Remote PropertySource - spring

Question

Has anyone had any luck constructing a PropertySource that uses a remote source (for example a database) from which to retrieve property values. The idea would be to construct a PropertySource (needs some connection information such as host/port) and plug that into a PropertySourcePlaceholderConfigurer.
The problem seems to be a chicken and egg problem. How can I get the connection information down to the PropertySource? I could first instantiate the PropertySourcePlaceholderConfigurer with configuration to load a property file with the remote host and port properties and then later instantiate the PropertySource and inject that back into the configurer. However, I can't seem to figure a way to ensure that the very first bean to be instantiated (and quickly injected into the configurer) is my property source. I need to have this because, of course, all my other beans depend on the remote properties.

Answer 1

Commons Configuration supports loading properties from a variety of sources (including JDBC Datasources) into a org.apache.commons.configuration.Configuration object via a org.apache.commons.configuration.ConfigurationBuilder.
Using the org.apache.commons.configuration.ConfiguratorConverter, you can convert the Configuration object into a java.util.Properties object which can be passed to the PropertySourcesPlaceholderConfigurer.
As to the chicken and egg question of how to configure the ConfigurationBuilder, I recommend using the org.springframework.core.env.Environment to query for system properties, command-line properties or JNDI properties.
In this exampe:
#Configuration
public class RemotePropertyConfig {
#Bean
public static PropertySourcesPlaceholderConfigurer propertyPlaceholderConfigurer(Environment environment)
throws Exception {
final PropertySourcesPlaceholderConfigurer props = new PropertySourcesPlaceholderConfigurer();
final ConfigurationBuilder configurationBuilder = new DefaultConfigurationBuilder(environment.getProperty("configuration.definition.file"));
props.setProperties(ConfigurationConverter.getProperties(configurationBuilder.getConfiguration()));
return props;
}
You will need to specify the environment property configuration.definition.file which points to a file needed to configure Commons Configuration:

Answer 2

Similar to Recardo's answer above, I used Spring's PropertiesLoaderUtils instead of Apache's, but it amounts to the same thing. It's not exactly ideal.. hard coded dependency injection, but hey, it works!
/**
* This method must remain static as it's part of spring's initialization effort.
* #return
**/
#Bean
public static PropertySourcesPlaceholderConfigurer propertySourcesPlaceholderConfigurer() {
PropertySourcesPlaceholderConfigurer configurer = new PropertySourcesPlaceholderConfigurer();
String dbHost = null;
Integer dbPort = null;
// check system / environment properties first
Environment environment = new StandardEnvironment();
if (environment.containsProperty(DB_HOST_KEY)) {
dbHost = environment.getProperty(DB_HOST_KEY);
}
if (environment.containsProperty(DB_PORT_KEY)) {
dbPort = Integer.valueOf(environment.getProperty(DB_PORT_KEY));
}
if (dbHost == null || dbPort == null) {
// ok one or (probably) both properties null, let's go find the database.properties file
Properties dbProperties;
try {
dbProperties = PropertiesLoaderUtils.loadProperties(new EncodedResource(new ClassPathResource("database.properties"), "UTF-8"));
}
catch (IOException e) {
throw new RuntimeException("Could not load database.properties. Please confirm the file is in the classpath");
}
if (dbHost == null) {
dbHost = dbProperties.getProperty(DB_HOST_KEY);
}
if (dbPort == null) {
dbPort = Integer.valueOf(dbProperties.getProperty(DB_PORT_KEY));
}
}
PropertySourceService propertySourceService = new DBPropertySourceService(dbHost, dbPort);
PropertySource<PropertySourceService> propertySource = new DBPropertySource(propertySourceService);
MutablePropertySources propertySources = new MutablePropertySources();
propertySources.addFirst(propertySource);
configurer.setPropertySources(propertySources);
return configurer;
}
per request, here is the source of the remote property source. It depends on a 'service' class that might do.. well.. anything.. remote access of a property over a socket, talk to a database, whatever.
/**
* Property source for use with spring's PropertySourcesPlaceholderConfigurer where the source is a service
* that connects to remote server for property values.
**/
public class RemotePropertySource extends PropertySource<PropertySourceService> {
private final Environment environment;
/**
* Constructor...
* #param name
* #param source
**/
public RemotePropertySource(PropertySourceService source) {
super("RemotePropertySource", source);
environment = new StandardEnvironment();
}
/* (non-Javadoc)
* #see org.springframework.core.env.PropertySource#getProperty(java.lang.String)
*/
#Override
public Object getProperty(String name) {
// check system / environment properties first
String value;
if (environment.containsProperty(name)) {
value = environment.getProperty(name);
}
else {
value = source.getProperty(name);
}
return value;
}
}