M01 Q28 How do you inject scalar/literal values into Spring beans?

To inject scalar/literal values into Spring Beans, you need to use @Value annotation. @Value annotation has only one field value.

@Value annotation has one field value that accepts:

• Simple value
• Property reference
• SpEL String

@Value annotation can be used on top of:

• Field

• Constructor Parameter

• Method – all fields will have injected the same value. All of the parameters in the method will have the same value injected

• Method parameter – Injection will not be performed automatically if @Value is not present on method level or if @Autowired is not present at the method level

• Annotation type

Inside @Value you can specify:

• Simple value - @Value("John"), @Value("true")
• Reference a property - @Value("${app.department.id}")
• Perform SpEL inline computation - @Value("#{'Wall Street'.toUpperCase()}"), @Value("#{5000 * 0.9}"), @Value("#{'${app.department.id}'.toUpperCase()}")
• Inject values into an array, list, set, map. To do this you need to implement ConversionService to convert the string from the application.properties to set or array.

What is the difference between $ and # in @Value expressions?

@Value annotation supports two types of expressions:

• Expressions starting with $ - used to reference a property in Spring Environment Abstraction
• Expressions starting with # - SpEL expressions parsed and evaluated by SpEL