Properties Withspringandspringboot Baeldung

https://www.baeldung.com/properties-with-spring 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: One other very useful way of registering a new properties file is using a placeholder to allow you to dynamically select the right file at runtime; for example: 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: 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: 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: 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: 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: A default value of the property can also be specified: Using properties in Spring XML configuration: 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: 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: 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: 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/*/: 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: If we don't want to use a file, we can specify names and values directly: We can also achieve a similar effect using the properties argument of the @SpringBootTest annotation: 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: And then let's use the annotation to map them to a database object: 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 the in-depth article. 5.6. Alternative – YAML Files YAML files are also supported. 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 your classpath.

YAML is particularly good for hierarchical property storage; the following property file: Is synonymous to the following YAML file: 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 As opposed to using files, properties can be passed directly on the command line: You can also do this via system properties, which are provided before the -jar command rather than after it: 5.8.

Properties from Environment Variables Spring Boot will also detect environment variables, treating them as properties: 5.9 Randomization of Property Values If we don't want determinist property values, RandomValuePropertySource can be used to randomize the values of properties: 5.10. Additional Types of Property Sources Spring Boot supports a multitude of property sources, implementing a well-thought 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. 6.1. Java configuration 6.2. XML configuration 7.

Configuration Using Raw Beans in Spring 3.1 – the PropertySourcesPlaceholderConfigurer Similarly, in Spring 3.1, the new PropertySourcesPlaceholderConfigurer can also be configured manually: 7.1. Java configuration 7.2. XML configuration 8. Properties in Parent-Child Contexts This question keeps coming up again and again – what happens when your 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? What's more – how to best retrieve these properties from Spring? Here is 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 shows several examples of working with properties and properties files in Spring. As always, the entire code backing the article is available over on Github. This is a Maven-based project, so it should be easy to import and run as it is. 微信公众号: 架构师日常笔记 欢迎关注！

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