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Original | Java 2021 Super God Road, very liver~
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An open source project with detailed annotations in Chinese
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Source: blog.csdn.net/weixin_43715214/
article/details/127858049
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What’s the difference between @Autowired and @Resource?
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Same point
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difference
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Why is @Resource more recommended?
What is the difference between @Autowired and @Resource?
Both @Autowired and @Resource annotations are used for bean injection!
Among them, @Autowired is the annotation provided by Spring; @Resource is not provided by Spring, but by JDK, but Spring supports the injection of this annotation, which is not required when using it Import out-of-shelf packages.
Background management system + user applet based on Spring Boot + MyBatis Plus + Vue & amp; Element, supports RBAC dynamic permissions, multi-tenancy, data permissions, workflow, three-party login, payment, SMS, mall and other functions
Project address: https://github.com/YunaiV/ruoyi-vue-pro
Video tutorial: https://doc.iocoder.cn/video/
The same point
Both can be written on properties or setter methods.
If both are written on the field, then there is no need to write the setter method anymore!
Background management system + user applet based on Spring Cloud Alibaba + Gateway + Nacos + RocketMQ + Vue & amp; Element, supporting RBAC dynamic permissions, multi-tenancy, data permissions, workflow, three-party login, payment, SMS, mall and other functions
Project address: https://github.com/YunaiV/yudao-cloud
Video tutorial: https://doc.iocoder.cn/video/
The difference
@Autowired
By default, it is injected according to byType!
we can give an example
public class TestServiceImpl() {
@Autowired
private UserDao userDao;
...
}
The above code will first go to the container to find out which objects are of type UserDao, and assign specific values to userDao after finding them (but if more than one is found, an error will be reported!)
The @Autowired annotation assembles dependent objects according to type (byType). By default, it requires that dependent objects must exist; if null values are allowed, we can set the required attribute to false.
If we want to assemble by name, we can use it in conjunction with the @Qualifier annotation
Q: If our UserDao has multiple implementation classes, such as
UserDaoImpl1,UserDaoImpl2, how should we write our code?
If you don’t use @Qualifier, then byType is used by default, and multiple UserDao types will be found, and an error will be reported! ! ! So write it like the code below! ! !
Option 1 (@Qualifier)
public class TestServiceImpl() {
@Autowired
@Qualifier("userDaoImpl1") // specify which implementation class
private UserDao userDao;
...
}
Option Two (@Primary)
In @Autowired, if there are multiple beans, but we don’t want to use @Qualifier, we can do this:
Use the @Primary annotation to specify one for injection! ! !
@Primary
@Mapper
public class UserDaoImpl01 implements UserDao {
...
}
@Mapper
public class UserDaoImpl02 implements UserDao {
...
}
@Resource
The default is to inject byName, and if the name cannot be found, it will be injected by type.
There are two important attributes name and type in @Resource
In Spring, the name attribute of the @Resource annotation is parsed into the name of the bean, and the type is the type of the bean.
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If the name attribute is used, the automatic injection strategy of byName is used
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If the type attribute is used, the automatic injection strategy of byType is used
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If not specified, this will use the byName automatic injection strategy through the reflection mechanism
Assembly order of @Resource
1) If both name and type are specified, the only matching bean is found from the Spring context for assembly, and an exception is thrown if it cannot be found
2) If name is specified, look for a bean with a matching name (id) from the context for assembly, and throw an exception if it cannot be found
3) If type is specified, the only bean that matches the type is found from the context for assembly. If no or multiple beans are found, an exception will be thrown
4) If neither name nor type is specified, it will be automatically assembled according to the byName method. If there is no match, it will fall back to a primitive type (UserDao) for matching, and if it matches, it will be automatically assembled. (Name first, then type)
Why is it recommended to use @Resource?
The Resource annotation is on the field. This annotation belongs to J2EE, which reduces the coupling with spring.
But in fact, I think many people may have misunderstood this question!
It is more recommended to use @Resource , I don’t think it is because the @Resource annotation has better performance or something.
It is because it can specify whether to inject by name or type, and the @Autowired annotation itself cannot achieve this effect, it must be used together with @Qualifier !
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