SpEL @ConditionalOnProperty字符串属性为空或为空 [英] SpEL @ConditionalOnProperty string property empty or nulll

问题描述

我目前在我的application.yaml文件中具有String属性的情况下无法创建dataSource bean.

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

理想情况下，仅当在application.yaml文件中设置了URL时，我才想创建dataSource bean.如果bean不存在(空或null)，则不应创建.我知道这种情况会检查布尔值，但是是否仍然可以检查string属性为空还是null?

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

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(此字段为可选)

application.yml (This field will be optional)

database:
  url: http://localhost:9000

推荐答案

您可以将 @ConditionalOnExpression 与

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
}

为获得更好的可读性和可重用性，您可以将其转换为注释:

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
}

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