Spring: Autowiring modes

Auto wiring is a technique, where spring automatically inject a bean by using type, name (or) constructor arguments. Spring supports 4 modes of auto wiring.

         1. No Auto wiring

         2. Auto wiring by name

         3. Auto wiring by type

         4. Auto wiring by constructor.

        

In this post, I am going to explain these in brief, later posts explain each mode in detail with an example.

Mode	Description
no	This is the default mode, it specifies no auto wiring. Bean references are injected using ref element.
byName	Spring checks for a bean with same name as the proeperty that needs to be autowired.
byType	Allows a property to be autowired if exactly one bean of the property type exists in the container. If more than one bean of same property exists, then a fatal exception is thrown.
constructor	Analogous to byType, but applies to constructor arguments. If there is not exactly one bean of the constructor argument type in the container, a fatal error is raised.

Note

a.   Explicit dependencies in property and constructor-arg settings always override autowiring.

How to exclude a bean from autowiring?

In Spring’s XML format, set the autowire-candidate attribute of the <bean/> element to false; the container makes that specific bean definition unavailable to the autowiring infrastructure.

You can also limit autowire candidates based on pattern-matching against bean names. The top-level <beans/> element accepts one or more patterns within its default-autowire-candidates attribute. For example, to limit autowire candidate status to any bean whose name ends with Repository, provide a value of *Repository. To provide multiple patterns, define them in a comma-separated list. An explicit value of true or false for a bean definitions autowire-candidate attribute always takes precedence, and for such beans, the pattern matching rules do not apply.

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