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spring mvc开发相比较servlet-jsp-mysql而言，是简单很多。但是它也有一个缺点，就是xml配置文件较多，比如说pom.xml、web.xml、***-servlet.xml、applicationContext.xml等等。所以在spring基础之上，为了进一步简化spring开发的流程，人们开发了spring boot。它相当于一个spring全家桶，大大简化了spring的开发步骤。今天正好来学习下。
文章部分内容参考了这个链接，https://blog.csdn.net/hezhimin1124/article/details/103782745，在此表示感谢。
1、IDEA创建工程，选择Spring Initializr
2、略过group和artifact的设置，直接下一步，
3、选择web和spring web，下一步
目前这里设置的选项是web和spring web。但是大家可以看下左下角的选项，这里出现了很多spring cloud的内容，这说明spring cloud的很多配置本身也是依赖于spring boot来开发的。
4、工程命名为Hello，
5、在com.example.demo添加HelloController.java文件
package com.example.demo;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
@RestController
public class HelloController {
@RequestMapping("/hello")
public String get(){
return "Hello Spring Boot";
}
}
6、设置内置web server启动端口为8090
因为默认端口是8080，所以这部分一定要修改一下。
7、不需要继续配置tomcat server，直接使用默认server即可，单击绿色按钮，不出意外你会看到这样的打印，
"C:\Program Files (x86)\Java\jdk1.8.0_91\bin\java.exe" -Dserver.port=8090 -XX:TieredStopAtLevel=1 -noverify -Dspring.output.ansi.enabled=always -Dcom.sun.management.jmxremote -Dspring.jmx.enabled=true -Dspring.liveBeansView.mbeanDomain -Dspring.application.admin.enabled=true "-javaagent:C:\Program Files\JetBrains\IntelliJ IDEA 2020.1.1\lib\idea_rt.jar=63113:C:\Program Files\JetBrains\IntelliJ IDEA 2020.1.1\bin" -Dfile.encoding=UTF-8 -classpath "C:\Program Files (x86)\Java\jdk1.8.0_91\jre\lib\charsets.jar;C:\Program Files (x86)\Java\jdk1.8.0_91\jre\lib\deploy.jar;C:\Program Files (x86)\Java\jdk1.8.0_91\jre\lib\ext\access-bridge-32.jar;C:\Program Files (x86)\Java\jdk1.8.0_91\jre\lib\ext\cldrdata.jar;C:\Program Files (x86)\Java\jdk1.8.0_91\jre\lib\ext\dnsns.jar;C:\Program Files (x86)\Java\jdk1.8.0_91\jre\lib\ext\jaccess.jar;C:\Program Files (x86)\Java\jdk1.8.0_91\jre\lib\ext\jfxrt.jar;C:\Program Files (x86)\Java\jdk1.8.0_91\jre\lib\ext\localedata.jar;C:\Program Files (x86)\Java\jdk1.8.0_91\jre\lib\ext\nashorn.jar;C:\Program Files (x86)\Java\jdk1.8.0_91\jre\lib\ext\sunec.jar;C:\Program Files (x86)\Java\jdk1.8.0_91\jre\lib\ext\sunjce_provider.jar;C:\Program Files (x86)\Java\jdk1.8.0_91\jre\lib\ext\sunmscapi.jar;C:\Program Files (x86)\Java\jdk1.8.0_91\jre\lib\ext\sunpkcs11.jar;C:\Program Files (x86)\Java\jdk1.8.0_91\jre\lib\ext\zipfs.jar;C:\Program Files (x86)\Java\jdk1.8.0_91\jre\lib\javaws.jar;C:\Program Files (x86)\Java\jdk1.8.0_91\jre\lib\jce.jar;C:\Program Files (x86)\Java\jdk1.8.0_91\jre\lib\jfr.jar;C:\Program Files (x86)\Java\jdk1.8.0_91\jre\lib\jfxswt.jar;C:\Program Files (x86)\Java\jdk1.8.0_91\jre\lib\jsse.jar;C:\Program Files (x86)\Java\jdk1.8.0_91\jre\lib\management-agent.jar;C:\Program Files (x86)\Java\jdk1.8.0_91\jre\lib\plugin.jar;C:\Program Files (x86)\Java\jdk1.8.0_91\jre\lib\resources.jar;C:\Program Files (x86)\Java\jdk1.8.0_91\jre\lib\rt.jar;C:\Users\feixiaoxing\Desktop\Hello\target\classes;D:\software\apache-maven-3.6.3-bin\repository\org\springframework\boot\spring-boot-starter-web\2.7.4\spring-boot-starter-web-2.7.4.jar;D:\software\apache-maven-3.6.3-bin\repository\org\springframework\boot\spring-boot-starter\2.7.4\spring-boot-starter-2.7.4.jar;D:\software\apache-maven-3.6.3-bin\repository\org\springframework\boot\spring-boot\2.7.4\spring-boot-2.7.4.jar;D:\software\apache-maven-3.6.3-bin\repository\org\springframework\boot\spring-boot-autoconfigure\2.7.4\spring-boot-autoconfigure-2.7.4.jar;D:\software\apache-maven-3.6.3-bin\repository\org\springframework\boot\spring-boot-starter-logging\2.7.4\spring-boot-starter-logging-2.7.4.jar;D:\software\apache-maven-3.6.3-bin\repository\ch\qos\logback\logback-classic\1.2.11\logback-classic-1.2.11.jar;D:\software\apache-maven-3.6.3-bin\repository\ch\qos\logback\logback-core\1.2.11\logback-core-1.2.11.jar;D:\software\apache-maven-3.6.3-bin\repository\org\apache\logging\log4j\log4j-to-slf4j\2.17.2\log4j-to-slf4j-2.17.2.jar;D:\software\apache-maven-3.6.3-bin\repository\org\apache\logging\log4j\log4j-api\2.17.2\log4j-api-2.17.2.jar;D:\software\apache-maven-3.6.3-bin\repository\org\slf4j\jul-to-slf4j\1.7.36\jul-to-slf4j-1.7.36.jar;D:\software\apache-maven-3.6.3-bin\repository\jakarta\annotation\jakarta.annotation-api\1.3.5\jakarta.annotation-api-1.3.5.jar;D:\software\apache-maven-3.6.3-bin\repository\org\yaml\snakeyaml\1.30\snakeyaml-1.30.jar;D:\software\apache-maven-3.6.3-bin\repository\org\springframework\boot\spring-boot-starter-json\2.7.4\spring-boot-starter-json-2.7.4.jar;D:\software\apache-maven-3.6.3-bin\repository\com\fasterxml\jackson\core\jackson-databind\2.13.4\jackson-databind-2.13.4.jar;D:\software\apache-maven-3.6.3-bin\repository\com\fasterxml\jackson\core\jackson-annotations\2.13.4\jackson-annotations-2.13.4.jar;D:\software\apache-maven-3.6.3-bin\repository\com\fasterxml\jackson\core\jackson-core\2.13.4\jackson-core-2.13.4.jar;D:\software\apache-maven-3.6.3-bin\repository\com\fasterxml\jackson\datatype\jackson-datatype-jdk8\2.13.4\jackson-datatype-jdk8-2.13.4.jar;D:\software\apache-maven-3.6.3-bin\repository\com\fasterxml\jackson\datatype\jackson-datatype-jsr310\2.13.4\jackson-datatype-jsr310-2.13.4.jar;D:\software\apache-maven-3.6.3-bin\repository\com\fasterxml\jackson\module\jackson-module-parameter-names\2.13.4\jackson-module-parameter-names-2.13.4.jar;D:\software\apache-maven-3.6.3-bin\repository\org\springframework\boot\spring-boot-starter-tomcat\2.7.4\spring-boot-starter-tomcat-2.7.4.jar;D:\software\apache-maven-3.6.3-bin\repository\org\apache\tomcat\embed\tomcat-embed-core\9.0.65\tomcat-embed-core-9.0.65.jar;D:\software\apache-maven-3.6.3-bin\repository\org\apache\tomcat\embed\tomcat-embed-el\9.0.65\tomcat-embed-el-9.0.65.jar;D:\software\apache-maven-3.6.3-bin\repository\org\apache\tomcat\embed\tomcat-embed-websocket\9.0.65\tomcat-embed-websocket-9.0.65.jar;D:\software\apache-maven-3.6.3-bin\repository\org\springframework\spring-web\5.3.23\spring-web-5.3.23.jar;D:\software\apache-maven-3.6.3-bin\repository\org\springframework\spring-beans\5.3.23\spring-beans-5.3.23.jar;D:\software\apache-maven-3.6.3-bin\repository\org\springframework\spring-webmvc\5.3.23\spring-webmvc-5.3.23.jar;D:\software\apache-maven-3.6.3-bin\repository\org\springframework\spring-aop\5.3.23\spring-aop-5.3.23.jar;D:\software\apache-maven-3.6.3-bin\repository\org\springframework\spring