SpringBoot 加载后初始化的N种方式
0、SpringBoot 环境搭建
本人使用的是SpringBoot 2.7.18 + Java11，pom.xml 如下：
<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>2.7.18</version>
<relativePath/> <!-- lookup parent from repository -->
</parent>
<groupId>com.example</groupId>
<artifactId>SpringBootTech_1</artifactId>
<version>0.0.1-SNAPSHOT</version>
<name>SpringBootTech_1</name>
<description>SpringBootTech_1</description>
<properties>
<maven.compiler.source>11</maven.compiler.source>
<maven.compiler.target>11</maven.compiler.target>
</properties>
<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
</dependency>
<dependency>
<groupId>org.projectlombok</groupId>
<artifactId>lombok</artifactId>
<optional>true</optional>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-test</artifactId>
<scope>test</scope>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
<configuration>
<excludes>
<exclude>
<groupId>org.projectlombok</groupId>
<artifactId>lombok</artifactId>
</exclude>
</excludes>
</configuration>
</plugin>
</plugins>
</build>
<repositories>
<repository>
<id>nexus-aliyun</id>
<name>nexus-aliyun</name>
<url>http://maven.aliyun.com/nexus/content/groups/public/</url>
<releases>
<enabled>true</enabled>
</releases>
<snapshots>
<enabled>false</enabled>
</snapshots>
</repository>
</repositories>
<pluginRepositories>
<pluginRepository>
<id>public</id>
<name>ali nexus</name>
<url>http://maven.aliyun.com/nexus/content/groups/public/</url>
<releases>
<enabled>true</enabled>
</releases>
<snapshots>
<enabled>false</enabled>
</snapshots>
</pluginRepository>
</pluginRepositories>
</project>
1、构造方法和静态代码块
构造方法和静态代码块属于 Java 自身的启动时加载方式：
- 静态代码块：static静态代码块，在类加载的时候即自动执行。
- 构造方法：在对象初始化时执行。执行顺序在static静态代码块之后。
- 加载顺序：static代码块 > 构造方法
在Spring或者SpringBoot中使用时，想要在SpringBoot启动时就初始化，需要把Bean加入IOC容器管理，所以会使用到@Component等注解。
import org.springframework.stereotype.Component;
@Component
public class TestConstruct {
static {
System.out.println("Static");
}
public TestPostConstruct() {
System.out.println("Construct");
}
}
启动加载Spring或者SpringBoot容器时，会输出如下信息：
. ____ _ __ _ _
/\\ / ___'_ __ _ _(_)_ __ __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
\\/ ___)| |_)| | | | | || (_| | ) ) ) )
' |____| .__|_| |_|_| |_\__, | / / / /
=========|_|==============|___/=/_/_/_/
:: Spring Boot :: (v2.7.18)
2023-12-01 13:58:08.576 INFO 85202 --- [main] c.e.s.tech.SpringBootTechApplication : Starting SpringBootTechApplication using Java 11 on MacBook-Pro.local with PID 85202 (/Users/lsx/IdeaProjects/SpringBootTech_1/target/classes started by lsx in /Users/lsx/IdeaProjects/SpringBootTech_1)
2023-12-01 13:58:08.581 INFO 85202 --- [main] c.e.s.tech.SpringBootTechApplication : No active profile set, falling back to 1 default profile: "default"
2023-12-01 13:58:09.416 INFO 85202 --- [main] o.s.b.w.embedded.tomcat.TomcatWebServer : Tomcat initialized with port(s): 8080 (http)
2023-12-01 13:58:09.427 INFO 85202 --- [main] o.apache.catalina.core.StandardService : Starting service [Tomcat]
2023-12-01 13:58:09.427 INFO 85202 --- [main] org.apache.catalina.core.StandardEngine : Starting Servlet engine: [Apache Tomcat/9.0.83]
2023-12-01 13:58:09.519 INFO 85202 --- [main] o.a.c.c.C.[Tomcat].[localhost].[/] : Initializing Spring embedded WebApplicationContext
2023-12-01 13:58:09.520 INFO 85202 --- [main] w.s.c.ServletWebServerApplicationContext : Root WebApplicationContext: initialization completed in 866 ms
Static
Construct
2023-12-01 13:58:09.934 INFO 85202 --- [ main] o.s.b.w.embedded.tomcat.TomcatWebServer : Tomcat started on port(s): 8080 (http) with context path ''
2023-12-01 13:58:09.947 INFO 85202 --- [ main] c.e.s.tech.SpringBootTechApplication : Started SpringBootTechApplication in 1.853 seconds (JVM running for 2.658)
2、@PostConstruct 注解
PostConstruct注解修饰的方式，是在Spring容器启动时运行的。
import org.springframework.stereotype.Component;
import javax.annotation.PostConstruct;
@Component
public class TestPostConstruct {
