全网最细的SpringBoot3系列教程

1、开发第⼀个Spring Boot应用

创建POM

因为是3.0.0-M1版本，是⾥程碑版本，不是正式发布版，需要从Spring提⾼的Maven仓库中才能下载到3.0.0-M1版本的依赖包，需要在pom.xml⽂件中单独指定仓库地址。

如果使⽤的是正式版，是不需要加下⾯这段配置的

<!-- jar包的仓库地址-->
 <repositories>
        <repository>
            <id>spring-snapshots</id>
            <url>https://repo.spring.io/snapshot</url>
            <snapshots><enabled>true</enabled></snapshots>
        </repository>
        <repository>
            <id>spring-milestones</id>
            <url>https://repo.spring.io/milestone</url>
        </repository>
    </repositories>
 <!-- maven插件的仓库地址 -->
    <pluginRepositories>
        <pluginRepository>
            <id>spring-snapshots</id>
            <url>https://repo.spring.io/snapshot</url>
        </pluginRepository>
        <pluginRepository>
            <id>spring-milestones</id>
            <url>https://repo.spring.io/milestone</url>
        </pluginRepository>
    </pluginRepositories>

另外还要在pom.xml⽂件中，添加Spring Boot所提供的⽗pom.xml。

 <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>3.0.0-M1</version>
    </parent>

关于这个parent的作⽤，后续课程中会介绍。

添加依赖

最后添加⼀个开发web应⽤的starter依赖

<dependencies>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-web</artifactId>
    </dependency>
</dependencies>

写代码

在写代码之前，请注意，我现在⽤的JDK8，也许你也是。
创建⼀个类，类名随便取，我的叫MyApplication，包路径为com.zhouyu

package com.zhouyu;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
@RestController
@EnableAutoConfiguration
public class MyApplication {
    @RequestMapping("/")
    String home() {
        return "Hello World!";
   }
    public static void main(String[] args) {
        SpringApplication.run(MyApplication.class, args);
   }
}

