Hot deploy java applications

Hey everyone, this is Justin at level up lunch. If you are getting started with spring boot or working with a traditional spring application you are probably looking for ways to reduce your cycle time. Spring has created a submodule called spring-loaded which allows you to hot deploy your application within your application server. Unlike traditional hot code replacements which allow simple changes on the JVM, spring-loaded provides you with the ability to add, modify or delete methods.

Project set up

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By using a spring starter project, we created a spring-boot application. We are using spring sts for demonstration purposes but you should use an IDE of your choice. Next, we went ahead and created a sample controller with a method that returns a string to the default RequestMapping.

@RestController
public class MySampleController {

    @RequestMapping("/")
    public String home () {
        return "www.leveluplunch.com/";
    }
}

Download spring loaded

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The next thing you will want to do is download spring loaded. Once you have it in a directory we will navigate to the run configuration in eclipse and in the VM arguments we will paste a string pointing to the jar. While pasting the location, don't forget the version of downloaded jar.

-javaagent:/Users/justinm/Documents/spring/spring-loaded/springloaded-1.1.5.RELEASE.jar -noverify

Now it is configured with spring loaded and it will give us the ability to perform hot deployments with our java application.

Demonstrating hot deployment

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Once configured lets add another @RequestMapping to demonstrate the hot deployment in action. We create a snippet which contains a HotDeployment class and an associated @Requestmapping. When a file is saved, in our console we will see that it reloaded or refreshed. Once we navigate to localhost:8080/hotdeploy the changes were picked up and we don't need to stop and restart the application server.

@RequestMapping("/")
public String home () {
    return "www.leveluplunch.com/";
}

class HotDeploy {
    boolean isHotDeployable = false;

    public boolean isHotDeployable() {
        return isHotDeployable;
    }

    public void setHotDeployable(boolean isHotDeployable) {
        this.isHotDeployable = isHotDeployable;
    }
}

@RequestMapping(
        value = "/hotdeploy",
        method = RequestMethod.GET,
        produces = {MediaType.APPLICATION_JSON_VALUE}
        )
public HotDeploy hotDeployable () {

    HotDeploy hotDeploy = new HotDeploy();

    return hotDeploy;
}

The output when navigating to localhost:8080/hotdeploy:

Output

{"hotDeployable":false}

Adding a @RequestParam

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We will add a @RequestParam to the /hotdeploy @RequestMapping named isHotDeployable. Based on that parameter we will set the value in the HotDeployable object. Once again, you will see in the console that application server refreshed.

@RequestMapping(
            value = "/hotdeploy",
            method = RequestMethod.GET,
            produces = {MediaType.APPLICATION_JSON_VALUE}
            )
public HotDeploy hotDeployable (@RequestParam(required=false) boolean isHotDeployable) {

    HotDeploy hotDeploy = new HotDeploy();

    if (isHotDeployable) {
        hotDeploy.setHotDeployable(isHotDeployable);
    }

    return hotDeploy;
}

The output when navigating to localhost:8080/hotdeploy?isHotDeployable=true:

Output

{"hotDeployable":true}

For the most part spring-loaded works pretty well but it does have limitations so be sure to check out the documentation.

Thanks for joining in today's screencast at level up lunch. Have a great day!