static {
System.out.println("Static");
}
public TestPostConstruct() {
System.out.println("Construct");
}
@PostConstruct
public void init() {
System.out.println("PostConstruct");
}
}
启动加载Spring或者SpringBoot容器时，会输出如下信息：
. ____ _ __ _ _
/\\ / ___'_ __ _ _(_)_ __ __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
\\/ ___)| |_)| | | | | || (_| | ) ) ) )
' |____| .__|_| |_|_| |_\__, | / / / /
=========|_|==============|___/=/_/_/_/
:: Spring Boot :: (v2.7.18)
2023-12-01 13:58:08.576 INFO 85202 --- [main] c.e.s.tech.SpringBootTechApplication : Starting SpringBootTechApplication using Java 11 on MacBook-Pro.local with PID 85202 (/Users/lsx/IdeaProjects/SpringBootTech_1/target/classes started by lsx in /Users/lsx/IdeaProjects/SpringBootTech_1)
2023-12-01 13:58:08.581 INFO 85202 --- [main] c.e.s.tech.SpringBootTechApplication : No active profile set, falling back to 1 default profile: "default"
2023-12-01 13:58:09.416 INFO 85202 --- [main] o.s.b.w.embedded.tomcat.TomcatWebServer : Tomcat initialized with port(s): 8080 (http)
2023-12-01 13:58:09.427 INFO 85202 --- [main] o.apache.catalina.core.StandardService : Starting service [Tomcat]
2023-12-01 13:58:09.427 INFO 85202 --- [main] org.apache.catalina.core.StandardEngine : Starting Servlet engine: [Apache Tomcat/9.0.83]
2023-12-01 13:58:09.519 INFO 85202 --- [main] o.a.c.c.C.[Tomcat].[localhost].[/] : Initializing Spring embedded WebApplicationContext
2023-12-01 13:58:09.520 INFO 85202 --- [main] w.s.c.ServletWebServerApplicationContext : Root WebApplicationContext: initialization completed in 866 ms
Static
Construct
PostConstruct
2023-12-01 13:58:09.934 INFO 85202 --- [ main] o.s.b.w.embedded.tomcat.TomcatWebServer : Tomcat started on port(s): 8080 (http) with context path ''
2023-12-01 13:58:09.947 INFO 85202 --- [ main] c.e.s.tech.SpringBootTechApplication : Started SpringBootTechApplication in 1.853 seconds (JVM running for 2.658)
3、InitializingBean
InitializingBean是spring容器在启动并初始化好内部示例后调用的，用来最终为总体bean添加最后属性和操作。 官方原话：This method allows the bean instance to perform validation of its overall configuration and final initialization when all bean properties have been set.
import org.springframework.beans.factory.InitializingBean;
import org.springframework.stereotype.Component;
@Component
public class TestInitializingBean implements InitializingBean {
@Override
public void afterPropertiesSet() {
System.out.println("InitializingBean");
}
}
启动加载Spring或者SpringBoot容器时，会输出如下信息：
. ____ _ __ _ _
/\\ / ___'_ __ _ _(_)_ __ __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
\\/ ___)| |_)| | | | | || (_| | ) ) ) )
' |____| .__|_| |_|_| |_\__, | / / / /
=========|_|==============|___/=/_/_/_/
:: Spring Boot :: (v2.7.18)
2023-12-01 13:58:08.576 INFO 85202 --- [main] c.e.s.tech.SpringBootTechApplication : Starting SpringBootTechApplication using Java 11 on MacBook-Pro.local with PID 85202 (/Users/lsx/IdeaProjects/SpringBootTech_1/target/classes started by lsx in /Users/lsx/IdeaProjects/SpringBootTech_1)
2023-12-01 13:58:08.581 INFO 85202 --- [main] c.e.s.tech.SpringBootTechApplication : No active profile set, falling back to 1 default profile: "default"
2023-12-01 13:58:09.416 INFO 85202 --- [main] o.s.b.w.embedded.tomcat.TomcatWebServer : Tomcat initialized with port(s): 8080 (http)
2023-12-01 13:58:09.427 INFO 85202 --- [main] o.apache.catalina.core.StandardService : Starting service [Tomcat]
2023-12-01 13:58:09.427 INFO 85202 --- [main] org.apache.catalina.core.StandardEngine : Starting Servlet engine: [Apache Tomcat/9.0.83]
2023-12-01 13:58:09.519 INFO 85202 --- [main] o.a.c.c.C.[Tomcat].[localhost].[/] : Initializing Spring embedded WebApplicationContext
2023-12-01 13:58:09.520 INFO 85202 --- [main] w.s.c.ServletWebServerApplicationContext : Root WebApplicationContext: initialization completed in 866 ms
InitializingBean
Static
Construct
PostConstruct
