Spring @Value annotation not using defaults when property is not present

Question

I am trying to use @Value annotation in the parameters of a constructor as follows:

@Autowired
public StringEncryptor(
    @Value(\"${encryptor.password:\\\"\\\"         


        

Answer 1

In my case, resolving the property values (and the defaults) did not work in test, where I use an annotation based configuration. It turned out that I had to add a PropertySourcesPlaceholderConfigurer so that properties actually get resolved. It was explained in the PropertySource Annotation JavaDoc:

In order to resolve ${...} placeholders in definitions or @Value annotations using properties from a PropertySource, one must register a PropertySourcesPlaceholderConfigurer. This happens automatically when using in XML, but must be explicitly registered using a static @Bean method when using @Configuration classes. See the "Working with externalized values" section of @Configuration Javadoc and "a note on BeanFactoryPostProcessor-returning @Bean methods" of @Bean Javadoc for details and examples.

The following did the trick:

@Bean
public static PropertySourcesPlaceholderConfigurer propertySourcesPlaceholderConfigurer() {
    return new PropertySourcesPlaceholderConfigurer();
}

And if you want to add individual properties:

@Bean
public static PropertySourcesPlaceholderConfigurer propertySourcesPlaceholderConfigurer() {

    PropertySourcesPlaceholderConfigurer propertySourcesPlaceholderConfigurer = new PropertySourcesPlaceholderConfigurer();

    Properties properties = new Properties();
    properties.put("batchSize", "250");
    propertySourcesPlaceholderConfigurer.setProperties(properties);

    return propertySourcesPlaceholderConfigurer;
}

Answer 2

Perhaps initialization of property placeholder configurer fails due to missed properties file, so that placeholders are not resolved. You can configure it to ignore missed files as follows (if you use context namespace to configure it):

<context:property-placeholder ignore-resource-not-found="true" ... />

Also you don't need "..." around default values.

Answer 3

ignore-resource-not-found="true" is not necessary for the defaults to be picked up. The point of specifying the default value is for it to be used if the property is not found anywhere.

I think the last sentence in the previous answer points to the problem - incorrect EL that you must have originally provided but then removed from the example. The fact that you were getting format conversion exceptions points to that as well. Normally, Spring will automatically convert Strings to the appropriate "standard" Java type, and if you provide your own implementation of the Spring Conversion Service, to your custom objects as well - as long as your conversion service is defined in the app context.

"ignore-resource-not-found" is useful when you are injecting properties via XML without defaults and don't want the container to throw an exception instantiating the bean in case no property is found. In such cases the bean properties will be initialized with the Java defaults, e.g. nulls fro objects, 0s for primitive numeric values, etc.