1. Overview

This tutorial will show how to set up and use properties in Spring via Java configuration and @PropertySource or via XML and <property-placeholder>.

We'll also see how properties work in Spring Boot.

2. Register a Properties File via Java Annotations

Spring 3.1 also introduces the new @PropertySource annotation as a convenient mechanism for adding property sources to the environment.

This annotation is to be used in conjunction with Java-based configuration and the @Configuration annotation:

@Configuration @PropertySource("classpath:foo.properties") public class PropertiesWithJavaConfig { //... }

Another very useful way to register a new properties file is using a placeholder, which allows us to dynamically select the right file at runtime:

@PropertySource({ "classpath:persistence-${envTarget:mysql}.properties" }) ...

2.1. Defining Multiple Property Locations

The @PropertySource annotation is repeatable according to Java 8 conventions. Therefore, if we're using Java 8 or higher, we can use this annotation to define multiple property locations:

@PropertySource("classpath:foo.properties") @PropertySource("classpath:bar.properties") public class PropertiesWithJavaConfig { //... }

Of course, we can also use the @PropertySources annotation and specify an array of @PropertySource. This works in any supported Java version, not just in Java 8 or higher:

@PropertySources({ @PropertySource("classpath:foo.properties"), @PropertySource("classpath:bar.properties") }) public class PropertiesWithJavaConfig { //... }

In either case, it's worth noting that in the event of a property name collision, the last source read takes precedence.

3. Register a Properties File in XML

In XML, new properties files can be made accessible to Spring via the <context:property-placeholder … > namespace element:

<context:property-placeholder location="classpath:foo.properties" />

The foo.properties file should be placed under /src/main/resources so that it will be available on the classpath at runtime.

In case multiple <property-placeholder> elements are present in the Spring context, there are a few recommended best practices:

The order attribute needs to be specified to fix the order in which these are processed by Spring.

All property placeholders minus the last one (highest order) should have ignore-unresolvable=”true” to allow the resolution mechanism to pass to others in the context without throwing an exception.

3.1. Register Multiple Properties Files in XML

In the previous section, we saw how to define multiple properties files using annotations in Java 8 or later.

Similarly, we can define multiple properties files using XML configuration:

<context:property-placeholder location="classpath:foo.properties, classpath:bar.properties"/>

And as before, in the event of a property name collision, the last source read takes precedence.

4. Using/Injecting Properties

Injecting a property with the @Value annotation is straightforward:

@Value( "${jdbc.url}" ) private String jdbcUrl;

We can also specify a default value for the property:

@Value( "${jdbc.url:aDefaultUrl}" ) private String jdbcUrl;

And we can do the same using XML configuration:

<bean id="dataSource"> <property name="url" value="${jdbc.url}" /> </bean>

Both the older PropertyPlaceholderConfigurer and the new PropertySourcesPlaceholderConfigurer added in Spring 3.1 resolve ${…} placeholders within bean definition property values and @Value annotations.

Finally, we can obtain the value of a property using the Environment API:

@Autowired private Environment env; ... dataSource.setUrl(env.getProperty("jdbc.url"));

A very important caveat here is that using <property-placeholder> will not expose the properties to the Spring Environment.

This means that retrieving the value like this will not work — it will return null:

env.getProperty("key.something")

5. Properties With Spring Boot

Before we go into more advanced configuration options for properties, let's spend some time looking at the new properties support in Spring Boot.

Generally speaking, this new support involves less configuration compared to standard Spring, which is of course one of the main goals of Boot.

5.1. application.properties: The Default Property File

Boot applies its typical convention over configuration approach to property files. This means that we can simply put an application.properties file in our src/main/resources directory, and it will be auto-detected. We can then inject any loaded properties from it as normal.

So, by using this default file, we don’t have to explicitly register a PropertySource or even provide a path to a property file.

We can also configure a different file at runtime if we need to, using an environment property:

java -jar app.jar --spring.config.location=classpath:/another-location.properties

As of Spring Boot 2.3, we can also specify wildcard locations for configuration files.

For example, we can set the spring.config.location property to config/*/:

java -jar app.jar --spring.config.location=config/*/

This way, Spring Boot will look for configuration files matching the config/*/ directory pattern outside of our jar file. This comes in handy when we have multiple sources of configuration properties.

5.2. Environment-Specific Properties File

If we need to target different environments, there's a built-in mechanism for that in Boot.

We can simply define an application-environment.properties file in the src/main/resources directory, and then set a Spring profile with the same environment name.

For example, if we define a “staging” environment, that means we'll have to define a staging profile and then application-staging.properties.

This env file will be loaded and will take precedence over the default property file. Note that the default file will still be loaded, it's just that when there is a property collision, the environment-specific property file takes precedence.

5.3. Test-Specific Properties File

We might also have a requirement to use different property values when our application is under test.

Spring Boot handles this for us by looking in our src/test/resources directory during a test run. Again, default properties will still be injectable as normal but will be overridden by these if there is a collision.

5.4. The @TestPropertySource Annotation

If we need more granular control over test properties, then we can use the @TestPropertySource annotation.