2023-12-01 13:58:09.934 INFO 85202 --- [main] o.s.b.w.embedded.tomcat.TomcatWebServer : Tomcat started on port(s): 8080 (http) with context path ''
2023-12-01 13:58:09.947 INFO 85202 --- [main] c.e.s.tech.SpringBootTechApplication : Started SpringBootTechApplication in 1.853 seconds (JVM running for 2.658)
4、实现 SmartInitializingSingleton 接口
SmartInitializingSingleton是Bean容器在初始化所有非懒加载的单例Bean后调用的方法。
import org.springframework.beans.factory.SmartInitializingSingleton;
import org.springframework.stereotype.Component;
@Component
public class TestSmartInitializingSingleton implements SmartInitializingSingleton {
@Override
public void afterSingletonsInstantiated() {
System.out.println("SmartInitializingSingleton");
}
}
启动加载Spring或者SpringBoot容器时，会输出如下信息：
. ____ _ __ _ _
/\\ / ___'_ __ _ _(_)_ __ __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
\\/ ___)| |_)| | | | | || (_| | ) ) ) )
' |____| .__|_| |_|_| |_\__, | / / / /
=========|_|==============|___/=/_/_/_/
:: Spring Boot :: (v2.7.18)
2023-12-01 13:58:08.576 INFO 85202 --- [main] c.e.s.tech.SpringBootTechApplication : Starting SpringBootTechApplication using Java 11 on MacBook-Pro.local with PID 85202 (/Users/lsx/IdeaProjects/SpringBootTech_1/target/classes started by lsx in /Users/lsx/IdeaProjects/SpringBootTech_1)
2023-12-01 13:58:08.581 INFO 85202 --- [main] c.e.s.tech.SpringBootTechApplication : No active profile set, falling back to 1 default profile: "default"
2023-12-01 13:58:09.416 INFO 85202 --- [main] o.s.b.w.embedded.tomcat.TomcatWebServer : Tomcat initialized with port(s): 8080 (http)
2023-12-01 13:58:09.427 INFO 85202 --- [main] o.apache.catalina.core.StandardService : Starting service [Tomcat]
2023-12-01 13:58:09.427 INFO 85202 --- [main] org.apache.catalina.core.StandardEngine : Starting Servlet engine: [Apache Tomcat/9.0.83]
2023-12-01 13:58:09.519 INFO 85202 --- [main] o.a.c.c.C.[Tomcat].[localhost].[/] : Initializing Spring embedded WebApplicationContext
2023-12-01 13:58:09.520 INFO 85202 --- [main] w.s.c.ServletWebServerApplicationContext : Root WebApplicationContext: initialization completed in 866 ms
InitializingBean
Static
Construct
PostConstruct
SmartInitializingSingleton
2023-12-01 13:58:09.934 INFO 85202 --- [main] o.s.b.w.embedded.tomcat.TomcatWebServer : Tomcat started on port(s): 8080 (http) with context path ''
2023-12-01 13:58:09.947 INFO 85202 --- [main] c.e.s.tech.SpringBootTechApplication : Started SpringBootTechApplication in 1.853 seconds (JVM running for 2.658)
5、BeanFactoryPostProcessor.initMethod 方法
这种方法有一定的局限性，并且可能会覆盖曾经的init操作，需要慎用。
Bean在加载到Spring容器中时需要先将Bean的定义信息抽象为BeanDefinition，其中有一个属性init-method代表将来Bean初始化时要调用的方法。
我们通过BeanFactoryPostProcessor来注入init-method方法，并且该方法必须是没有参数的 。
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.BeanFactoryPostProcessor;
import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
import org.springframework.stereotype.Component;
@Component
public class TestBeanFactoryPostProcessor implements BeanFactoryPostProcessor {
@Override
public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
// BeanDefinition beanDefinition = beanFactory.getBeanDefinition("person");
// beanDefinition.setAttribute("setName", "123");
// beanDefinition.setInitMethodName("run");
System.out.println("BeanFactoryPostProcessor");
}
}
启动加载Spring或者SpringBoot容器时，会输出如下信息：
. ____ _ __ _ _
/\\ / ___'_ __ _ _(_)_ __ __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
\\/ ___)| |_)| | | | | || (_| | ) ) ) )
' |____| .__|_| |_|_| |_\__, | / / / /
=========|_|==============|___/=/_/_/_/
:: Spring Boot :: (v2.7.18)
2023-12-01 13:58:08.576 INFO 85202 --- [main] c.e.s.tech.SpringBootTechApplication : Starting SpringBootTechApplication using Java 11 on MacBook-Pro.local with PID 85202 (/Users/lsx/IdeaProjects/SpringBootTech_1/target/classes started by lsx in /Users/lsx/IdeaProjects/SpringBootTech_1)