然后，运⾏main⽅法。
我这报错了：

因为Spring Boot 3⽤的是Spring 6，⽽Spring 6需要⽤JDK17。

所以，我们要在IDEA中配上JDK17，JDk17的安装没什么特殊的，和JDK8的安装⼀样，就不在笔记⾥浪费篇幅了。

⽤上JDK17之后，再次运⾏main⽅法，就能正常启动我们的第⼀个Spring Boot应⽤程序了，并且会看到如下⽇志： 

"C:\Program Files\Java\jdk-17.0.1\bin\java.exe" "-javaagent:C:\Program
Files\JetBrains\IntelliJ IDEA 2021.1.3\lib\idea_rt.jar=64855:C:\Program
Files\JetBrains\IntelliJ IDEA 2021.1.3\bin" -Dfile.encoding=UTF-8 -
classpath D:\IdeaProjects\ZhouyuSpringBootTeacher\target\classes;C:\Users\zhouyu\.m2\repository\org\springframework
\boot\spring-boot-starter-web\3.0.0-M1\spring-boot-starter-web-3.0.0-
M1.jar;C:\Users\zhouyu\.m2\repository\org\springframework\boot\springboot-starter\3.0.0-M1\spring-boot-starter-3.0.0-
M1.jar;C:\Users\zhouyu\.m2\repository\org\springframework\boot\springboot\3.0.0-M1\spring-boot-3.0.0-
M1.jar;C:\Users\zhouyu\.m2\repository\org\springframework\boot\springboot-autoconfigure\3.0.0-M1\spring-boot-autoconfigure-3.0.0-
M1.jar;C:\Users\zhouyu\.m2\repository\org\springframework\boot\springboot-starter-logging\3.0.0-M1\spring-boot-starter-logging-3.0.0-
M1.jar;C:\Users\zhouyu\.m2\repository\ch\qos\logback\logbackclassic\1.2.10\logback-classic1.2.10.jar;C:\Users\zhouyu\.m2\repository\ch\qos\logback\logbackcore\1.2.10\logback-core1.2.10.jar;C:\Users\zhouyu\.m2\repository\org\slf4j\slf4japi\1.7.33\slf4j-api1.7.33.jar;C:\Users\zhouyu\.m2\repository\org\apache\logging\log4j\log4jto-slf4j\2.17.1\log4j-to-slf4j2.17.1.jar;C:\Users\zhouyu\.m2\repository\org\apache\logging\log4j\log4japi\2.17.1\log4j-api2.17.1.jar;C:\Users\zhouyu\.m2\repository\org\slf4j\jul-toslf4j\1.7.33\jul-to-slf4j1.7.33.jar;C:\Users\zhouyu\.m2\repository\jakarta\annotation\jakarta.anno
tation-api\2.0.0\jakarta.annotation-api2.0.0.jar;C:\Users\zhouyu\.m2\repository\org\springframework\springcore\6.0.0-M2\spring-core-6.0.0-
M2.jar;C:\Users\zhouyu\.m2\repository\org\springframework\springjcl\6.0.0-M2\spring-jcl-6.0.0-
M2.jar;C:\Users\zhouyu\.m2\repository\org\yaml\snakeyaml\1.30\snakeyaml1.30.jar;C:\Users\zhouyu\.m2\repository\org\springframework\boot\springboot-starter-json\3.0.0-M1\spring-boot-starter-json-3.0.0-
M1.jar;C:\Users\zhouyu\.m2\repository\com\fasterxml\jackson\core\jacksondatabind\2.13.1\jackson-databind2.13.1.jar;C:\Users\zhouyu\.m2\repository\com\fasterxml\jackson\core\jack
son-annotations\2.13.1\jackson-annotations2.13.1.jar;C:\Users\zhouyu\.m2\repository\com\fasterxml\jackson\core\jack
son-core\2.13.1\jackson-core2.13.1.jar;C:\Users\zhouyu\.m2\repository\com\fasterxml\jackson\datatype\
jackson-datatype-jdk8\2.13.1\jackson-datatype-jdk8-
2.13.1.jar;C:\Users\zhouyu\.m2\repository\com\fasterxml\jackson\datatype\
jackson-datatype-jsr310\2.13.1\jackson-datatype-jsr310-
16
2.13.1.jar;C:\Users\zhouyu\.m2\repository\com\fasterxml\jackson\module\ja
ckson-module-parameter-names\2.13.1\jackson-module-parameter-names2.13.1.jar;C:\Users\zhouyu\.m2\repository\org\springframework\boot\spring
-boot-starter-tomcat\3.0.0-M1\spring-boot-starter-tomcat-3.0.0-
M1.jar;C:\Users\zhouyu\.m2\repository\org\apache\tomcat\embed\tomcatembed-core\10.0.16\tomcat-embed-core10.0.16.jar;C:\Users\zhouyu\.m2\repository\org\apache\tomcat\embed\tomcat
-embed-el\10.0.16\tomcat-embed-el10.0.16.jar;C:\Users\zhouyu\.m2\repository\org\apache\tomcat\embed\tomcat
-embed-websocket\10.0.16\tomcat-embed-websocket10.0.16.jar;C:\Users\zhouyu\.m2\repository\org\springframework\springweb\6.0.0-M2\spring-web-6.0.0-
M2.jar;C:\Users\zhouyu\.m2\repository\org\springframework\springbeans\6.0.0-M2\spring-beans-6.0.0-
M2.jar;C:\Users\zhouyu\.m2\repository\org\springframework\springwebmvc\6.0.0-M2\spring-webmvc-6.0.0-
M2.jar;C:\Users\zhouyu\.m2\repository\org\springframework\springaop\6.0.0-M2\spring-aop-6.0.0-
M2.jar;C:\Users\zhouyu\.m2\repository\org\springframework\springcontext\6.0.0-M2\spring-context-6.0.0-
M2.jar;C:\Users\zhouyu\.m2\repository\org\springframework\springexpression\6.0.0-M2\spring-expression-6.0.0-M2.jar
com.zhouyu.MyApplication
 .   ____          _            __ _ _
/\\ / ___'_ __ _ _(_)_ __ __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
\\/  ___)| |_)| | | | | || (_| | ) ) ) )
  ' |____| .__|_| |_|_| |_\__, | / / / /
=========|_|==============|___/=/_/_/_/
 :: Spring Boot ::             (v3.0.0-M1)
2022-03-16 20:43:21.849  INFO 17520 --- [           main]
com.zhouyu.MyApplication                 : Starting MyApplication using
Java 17.0.1 on DESKTOP-P9KHN97 with PID 17520
(D:\IdeaProjects\ZhouyuSpringBoot-Teacher\target\classes started by
zhouyu in D:\IdeaProjects\ZhouyuSpringBoot-Teacher)
2022-03-16 20:43:21.852  INFO 17520 --- [           main]
com.zhouyu.MyApplication                 : No active profile set, falling
back to default profiles: default
2022-03-16 20:43:23.257  INFO 17520 --- [           main]
o.s.b.w.embedded.tomcat.TomcatWebServer : Tomcat initialized with
port(s): 8080 (http)
2022-03-16 20:43:23.271  INFO 17520 --- [           main]
o.apache.catalina.core.StandardService   : Starting service [Tomcat]
2022-03-16 20:43:23.272  INFO 17520 --- [           main]
org.apache.catalina.core.StandardEngine : Starting Servlet engine:
[Apache Tomcat/10.0.16]
2022-03-16 20:43:23.406  INFO 17520 --- [           main] o.a.c.c.C.
[Tomcat].[localhost].[/]       : Initializing Spring embedded
WebApplicationContext
2022-03-16 20:43:23.409  INFO 17520 --- [           main]
w.s.c.ServletWebServerApplicationContext : Root WebApplicationContext:
initialization completed in 1472 ms
2022-03-16 20:43:24.147  INFO 17520 --- [           main]
o.s.b.w.embedded.tomcat.TomcatWebServer : Tomcat started on port(s):
8080 (http) with context p