# Lazy Tool Download Implementation - January 6, 2026
## Problem
The Apache Tomcat migration tool was being downloaded at startup when `RefactoringEngine` was created, causing:
- Startup delays
- Startup failures if download fails (HTTP 404/403)
- Unnecessary network calls when the tool might never be used
## Solution
Made the tool download **lazy/on-demand** - it only downloads when the tool is actually used.
## Changes Made
### 1. Lazy Initialization in Constructor
**Before:**
```java
public ApacheTomcatMigrationTool() {
this.toolJarPath = findToolJar(); // Downloads immediately!
this.timeoutSeconds = DEFAULT_TIMEOUT_SECONDS;
}
```
**After:**
```java
public ApacheTomcatMigrationTool() {
this.toolJarPath = null; // Will be resolved lazily when migrate() is called
this.timeoutSeconds = DEFAULT_TIMEOUT_SECONDS;
}
```
### 2. Lazy Resolution in `migrate()` Method
**Before:**
- Tool path was already resolved in constructor
**After:**
```java
public MigrationResult migrate(Path sourcePath, Path destinationPath) throws IOException {
// ... validation ...
// Lazy initialization: find/download tool only when actually needed
if (toolJarPath == null) {
toolJarPath = findToolJar();
}
// ... rest of method ...
}
```
### 3. Cache Check Before Download
**Before:**
- Always tried to download immediately
**After:**
- First checks cache directory for existing tool
- Only downloads if not found in cache
- Downloads happen on-demand when `migrate()` is called
### 4. Helper Methods Added
Added `getCacheDirectory()` and `findCachedJar()` methods to check cache without downloading:
- `getCacheDirectory()` - Returns cache directory path if it exists (doesn't create it)
- `findCachedJar()` - Searches cache directory for existing JAR files
## Impact
### Benefits
1. ✅ **Faster Startup** - No download attempts at startup
2. ✅ **No Startup Failures** - Download failures don't prevent application from starting
3. ✅ **On-Demand Download** - Tool only downloads when actually needed
4. ✅ **Cache-First** - Checks cache before attempting download
### Behavior
- **At Startup**: `ApacheTomcatMigrationTool` is created, but no download happens
- **On First Use**: When `migrate()` is called, tool is found/downloaded
- **Subsequent Uses**: Uses cached tool (if available)
## Testing
The MCP server should now:
- Start without download attempts
- Only download tool when a migration is actually requested
- Handle download failures gracefully (returns null, migration fails with clear error)
**Status:** ✅ Implemented