2023-12-01 13:58:08.581 INFO 85202 --- [main] c.e.s.tech.SpringBootTechApplication : No active profile set, falling back to 1 default profile: "default"
BeanFactoryPostProcessor
2023-12-01 13:58:09.416 INFO 85202 --- [main] o.s.b.w.embedded.tomcat.TomcatWebServer : Tomcat initialized with port(s): 8080 (http)
2023-12-01 13:58:09.427 INFO 85202 --- [main] o.apache.catalina.core.StandardService : Starting service [Tomcat]
2023-12-01 13:58:09.427 INFO 85202 --- [main] org.apache.catalina.core.StandardEngine : Starting Servlet engine: [Apache Tomcat/9.0.83]
2023-12-01 13:58:09.519 INFO 85202 --- [main] o.a.c.c.C.[Tomcat].[localhost].[/] : Initializing Spring embedded WebApplicationContext
2023-12-01 13:58:09.520 INFO 85202 --- [main] w.s.c.ServletWebServerApplicationContext : Root WebApplicationContext: initialization completed in 866 ms
InitializingBean
Static
Construct
PostConstruct
SmartInitializingSingleton
2023-12-01 13:58:09.934 INFO 85202 --- [main] o.s.b.w.embedded.tomcat.TomcatWebServer : Tomcat started on port(s): 8080 (http) with context path ''
2023-12-01 13:58:09.947 INFO 85202 --- [main] c.e.s.tech.SpringBootTechApplication : Started SpringBootTechApplication in 1.853 seconds (JVM running for 2.658)
6、监听器监听 ContextRefreshedEvent 事件
ContextRefreshedEvent：是Spring容器初始化完成后调用的事件。 ContextRefreshedEvent的父类是ApplicationContextEvent，是一个事件。所以我们通过ApplicationListener来实现。
import org.springframework.context.ApplicationListener;
import org.springframework.context.event.ContextRefreshedEvent;
import org.springframework.stereotype.Component;
@Component
public class TestApplicationListenerByContextRefreshedEvent implements ApplicationListener<ContextRefreshedEvent> {
@Override
public void onApplicationEvent(ContextRefreshedEvent event) {
System.out.println("ApplicationListener.ContextRefreshedEvent");
}
}
启动加载Spring或者SpringBoot容器时，会输出如下信息：
. ____ _ __ _ _
/\\ / ___'_ __ _ _(_)_ __ __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
\\/ ___)| |_)| | | | | || (_| | ) ) ) )
' |____| .__|_| |_|_| |_\__, | / / / /
=========|_|==============|___/=/_/_/_/
:: Spring Boot :: (v2.7.18)
2023-12-01 13:58:08.576 INFO 85202 --- [main] c.e.s.tech.SpringBootTechApplication : Starting SpringBootTechApplication using Java 11 on MacBook-Pro.local with PID 85202 (/Users/lsx/IdeaProjects/SpringBootTech_1/target/classes started by lsx in /Users/lsx/IdeaProjects/SpringBootTech_1)
2023-12-01 13:58:08.581 INFO 85202 --- [main] c.e.s.tech.SpringBootTechApplication : No active profile set, falling back to 1 default profile: "default"
BeanFactoryPostProcessor
2023-12-01 13:58:09.416 INFO 85202 --- [main] o.s.b.w.embedded.tomcat.TomcatWebServer : Tomcat initialized with port(s): 8080 (http)
2023-12-01 13:58:09.427 INFO 85202 --- [main] o.apache.catalina.core.StandardService : Starting service [Tomcat]
2023-12-01 13:58:09.427 INFO 85202 --- [main] org.apache.catalina.core.StandardEngine : Starting Servlet engine: [Apache Tomcat/9.0.83]
2023-12-01 13:58:09.519 INFO 85202 --- [main] o.a.c.c.C.[Tomcat].[localhost].[/] : Initializing Spring embedded WebApplicationContext
2023-12-01 13:58:09.520 INFO 85202 --- [main] w.s.c.ServletWebServerApplicationContext : Root WebApplicationContext: initialization completed in 866 ms
InitializingBean
Static
Construct
PostConstruct
SmartInitializingSingleton
2023-12-01 13:58:09.934 INFO 85202 --- [main] o.s.b.w.embedded.tomcat.TomcatWebServer : Tomcat started on port(s): 8080 (http) with context path ''
ApplicationListener.ContextRefreshedEvent
2023-12-01 13:58:09.947 INFO 85202 --- [main] c.e.s.tech.SpringBootTechApplication : Started SpringBootTechApplication in 1.853 seconds (JVM running for 2.658)
7、监听器监听 ApplicationStartedEvent 事件
ApplicationStartedEvent 是 Spring Boot 中的一个事件类，它表示应用程序已经启动完成的事件。当 Spring Boot 应用程序启动并且应用程序上下文准备好接收请求时，将发布 ApplicationStartedEvent 事件。你可以监听这个事件，以执行在应用程序启动后需要进行的操作。
这个事件通常用于执行一些在应用程序完全启动后立即执行的逻辑。你可以创建一个监听器（实现 ApplicationListener<ApplicationStartedEvent> 接口）来响应这个事件。
