Spring Boot - 引导启动

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本章将向您解释如何在 Spring Boot 应用程序上执行引导启动。

Spring Initializer

引导启动 Spring Boot 应用程序的一种方法是使用 Spring Initializer。为此，您需要访问 Spring Initializer 网页 www.start.spring.io 并选择您的构建、Spring Boot 版本和平台。此外，您需要提供一个组、工件和运行应用程序所需的依赖项。

观察以下屏幕截图，其中显示了一个示例，我们在其中添加了spring-boot-starter-web依赖项以编写 REST 端点。

Spring Initializer

提供完组、工件、依赖项、构建项目、平台和版本后，单击生成项目按钮。zip 文件将下载，并且文件将被提取。

本节将通过使用 Maven 和 Gradle 来解释示例。

Maven

下载项目后，解压缩文件。现在，您的pom.xml文件如下所示：

<?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>3.3.3</version>
      <relativePath/> <!-- lookup parent from repository -->
   </parent>
   <groupId>com.tutorialspoint</groupId>
   <artifactId>demo</artifactId>
   <version>0.0.1-SNAPSHOT</version>
   <name>demo</name>
   <description>Demo project for Spring Boot</description>
   <url/>
   <licenses>
      <license/>
   </licenses>
   <developers>
      <developer/>
   </developers>
   <scm>
      <connection/>
      <developerConnection/>
      <tag/>
      <url/>
   </scm>
   <properties>
      <java.version>21</java.version>
   </properties>
   <dependencies>
      <dependency>
         <groupId>org.springframework.boot</groupId>
         <artifactId>spring-boot-starter-web</artifactId>
      </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>
         </plugin>
      </plugins>
   </build>
</project>

Gradle

对于 Gradle，您可以检查 build.gradle 如下

build.gradle

buildscript {
   ext {
      springBootVersion = '3.3.3'
   }
   repositories {
      mavenCentral()
   }
   dependencies {
      classpath("org.springframework.boot:spring-boot-gradle-plugin:${springBootVersion}")
   }
}
apply plugin: 'java'
apply plugin: 'eclipse'
apply plugin: 'org.springframework.boot'

group = 'com.tutorialspoint'
version = '0.0.1-SNAPSHOT'
sourceCompatibility = 21

repositories {
   mavenCentral()
}
dependencies {
   compile('org.springframework.boot:spring-boot-starter-web')
   testCompile('org.springframework.boot:spring-boot-starter-test')
}

类路径依赖项

Spring Boot 提供了许多启动器以将 jar 添加到我们的类路径中。例如，要编写 Rest 端点，我们需要在类路径中添加spring-boot-starter-web依赖项。观察下面显示的代码以更好地理解：

Maven 依赖项

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

Gradle 依赖项

dependencies {
   compile('org.springframework.boot:spring-boot-starter-web')
}

主方法

主方法应该编写 Spring Boot 应用程序类。此类应使用@SpringBootApplication进行注释。这是启动 Spring Boot 应用程序的入口点。您可以在src/java/main目录下找到默认包的主类文件。

在此示例中，主类文件位于src/java/main目录下，默认包为com.tutorialspoint.demo。观察此处显示的代码以更好地理解：

package com.tutorialspoint.demo;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class DemoApplication {
   public static void main(String[] args) {
      SpringApplication.run(DemoApplication.class, args);
   }
}

编写 Rest 端点

要在 Spring Boot 应用程序的主类文件中编写一个简单的 Hello World Rest 端点，请按照以下步骤操作：

  • 首先，在类的顶部添加@RestController注释。

  • 现在，使用@GetMapping注释编写一个请求 URI 方法。

  • 然后，请求 URI 方法应返回Hello World字符串。

现在，您的 Spring Boot 应用程序主类文件将如下所示：

package com.tutorialspoint.demo;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
@SpringBootApplication
public class DemoApplication {

   public static void main(String[] args) {
      SpringApplication.run(DemoApplication.class, args);
   }
   @GetMapping(value = "/")
   public String hello() {
      return "Hello World";
   }
}

