Hot swapping in Spring Boot

Question

I've been doing a P.O.C with Spring Boot.

So far it's been going really good and promising, but there's one major drawback: I'm using an embedded server (i.e., packaging the web app in a .jar), so when developing I have to rebuild the jar and restart the server every time I change the CSS, HTML or JS files. There's not hot-swap. This really slows down the UI development.

I can think of several quick fixes, such as loading static resources off a different domain and serving it from a local nginx, and some more variations like this, but isn't there a built-in option of some sort when working with IntelliJ/Eclipse?

Answer 1

There are several options. Running in an IDE (especially with debugging on) is a good way to do development (all modern IDEs allow reloading of static resources and usually also hotswapping of Java class changes). Spring Boot devtools is a cheap way to get quite a big boost (just add it to your classpath). It works by restarting your application in a hot JVM when changes are detected. It also switches off things like thymeleaf caches while it is running, so you don't have to remember to do that yourself. You can use it with an external css/js compiler process if you are writing that code with higher level tools.

Spring Loaded is no longer recommended, but probably still in use. More sophisticated agent-based tools work much better if you need hot swapping with zero delay (e.g. JRebel).

See the docs for some up to date content

Answer 2

but isn't there a built-in option of some sort when working with IntelliJ/Eclipse?

What helped me in IntelliJ 15.0, windows 10, was the following sequence:

STEP 1: Added the following dependency in pom (This is mentioned everywhere but this alone dint solve it), as mentioned by @jonashackt

<dependency>
     <groupId>org.springframework.boot</groupId>
     <artifactId>spring-boot-devtools</artifactId>
</dependency>

STEP 2: Then from File->Settings-> Build-Execution-Deployment -> Compiler (make sure main compiler option is selected and not any of its sub-options)

enable Make Project Automatically. Click ok and close the dialog Note : In latest version it will be Build project automatically

STEP 3: Hold Shift+Ctrl+A (on windows) you will see a search dialog with title "Enter Action or option name", type registry. Double click the first option that says "Registry..." it will open another window. Look for the following option:

compiler.automake.allow.when.app.running

and enable it, click close

STEP 4: Restart IDE

Elaborated from this source

Answer 3

You can get hot swapping:

• for java code: using spring-loaded
• for Thymeleaf templates: disabling the cache

Check this post to see more details: http://blog.netgloo.com/2014/05/21/hot-swapping-in-spring-boot-with-eclipse-sts/

Answer 4

I do not know how far this kind of support goes, but in case you use Eclipse IDE (or anyone reading this): starting up your Spring-Boot application via m2e in debug-mode (press the "Debug"-dropdown button and pick your maven run configuration item).

It works for me like a charm.

My maven run configuration item is configured as follows:

• goal is set to "spring-boot:run"
• base directory is the project directory

I am not using any further libraries (not even spring-boot-devtools).

That's it.

Answer 5

You can also use JRebel - it will reload all changes (better hotswap) including spring beans. It is easily integratred with both Intellij and Eclipse.

Answer 6

Assuming you are using gradle; use the following config in your build.gradle

apply plugin: 'java'
apply plugin: 'idea'
apply plugin: 'spring-boot'
apply plugin: 'application'

applicationDefaultJvmArgs = ["-agentlib:jdwp=transport=dt_socket,address=localhost:7000,server=y,suspend=n"]

mainClassName = "package.ApplicationRunner"

Run the application from the IDE or command line using the command gradle build run

Now the IDE can connect to the remote JVM (on port 7000) where the spring boot application runs. It also supports hot deployment of static files.

or even you can run the main class from intelliJ if the dependencies are properly managed in the IDE. The main class is the class that contains the main method which will call SpringApplication.run("classpath:/applicationContext.xml", args);

Answer 7

In Intellij, I can get this behavior. When the program is running in debug mode, select Run > Reload Changed Classes

Note: After Intellij completes the action, it might say Loaded classes are up to date. Nothing to reload. This is misleading, because it actually DID reload your classpath resources.

My environment/setup includes:
Intellij 13
Embedded Tomcat
Run/Debug configuration of type 'Application' (which just uses a main class)
Serving static html, css and js (no jsp)

Answer 8

Try using this spring-boot-devtools tag in pom.xml

<dependencies>
       <dependency>
           <groupId>org.springframework.boot</groupId>
           <artifactId>spring-boot-devtools</artifactId>
           <optional>true</optional>
       </dependency>
</dependencies>

http://mytechnologythought.blogspot.com/2017/07/how-to-run-server-of-spring-boot-auto.html

Answer 9

From 1.3.0. (now in Milestone 2) on, you can use the spring-boot-devtools for that as a lightweigt approach - see the docs or this blogpost. Simply upgrade to >= 1.3.0. and add the following to your pom.xml:

<dependencies>
  <dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-devtools</artifactId>
  </dependency>
</dependencies>

Than start your SpringBootApplication with Run As... and you´re fine.

Answer 10

I recommend Thymeleaf (template engine), jRebel for personal developer. Thymeleaf template files are just HTML resources. So, they`re changed immediately after you edit template files.

Answer 11

If you're using maven, the spring-boot-maven-plugin in your pom.xml needs to be like this to get the hot swap:

  <plugin>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-maven-plugin</artifactId>
        <dependencies>
            <dependency>
                <groupId>org.springframework</groupId>
                <artifactId>springloaded</artifactId>
                <version>1.2.0.RELEASE</version>
            </dependency>
        </dependencies>
    </plugin>

and if you're using thymeleaf, add this to your application properties:

spring.thymeleaf.cache=false

But remember something: Don't use this in your production environment..

Answer 12

How to perform Hot Swap in Springboot Application

1. When using gradle include following in the dependency: compile group: 'org.springframework.boot', name: 'spring-boot-devtools', version: '2.0.1.RELEASE' & providedRuntime('org.springframework.boot:spring-boot-starter-tomcat')

2. In application.properties add the property spring.devtools.restart.additional-paths=.

3. Build Gradle and then run application as bootRun

The application is ready to perform hot swap on modification of classes