Spring: How to Resolve a Property When There Are Multiple Resolvers? - spring

Question

We are building several Microservices using the Spring Cloud framework. One of the services has dependencies on some legacy shared libraries, and imports various XML files for bean configuration. The problem we are facing is that through these imports, multiple property resolvers are brought in and thus the following code in AbstractBeanFactory is failing to resolve spring.application.name because the value comes in as ${spring.application.name:unknown} that the first resolver fails to resolve and thus sets result to unknown. embeddedValueResolver does have a resolver than can resolve the property but because the property is set to it's default by a previous resolver, it doesn't get a chance. This is causing the service registration with Eureka to fail with a NPE.
#Override
public String resolveEmbeddedValue(String value) {
String result = value;
for (StringValueResolver resolver : this.embeddedValueResolvers) {
if (result == null) {
return null;
}
result = resolver.resolveStringValue(result);
}
return result;
}

Answer 1

Answering my own question, I fixed the issue using a BeanDefinitionRegistryPostProcessor. Related JIRA SPR-6428 had been filed by another user but was closed.
/**
* Removes {#link org.springframework.beans.factory.config.PropertyPlaceholderConfigurer} classes that come before
* {#link PropertySourcesPlaceholderConfigurer} and fail to resolve Spring Cloud properties, thus setting them to default.
* One such property is {#code spring.application.name} that gets set to 'unknown' thus causing registration with
* discovery service to fail. This class collects the {#code locations} from these offending
* {#code PropertyPlaceholderConfigurer} and later adds to the end of property sources available from
* {#link org.springframework.core.env.Environment}.
* <p>
* c.f. https://jira.spring.io/browse/SPR-6428
*
* #author Abhijit Sarkar
*/
#Component
#Slf4j
public class PropertyPlaceholderConfigurerPostProcessor implements BeanDefinitionRegistryPostProcessor {
private final Set<String> locations = new HashSet<>();
#Override
public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry beanDefinitionRegistry) throws BeansException {
String[] beanDefinitionNames = beanDefinitionRegistry.getBeanDefinitionNames();
List<String> propertyPlaceholderConfigurers = Arrays.stream(beanDefinitionNames)
.filter(name -> name.contains("PropertyPlaceholderConfigurer"))
.collect(toList());
for (String name : propertyPlaceholderConfigurers) {
BeanDefinition beanDefinition = beanDefinitionRegistry.getBeanDefinition(name);
TypedStringValue location = (TypedStringValue) beanDefinition.getPropertyValues().get("location");
if (location != null) {
String value = location.getValue();
log.info("Found location: {}.", location);
/* Remove 'classpath:' prefix, if present. It later creates problem with reading the file. */
locations.add(removeClasspathPrefixIfPresent(value));
log.info("Removing bean definition: {}.", name);
beanDefinitionRegistry.removeBeanDefinition(name);
}
}
}
private String removeClasspathPrefixIfPresent(String location) {
int classpathPrefixIdx = location.lastIndexOf(':');
return classpathPrefixIdx > 0 ? location.substring(++classpathPrefixIdx) : location;
}
#Override
public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
PropertySourcesPlaceholderConfigurer configurer =
beanFactory.getBean(PropertySourcesPlaceholderConfigurer.class);
MutablePropertySources propertySources = getPropertySources(configurer);
locations.stream()
.map(locationToPropertySrc)
.forEach(propertySources::addLast);
}
private MutablePropertySources getPropertySources(PropertySourcesPlaceholderConfigurer configurer) {
/* I don't like this but PropertySourcesPlaceholderConfigurer has no getter for environment. */
Field envField = null;
try {
envField = PropertySourcesPlaceholderConfigurer.class.getDeclaredField("environment");
envField.setAccessible(true);
ConfigurableEnvironment env = (ConfigurableEnvironment) envField.get(configurer);
return env.getPropertySources();
} catch (ReflectiveOperationException e) {
throw new ApplicationContextException("Our little hack didn't work. Failed to read field: environment.", e);
}
}
Function<String, PropertySource> locationToPropertySrc = location -> {
ClassPathResource resource = new ClassPathResource(location);
try {
Properties props = PropertiesLoaderUtils.loadProperties(resource);
String filename = getFilename(location);
log.debug("Adding property source with name: {} and location: {}.", filename, location);
return new PropertiesPropertySource(filename, props);
} catch (IOException e) {
throw new ApplicationContextException(
String.format("Failed to read from location: %s.", location), e);
}
};
private String getFilename(String location) {
return location.substring(location.lastIndexOf('/') + 1);
}
}