创建Maven项目

配置pom

<?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 http://maven.apache.org/xsd/maven-4.0.0.xsd"><modelVersion>4.0.0</modelVersion><groupId>com.davieyang</groupId><artifactId>SpringBootDemo</artifactId><version>1.0-SNAPSHOT</version><name>SpringBootDemo</name><!-- FIXME change it to the project's website --><url>http://www.example.com</url><properties><project.build.sourceEncoding>UTF-8</project.build.sourceEncoding><maven.compiler.source>1.7</maven.compiler.source><maven.compiler.target>1.7</maven.compiler.target></properties><dependencies><!-- https://mvnrepository.com/artifact/org.springframework.boot/spring-boot-starter-test --><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-test</artifactId><version>2.3.3.RELEASE</version><scope>test</scope></dependency><!-- https://mvnrepository.com/artifact/org.springframework.boot/spring-boot-starter-web --><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-web</artifactId><version>2.3.3.RELEASE</version></dependency><!-- https://mvnrepository.com/artifact/org.springframework.boot/spring-boot-starter-thymeleaf --><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-thymeleaf</artifactId><version>2.3.3.RELEASE</version></dependency><!-- https://mvnrepository.com/artifact/org.springframework.boot/spring-boot-starter-parent --><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-parent</artifactId><version>2.3.3.RELEASE</version><type>pom</type></dependency></dependencies><build><pluginManagement><!-- lock down plugins versions to avoid using Maven defaults (may be moved to parent pom) --><plugins><!-- clean lifecycle, see https://maven.apache.org/ref/current/maven-core/lifecycles.html#clean_Lifecycle --><plugin><artifactId>maven-clean-plugin</artifactId><version>3.1.0</version></plugin><!-- default lifecycle, jar packaging: see https://maven.apache.org/ref/current/maven-core/default-bindings.html#Plugin_bindings_for_jar_packaging --><plugin><artifactId>maven-resources-plugin</artifactId><version>3.0.2</version></plugin><plugin><artifactId>maven-compiler-plugin</artifactId><version>3.8.0</version></plugin><plugin><artifactId>maven-surefire-plugin</artifactId><version>2.22.1</version></plugin><plugin><artifactId>maven-jar-plugin</artifactId><version>3.0.2</version></plugin><plugin><artifactId>maven-install-plugin</artifactId><version>2.5.2</version></plugin><plugin><artifactId>maven-deploy-plugin</artifactId><version>2.8.2</version></plugin><!-- site lifecycle, see https://maven.apache.org/ref/current/maven-core/lifecycles.html#site_Lifecycle --><plugin><artifactId>maven-site-plugin</artifactId><version>3.7.1</version></plugin><plugin><artifactId>maven-project-info-reports-plugin</artifactId><version>3.0.0</version></plugin></plugins></pluginManagement></build>
</project>

业务逻辑层实现

package com.davieyang.springboot.service;
import org.springframework.stereotype.Service;@Service
// @Service是Spring框架的业务逻辑层注解
public class CalculatorForPpiService {public long calculate(int width, int height, double size){long result;if (width > 0 && height > 0 && size >0){result = Math.round(Math.pow((Math.pow(width, 2) + Math.pow(height, 2)) / Math.pow(size, 2), 0.5));}else {result = -1;}return result;}
}

控制器层实现

package com.davieyang.springboot.controller;
import javax.annotation.Resource;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RestController;
import com.davieyang.springboot.service.CalculatorForPpiService;@RestController
public class CalculatorForPpiController {@Resource//@Resource是一种注入注解，讲一个Bean注入当前类中，即可使用该Beanprivate CalculatorForPpiService calculatorForPpiService;@RequestMapping("/calculate")public String calculate(@RequestParam("width") int width, @RequestParam("height") int height, @RequestParam("size") double size){//@RequestParam注解用于接收请求参数long result=calculatorForPpiService.calculate(width, height, size);return "{\"PPI\":" + result + "}";//返回JSON格式的字符串}
}

package com.davieyang.springboot.controller;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;@Controller
//@Controller 是Spring框架的控制器层注解，常用的Spring框架的控制器层注解还有@RestController
//@RequestMapping 表示接收用户请求，当用户请求/index时，使用index方法处理，index方法返回的“index-page”代表名为“index-page”的页面
public class IndexController {@RequestMapping("/index")public String index(){return "index-page";}
}

