Spring Bootstrap

Experimental work based on discussions at SpringOne2GX 2012. See also the 'bootstrap' branch of Spring.

Elevator Pitch

Opinionated view of the Spring family so that new users can quickly get to the 'meat and potatoes'. Assumes no knowledge of the Java development ecosystem. Absolutely no code generation and no XML.

Installing

You need to build from source for now, but when it's done instructions will look like this:

1. Get Java Download and install the Java SDK from www.java.com

2. Get Spring curl -s try.springsource.org | bash or use the Windows installer

3. Get to Work! spr run yoursourcefile.groovy

What? It's Groovy then? or like Grails? or another Roo?

There is a command line tool that uses Groovy underneath so that we can present simple snippets that can just run:

@Controller
class ThisWillActuallyRun {

	@RequestMapping("/")
	@ResponseBody
	String home() {
		return "Hello World!"
	}
}

By inspecting the code for well known annotations we can @Grab appropriate dependencies and also dynamically add import statements. Groovy makes this really easy.

If you don't want to use the command line tool, and you would rather work using Java and an IDE you can. Just add a main() method that calls SpringApplication and add @EnableAutoConfiguration:

import org.springframework.bootstrap.*;
import org.springframework.context.annotation.*;

@Configuration
@EnableAutoConfiguration
@ComponentScan
public class MyApplication {

	public static void main(String[] args) throws Exception {
		SpringApplication.run(MyApplication.class, args);
	}

}


import org.springframework.beans.factory.annotation.*;
import org.springframework.stereotype.*;
import org.springframework.web.bind.annotation.*;

@Controller
public class SampleController {

		@RequestMapping("/")
		@ResponseBody
		String home() {
			return "Hello World!"
		}

}

Under the hood

There are a number of disparate parts of Bootstrap. Here are the important classes:

The Spring CLI

The 'spr' command line application compiles and runs Groovy source, adding import statements and @Grab annotations. The application can also watch files, automatically recompiling and restarting when they change.

SpringApplication

The SpringApplication class provides the main entry point for a standalone Spring Application. Its sole job is to create and refresh an appropriate Spring ApplicationContext. Any contained beans that implements CommandLineRunner will be executed after the context has started. A SpringApplication can load beans from a number of different sources, including classes, packages (scanned) or XML files. By default a AnnotationConfigApplicationContext or AnnotationConfigEmbeddedWebApplicationContext depending on your classpath.

EmbeddedWebApplicationContext

The EmbeddedWebApplicationContext will probably be part of Spring 4.0. It provides a Spring 'WebApplicationContext' that can bootstrap itself and start and embedded servlet container. Support is provided for Tomcat and Jetty.

@EnableAutoConfigure

The @EnableAutoConfigure can be used on a @Configuration class to trigger auto-configuration of the Spring context. Auto-configuration attempts to guess what beans a user might want based on their classpath. For example, If a 'HSQLDB' is on the classpath the user probably wants an in-memory database to be defined. Auto-configuration will back away as the user starts to define their own beans.

@Conditional

The @Conditional annotation will probably be part of Spring 4.0. It provides allows @Configuration classes to be skipped depending on conditions. Bootstrap provides @ConditionalOnBean, @ConditionalOnMissingBean and @ConditionalOnClass annotations are used when defining auto-configuration classes.

Building the code

Use maven to build the source code.

mvn clean install

Importing into eclipse

You can use m2e or maven eclipse:eclipse.

Project specific settings are configured for source formatting. If you are using m2e please follow these steps to install eclipse support:

• Select Install new software from the help menu
• Click Add... to add a new repository
• Click the Archive... button
• Select org.eclipse.m2e.maveneclipse.site-0.0.1-SNAPSHOT-site.zip from the eclipse folder in this checkout
• Install "Maven Integration for the maven-eclipse-plugin"

If you prefer you can import settings manually from the /eclipse folder.

Samples

The following samples are included. To run use java -jar <archive>-full.jar

• spring-bootstrap-simple-sample - A simple command line application
• spring-bootstrap-jetty-sample - Embedded Jetty
• spring-bootstrap-tomcat-sample - Embedded Tomcat
• spring-bootstrap-data-sample - Spring Data JPA + Hibernate + HSQLDB