workflow mapping visualizing legacy logic, identifying components, states, and routes.
3. •Refine: Developers use the Blueprint to tweak the generated TypeScript code, ensuring it aligns with internal coding standards.
4. •Export: The documented React components and Design System are exported directly into the new repository.

This process eliminates the "blank page" problem. Instead of starting with an empty

, developers start with a library of components that already reflect the reality of their business logic.

Learn more about Automated Documentation and how it fits into your CI/CD pipeline.

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Conclusion: Stop Rewriting, Start Replaying#

The 18-month average enterprise rewrite timeline is a relic of the past. It is a timeline predicated on manual discovery, manual documentation, and manual coding. By shifting to a strategy of workflow mapping visualizing legacy systems, you are choosing a data-driven path to modernization.

Replay transforms the "black box" of JSP into a transparent, documented, and modern React ecosystem. You save 70% of the time, eliminate the risk of logic loss, and finally pay down the technical debt that has been holding your organization back.

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Frequently Asked Questions#

How does Replay handle complex server-side Java logic that isn't visible in the UI?#

While Replay focuses on workflow mapping visualizing legacy UIs, it captures all network requests and state changes triggered by those UI actions. This allows architects to see exactly which backend endpoints are called, with what parameters, and how the UI reacts to the returned data, effectively mapping the "contract" between the legacy Java backend and the new React frontend.

Can Replay generate code for specific React frameworks like Next.js or Remix?#

Yes. Replay’s AI Automation Suite is designed to be framework-agnostic. While the core output is clean TypeScript and React, the Blueprints can be configured to output code that follows the patterns of Next.js, Remix, or even standard Vite-based SPAs, including specific styling libraries like Tailwind CSS or Material UI.

What happens to the "dead code" in our legacy JSP files?#

According to Replay's analysis, up to 30% of legacy enterprise code is never executed in production. Because Replay uses a recording-based approach, it only maps the workflows that are actually used by your team. This naturally filters out "dead code," ensuring your new React application is lean, performant, and free of historical clutter.

Is my data secure during the recording process?#

Replay is built for highly regulated industries. We offer SOC2 and HIPAA-compliant cloud environments, but for organizations with strict data residency requirements, we also provide On-Premise deployment options. This ensures that your source code and session recordings never leave your secure network.

Ready to modernize without rewriting? Book a pilot with Replay