SpEL @ConditionalOnProperty string property empty or nulll

Question

I am currently having trouble with my dataSource bean creation on condition of String property from my applications.yaml file.

Ideally, I would only like to create the dataSource bean only if the url is set in my application.yaml file. Shouldn't create the bean if its not present (empty or null). I know this condition checks on boolean but is there anyway to check if the string property is empty or null?

DatabaseConfig.java

@Configuration
public class DatabaseConfig {
    @Value("${database.url:}")
    private String databaseUrl;

    @Value("${database.username:}")
    private String databaseUsername;

    @Value("${database.password:}")
    private String databasePassword;

    protected static final String DRIVER_CLASS_NAME = "com.sybase.jdbc4.jdbc.SybDriver";


    /**
     * Configures and returns a datasource. Optional
     *
     * @return A datasource.
     */
    @ConditionalOnProperty(value = "database.url")
    @Bean
    public DataSource dataSource() {
        return DataSourceBuilder.create()
            .url(testDatabaseUrl)
            .username(testDatabaseUsername)
            .password(testDatabasePassword)
            .build();
    }
}

application.yml (This field will be optional)

database:
  url: http://localhost:9000

Solution 1

You could use @ConditionalOnExpression with a Spring Expression Language (SpEL) expression as value:

@ConditionalOnExpression("!T(org.springframework.util.StringUtils).isEmpty('${database.url:}')")
@Bean
public DataSource dataSource() {
    // snip
}

For better readability and reusability you could turn this into an annotation:

@Target({ ElementType.TYPE, ElementType.METHOD })
@Retention(RetentionPolicy.RUNTIME)
@Documented
@ConditionalOnExpression("!T(org.springframework.util.StringUtils).isEmpty('${database.url:}')")
public @interface ConditionalOnDatabaseUrl {
}

@ConditionalOnDatabaseUrl
@Bean
public DataSource dataSource() {
    // snip
}

Solution 2

I'm having the same issue. As I undestood, you'r looking for "property exists and not empty" condition. This condition doesn't come out of the box, therefore some coding required. Solution using org.springframework.context.annotation.Conditional works for me:

1. Create ConditionalOnPropertyNotEmpty annotation and accompanied OnPropertyNotEmptyCondition class as follows:

   // ConditionalOnPropertyNotEmpty.java
   
   import org.springframework.context.annotation.Condition;
   import org.springframework.context.annotation.ConditionContext;
   import org.springframework.context.annotation.Conditional;
   import org.springframework.core.type.AnnotatedTypeMetadata;
   import java.lang.annotation.ElementType;
   import java.lang.annotation.Retention;
   import java.lang.annotation.RetentionPolicy;
   import java.lang.annotation.Target;
   import java.util.Map;
   
   @Target({ ElementType.TYPE, ElementType.METHOD })
   @Retention(RetentionPolicy.RUNTIME)
   @Conditional(ConditionalOnPropertyNotEmpty.OnPropertyNotEmptyCondition.class)
   public @interface ConditionalOnPropertyNotEmpty {
       String value();
   
       class OnPropertyNotEmptyCondition implements Condition {
   
           @Override
           public boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata) {
               Map<String, Object> attrs = metadata.getAnnotationAttributes(ConditionalOnPropertyNotEmpty.class.getName());
               String propertyName = (String) attrs.get("value");
               String val = context.getEnvironment().getProperty(propertyName);
               return val != null && !val.trim().isEmpty();
           }
       }
   }
   

2. Annotate your bean with ConditionalOnPropertyNotEmpty, like:

   @ConditionalOnPropertyNotEmpty("database.url")
   @Bean
   public DataSource dataSource() { ... }
   

--

Alternatively, you can either set detabase.url to false explicitly (e.g. detabase.url: false) or do not define detabase.url at all in your config. Then, @ConditionalOnProperty(value = "database.url") will work for you as expected.

Solution 3

You can try more generic purpose annotation which is standard for the Spring Core: org.springframework.context.annotation.Conditional.

In the context objects for your callback you can get all the information you need: org.springframework.context.annotation.Condition

Also you can consider using Profiles.

Comments

[Hong]

May I know why we need generic type over there? T(org.springframework.util.StringUtils)

[sfussenegger]

@Hong the T(..) is to reference types and has nothing to do with generics. I assume you were thinking of <T>. Here's the SpEL reference: docs.spring.io/spring-framework/docs/current/reference/html/‌​…