Super detailed spring boot annotation summary

Wolf king programming 2021-04-16 18:08:23
super detailed spring boot annotation


Hello everyone , I'm wolf king , A programmer who loves playing

I'm sure you've used it in daily programming spring, Used it, too spring Annotations , Even in the interview, I am often asked some questions spring and spring boot The function and meaning of annotation, etc , So this article will take you to see the super detailed Spring Boot annotation summary ! start doing sth. !


Let's take a look at the notes that we'll talk about in this article , You can look at the annotation and think about what this is for , What scene will be used , What you don't know , Go on with your answers and questions !

1@SpringBootApplication
2@EnableAutoConfiguration
3@Configuration
4@SpringBootConfiguration
5@ComponentScan
6@Conditional
7@ConditionalOnBean
8@ConditionalOnMissingBean
9@ConditionalOnClass
10@ConditionalOnMissingClass
11@ConditionalOnWebApplication
12@ConditionalOnNotWebApplication
13@ConditionalOnProperty
14@ConditionalOnExpression
15@ConditionalOnJava
16@ConditionalOnResource
17@ConditionalOnJndi
18@ConditionalOnCloudPlatform
19@ConditionalOnSingleCandidate
20@ConfigurationProperties
21@EnableConfigurationProperties
22@AutoConfigureAfter
23@AutoConfigureBefore
24@Import
25@ImportResource
26、 Read configuration summary

Notes and introduction

1、@SpringBootApplication

This is a Spring Boot The most core annotation , Use in Spring Boot Main class , Identity this is a Spring Boot application , Used to open Spring Boot Various abilities .

In fact, this annotation is @SpringBootConfiguration、@EnableAutoConfiguration、@ComponentScan The combination of these three notes , You can also use these three notes instead @SpringBootApplication annotation [email protected] By default, scan all packages and their sub packages of this class at the same level

2、@EnableAutoConfiguration

allow Spring Boot Auto configuration annotation , After opening this annotation ,Spring Boot Can be configured according to the package or class under the current classpath Spring Bean.

Such as : Under the current classpath Mybatis This JAR package ,MybatisAutoConfiguration Annotations can then be configured according to the relevant parameters Mybatis Each of them Spring Bean.

3、@Configuration

This is a Spring 3.0 A comment added , Used in place of applicationContext.xml The configuration file , All the things that can be done in this configuration file can be registered through the class of this annotation . Replaced the xml Configuration file in the form , Develop with configuration class

4、@SpringBootConfiguration

And this annotation is @Configuration Variant of annotation , It's just a way of saying yes Spring Boot Configure it , Or in favor of Spring Boot Subsequent expansion .

5、@ComponentScan

This is a Spring 3.1 A comment added , To replace the component-scan To configure , Turn on component scanning , That is, automatically scan the @Component Annotation for registration bean Instance to context in .

6、@Conditional

This is a Spring 4.0 New comments added , To identify a Spring Bean perhaps Configuration The configuration file , Enable configuration when specified conditions are met .

7、@ConditionalOnBean

Combine @Conditional annotation , When the specified Bean Enable configuration .

8、@ConditionalOnMissingBean

Combine @Conditional annotation , and @ConditionalOnBean Annotations instead , When there is no specified Bean Enable configuration .

9、@ConditionalOnClass

Combine @Conditional annotation , When the specified Class Enable configuration .

10、@ConditionalOnMissingClass

Combine @Conditional annotation , and @ConditionalOnMissingClass Annotations instead , When there is no specified Class Enable configuration .

11、@ConditionalOnWebApplication

Combine @Conditional annotation , The current project type is WEB The project opens the configuration .

The current project has the following 3 Types .

enum Type {
/**
 *  Match all web application
 */

ANY,

/**
 * Only match servlet web applicaiton
 */

SERVLET,

/**
 *  Only match reactice-based web application
 */

REACTIVE
}

12、@ConditionalOnNotWebApplication

Combine @Conditional annotation , and @ ConditionalOnWebApplication Annotations instead , The current project type is not WEB The project opens the configuration .

13、@ConditionalOnProperty

Combine @Conditional annotation , Opens the configuration when the specified property has the specified value .

14、@ConditionalOnExpression

Combine @Conditional annotation , When SpEL Expression for true Opens the configuration when .

15、@ConditionalOnJava

Combine @Conditional annotation , When running the Java JVM The configuration is not turned on until the specified version range is specified .

16、@ConditionalOnResource

Combine @Conditional annotation , The configuration is not opened until there is a specified resource under the classpath .

17、@ConditionalOnJndi

Combine @Conditional annotation , When the specified JNDI The configuration is not turned on until it exists .JDNI(Java Naming and Directory Interface Java Naming and Directory Interface)

18、@ConditionalOnCloudPlatform

Combine @Conditional annotation , The configuration is enabled when the specified cloud platform is active .

19、@ConditionalOnSingleCandidate

Combine @Conditional annotation , When the specified class There's only one in the container Bean, Or if you have more than one configuration at a time but it is preferred .

20、@ConfigurationProperties

Used to load additional configuration ( Such as .properties file ), Available in @Configuration Annotation class , perhaps @Bean Above annotation method .

21、@EnableConfigurationProperties

General cooperation @ConfigurationProperties Annotations use , To open the right @ConfigurationProperties Annotation configuration Bean Support for .

22、@AutoConfigureAfter

Used on the auto configuration class , Indicates that the auto-configuration class needs to be configured after another specified auto-configuration class is configured .

Such as Mybatis The automatic configuration class , You need to configure the class automatically after the data source .

@AutoConfigureAfter(DataSourceAutoConfiguration.class)
public class MybatisAutoConfiguration 
{
}

23、@AutoConfigureBefore

This and @AutoConfigureAfter Comments use the opposite , Indicates that the automatic configuration class needs to be configured before another specified automatic configuration class is configured .

24、@Import

This is a Spring 3.0 New comments added , Used to import one or more @Configuration Annotated class , This is in Spring Boot There are many applications in it .

25、@ImportResource

This is a Spring 3.0 New comments added , Used to import one or more Spring The configuration file , This is right Spring Boot Compatibility with old projects is very useful , Because some configurations fail Java Config Only this annotation can be used to import .

Read configuration summary

1. Read application file

stay application.yml perhaps properties Add... To the file :

user.name =  Wolf king 
user.age = 25
user.sex = man 

@value The way

@Component
public class User {

    @Value("${user.name}")
    private String name;
    @Value("${user.age}")
    private int age;
    @Value("${user.sex}")
    private boolean sex;

    public User() {
    }

    public User(String name, int age, boolean man) {
        this.name = name;
        this.age = age;
        this.man = man;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public boolean isMan() {
        return man;
    }

    public void setMan(boolean man) {
        this.man = man;
    }
}

[email protected] How to read comments

@Component
@ConfigurationProperties(prefix = "user")
public class User2 {
    private String name;

    private int age;

    private boolean sex;

    public User2() {
    }

    public User2(String name, int age, boolean man)     {
        this.name = name;
        this.age = age;
        this.man = man;
    }
}

3. Read the specified file

Create... In the resource directory config/myConfig.properties:

db.username=root
db.password=123

@[email protected] How to read comments

@Component
@PropertySource(value = {"config/myConfig.properties"})
public class User2 {

    @Value("${db.userName}")
    private String userName;
    @Value("${db.userName}")
    private String passWord;

    public User2() {
    }

    public User2(String userName,String passWord){
        this.userName = userName;
        this.passWord = passWord;
    }
}

It can also be done through @[email protected] How to read comments



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