How to Build a Custom Spring Boot Starter

My code library can be configured automatically using spring boot. It’s so cool.

As an enterprise java programmer, spring boot is so convenient that I can’t live without it. Its auto-configuration feature allows us to run your application in a few simple steps. Spring boot provides many starters to make your development faster and simpler. You don’t have to worry about complex configurations and class library references. Take developing a web service as an example.

• Using some starters dependencies such as spring-boot-starter and spring-boot-starter-web
• Add Webserver related parameters, such as server.port
• Start Server

Can we use spring boot to package our own starter library? The answer is yes. That is spring-boot, a framework with excellent extensibility.

Understanding Auto Configuration

Now let’s try to understand the principle of spring boot's auto-configuration function. To understand this part, you need to have a specific understanding of the life cycle of spring boot beans.

Spring boot uses the @EnableAutoConfigurationannotation to implement the auto-configuration. This annotation import the autoconfigurationImportSelectorclass, which resolves META-INF/spring.factories file when spring boot starts, and then all configuration classes in the file are loaded into memory and registered in the spring container. The spring.factories file is like this.

# Auto Configure
org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
org.springframework.boot.autoconfigure.aop.AopAutoConfiguration

After the BeanFactory is created, spring boot will call a specific beanFactoryPostProcessor--ConfigurationClassPostProcessorto complete the configuration classes resolution. The purpose is to register the methods modified by the @Bean annotation in the configuration class in the spring container as special beans. The beans defined in the configuration class are managed by the spring container, and we can do anything with spring. This is the auto configuration principle of spring boot.

Create a Custom Starter Library

First, you need to create a spring project. Here is the pom.xml of my example.

Then create your auto configuration class, and add the @configuration annotation on the class like this.

In this demo, I created a MyAutoConfiguration class, which hopes to inject a java bean of UserManager.

Finally, create a directory called META-INF under the resources directory, and create a file called spring.factories, which needs to configure your configuration class. As shown in the following figure:

Congratulations. Your spring boot starter is ready to work. You can use this starter in maven pom.xml like this.

<dependency>
        <groupId>com.lance.demo</groupId>
        <artifactId>my-spring-boot-starter</artifactId>
        <version>1.0.0-SNAPSHOT</version>
   </dependency>

Here is the output of running this application.

Now try to package your class library with spring boot. Thanks for reading.