1. Overview
Spring’s @Value annotation provides a convenient way to inject property values into components. It’s also quite useful to provide sensible defaults for cases where a property may not be present.
That’s what we’re going to be focusing on in this tutorial — how to specify a default value for the @Value Spring annotation.
For a more detailed quick guide on @Value, see the article here.
2. String Defaults
Let’s look at the basic syntax for setting a default value for a String property:
@Value("${some.key:my default value}")
private String stringWithDefaultValue;
If some.key cannot be resolved, stringW**ithDefaultValue will be set to the default value of my default value.
Similarly, we can set a zero-length String as the default value:
@Value("${some.key:})"
private String stringWithBlankDefaultValue;
3. Primitives
To set a default value for primitive types such as boolean and int, we use the literal value:
@Value("${some.key:true}")
private boolean booleanWithDefaultValue;
@Value("${some.key:42}")
private int intWithDefaultValue;
If we wanted to, we could use primitive wrappers instead by changing the types to Boolean and Integer.
4. Arrays
We can also inject a comma separated list of values into an array:
@Value("${some.key:one,two,three}")
private String[] stringArrayWithDefaults;
@Value("${some.key:1,2,3}")
private int[] intArrayWithDefaults;
In the first example above, the values one, two and three are injected as defaults into stringArrayWithDefaults.
In the second example, the values 1, 2 and 3 are injected as defaults into intArrayWithDefaults.
5. Using SpEL
We can also use Spring Expression Language (SpEL) to specify an expression and a default.
In the example below, we expect some.system.key to be set as a system property, and if it is not set, we want to use my default system property value as a default:
@Value("#{systemProperties['some.key'] ?: 'my default system property value'}")
private String spelWithDefaultValue;
6. Conclusion
In this quick article, we looked at how we can set a default value for a property whose value we would like to have injected using Spring’s @Value annotation.
As usual, all the code samples used in this article can found in the GitHub project.