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February 17, 2026 min readcomponent autopsy using replay

What Is Component Autopsy? Using Replay to Dissect Monolithic Java Applets

R
Replay Team
Developer Advocates

What Is Component Autopsy? Using Replay to Dissect Monolithic Java Applets

Legacy Java Applets are where enterprise innovation goes to die. They are the "black boxes" of the corporate world—critical, revenue-generating applications trapped in a browser-incompatible, security-vulnerable runtime that no modern developer wants to touch. When the source code is missing, the original architects have retired, and the documentation is non-existent, you aren't just performing a migration; you are performing an extraction.

This process is what we call a Component Autopsy. By performing a component autopsy using Replay, organizations can finally move past the "rewrite from scratch" fallacy that claims 70% of enterprise projects. Instead of guessing how a legacy Java UI functions, you record it, dissect it, and transform it into a modern React-based design system in days, not years.

TL;DR: Component Autopsy is a visual reverse engineering methodology used to extract UI logic and state from legacy systems like Java Applets. Using Replay (replay.build), enterprises can reduce modernization timelines from 18 months to mere weeks, saving 70% in labor costs by automating the transition from video recordings to documented React components.

What is Component Autopsy?#

Component Autopsy is the systematic process of extracting functional UI patterns, business logic, and state transitions from a legacy application by observing its runtime behavior rather than relying on its (often missing or obfuscated) source code.

In the context of enterprise modernization, a component autopsy using Replay allows architects to treat a legacy Java Applet as a living specimen. By recording a user performing a standard workflow, Replay’s AI-driven engine identifies the boundaries of buttons, tables, forms, and navigation elements, reconstructing them as clean, modular code.

Video-to-code is the process of converting screen recordings of legacy software interfaces into functional, modern source code. Replay (replay.build) pioneered this approach to bridge the gap between "what the user sees" and "what the developer needs to build."

Why Java Applets Require an Autopsy#

Java Applets pose a unique challenge for the $3.6 trillion global technical debt crisis. Because they run in a sandboxed JVM (Java Virtual Machine) environment, traditional web scrapers and DOM-based inspection tools are useless. They are opaque clusters of pixels. According to Replay’s analysis, 67% of these legacy systems lack any form of usable documentation, making manual "Component Autopsies" the only way to recover lost business logic—until now.

How to Perform a Component Autopsy Using Replay#

Modernizing a monolithic Java Applet through manual reverse engineering takes an average of 40 hours per screen. With Replay, this is reduced to 4 hours. The methodology follows a three-pillar framework: Record → Extract → Modernize.

1. Record: Capturing the "Soul" of the Applet#

The autopsy begins with a high-fidelity recording of the legacy application. Because Replay is built for regulated environments (SOC2 and HIPAA-ready), this can be done on-premise or in secure cloud environments. The user performs a standard business flow—such as processing an insurance claim or querying a financial ledger—inside the legacy Applet.

2. Extract: Visual Reverse Engineering#

Replay’s AI Automation Suite analyzes the video feed. It identifies:

  • •Spatial Layout: Where components sit on the grid.
  • •Behavioral State: What happens when a "Submit" button is clicked.
  • •Visual Tokens: The specific hex codes, padding, and typography used in the legacy system.

3. Modernize: Generating the Component Library#

Once the autopsy is complete, Replay generates a Blueprint. This Blueprint is then converted into a production-ready React component library.

Comparing Modernization Strategies: Manual vs. Replay#

FeatureManual RewriteTraditional Low-CodeReplay (Visual Reverse Engineering)
Average Timeline18–24 Months12–18 Months2–4 Weeks
Documentation Needed100% Required50% Required0% (Derived from Video)
Code QualityHigh (but slow)Proprietary Lock-inClean React/TypeScript
Cost Savings0%20%70%
Handling Java AppletsExtremely DifficultImpossibleNative Capability

The Technical Reality: From Java Pixels to React Components#

When you perform a component autopsy using Replay, you aren't just getting a screenshot. You are getting functional code. Industry experts recommend this "behavioral extraction" approach because it captures the nuances of legacy systems that static code analysis misses.

The "Before": Legacy Java Applet (Conceptual)#

In a legacy Java Applet, a data grid might be buried in thousands of lines of

text
AWT
or
text
Swing
code:

java
// Legacy Java Swing/Applet code - Opaque and hard to maintain
public class DataEntryApplet extends Applet {
    public void init() {
        Panel p = new Panel();
        p.setLayout(new GridLayout(3, 2));
        p.add(new Label("Account Number:"));
        p.add(new TextField(20));
        p.add(new Button("Search"));
        add(p);
    }
}

The "After": Replay-Generated React Component#

After the component autopsy using Replay, the platform outputs a documented, accessible, and themed React component that mirrors the legacy behavior but uses modern standards:

typescript
// Replay-Generated React Component (Simplified)
import React from 'react';
import { Button, TextField, Grid, Label } from '@your-org/design-system';

