spring-properties-example

In Spring, you can use @PropertySource annotation to externalize your configuration to a properties file. In this tutorial, we will show you how to use @PropertySource to read a properties file and display the values with @Value and Environment.

P.S @PropertySource has been available since Spring 3.1

1. @PropertySource and @Value

A classic example, read a properties file and display with ${}.

config.properties

mongodb.url=1.2.3.4
mongodb.db=hello
AppConfigMongoDB

package com.mkyong.config;

import org.springframework.beans.factory.annotation.Value;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.PropertySource;
import org.springframework.context.support.PropertySourcesPlaceholderConfigurer;
//...

@Configuration
@ComponentScan(basePackages = { "com.mkyong.*" })
@PropertySource("classpath:config.properties")
public class AppConfigMongoDB {

	//1.2.3.4
	@Value("${mongodb.url}")
	private String mongodbUrl;

	//hello
	@Value("${mongodb.db}")
	private String defaultDb;

	@Bean
	public MongoTemplate mongoTemplate() throws Exception {

		MongoClientOptions mongoOptions = 
			new MongoClientOptions.Builder().maxWaitTime(1000 * 60 * 5).build();
		MongoClient mongo = new MongoClient(mongodbUrl, mongoOptions);
		MongoDbFactory mongoDbFactory = new SimpleMongoDbFactory(mongo, defaultDb);
		return new MongoTemplate(mongoDbFactory);

	}

	//To resolve ${} in @Value
	@Bean
	public static PropertySourcesPlaceholderConfigurer propertyConfigInDev() {
		return new PropertySourcesPlaceholderConfigurer();
	}

}
Note
To resolve ${} in @Values, you must register a static PropertySourcesPlaceholderConfigurer in either XML or annotation configuration file.

2. @PropertySource and Environment

Spring recommends to use Environment to get the property values.

AppConfigMongoDB

package com.mkyong.config;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.PropertySource;
import org.springframework.core.env.Environment;
//...

@Configuration
@ComponentScan(basePackages = { "com.mkyong.*" })
@PropertySource("classpath:config.properties")
public class AppConfigMongoDB {

	@Autowired
	private Environment env;

	@Bean
	public MongoTemplate mongoTemplate() throws Exception {

		String mongodbUrl = env.getProperty("mongodb.url");
		String defaultDb = env.getProperty("mongodb.db");
		
		MongoClientOptions mongoOptions = 
			new MongoClientOptions.Builder().maxWaitTime(1000 * 60 * 5).build();
		MongoClient mongo = new MongoClient(mongodbUrl, mongoOptions);
		MongoDbFactory mongoDbFactory = new SimpleMongoDbFactory(mongo, defaultDb);
		return new MongoTemplate(mongoDbFactory);

	}

}

3. More @PropertySource Examples

More common examples.

3.1 Example to resolve ${} within @PropertySource resource locations.


	@Configuration
	@PropertySource("file:${app.home}/app.properties")
	public class AppConfig {
		@Autowired
		Environment env;
	}

Set a system property during startup.


	System.setProperty("app.home", "test");

	java -jar -Dapp.home="/home/mkyon/test" example.jar

3.2 Include multiple properties files.


	@Configuration
	@PropertySource({
		"classpath:config.properties",
		"classpath:db.properties" //if same key, this will 'win'
	})
	public class AppConfig {
		@Autowired
		Environment env;
	}
Note
If a property key is duplicated, the last declared file will ‘win’ and override.

4. Spring 4 and @PropertySources

Some enhancements on Spring 4.

4.1 Introduces new @PropertySources to support Java 8 and better way to include multiple properties files.


	@Configuration
	@PropertySources({
		@PropertySource("classpath:config.properties"),
		@PropertySource("classpath:db.properties")
	})
	public class AppConfig {
		//...
	}

4.2 Allow @PropertySource to ignore the not found properties file.


	@Configuration
	@PropertySource("classpath:missing.properties")
	public class AppConfig {
		//...
	}

If missing.properties is not found, the system is unable to start and throws FileNotFoundException


	Caused by: java.io.FileNotFoundException: 
		class path resource [missiong.properties] cannot be opened because it does not exist

In Spring 4, you can use ignoreResourceNotFound to ignore the not found properties file


	@Configuration
	@PropertySource(value="classpath:missing.properties", ignoreResourceNotFound=true)
	public class AppConfig {
		//...
	}

        @PropertySources({
		@PropertySource(value = "classpath:missing.properties", ignoreResourceNotFound=true),
		@PropertySource("classpath:config.properties")
        })

Done.

References

  1. Sprong IO – PropertySource
  2. Spring IO – PropertySources
  3. Spring IO – Configuration
  4. Spring @Value default value
  5. Spring JIRA : SPR-8539