When we develop a Spring Boot application we can hot reload newly compiled classes using Gradle. The bootRun task of the Spring Boot Gradle plugin has support for Spring Loaded. We must add a dependency to Spring Loaded as a dependency for the classpath configuration in the buildscript block. If we now use the bootRun task everything is ready to reload changed classes. Now we can use the continuous build feature of Gradle to listen for changes in our source files to recompile them. The recompiled classes are then reloaded in the running Spring Boot application started with bootRun. We start a second Gradle instance with the -t option for the classes task. This way when we change a source file it gets recompiled automatically and reloaded.

The following build script shows how we add Spring Loaded:

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In Spring we can use the @Value annotation to set property or arguments values based on a SpEL expression. If we want to use the @Value annotation for a constructor argument we must not forget to add the @Autowired annotation on the constructor as well.

// File: sample/Message.groovy
package sample

import org.springframework.beans.factory.annotation.*
import org.springframework.stereotype.*

@Component
class Message {

    final String text

    // Use @Autowired to get @Value to work.
    @Autowired
    Message(
        // Refer to configuration property
        // app.message.text to set value for
        // constructor argument text.
        @Value('${app.message.text}') final String text) {
        this.text = text
    }

}

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