Prerequisite
To create a new Spring Boot Application project in Intellij go to File -> New -> Project…
Select “Spring Initializer” and give your project a name.
I prefer “Gradle”, so I selected Gradle instead of Maven. Select your JDK, etc.
Go to the next page and under “Web” select Spring Web.
For the example that follows I named it “Springy” and set the group to “com.slinky.springy”.
Introduction
This “example” will show how to use @Conditional in an @Configuration.
You should be familiar with the basic terminology of Spring Boot dependency injection. I recommend reading “Baeldung : Spring Dependency Injection”.
This example will use dependency injection to choose a specific implementation based on some logical condition. The condition I have chosen is simple: the value of an environment variable.
I use Intelli, so edit the configuration by adding “Environment variables:”. If you don’t see “Environment variables:” choose the “Modify options ⌄” to add the field to the dialog.
Create the Following Java Classes
StringStuff.java
package com.slinky.springy;
public interface StringStuff
{
String getString();
}
DevStringStuff.java
package com.slinky.springy;
import org.springframework.context.annotation.Conditional;
@Conditional(DevCondition.class)
public class DevStringStuff implements StringStuff
{
@Override
public String getString()
{
return "dev";
}
}
StageStringStuff.java
package com.slinky.springy;
import org.springframework.context.annotation.Conditional;
@Conditional(StageCondition.class)
public class StageStringStuff implements StringStuff
{
@Override
public String getString()
{
return "stage";
}
}
DevCondtion.java
package com.slinky.springy;
import org.springframework.context.annotation.Condition;
import org.springframework.context.annotation.ConditionContext;
import org.springframework.core.type.AnnotatedTypeMetadata;
public class DevCondition implements Condition
{
@Override
public boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata)
{
String environment = context.getEnvironment().getProperty("env");
return environment != null && environment.contains("dev");
}
}
StageCondition.java
package com.slinky.springy;
import org.springframework.context.annotation.Condition;
import org.springframework.context.annotation.ConditionContext;
import org.springframework.core.type.AnnotatedTypeMetadata;
public class StageCondition implements Condition
{
@Override
public boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata)
{
String environment = context.getEnvironment().getProperty("env");
return environment != null && environment.contains("stage");
}
}
Configurator.java
package com.slinky.springy;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Conditional;
import org.springframework.context.annotation.Configuration;
@Configuration
@ComponentScan("com.slinky.springy")
public class Configurator
{
@Bean
@Conditional(DevCondition.class)
public StringStuff getDevStringStuff() {
return new DevStringStuff();
}
@Bean
@Conditional(StageCondition.class)
public StringStuff getStageStringStuff() {
return new StageStringStuff();
}
}
SpringyApplication.java
package com.slinky.springy;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;
@SpringBootApplication(scanBasePackages = {"com.slinky.springy"})
@RestController
public class SpringyApplication
{
@Autowired(required = false)
private StringStuff stuffService;
public static void main(String[] args)
{
SpringApplication.run(SpringyApplication.class, args);
}
@GetMapping("/env")
public String env() {
if (null != stuffService) {
return stuffService.getString();
}
return "env error";
}
}
Conclusion
The preceding example is so that you can create a working solution that uses @Condition. I am not going to explain why it works or comment on Spring IOC. This is to help you see a working version instead of trying to decipher the documentation and tutorials you may find on the Web.
Run the Java project and open a browser window to this location:
http://localhost:8080/env
The use of an environment variable is just a simple way to create a condition. This may not be the best way to inject behavior based on a runtime environment variable.