-context\5.3.23\spring-context-5.3.23.jar;D:\software\apache-maven-3.6.3-bin\repository\org\springframework\spring-expression\5.3.23\spring-expression-5.3.23.jar;D:\software\apache-maven-3.6.3-bin\repository\org\slf4j\slf4j-api\1.7.36\slf4j-api-1.7.36.jar;D:\software\apache-maven-3.6.3-bin\repository\org\springframework\spring-core\5.3.23\spring-core-5.3.23.jar;D:\software\apache-maven-3.6.3-bin\repository\org\springframework\spring-jcl\5.3.23\spring-jcl-5.3.23.jar" com.example.demo.DemoApplication
. ____ _ __ _ _
/\\ / ___'_ __ _ _(_)_ __ __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
\\/ ___)| |_)| | | | | || (_| | ) ) ) )
' |____| .__|_| |_|_| |_\__, | / / / /
=========|_|==============|___/=/_/_/_/
:: Spring Boot :: (v2.7.4)
2022-10-06 18:29:19.419 INFO 19036 --- [ main] com.example.demo.DemoApplication : Starting DemoApplication using Java 1.8.0_91 on DESKTOP-IG2CVO4 with PID 19036 (C:\Users\feixiaoxing\Desktop\Hello\target\classes started by feixiaoxing in C:\Users\feixiaoxing\Desktop\Hello)
2022-10-06 18:29:19.422 INFO 19036 --- [ main] com.example.demo.DemoApplication : No active profile set, falling back to 1 default profile: "default"
2022-10-06 18:29:20.033 INFO 19036 --- [ main] o.s.b.w.embedded.tomcat.TomcatWebServer : Tomcat initialized with port(s): 8090 (http)
2022-10-06 18:29:20.039 INFO 19036 --- [ main] o.apache.catalina.core.StandardService : Starting service [Tomcat]
2022-10-06 18:29:20.039 INFO 19036 --- [ main] org.apache.catalina.core.StandardEngine : Starting Servlet engine: [Apache Tomcat/9.0.65]
2022-10-06 18:29:20.116 INFO 19036 --- [ main] o.a.c.c.C.[Tomcat].[localhost].[/] : Initializing Spring embedded WebApplicationContext
2022-10-06 18:29:20.116 INFO 19036 --- [ main] w.s.c.ServletWebServerApplicationContext : Root WebApplicationContext: initialization completed in 661 ms
2022-10-06 18:29:20.382 INFO 19036 --- [ main] o.s.b.w.embedded.tomcat.TomcatWebServer : Tomcat started on port(s): 8090 (http) with context path ''
2022-10-06 18:29:20.389 INFO 19036 --- [ main] com.example.demo.DemoApplication : Started DemoApplication in 1.24 seconds (JVM running for 1.724)
2022-10-06 18:30:59.461 INFO 19036 --- [nio-8090-exec-4] o.a.c.c.C.[Tomcat].[localhost].[/] : Initializing Spring DispatcherServlet 'dispatcherServlet'
2022-10-06 18:30:59.461 INFO 19036 --- [nio-8090-exec-4] o.s.web.servlet.DispatcherServlet : Initializing Servlet 'dispatcherServlet'
2022-10-06 18:30:59.462 INFO 19036 --- [nio-8090-exec-4] o.s.web.servlet.DispatcherServlet : Completed initialization in 1 ms
8、打开一个浏览器，输入localhost:8090/hello，如果你看到这样的网页，那基本上代表配置ok了，那代表第一个spring boot程序ok了。
9、总结
和之前spring mvc生成class、lib、resources文件，拷贝到tomcat开启服务不同，spring boot可以直接和web server打包，单独形成一个服务。所以这也就是所谓的微服务。微服务的功能不多，相互之间实现解耦，每一个服务除了对外的接口之外，没有共享的内容，我想着这也许就是微服务的由来把。
spring boot是spring cloud的重要基础。spring boot一般用来开发单个服务，而spring cloud用于集成很多的服务，并在上面做流量管制，spring cloud上面继承的这些服务一般也是基于spring boot开发的，只是在上面添加了不同的注解，比如@RestController、@EnableConfigServer、@EnableEurekaServer、@EnableCircuitBreaker、@EnableFeinClients等等。
如果只是开发单个web程序，学习spring boot就可以了。如果需要进一步深造，spring cloud是一个相对比较成熟的方案，值得学习一下。