You can run a Spring Boot application from your IDE as a simple Java application, however, first you will need to import your project. Import steps will vary depending on your IDE and build system. Most IDEs can import Maven projects directly, for example Eclipse users can select Import…​ → Existing Maven Projects from the File menu.

If you can’t directly import your project into your IDE, you may be able to generate IDE metadata using a build plugin. Maven includes plugins for Eclipse and IDEA; Gradle offers plugins for various IDEs.

	Tip
	If you accidentally run a web application twice you will see a “Port already in use” error. STS users can use the Relaunch button rather than Run to ensure that any existing instance is closed.

If you use the Spring Boot Maven or Gradle plugins to create an executable jar you can run your application using java -jar. For example:

$ java -jar target/myproject-0.0.1-SNAPSHOT.jar

It is also possible to run a packaged application with remote debugging support enabled. This allows you to attach a debugger to your packaged application:

$ java -Xdebug -Xrunjdwp:server=y,transport=dt_socket,address=8000,suspend=n \
       -jar target/myproject-0.0.1-SNAPSHOT.jar

The Spring Boot Maven plugin includes a run goal which can be used to quickly compile and run your application. Applications run in an exploded form, and you can edit resources for instant “hot” reload.

$ mvn spring-boot:run

You might also want to use the useful operating system environment variable:

$ export MAVEN_OPTS=-Xmx1024m -XX:MaxPermSize=128M -Djava.security.egd=file:/dev/./urandom

(The “egd” setting is to speed up Tomcat startup by giving it a faster source of entropy for session keys.)

The Spring Boot Gradle plugin also includes a bootRun task which can be used to run your application in an exploded form. The bootRun task is added whenever you import the spring-boot-gradle-plugin:

$ gradle bootRun

You might also want to use this useful operating system environment variable:

$ export JAVA_OPTS=-Xmx1024m -XX:MaxPermSize=128M -Djava.security.egd=file:/dev/./urandom

Since Spring Boot applications are just plain Java applications, JVM hot-swapping should work out of the box. JVM hot swapping is somewhat limited with the bytecode that it can replace, for a more complete solution JRebel or the Spring Loaded project can be used. The spring-boot-devtools module also includes support for quick application restarts.

See the Chapter 20, Developer tools section below and the Hot swapping “How-to” for details.