import org.springframework.boot.context.event.ApplicationStartedEvent;
import org.springframework.context.ApplicationListener;
import org.springframework.stereotype.Component;
@Component
public class TestApplicationListenerByApplicationStartedEvent implements ApplicationListener<ApplicationStartedEvent> {
@Override
public void onApplicationEvent(ApplicationStartedEvent event) {
System.out.println("ApplicationListener.ApplicationStartedEvent");
}
}
启动加载Spring或者SpringBoot容器时，会输出如下信息：
. ____ _ __ _ _
/\\ / ___'_ __ _ _(_)_ __ __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
\\/ ___)| |_)| | | | | || (_| | ) ) ) )
' |____| .__|_| |_|_| |_\__, | / / / /
=========|_|==============|___/=/_/_/_/
:: Spring Boot :: (v2.7.18)
2023-12-01 13:58:08.576 INFO 85202 --- [main] c.e.s.tech.SpringBootTechApplication : Starting SpringBootTechApplication using Java 11 on MacBook-Pro.local with PID 85202 (/Users/lsx/IdeaProjects/SpringBootTech_1/target/classes started by lsx in /Users/lsx/IdeaProjects/SpringBootTech_1)
2023-12-01 13:58:08.581 INFO 85202 --- [main] c.e.s.tech.SpringBootTechApplication : No active profile set, falling back to 1 default profile: "default"
BeanFactoryPostProcessor
2023-12-01 13:58:09.416 INFO 85202 --- [main] o.s.b.w.embedded.tomcat.TomcatWebServer : Tomcat initialized with port(s): 8080 (http)
2023-12-01 13:58:09.427 INFO 85202 --- [main] o.apache.catalina.core.StandardService : Starting service [Tomcat]
2023-12-01 13:58:09.427 INFO 85202 --- [main] org.apache.catalina.core.StandardEngine : Starting Servlet engine: [Apache Tomcat/9.0.83]
2023-12-01 13:58:09.519 INFO 85202 --- [main] o.a.c.c.C.[Tomcat].[localhost].[/] : Initializing Spring embedded WebApplicationContext
2023-12-01 13:58:09.520 INFO 85202 --- [main] w.s.c.ServletWebServerApplicationContext : Root WebApplicationContext: initialization completed in 866 ms
InitializingBean
Static
Construct
PostConstruct
SmartInitializingSingleton
2023-12-01 13:58:09.934 INFO 85202 --- [main] o.s.b.w.embedded.tomcat.TomcatWebServer : Tomcat started on port(s): 8080 (http) with context path ''
ApplicationListener.ContextRefreshedEvent
2023-12-01 13:58:09.947 INFO 85202 --- [main] c.e.s.tech.SpringBootTechApplication : Started SpringBootTechApplication in 1.853 seconds (JVM running for 2.658)
ApplicationListener.ApplicationStartedEvent
8、实现 ApplicationRunner 接口（仅限SpringBoot）
ApplicationRunner 也是一个SpringBoot 接口，在应用初始化后执行，且仅会执行一次。可以用来打印项目中配置文件的参数，参数为ApplicationRunner。
import org.springframework.boot.ApplicationArguments;
import org.springframework.boot.ApplicationRunner;
import org.springframework.stereotype.Component;
@Component
public class TestApplicationRunner implements ApplicationRunner {
@Override
public void run(ApplicationArguments applicationArguments) {
System.out.println("ApplicationRunner");
}
}
启动加载Spring或者SpringBoot容器时，会输出如下信息：
. ____ _ __ _ _
/\\ / ___'_ __ _ _(_)_ __ __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
\\/ ___)| |_)| | | | | || (_| | ) ) ) )
' |____| .__|_| |_|_| |_\__, | / / / /
=========|_|==============|___/=/_/_/_/
:: Spring Boot :: (v2.7.18)
2023-12-01 13:58:08.576 INFO 85202 --- [main] c.e.s.tech.SpringBootTechApplication : Starting SpringBootTechApplication using Java 11 on MacBook-Pro.local with PID 85202 (/Users/lsx/IdeaProjects/SpringBootTech_1/target/classes started by lsx in /Users/lsx/IdeaProjects/SpringBootTech_1)
2023-12-01 13:58:08.581 INFO 85202 --- [main] c.e.s.tech.SpringBootTechApplication : No active profile set, falling back to 1 default profile: "default"
BeanFactoryPostProcessor
2023-12-01 13:58:09.416 INFO 85202 --- [main] o.s.b.w.embedded.tomcat.TomcatWebServer : Tomcat initialized with port(s): 8080 (http)
2023-12-01 13:58:09.427 INFO 85202 --- [main] o.apache.catalina.core.StandardService : Starting service [Tomcat]
2023-12-01 13:58:09.427 INFO 85202 --- [main] org.apache.catalina.core.StandardEngine : Starting Servlet engine: [Apache Tomcat/9.0.83]
