@Autowire default mode

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How does Spring @Autowire beans: byName or byType? If one is not possible, is a second trial done using another mode?

If annotated with @Autowired it will inject the bean with the matching type (An exception will be thrown if there are more than one of a type). To specify a name use the @Qualifier annotation.

Spring Bean Autowiring - @Autowired, The default autowire mode in java configuration is byType . Spring bean autowiring modes. Table of Contents 1. Autowiring modes 2. @Autowired annotation 3. The default autowire mode in XML configuration is no.; The default autowire mode in java configuration is byType.; Spring bean autowiring modes Table of Contents 1. Autowiring modes 2.

Springs @Autowire wires by type. For wiring by name you can also use

@Resource(name = "id")

Autowiring in Spring, The XML-configuration-based autowiring functionality has five modes – no , byName , byType , constructor , and autodetect . The default mode� Mode Description; 1) no: It is the default autowiring mode. It means no autowiring bydefault. 2) byName: The byName mode injects the object dependency according to name of the bean. In such case, property name and bean name must be same. It internally calls setter method. 3) byType: The byType mode injects the object dependency according to type.

The default mode of the @Autowired is byType.

Autowiring In Spring, The XML configuration based autowiring functionality has five modes – no , byName , byType , constructor , and autodetect . The default mode� Autowire Conflict Resolution. By default, Spring resolves @Autowired entries byType. If more than one bean of the same type is available in the container, the framework will throw

Autowired annotation on variable or setters method is equivalent to xml attribute autowire="byType"

XML attribute autowire is defaut as no

"no": 

The traditional Spring default. No automagical wiring. Bean references
must be defined in the XML file via the <ref/> element (or "ref"
attribute). We recommend this in most cases as it makes documentation
more explicit.

Spring Bean Autowire "no" and "default" no autowire means dependency injection will not be achieved using @Autowired annotation, it will be achieved using ref attribute. "default" autowiring is "no". But when the bean is nested bean, then the default autowiring is parent bean autowiring. Suppose we have Employee class as follows. Employee.java

These are no, byName, byType, constructor, and autodetect. The default mode is no i.e. by default autowiring is turned off in traditional XML based configuration.

Using @Autowired annotation-

1) @Autowired on properties:

When @Autowired is used on properties, it is equivalent to autowiring by byType in configuration file.

2) @Autowired on property setters:

When @Autowired is used on setters, it is also equivalent to autowiring by byType in configuration file.

3) @Autowired on constructors:

When @Autowired is used on bean’s constructor, it is also equivalent to autowiring by constructor in configuration file.

Use @Qualifier for conflict in dependency resolution

As we learned that if we are using autowiring in byType mode and dependencies are looked for property class types. If no such type is found, an error is thrown. But, what if there are two or more beans for same class type.

In this case spring will not be able to choose correct bean to inject into property, and you will need to help the container using qualifiers.

To resolve a specific bean using qualifier, we need to use @Qualifier annotation along with @Autowired annotation and pass the bean name in annotation parameter.

Spring auto-wiring mode byType If you specify auto-wiring by type, then the injection will be based on data type of the bean and should be compatible with assigning bean property data type. In spring, auto-wiring by type allows a property to be autowired if there is exactly one bean of the property type in the container.

By default, the @Autowired annotation implies the dependency is required similar to @Required annotation, however, you can turn off the default behavior by using (required=false) option with @Autowired. The following example will work even if you do not pass any value for age property but still it will demand for name property.

Spring first tries to wire using autowire by constructor, if it does not work, Spring tries to autowire by byType. You can use byType or constructor autowiring mode to wire arrays and other typed-collections.

Spring uses the bean's name as a default qualifier value. It will inspect the container and look for a bean with the exact name as the property to autowire it. Hence, in our example, Spring matches the fooFormatter property name to the FooFormatter implementation. Therefore, it injects that specific implementation when constructs FooService:

Comments
  • Something to add: In Spring 5( I didn't check other versions), when there are more than one of a matching type, spring framework will try to use field name as bean name to determine a proper candidate. This strategy can be found in DefaultListBeanFacotory#determineAutowireCandidate(Map<String, Object> candidates, DependencyDescriptor descriptor)
  • False, the default mode of the @Autowired is 'no' No autowiring is performed. All references to other beans must be explicitly injected. This is the default mode.
  • You refer to autowire attribute which is 'no' by default, @Autowired annotation is byType