Spring - AutoWiring

Spring automatically resolves the dependencies between the collaborating beans by inspecting the contents of the BeanFactory. This is called Autowiring.

Spring has 5 modes of autowiring:

1. no

    - default

    - means no autowiring

    - we have to use explicit bean reference for wiring

2. byName

    - autowiring by property name

    - The IoC container looks at the properties of the beans on which autowire attribute is set to byName in the XML configuration file

3. byType

    - autowiring by property datatype

    - The IoC container tries to match and wire a property if its type matches with exactly one of the beans name in configuration file.

    - if more than one such bean exists, a fatal exception is thrown

4. constructor

    - similar to byType but type applies to constructor arguments.

5. autodetect

    - spring first tries to autowire by constructor, if it fails, spring tries to autowire by type.

Limitations of autowiring

- overriding possibility 

    dependencies can still be specified using <constructor-arg> and <property> setting which will override autowiring

- primitive datatypes

    we cannot autowire primitive datatypes

- less exact

    autowiring is less exact than explicit wiring