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Tomcat Auto Deploy

A VS Code extension that automatically compiles and deploys your Java web application to a local Tomcat server every time you save a file — with zero restarts.

Save a .java file, and it gets compiled and hot-swapped into the running JVM instantly. Save a .jsp, .html, .css, or .js file, and it's copied to the deployment directory right away. No need to restart Tomcat, no need to redeploy the WAR.

[!TIP] Develop without restarting Tomcat — class hot-deploy works right in VS Code.

How It Works

You save a .java file
        │
        ▼
   javac compiles it
        │
        ▼
   JDWP HotSwap replaces the class
   in the running JVM (no restart)
        │
        ▼
   Changes are live immediately

For static files (JSP, HTML, CSS, JS, images, etc.), saving simply copies the file to the Tomcat deployment directory — changes are reflected on the next browser refresh.

Features

• Instant Java HotSwap — Compile on save + JDWP class replacement, no Tomcat restart needed
• Static file deployment — JSP, HTML, CSS, JS files are deployed immediately on save
• Maven & Gradle support — Dependencies are automatically resolved and added to the classpath
• Java version detection — Reads source/target from pom.xml or build.gradle to ensure bytecode compatibility
• Tomcat lifecycle management — Start, stop, restart, force kill from the status bar or sidebar
• Orphan process detection — Finds Tomcat processes left running from a previous session
• Real-time log streaming — Tomcat stdout and localhost.log displayed in dedicated output panels
• Cross-platform — Windows, Linux, macOS

Installation

1. Package

# Linux / macOS
./package.sh

# Windows
package.bat

2. Install in VS Code

Option A) Install from UI:

1. Open the Extensions panel in VS Code (Ctrl+Shift+X)
2. Click the ··· menu at the top
3. Select Install from VSIX...
4. Choose the generated .vsix file

Option B) Install from command line:

code --install-extension tomcat-auto-deploy-0.0.1.vsix

Getting Started

1. Set catalinaHome

On first activation, the extension creates a settings template in .vscode/settings.json. You only need to set one thing — the path to your Tomcat installation:

{
  "tomcatAutoDeploy.catalinaHome": "/path/to/apache-tomcat-9.x"
}

2. Start Tomcat

Click the Tomcat button in the status bar, or run Tomcat: Start from the Command Palette (Ctrl+Shift+P).

The extension will:

1. Initialize a local Tomcat base directory (.vscode/tomcat/)
2. Sync all compiled classes, dependencies, and static files
3. Start Tomcat in JPDA debug mode (for HotSwap)
4. Open your browser when Tomcat is ready

3. Edit and Save

Just write code and save. That's it.

• Java files → compiled → hot-swapped into the running JVM
• JSP / HTML / CSS / JS → copied to the deployment directory

Settings

All settings live under tomcatAutoDeploy.* in your workspace settings (.vscode/settings.json).

You can also open the settings GUI via Command Palette → Tomcat: Open Settings or the gear icon in the sidebar.

Commands

Available from the Command Palette (Ctrl+Shift+P) and the sidebar:

Status Bar

Sidebar

The Tomcat panel in the Activity Bar provides quick access to all server controls, log panels, and settings.

HotSwap Limitations

JDWP HotSwap is a JVM feature with inherent limitations. Understanding what it can and cannot do will save you from confusion:

Works (no restart needed):

• Changing code inside a method body
• Modifying log statements, fixing bugs, tweaking logic

Doesn't work (Tomcat restart required):

• Adding or removing methods
• Adding or removing fields
• Changing method signatures
• Changing class hierarchy (extends/implements)
• Adding or removing lambda expressions (they compile to synthetic methods)

When HotSwap fails, you'll see a warning in the Output panel. Just restart Tomcat to pick up the changes.

Build Tool Integration

Maven

• Dependencies are resolved via mvn dependency:build-classpath and cached
• Java source/target version is read from pom.xml (properties or maven-compiler-plugin config)
• Run mvn compile once before first use (the extension syncs from target/classes)
• Changing pom.xml automatically invalidates the dependency cache

Gradle

• Dependencies are resolved via a temporary init script that prints compileClasspath
• Java version is read from sourceCompatibility/targetCompatibility or javaToolchain
• Run gradle compileJava once before first use (the extension syncs from build/classes)
• Changing build.gradle or build.gradle.kts automatically invalidates the dependency cache

No Build Tool

If there's no pom.xml or build.gradle, the extension compiles all .java files directly with javac.

Good to Know

• The .vscode/tomcat/ directory is the local Tomcat base — add it to .gitignore
• Tomcat's servlet-api and other libraries are automatically included in the classpath
• Compilation errors are shown in the Output panel (Tomcat Auto Deploy)
• If VS Code crashes, the extension will detect the orphan Tomcat process on next startup and offer to kill it
• The extension starts Tomcat with -Dfile.encoding=UTF-8 to prevent encoding issues in logs