2023-12-01 13:58:09.519 INFO 85202 --- [main] o.a.c.c.C.[Tomcat].[localhost].[/] : Initializing Spring embedded WebApplicationContext
2023-12-01 13:58:09.520 INFO 85202 --- [main] w.s.c.ServletWebServerApplicationContext : Root WebApplicationContext: initialization completed in 866 ms
InitializingBean
Static
Construct
PostConstruct
SmartInitializingSingleton
2023-12-01 13:58:09.934 INFO 85202 --- [main] o.s.b.w.embedded.tomcat.TomcatWebServer : Tomcat started on port(s): 8080 (http) with context path ''
ApplicationListener.ContextRefreshedEvent
2023-12-01 13:58:09.947 INFO 85202 --- [main] c.e.s.tech.SpringBootTechApplication : Started SpringBootTechApplication in 1.853 seconds (JVM running for 2.658)
ApplicationListener.ApplicationStartedEvent
ApplicationRunner
9、实现 CommandLineRunner 接口（仅限SpringBoot）
CommandLineRunner 是一个SpringBoot 接口，在应用初始化后执行，且仅会执行一次。可以用来打印项目中配置文件的参数，参数为String数组。
import org.springframework.boot.CommandLineRunner;
import org.springframework.stereotype.Component;
@Component
public class TestCommandLineRunner implements CommandLineRunner {
@Override
public void run(String... strings) {
System.out.println("CommandLineRunner");
}
}
启动加载Spring或者SpringBoot容器时，会输出如下信息：
. ____ _ __ _ _
/\\ / ___'_ __ _ _(_)_ __ __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
\\/ ___)| |_)| | | | | || (_| | ) ) ) )
' |____| .__|_| |_|_| |_\__, | / / / /
=========|_|==============|___/=/_/_/_/
:: Spring Boot :: (v2.7.18)
2023-12-01 13:58:08.576 INFO 85202 --- [main] c.e.s.tech.SpringBootTechApplication : Starting SpringBootTechApplication using Java 11 on MacBook-Pro.local with PID 85202 (/Users/lsx/IdeaProjects/SpringBootTech_1/target/classes started by lsx in /Users/lsx/IdeaProjects/SpringBootTech_1)
2023-12-01 13:58:08.581 INFO 85202 --- [main] c.e.s.tech.SpringBootTechApplication : No active profile set, falling back to 1 default profile: "default"
BeanFactoryPostProcessor
2023-12-01 13:58:09.416 INFO 85202 --- [main] o.s.b.w.embedded.tomcat.TomcatWebServer : Tomcat initialized with port(s): 8080 (http)
2023-12-01 13:58:09.427 INFO 85202 --- [main] o.apache.catalina.core.StandardService : Starting service [Tomcat]
2023-12-01 13:58:09.427 INFO 85202 --- [main] org.apache.catalina.core.StandardEngine : Starting Servlet engine: [Apache Tomcat/9.0.83]
2023-12-01 13:58:09.519 INFO 85202 --- [main] o.a.c.c.C.[Tomcat].[localhost].[/] : Initializing Spring embedded WebApplicationContext
2023-12-01 13:58:09.520 INFO 85202 --- [main] w.s.c.ServletWebServerApplicationContext : Root WebApplicationContext: initialization completed in 866 ms
InitializingBean
Static
Construct
PostConstruct
SmartInitializingSingleton
2023-12-01 13:58:09.934 INFO 85202 --- [main] o.s.b.w.embedded.tomcat.TomcatWebServer : Tomcat started on port(s): 8080 (http) with context path ''
ApplicationListener.ContextRefreshedEvent
2023-12-01 13:58:09.947 INFO 85202 --- [main] c.e.s.tech.SpringBootTechApplication : Started SpringBootTechApplication in 1.853 seconds (JVM running for 2.658)
ApplicationListener.ApplicationStartedEvent
ApplicationRunner
CommandLineRunner
ApplicationRunner 和 CommandLineRunner：SpringBoot提供了两个接口来实现Spring容器启动完成后执行的功能
- 这两个接口需要实现一个run方法，将代码在run中实现即可。这两个接口功能基本一致，其区别在于run方法的入参。ApplicationRunner的run方法入参为ApplicationArguments，而CommandLineRunner的run方法入参为String数组。
10、实现 SpringApplicationRunListener 接口（仅限SpringBoot）
SpringBoot的生命周期事件监听方法，需要搭配resource/META-INF/spring.factories 文件使用。【SpringBoot3.0 无需定义SpringApplication和args】
package com.example.springboot.tech;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.SpringApplicationRunListener;
import org.springframework.context.ConfigurableApplicationContext;
import java.time.Duration;
public class TestSpringApplicationRunListener implements SpringApplicationRunListener {
private final SpringApplication application;
private final String[] args;
