IntelliJ IDEA Integration

IntelliJ IDEA Integration

Use LeanJ directly in IntelliJ IDEA to see performance metrics in your code editor.

Prerequisites

• IntelliJ IDEA 2023.1+ (2025.2 tested)
• LeanJ CLI installed and in PATH (or configured via system property)
• Java JDK 11+ for the profiled application

Installation

Install the Plugin

1. In IntelliJ IDEA, go to File → Settings → Plugins
2. Search for “LeanJ”
3. Click Install
4. Restart IDE when prompted

Configure CLI Path

The plugin needs to find the CLI. It searches in this order:

1. System property: -Dleanj.cli.path=<path>
2. PATH environment variable
3. Plugin bundle (future)

Set system property:

• Go to Help → Edit Custom VM Options…
• Add: -Dleanj.cli.path=C:\path\to\leanj.exe
• Restart IDE

Or add CLI to PATH (recommended):

• See Installation Guide for PATH setup

Usage

Method 1: Automatic (Recommended)

1. Start LeanJ Profiling:
   • Go to Run → Start LeanJ Profiling

The plugin automatically:

• Calls the CLI
• Starts the controller (if not running)
• Discovers JVMs
• Attaches the agent

2. Run your application:

   • Use your normal Run Configuration
   • The agent is already attached

3. View metrics:

   • Open your Java files
   • See inline hints above methods
   • Hover for detailed popup
   • Check the Profiler tool window

Method 2: Manual CLI + IDE

1. Start controller manually:

   leanj controller start

2. Discover JVMs:

   leanj jvms

3. Attach agent:

   leanj attach --pid <pid>

4. Start profiling in IntelliJ:

   • Run → Start LeanJ Profiling

Viewing Metrics

CodeVision Inline Hints

Metrics appear directly above method declarations:

╰─ Estimated avg execution time: 2.1ms
╰─ Max time last run: 4.8ms
╰─ Allocations per call: ~12KB
╰─ Call count: 150
╰─ Trend: +15%

public void processPayments() {
    // your code
}

Hover Popup

Hover over a method to see detailed metrics:

• Average execution time
• Maximum time
• Allocations
• Call count
• Trend (percentage change)
• Context information

Profiler Tool Window

1. Open View → Tool Windows → Profiler
2. Or click the Profiler tab at the bottom

The tool window shows:

• All profiled methods
• Real-time statistics
• Filtering and sorting options

Metrics Explained

Average Execution Time

Cumulative average from profiling start. Shows typical performance.

Max Time

Maximum execution time in the last measurement window. Helps identify outliers.

Allocations

Memory allocated per call. Useful for finding memory-intensive operations.

Call Count

Total number of method invocations since profiling started.

Trend

Percentage change compared to previous measurement. Positive means slower, negative means faster.

CodeVision Settings

Enable CodeVision in IntelliJ:

1. File → Settings → Editor → Inlay Hints
2. Enable Code Vision
3. Enable LeanJ hints

Multiple JVM Support

You can profile multiple JVMs simultaneously:

1. Attach to multiple JVMs using CLI:

   leanj attach --pid 12345
   leanj attach --pid 67890

2. The plugin shows metrics from all attached JVMs

3. Metrics are aggregated per method

Docker JVMs

Docker containers with the agent automatically appear in the JVM list:

1. Ensure agent is configured in Dockerfile:

   ENV JAVA_TOOL_OPTIONS="-javaagent:/agent/agent.jar"
   ENV LEANJ_PROJECT=my-service

2. Container starts and registers with controller

3. Appears in leanj jvms output

4. Plugin can attach and show metrics

Troubleshooting

CLI Not Found

Error: CLI not found

Solution:

1. Verify CLI is installed: See Installation Guide
2. Check CLI is in PATH: leanj --version
3. Add to PATH or set system property: -Dleanj.cli.path=<path>
4. Restart IDE

Controller Not Running

Error: Controller not running

Solution:

1. Start controller manually: leanj controller start
2. Or let plugin start it automatically
3. Check logs: logs/profiler-controller.log

No Metrics Visible

Issue: CodeVision hints not showing

Solution:

1. Enable CodeVision: Settings → Editor → Inlay Hints
2. Ensure agent is attached: leanj status
3. Check controller logs for errors
4. Verify application is running and being profiled

Metrics Not Updating

Issue: Metrics are stale

Solution:

1. Check controller is receiving data: leanj status
2. Verify agent is connected: check controller logs
3. Restart profiling: Run → Start LeanJ Profiling

Advanced Configuration

Custom Controller Port

Set environment variable:

export LEANJ_CONTROLLER_PORT=8888

Or use CLI:

leanj controller start --port 8888

Workspace Matching

The CLI automatically matches JVMs to your workspace:

• Compares Git root
• Matches IDE workspace path
• Uses user.dir comparison

This helps identify the correct JVM when multiple are running.

Next Steps

• Learn about Docker integration
• Explore CLI commands
• Configure advanced settings
• Read How It Works for architecture details