In the dynamic world of Java development, the efficiency and speed of workflow are critical. One tool that has traditionally helped Java developers reduce their build and redeploy time is JRebel. However, developers often seek alternatives due to various reasons, including cost, licensing issues, or simply the desire for open-source solutions. This article discusses some notable alternatives to JRebel for redeploy-less Java development, explaining their features, advantages, and technical specifics.

1. Spring Boot DevTools

Spring Boot DevTools is an excellent choice for projects built on Spring Boot. It provides a set of developer tools that enhance the development experience.

Features

• Automatic Restart: Spring Boot DevTools automatically restarts the application when changes are detected, aiming to minimize the time required for code-hotswap.
• Live Reload: It integrates with a browser extension to refresh the browser when resources change.

Usage

To use Spring Boot DevTools, include the dependency in your pom.xml for Maven or build.gradle for Gradle:

Maven:

1<dependency>
2    <groupId>org.springframework.boot</groupId>
3    <artifactId>spring-boot-devtools</artifactId>
4    <optional>true</optional>
5</dependency>

Gradle:

developmentOnly 'org.springframework.boot:spring-boot-devtools'

2. HotSwapAgent

HotSwapAgent is another robust alternative. It enhances the standard Java Hotswap, allowing developers to reload classes during runtime.

Features

• Wide Framework Support: Works well with various Java frameworks, including Spring and Hibernate.
• Configuration-Based: Extensible via plugins and configuration files.

Configuration

To set up HotSwapAgent, add the following VM argument to enable its functionality:

-javaagent:/path/to/hotswap-agent.jar

Limitations

It's important to note that HotSwapAgent, while powerful, may require some setting adjustments based on your specific development environment.

3. DCEVM (Dynamic Code Evolution VM)

DCEVM is an alternative Java Virtual Machine with advanced hotswap capabilities.

Features

• Extends JVM: Unlike standard JVM, DCEVM allows for class redefinition where method changes, class field changes, etc., are supported.
• Seamless Integration: Installed as a custom JVM, enabling regular development IDEs to leverage its capabilities.

Implementation

You can install DCEVM and switch the JVM in your IDE settings:

java -jar DCEVM-light-<version>.jar

4. JReload

JReload is an open-source solution focused on reducing application downtimes during development.

Features

• Selective Hotswap: Offers selective class reloading without restarting the entire server.
• Simple Integration: Works with simple configuration changes in build tools.

Example

Add the plugin to your build.gradle:

plugins {
    id "org.jreload.gradle" version "1.0"
}

5. JRebel Open Source Edition

Though not entirely separate from JRebel, the open-source edition provides basic capabilities needed for smaller projects or educational purposes.

Features

• Provides a stripped-down version freely available for development and educational use.
• Limited support for frameworks compared to the full version.

Comparison Table

Additional Considerations

Performance Impact: While these tools aim to mitigate redeploy times, it's crucial to evaluate their performance impact on your system. Tools like DCEVM, which operate on a JVM level, might have different performance characteristics compared to others operating as agents.

IDE Compatibility: Ensure that your chosen alternative works seamlessly with your Integrated Development Environment (IDE). Tools like Spring Boot DevTools often integrate more smoothly with Spring Tool Suite or IntelliJ IDEA's Spring Boot support.

Community and Support: The choice of tool may also depend on community and support availability. Tools with actively contributing communities often provide regular updates and better troubleshooting aids.

In conclusion, while JRebel offers an efficient commercial solution for Java application redeployment, various alternatives can suit different needs, from open-source projects to specific framework compatibility. Evaluating alternatives based on project requirements, including framework support, cost considerations, and the ease of integration, ensures optimal efficiency in Java development environments.