public TestSpringApplicationRunListener(SpringApplication application, String[] args) {
this.application = application;
this.args = args;
}
@Override
public void started(ConfigurableApplicationContext context, Duration timeTaken) {
System.out.println("SpringApplicationRunListener:started");
}
@Override
public void ready(ConfigurableApplicationContext context, Duration timeTaken) {
System.out.println("SpringApplicationRunListener:ready");
}
}
在resources目录下添加 META-INF/spring.factories 配置文件，内容如下，将自定义的初始化器和监听器注册进去；
org.springframework.boot.SpringApplicationRunListener=com.example.springboot.tech.TestSpringApplicationRunListener
启动加载Spring或者SpringBoot容器时，会输出如下信息：
. ____ _ __ _ _
/\\ / ___'_ __ _ _(_)_ __ __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
\\/ ___)| |_)| | | | | || (_| | ) ) ) )
' |____| .__|_| |_|_| |_\__, | / / / /
=========|_|==============|___/=/_/_/_/
:: Spring Boot :: (v2.7.18)
2023-12-01 13:58:08.576 INFO 85202 --- [main] c.e.s.tech.SpringBootTechApplication : Starting SpringBootTechApplication using Java 11 on MacBook-Pro.local with PID 85202 (/Users/lsx/IdeaProjects/SpringBootTech_1/target/classes started by lsx in /Users/lsx/IdeaProjects/SpringBootTech_1)
2023-12-01 13:58:08.581 INFO 85202 --- [main] c.e.s.tech.SpringBootTechApplication : No active profile set, falling back to 1 default profile: "default"
BeanFactoryPostProcessor
2023-12-01 13:58:09.416 INFO 85202 --- [main] o.s.b.w.embedded.tomcat.TomcatWebServer : Tomcat initialized with port(s): 8080 (http)
2023-12-01 13:58:09.427 INFO 85202 --- [main] o.apache.catalina.core.StandardService : Starting service [Tomcat]
2023-12-01 13:58:09.427 INFO 85202 --- [main] org.apache.catalina.core.StandardEngine : Starting Servlet engine: [Apache Tomcat/9.0.83]
2023-12-01 13:58:09.519 INFO 85202 --- [main] o.a.c.c.C.[Tomcat].[localhost].[/] : Initializing Spring embedded WebApplicationContext
2023-12-01 13:58:09.520 INFO 85202 --- [main] w.s.c.ServletWebServerApplicationContext : Root WebApplicationContext: initialization completed in 866 ms
InitializingBean
Static
Construct
PostConstruct
SmartInitializingSingleton
2023-12-01 13:58:09.934 INFO 85202 --- [main] o.s.b.w.embedded.tomcat.TomcatWebServer : Tomcat started on port(s): 8080 (http) with context path ''
ApplicationListener.ContextRefreshedEvent
2023-12-01 13:58:09.947 INFO 85202 --- [main] c.e.s.tech.SpringBootTechApplication : Started SpringBootTechApplication in 1.853 seconds (JVM running for 2.658)
ApplicationListener.ApplicationStartedEvent
SpringApplicationRunListener:started
ApplicationRunner
CommandLineRunner
SpringApplicationRunListener:ready
11、自定义初始化器实现 ApplicationContextInitializer 接口
ApplicationContextInitializer 是 Spring Framework 提供的一个接口，用于在应用程序上下文（ApplicationContext）创建之前对其进行初始化配置。通过实现这个接口，你可以在 Spring 应用程序启动时执行一些定制化的初始化操作，例如设置一些属性、激活或禁用某些配置等。
该接口定义了一个方法 initialize，该方法接受一个 ConfigurableApplicationContext 参数，允许你对应用程序上下文进行配置。
package com.example.springboot.tech;
import org.springframework.context.ApplicationContextInitializer;
import org.springframework.context.ConfigurableApplicationContext;
/**
* 自定义的初始化器
*/
public class TestApplicationContextInitializer implements ApplicationContextInitializer<ConfigurableApplicationContext> {
@Override
public void initialize(ConfigurableApplicationContext configurableApplicationContext) {
// 在这里进行初始化操作，可以修改上下文的配置
System.out.println("TestApplicationContextInitializer...");
}
}
在resources目录下添加 META-INF/spring.factories 配置文件，内容如下，将自定义的初始化器和监听器注册进去；
org.springframework.context.ApplicationContextInitializer=com.example.springboot.tech.TestApplicationContextInitializer
启动加载Spring或者SpringBoot容器时，会输出如下信息：
. ____ _ __ _ _
/\\ / ___'_ __ _ _(_)_ __ __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
\\/ ___)| |_)| | | | | || (_| | ) ) ) )
' |____| .__|_| |_|_| |_\__, | / / / /
=========|_|==============|___/=/_/_/_/
:: Spring Boot :: (v2.7.18)
TestApplicationContextInitializer...