表现层实现

<!DOCTYPE html>
<html xmlns:th="http://www.thymeleaf.org" lang="en">
<head><script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.4.1/jquery.min.js"></script><meta charset="UTF-8"><title>CalculatorForPpi</title>
</head>
<body><form><input type="text" id="width" placeholder="屏幕宽(像素)"><br><input type="text" id="height" placeholder="屏幕高(像素)"><br><input type="text" id="size" placeholder="屏幕尺寸(英寸)"><br><button type="button" id="submit">计算</button><br><label id="result"></label></form><script>$("#submit").click(function() {$.ajax({url:"/calculate",type:"post",data:{"width":$("#width").val(),"height":$("#height").val(),"size":$("#size").val(),},success:function(data){let json = JSON.parse(data);$("#result").text("屏幕像素密度为:" + json["PPI"] + "PPI");}});});</script>
</body>
</html>

程序入口实现

package com.davieyang.springboot;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;@SpringBootApplication
//@SpringBootApplication 代表将程序作为SpringBoot应用来运行
public class Application {public static void main(String[] args){SpringApplication.run(Application.class, args);//调用run方法并传入当前Class作为参数来运行程序，同时传入main方法的args参数}
}

执行SpringBoot程序

"C:\Program Files\Java\jdk1.8.0_261\bin\java.exe" "-javaagent:C:\Program Files\JetBrains\IntelliJ IDEA Community Edition 2020.2\lib\idea_rt.jar=51816:C:\Program Files\JetBrains\IntelliJ IDEA Community Edition 2020.2\bin" -Dfile.encoding=UTF-8 -classpath "C:\Program Files\Java\jdk1.8.0_261\jre\lib\charsets.jar;C:\Program Files\Java\jdk1.8.0_261\jre\lib\deploy.jar;C:\Program Files\Java\jdk1.8.0_261\jre\lib\ext\access-bridge-64.jar;C:\Program Files\Java\jdk1.8.0_261\jre\lib\ext\cldrdata.jar;C:\Program Files\Java\jdk1.8.0_261\jre\lib\ext\dnsns.jar;C:\Program Files\Java\jdk1.8.0_261\jre\lib\ext\jaccess.jar;C:\Program Files\Java\jdk1.8.0_261\jre\lib\ext\jfxrt.jar;C:\Program Files\Java\jdk1.8.0_261\jre\lib\ext\localedata.jar;C:\Program Files\Java\jdk1.8.0_261\jre\lib\ext\nashorn.jar;C:\Program Files\Java\jdk1.8.0_261\jre\lib\ext\sunec.jar;C:\Program Files\Java\jdk1.8.0_261\jre\lib\ext\sunjce_provider.jar;C:\Program Files\Java\jdk1.8.0_261\jre\lib\ext\sunmscapi.jar;C:\Program Files\Java\jdk1.8.0_261\jre\lib\ext\sunpkcs11.jar;C:\Program Files\Java\jdk1.8.0_261\jre\lib\ext\zipfs.jar;C:\Program Files\Java\jdk1.8.0_261\jre\lib\javaws.jar;C:\Program Files\Java\jdk1.8.0_261\jre\lib\jce.jar;C:\Program Files\Java\jdk1.8.0_261\jre\lib\jfr.jar;C:\Program Files\Java\jdk1.8.0_261\jre\lib\jfxswt.jar;C:\Program Files\Java\jdk1.8.0_261\jre\lib\jsse.jar;C:\Program Files\Java\jdk1.8.0_261\jre\lib\management-agent.jar;C:\Program Files\Java\jdk1.8.0_261\jre\lib\plugin.jar;C:\Program Files\Java\jdk1.8.0_261\jre\lib\resources.jar;C:\Program Files\Java\jdk1.8.0_261\jre\lib\rt.jar;D:\Programs\Java\SpringBootDemo\target\classes;E:\apache-maven-3.6.2\Repository\org\springframework\boot\spring-boot-starter\2.3.3.RELEASE\spring-boot-starter-2.3.3.RELEASE.jar;E:\apache-maven-3.6.2\Repository\org\springframework\boot\spring-boot\2.3.3.RELEASE\spring-boot-2.3.3.RELEASE.jar;E:\apache-maven-3.6.2\Repository\org\springframework\boot\spring-boot-autoconfigure\2.3.3.RELEASE\spring-boot-autoconfigure-2.3.3.RELEASE.jar;E:\apache-maven-3.6.2\Repository