This allows us to set test properties for a specific test context, taking precedence over the default property sources:

@RunWith(SpringRunner.class) @TestPropertySource("/foo.properties") public class FilePropertyInjectionUnitTest { @Value("${foo}") private String foo; @Test public void whenFilePropertyProvided_thenProperlyInjected() { assertThat(foo).isEqualTo("bar"); } }

If we don't want to use a file, we can specify names and values directly:

@RunWith(SpringRunner.class) @TestPropertySource(properties = {"foo=bar"}) public class PropertyInjectionUnitTest { @Value("${foo}") private String foo; @Test public void whenPropertyProvided_thenProperlyInjected() { assertThat(foo).isEqualTo("bar"); } }

We can also achieve a similar effect using the properties argument of the @SpringBootTest annotation:

@RunWith(SpringRunner.class) @SpringBootTest( properties = {"foo=bar"}, classes = SpringBootPropertiesTestApplication.class) public class SpringBootPropertyInjectionIntegrationTest { @Value("${foo}") private String foo; @Test public void whenSpringBootPropertyProvided_thenProperlyInjected() { assertThat(foo).isEqualTo("bar"); } }

5.5. Hierarchical Properties

If we have properties that are grouped together, we can make use of the @ConfigurationProperties annotation, which will map these property hierarchies into Java objects graphs.

Let's take some properties used to configure a database connection:

database.url=jdbc:postgresql:/localhost:5432/instance database.username=foo database.password=bar

And then let's use the annotation to map them to a database object:

@ConfigurationProperties(prefix = "database") public class Database { String url; String username; String password; // standard getters and setters }

Spring Boot applies it's convention over configuration approach again, automatically mapping between property names and their corresponding fields. All that we need to supply is the property prefix.

If you want to dig deeper into configuration properties, have a look at our in-depth article.

5.6. Alternative: YAML Files

Spring also supports YAML files.

All the same naming rules apply for test-specific, environment-specific, and default property files. The only difference is the file extension and a dependency on the SnakeYAML library being on our classpath.

YAML is particularly good for hierarchical property storage; the following property file:

database.url=jdbc:postgresql:/localhost:5432/instance database.username=foo database.password=bar secret: foo

is synonymous to the following YAML file:

database: url: jdbc:postgresql:/localhost:5432/instance username: foo password: bar secret: foo

It's also worth mentioning that YAML files do not support the @PropertySource annotation, so if the use of the annotation was required, it would constrain us to using a properties file.

5.7. Properties From Command Line Arguments

Besides using files, we can pass properties directly on the command line:

java -jar app.jar --property="value"

We can also do this via system properties, which are provided before the -jar command rather than after it:

java -Dproperty.name="value" -jar app.jar

5.8. Properties From Environment Variables

Spring Boot will also detect environment variables, treating them as properties:

export name=value java -jar app.jar

5.9. Randomization of Property Values

If we don't want determinist property values, we can use RandomValuePropertySource to randomize the values of properties:

random.number=${random.int} random.long=${random.long} random.uuid=${random.uuid}

5.10. Additional Types of Property Sources

Spring Boot supports a multitude of property sources, implementing a well-thought-out ordering to allow sensible overriding. It's worth consulting the official documentation, which goes further than the scope of this article.

6. Configuration Using Raw Beans in Spring 3.0 — The PropertyPlaceholderConfigurer

Besides the convenient methods of getting properties into Spring — annotations and the XML namespace — the property configuration bean can also be defined and registered manually.

Working with the PropertyPlaceholderConfigurer gives us full control over the configuration, with the downside of being more verbose and most of the time, unnecessary.

Let's see how we can define this bean using Java configuration:

@Bean public static PropertyPlaceholderConfigurer properties() { PropertyPlaceholderConfigurer ppc = new PropertyPlaceholderConfigurer(); Resource[] resources = new ClassPathResource[] { new ClassPathResource( "foo.properties" ) }; ppc.setLocations( resources ); ppc.setIgnoreUnresolvablePlaceholders( true ); return ppc; }

And using XML configuration:

<bean class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer"> <property name="locations"> <list> <value>classpath:foo.properties</value> </list> </property> <property name="ignoreUnresolvablePlaceholders" value="true"/> </bean>

7. Configuration Using Raw Beans in Spring 3.1 — The PropertySourcesPlaceholderConfigurer

Similarly, in Spring 3.1, the new PropertySourcesPlaceholderConfigurer can also be configured manually:

@Bean public static PropertySourcesPlaceholderConfigurer properties(){ PropertySourcesPlaceholderConfigurer pspc = new PropertySourcesPlaceholderConfigurer(); Resource[] resources = new ClassPathResource[ ] { new ClassPathResource( "foo.properties" ) }; pspc.setLocations( resources ); pspc.setIgnoreUnresolvablePlaceholders( true ); return pspc; }

And the corresponding XML configuration:

<bean class="org.springframework.context.support.PropertySourcesPlaceholderConfigurer"> <property name="locations"> <list> <value>classpath:foo.properties</value> </list> </property> <property name="ignoreUnresolvablePlaceholders" value="true"/> </bean>

8. Properties in Parent-Child Contexts

This question comes up again and again: What happens when our web application has a parent and a child context? The parent context may have some common core functionality and beans, and then one (or multiple) child contexts, maybe containing servlet-specific beans.

In that case, what's the best way to define properties files and include them in these contexts? And how to best retrieve these properties from Spring?

We'll give a simple breakdown.

8.1. If the Properties File Is Defined in XML With <property-placeholder>

If the file is defined in the Parent context:

@Value works in Child context: NO

@Value works in Parent context: YES

If the file is defined in the Child context:

@Value works in Child context: YES

@Value works in Parent context: NO

Finally, as we discussed before, <property-placeholder> does not expose the properties to the environment, so:

environment.getProperty works in either context: NO

8.2. If the Properties File Is Defined in Java With @PropertySource

If the file is defined in the Parent context:

@Value works in Child context: YES

@Value works in Parent context: YES

environment.getProperty in Child context: YES

environment.getProperty in Parent context: YES

If the file is defined in the Child context:

@Value works in Child context: YES

@Value works in Parent context: NO

environment.getProperty in Child context: YES

environment.getProperty in Parent context: NO

9. Conclusion

This article showed several examples of working with properties and properties files in Spring.

As always, the entire code backing the article is available over on GitHub.