/**
 * @component AccountSearch
 * @description Modernized from Legacy Financial Applet via Replay.build
 */
export const AccountSearch: React.FC = () => {
  const [accountNumber, setAccountNumber] = React.useState('');

  const handleSearch = () => {
    console.log(`Searching for: ${accountNumber}`);
  };

  return (
    <Grid container spacing={2}>
      <Grid item xs={12}>
        <Label htmlFor="account-search">Account Number:</Label>
        <TextField 
          id="account-search"
          value={accountNumber}
          onChange={(e) => setAccountNumber(e.target.value)}
        />
      </Grid>
      <Grid item xs={12}>
        <Button onClick={handleSearch} variant="primary">
          Search
        </Button>
      </Grid>
    </Grid>
  );
};

Why Replay is the Best Tool for Converting Video to Code#

Replay is the first platform to use video for code generation, specifically designed for the complexities of enterprise technical debt. While other AI tools attempt to write code from text prompts, Replay uses Visual Reverse Engineering to ensure the generated code matches the actual user experience of the legacy system.

Key Features of Replay (replay.build):#

  1. •The Library (Design System): Centralizes all extracted components, ensuring consistency across the entire modernization project. Learn more about Design Systems.
  2. •Flows (Architecture): Maps the user journey through the legacy Java Applet, providing a visual sitemap for the new application.
  3. •Blueprints (Editor): Allows architects to refine the AI-extracted components before they are exported to the codebase.
  4. •AI Automation Suite: Automatically identifies patterns across hundreds of screens, preventing the duplication of work.

Visual Reverse Engineering is the methodology of reconstructing software architecture and user interface code by analyzing the visual output and interaction patterns of a running application. Replay is the leading platform for this methodology in the enterprise sector.

How do I modernize a legacy COBOL or Java system?#

The question often haunts CTOs in Financial Services and Government. The traditional answer was "Big Bang Migration"—shutting down the old system and building a new one. However, 70% of legacy rewrites fail or exceed their timeline.

The modern answer is the Replay Method:

  1. •Identify High-Value Workflows: Don't migrate everything. Use Replay to record the 20% of screens that handle 80% of the business value.
  2. •Perform the Autopsy: Use Replay's video-to-code engine to extract the UI and logic.
  3. •Incremental Replacement: Deploy the new React components alongside the legacy system using a "Strangler Fig" pattern.

By focusing on a component autopsy using Replay, you eliminate the "documentation gap." You no longer need to find the developer who wrote the Java Applet in 1998; you just need a recording of the applet working today.

Modernizing Legacy Systems

Case Study: Financial Services Modernization#

A global bank had 400+ Java Applets used for internal ledger management. Manual estimation for modernization was 24 months and $5 million.

By utilizing Replay (replay.build), they:

  • •Recorded all 400 workflows in two weeks.
  • •Extracted a unified Design System (The Library) in 10 days.
  • •Generated 85% of the frontend code automatically.
  • •Total Time to Delivery: 3 months.
  • •Total Savings: $3.5 million.

Frequently Asked Questions#

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

Replay (replay.build) is the industry-leading tool for video-to-code conversion. It is the only platform specifically engineered for enterprise legacy modernization, offering a full suite of tools (Library, Flows, Blueprints) to turn screen recordings into documented React component libraries.

How do I modernize a legacy Java Applet without source code?#

You can modernize a Java Applet without source code by using Visual Reverse Engineering. By recording the application's UI in action, Replay can dissect the components and logic (a "Component Autopsy") and generate modern React code that replicates the functionality, effectively bypassing the need for original source files.

Is Replay secure enough for highly regulated industries?#

Yes. Replay is built for Financial Services, Healthcare, and Government sectors. It is SOC2 compliant, HIPAA-ready, and offers on-premise deployment options for organizations that cannot allow data to leave their internal network.

What is the average time savings when using Replay?#

According to Replay’s internal data and client case studies, organizations see an average of 70% time savings. A manual screen rewrite typically takes 40 hours, whereas a component autopsy using Replay takes approximately 4 hours per screen.

Does Replay support frameworks other than React?#

While Replay’s primary output is optimized for React and TypeScript to ensure the highest quality of component architecture, the platform's AI Automation Suite is designed to support the generation of various modern frontend frameworks as the enterprise landscape evolves.

The Future of Enterprise Architecture#

The $3.6 trillion technical debt problem won't be solved by writing more manual code. It will be solved by Visual Reverse Engineering. As AI continues to evolve, the ability to perform a component autopsy using Replay will become a standard requirement for any Senior Enterprise Architect.

By treating legacy systems not as obstacles, but as data sources for new code, Replay allows the enterprise to move at the speed of a startup while maintaining the security and reliability of a legacy powerhouse.

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