Spring Learning (---@Autowired vs. @resource

Spring not only supports its own defined @autowired annotations, but also supports several annotations defined by the JSR-250 specification, such as: @Resource, @PostConstruct, and @predestroy.

1. @Autowired

@Autowired is provided by spring and needs to be imported into Package:org.springframework.beans.factory.annotation.Autowired;

Inject only according to Bytype.

2. @Resource

@Resource by default by ByName automatic injection, is provided by the Java EE, need to import Package:javax.annotation.Resource;

The @Resource has two important attributes: Name and type, and spring resolves the name property of the @resource annotation to the bean's name, while the type attribute resolves to the bean. So if you use the Name property, you use the ByName Auto-injection policy, and the Type property uses the Bytype auto-injection policy. If neither name nor the type attribute is specified, the ByName auto-injection policy is used through the reflection mechanism.

@Resource Assembly Order

(1) If name and type are specified at the same time, the uniquely matched bean is found from the spring context to assemble, and an exception is thrown if it is not found;

(2) If name is specified, a bean matching the name (ID) from the context is assembled, and an exception is thrown if it is not found;

(3) If a type is specified, an exception is thrown from the context in which the unique bean matching the match is found to be assembled, not found, or more than one is found;

(4) If neither name is specified and type is not specified, the assembly is automatically byname; if there is no match, the fallback is a match for the original type, and if the match is automatically assembled;

The function of @Resource is equivalent to @autowired, but @autowired is injected automatically by Bytype.

3. Usage differences

@Resource (name= "Loginservice")    private loginservice loginservice;      ---------------------------------@Autowired (required=false)     @Qualifier ("Loginservice")     

(1) Both @Autowired and @resource can be used to assemble beans. Can be written on a field, or written on a setter method;

(2) @Autowired by default assembly by type, by default must require that the dependent object must exist, if you want to allow null values, you can set its Required property to false, such as: @Autowired (Required=false). If we want to use the name assembly can be used in conjunction with @Qualifier annotations;

(3) @Resource (this annotation belongs to the Java EE), the default installation name for assembly, the name can be specified by the Name property, if the Name property is not specified, when the annotation is written on the field, the default name of the field name lookup, If the annotation is written on the setter method, the property name is assembled by default. When a bean matching the name cannot be found, it is assembled by type. However, it is important to note that if the Name property is specified once, it will only be assembled by name.

It is recommended to use @resource annotations on fields so that you do not have to write setter methods. And this annotation belongs to the Java EE, reducing the coupling with spring, so that the code looks more elegant.

In addition, through the practice, also summed up a rule:

If you write @requied or @autowired on top of the set method, the program goes inside the set method.

However, if it is written on a field, it will not enter the set method.

Spring Learning (---@Autowired vs. @resource