2023-12-01 13:58:08.576 INFO 85202 --- [main] c.e.s.tech.SpringBootTechApplication : Starting SpringBootTechApplication using Java 11 on MacBook-Pro.local with PID 85202 (/Users/lsx/IdeaProjects/SpringBootTech_1/target/classes started by lsx in /Users/lsx/IdeaProjects/SpringBootTech_1)
2023-12-01 13:58:08.581 INFO 85202 --- [main] c.e.s.tech.SpringBootTechApplication : No active profile set, falling back to 1 default profile: "default"
BeanFactoryPostProcessor
2023-12-01 13:58:09.416 INFO 85202 --- [main] o.s.b.w.embedded.tomcat.TomcatWebServer : Tomcat initialized with port(s): 8080 (http)
2023-12-01 13:58:09.427 INFO 85202 --- [main] o.apache.catalina.core.StandardService : Starting service [Tomcat]
2023-12-01 13:58:09.427 INFO 85202 --- [main] org.apache.catalina.core.StandardEngine : Starting Servlet engine: [Apache Tomcat/9.0.83]
2023-12-01 13:58:09.519 INFO 85202 --- [main] o.a.c.c.C.[Tomcat].[localhost].[/] : Initializing Spring embedded WebApplicationContext
2023-12-01 13:58:09.520 INFO 85202 --- [main] w.s.c.ServletWebServerApplicationContext : Root WebApplicationContext: initialization completed in 866 ms
InitializingBean
Static
Construct
PostConstruct
SmartInitializingSingleton
2023-12-01 13:58:09.934 INFO 85202 --- [main] o.s.b.w.embedded.tomcat.TomcatWebServer : Tomcat started on port(s): 8080 (http) with context path ''
ApplicationListener.ContextRefreshedEvent
2023-12-01 13:58:09.947 INFO 85202 --- [main] c.e.s.tech.SpringBootTechApplication : Started SpringBootTechApplication in 1.853 seconds (JVM running for 2.658)
ApplicationListener.ApplicationStartedEvent
SpringApplicationRunListener:started
ApplicationRunner
CommandLineRunner
SpringApplicationRunListener:ready
12、总结各个初始化方法的优先级
执行优先级：ApplicationContextInitializer »» BeanFactoryPostProcessor.initMethod »» InitializingBean »» 静态代码块 »» 构造方法 »» PostConstruct注解 »» SmartInitializingSingleton »» ApplicationListener.ContextRefreshedEvent »» ApplicationListener.ApplicationStartedEvent »» SpringApplicationRunListener:started »» ApplicationRunner »» CommandLineRunner »» SpringApplicationRunListener:ready
13、参考文献 & 鸣谢
- Spring加载后初始化的9种方式：https://blog.csdn.net/kinbridge/article/details/131366212
SpringBoot 加载后初始化简洁版
1、项目启动时行初始化方法前言
目前开发的SpringBoot项目在启动的时候需要预加载一些资源。而如何实现启动过程中执行代码，或启动成功后执行，是有很多种方式可以选择，我们可以在static代码块中实现，也可以在构造方法里实现，也可以使用**@PostConstruct**注解实现。
当然也可以去实现Spring的ApplicationRunner与CommandLineRunner接口去实现启动后运行的功能。在这里整理一下，在这些位置执行的区别以及加载顺序。
如下是Spring中常用的初始化方式
- 实现 CommandLineRunner 接口
- 实现 ApplicationRunner 接口
- 通过 EventListener 监听启动事件
- 通过 @Postconstruct 注解
- 实现 InitializingBean 接口
- 通过 @Bean 注解
2、Java 自身的启动时加载方式
1、static代码块：static静态代码块，在类加载的时候即自动执行。
2、构造方法：在对象初始化时执行。执行顺序在static静态代码块之后。
3、加载顺序：static代码块 > 构造方法
3、SpringBoot 启动时加载方式
1、@PostConstruct注解：PostConstruct注解使用在方法上，这个方法在对象依赖注入初始化之后执行。
2、ApplicationRunner 和 CommandLineRunner：SpringBoot提供了两个接口来实现Spring容器启动完成后执行的功能
这两个接口需要实现一个run方法，将代码在run中实现即可。这两个接口功能基本一致，其区别在于run方法的入参。ApplicationRunner的run方法入参为ApplicationArguments，而CommandLineRunner的run方法入参为String数组。
何为 ApplicationArguments
官方文档解释为：Provides access to the arguments that were used to run a SpringApplication.
在Spring应用运行时使用的访问应用参数。即我们可以获取到SpringApplication.run(…)的应用参数。
当有多个类实现了CommandLineRunner和ApplicationRunner接口时，可以通过在类上添加**@Order**注解来设定运行顺序。
4、启动时初始化方法代码测试
为了测试启动时运行的效果和顺序，编写几个测试代码来运行看看。
1、TestPostConstruct
@Component
public class TestPostConstruct {
static {
System.out.println("static");
}
public TestPostConstruct() {
System.out.println("constructer");
}
@PostConstruct
public void init() {
System.out.println("PostConstruct");
}
}
2、TestApplicationRunner
@Component
@Order(1)
public class TestApplicationRunner implements ApplicationRunner{
@Override
public void run(ApplicationArguments applicationArguments) throws Exception {
System.out.println("order1:TestApplicationRunner");
}
}
3、TestCommandLineRunner
@Component
@Order(2)
public class TestCommandLineRunner implements CommandLineRunner {
@Override
public void run(String... strings) throws Exception {
System.out.println("order2:TestCommandLineRunner");
}
}
3、执行结果
static
constructer
PostConstruct
order1:TestApplicationRunner
order2:TestCommandLineRunner
5、启动时初始化加载顺序总结
SpringBoot应用启动过程中，肯定是要自动扫描有@Component注解的类，加载类并初始化对象进行自动注入。加载类时首先要执行static静态代码块中的代码，之后再初始化对象时会执行构造方法。
在对象注入完成后，调用带有@PostConstruct注解的方法。当容器启动成功后，再根据@Order注解的顺序调用CommandLineRunner和ApplicationRunner接口类中的run方法。
因此加载顺序为：static > constructer > @PostConstruct > CommandLineRunner 和 ApplicationRunner
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