\org\springframework\boot\spring-boot-starter-logging\2.3.3.RELEASE\spring-boot-starter-logging-2.3.3.RELEASE.jar;E:\apache-maven-3.6.2\Repository\ch\qos\logback\logback-classic\1.2.3\logback-classic-1.2.3.jar;E:\apache-maven-3.6.2\Repository\ch\qos\logback\logback-core\1.2.3\logback-core-1.2.3.jar;E:\apache-maven-3.6.2\Repository\org\apache\logging\log4j\log4j-to-slf4j\2.13.3\log4j-to-slf4j-2.13.3.jar;E:\apache-maven-3.6.2\Repository\org\apache\logging\log4j\log4j-api\2.13.3\log4j-api-2.13.3.jar;E:\apache-maven-3.6.2\Repository\org\slf4j\jul-to-slf4j\1.7.30\jul-to-slf4j-1.7.30.jar;E:\apache-maven-3.6.2\Repository\jakarta\annotation\jakarta.annotation-api\1.3.5\jakarta.annotation-api-1.3.5.jar;E:\apache-maven-3.6.2\Repository\org\yaml\snakeyaml\1.26\snakeyaml-1.26.jar;E:\apache-maven-3.6.2\Repository\org\slf4j\slf4j-api\1.7.25\slf4j-api-1.7.25.jar;E:\apache-maven-3.6.2\Repository\org\springframework\spring-core\5.2.8.RELEASE\spring-core-5.2.8.RELEASE.jar;E:\apache-maven-3.6.2\Repository\org\springframework\spring-jcl\5.2.8.RELEASE\spring-jcl-5.2.8.RELEASE.jar;E:\apache-maven-3.6.2\Repository\org\springframework\boot\spring-boot-starter-web\2.3.3.RELEASE\spring-boot-starter-web-2.3.3.RELEASE.jar;E:\apache-maven-3.6.2\Repository\org\springframework\boot\spring-boot-starter-json\2.3.3.RELEASE\spring-boot-starter-json-2.3.3.RELEASE.jar;E:\apache-maven-3.6.2\Repository\com\fasterxml\jackson\core\jackson-databind\2.11.2\jackson-databind-2.11.2.jar;E:\apache-maven-3.6.2\Repository\com\fasterxml\jackson\core\jackson-annotations\2.11.2\jackson-annotations-2.11.2.jar;E:\apache-maven-3.6.2\Repository\com\fasterxml\jackson\core\jackson-core\2.11.2\jackson-core-2.11.2.jar;E:\apache-maven-3.6.2\Repository\com\fasterxml\jackson\datatype\jackson-datatype-jdk8\2.11.2\jackson-datatype-jdk8-2.11.2.jar;E:\apache-maven-3.6.2\Repository\com\fasterxml\jackson\datatype\jackson-datatype-jsr310\2.11.2\jackson-datatype-jsr310-2.11.2.jar;E:\apache-maven-3.6.2\Repository\com\fasterxml\jackson\module\jackson-module-parameter-names\2.11.2\jackson-module-parameter-names-2.11.2.jar;E:\apache-maven-3.6.2\Repository\org\springframework\boot\spring-boot-starter-tomcat\2.3.3.RELEASE\spring-boot-starter-tomcat-2.3.3.RELEASE.jar;E:\apache-maven-3.6.2\Repository\org\apache\tomcat\embed\tomcat-embed-core\9.0.37\tomcat-embed-core-9.0.37.jar;E:\apache-maven-3.6.2\Repository\org\glassfish\jakarta.el\3.0.3\jakarta.el-3.0.3.jar;E:\apache-maven-3.6.2\Repository\org\apache\tomcat\embed\tomcat-embed-websocket\9.0.37\tomcat-embed-websocket-9.0.37.jar;E:\apache-maven-3.6.2\Repository\org\springframework\spring-web\5.2.8.RELEASE\spring-web-5.2.8.RELEASE.jar;E:\apache-maven-3.6.2\Repository\org\springframework\spring-beans\5.2.8.RELEASE\spring-beans-5.2.8.RELEASE.jar;E:\apache-maven-3.6.2\Repository\org\springframework\spring-webmvc\5.2.8.RELEASE\spring-webmvc-5.2.8.RELEASE.jar;E:\apache-maven-3.6.2\Repository\org\springframework\spring-aop\5.2.8.RELEASE\spring-aop-5.2.8.RELEASE.jar;E:\apache-maven-3.6.2\Repository\org\springframework\spring-context\5.2.8.RELEASE\spring-context-5.2.8.RELEASE.jar;E:\apache-maven-3.6.2\Repository\org\springframework\spring-expression\5.2.8.RELEASE\spring-expression-5.2.8.RELEASE.jar;E:\apache-maven-3.6.2\Repository\org\springframework\boot\spring-boot-starter-thymeleaf\2.3.3.RELEASE\spring-boot-starter-thymeleaf-2.3.3.RELEASE.jar;E:\apache-maven-3.6.2\Repository\org\thymeleaf\thymeleaf-spring5\3.0.11.RELEASE\thymeleaf-spring5-3.0.11.RELEASE.jar;E:\apache-maven-3.6.2\Repository\org\thymeleaf\thymeleaf\3.0.11.RELEASE\thymeleaf-3.0.11.RELEASE.jar;E:\apache-maven-3.6.2\Repository\org\attoparser\attoparser\2.0.5.RELEASE\attoparser-2.0.5.RELEASE.jar;E:\apache-maven-3.6.2\Repository\org\unbescape\unbescape\1.1.6.RELEASE\unbescape-1.1.6.RELEASE.jar;E:\apache-maven-3.6.2\Repository\org\thymeleaf\extras\thymeleaf-extras-java8time\3.0.4.RELEASE\thymeleaf-extras-java8time-3.0.4.RELEASE.jar" com.davieyang.springboot.Application.   ____          _            __ _ _/\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \\\/  ___)| |_)| | | | | || (_| |  ) ) ) )'  |____| .__|_| |_|_| |_\__, | / / / /=========|_|==============|___/=/_/_/_/:: Spring Boot ::        (v2.3.3.RELEASE)2020-08-18 19:34:24.269  INFO 402884 --- [           main] com.davieyang.springboot.Application     : Starting Application on DESKTOP-KEOVP72 with PID 402884 (D:\Programs\Java\SpringBootDemo\target\classes started by Administrator in D:\Programs\Java\SpringBootDemo)
2020-08-18 19:34:24.284  INFO 402884 --- [           main] com.davieyang.springboot.Application     : No active profile set, falling back to default profiles: default
2020-08-18 19:34:25.476  INFO 402884 --- [           main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat initialized with port(s): 8080 (http)
2020-08-18 19:34:25.489  INFO 402884 --- [           main] o.apache.catalina.core.StandardService   : Starting service [Tomcat]
2020-08-18 19:34:25.489  INFO 402884 --- [           main] org.apache.catalina.core.StandardEngine  : Starting Servlet engine: [Apache Tomcat/9.0.37]
2020-08-18 19:34:25.575  INFO 402884 --- [           main] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring embedded WebApplicationContext
2020-08-18 19:34:25.575  INFO 402884 --- [           main] w.s.c.ServletWebServerApplicationContext : Root WebApplicationContext: initialization completed in 1222 ms
2020-08-18 19:34:25.772  INFO 402884 --- [           main] o.s.s.concurrent.ThreadPoolTaskExecutor  : Initializing ExecutorService 'applicationTaskExecutor'
2020-08-18 19:34:26.007  INFO 402884 --- [           main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat started on port(s): 8080 (http) with context path ''
2020-08-18 19:34:26.016  INFO 402884 --- [           main] com.davieyang.springboot.Application     : Started Application in 2.205 seconds (JVM running for 2.749)
2020-08-18 19:34:34.661  INFO 402884 --- [nio-8080-exec-1] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring DispatcherServlet 'dispatcherServlet'
2020-08-18 19:34:34.661  INFO 402884 --- [nio-8080-exec-1] o.s.web.servlet.DispatcherServlet        : Initializing Servlet 'dispatcherServlet'
2020-08-18 19:34:34.671  INFO 402884 --- [nio-8080-exec-1] o.s.web.servlet.DispatcherServlet        : Completed initialization in 10 ms

查看执行结果

用浏览器打开http://localhost:8080/index即可看到如下页面