创建可执行 JAR

让我们使用命令提示符中的 Maven 命令创建一个可执行 JAR 文件以运行 Spring Boot 应用程序，如下所示：

使用 Maven 命令 mvn clean install，如下所示：

E:\dev\demo>mvn clean install

您将看到类似于以下的结果

[INFO] Scanning for projects...
[INFO] 
[INFO] [1m----------------------< [0;36mcom.tutorialspoint:demo[0;1m >-----------------------[m
[INFO] [1mBuilding demo 0.0.1-SNAPSHOT[m
[INFO]   from pom.xml
[INFO] [1m--------------------------------[ jar ]---------------------------------[m
[INFO] Downloading from central: https://repo.maven.apache.org/maven2/org/apache/maven/plugins/maven-install-plugin/3.1.3/maven-install-plugin-3.1.3.pom
....
[INFO] 
[INFO] [1m--- [0;32mclean:3.3.2:clean[m [1m(default-clean)[m @ [36mdemo[0;1m ---[m
[INFO] Deleting E:\Dev\demo\target
[INFO] 
[INFO] [1m--- [0;32mresources:3.3.1:resources[m [1m(default-resources)[m @ [36mdemo[0;1m ---[m
[INFO] Copying 1 resource from src\main\resources to target\classes
[INFO] Copying 0 resource from src\main\resources to target\classes
[INFO] 
...
[INFO] 
[INFO] [1m--- [0;32msurefire:3.2.5:test[m [1m(default-test)[m @ [36mdemo[0;1m ---[m
[INFO] Using auto detected provider org.apache.maven.surefire.junitplatform.JUnitPlatformProvider
[INFO] Downloading from central: https://repo.maven.apache.org/maven2/org/junit/platform/junit-platform-launcher/1.10.3/junit-platform-launcher-1.10.3.pom
[INFO] Downloaded from central: https://repo.maven.apache.org/maven2/org/junit/platform/junit-platform-launcher/1.10.3/junit-platform-launcher-1.10.3.pom (3.0 kB at 13 kB/s)
[INFO] 
[INFO] -------------------------------------------------------
[INFO]  T E S T S
[INFO] -------------------------------------------------------
[INFO] Running com.tutorialspoint.demo.[1mDemoApplicationTests[m
17:35:15.626 [main] INFO org.springframework.test.context.support.AnnotationConfigContextLoaderUtils -- Could not detect default configuration classes for test class [com.tutorialspoint.demo.DemoApplicationTests]: DemoApplicationTests does not declare any static, non-private, non-final, nested classes annotated with @Configuration.
17:35:15.802 [main] INFO org.springframework.boot.test.context.SpringBootTestContextBootstrapper -- Found @SpringBootConfiguration com.tutorialspoint.demo.DemoApplication for test class com.tutorialspoint.demo.DemoApplicationTests

  .   ____          _            __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/

 :: Spring Boot ::                (v3.3.3)

2024-09-02T17:35:16.380+05:30  INFO 6204 --- [demo] [           main] c.t.demo.DemoApplicationTests            : Starting DemoApplicationTests using Java 21.0.3 with PID 6204 (started by Tutorialspoint in E:\Dev\demo)
2024-09-02T17:35:16.381+05:30  INFO 6204 --- [demo] [           main] c.t.demo.DemoApplicationTests            : No active profile set, falling back to 1 default profile: "default"
2024-09-02T17:35:18.173+05:30  INFO 6204 --- [demo] [           main] c.t.demo.DemoApplicationTests            : Started DemoApplicationTests in 2.162 seconds (process running for 4.295)
...
[INFO] Results:
[INFO] 
[INFO] [1;32mTests run: 1, Failures: 0, Errors: 0, Skipped: 0[m
[INFO] 
[INFO] 
[INFO] [1m--- [0;32mjar:3.4.2:jar[m [1m(default-jar)[m @ [36mdemo[0;1m ---[m
[INFO] Building jar: E:\Dev\demo\target\demo-0.0.1-SNAPSHOT.jar
[INFO] 
[INFO] [1m--- [0;32mspring-boot:3.3.3:repackage[m [1m(repackage)[m @ [36mdemo[0;1m ---[m
[INFO] Replacing main artifact E:\Dev\demo\target\demo-0.0.1-SNAPSHOT.jar with repackaged archive, adding nested dependencies in BOOT-INF/.
[INFO] The original artifact has been renamed to E:\Dev\demo\target\demo-0.0.1-SNAPSHOT.jar.original
[INFO] 
[INFO] [1m--- [0;32minstall:3.1.3:install[m [1m(default-install)[m @ [36mdemo[0;1m ---[m
....
[INFO] Downloaded from central: https://repo.maven.apache.org/maven2/org/codehaus/plexus/plexus-xml/3.0.1/plexus-xml-3.0.1.jar (94 kB at 806 kB/s)
[INFO] Installing E:\Dev\demo\pom.xml to C:\Users\Tutorialspoint\.m2\repository\com\tutorialspoint\demo\0.0.1-SNAPSHOT\demo-0.0.1-SNAPSHOT.pom
[INFO] Installing E:\Dev\demo\target\demo-0.0.1-SNAPSHOT.jar to C:\Users\Tutorialspoint\.m2\repository\com\tutorialspoint\demo\0.0.1-SNAPSHOT\demo-0.0.1-SNAPSHOT.jar
[INFO] [1m------------------------------------------------------------------------[m
[INFO] [1;32mBUILD SUCCESS[m
[INFO] [1m------------------------------------------------------------------------[m
[INFO] Total time:  18.938 s
[INFO] Finished at: 2024-09-02T17:35:25+05:30
[INFO] [1m------------------------------------------------------------------------[m

同样，对于 Gradle，您可以运行以下命令来构建 jar。

gradle clean build

使用 Java 运行 Hello World

创建可执行 JAR 文件后，您可以在 target 目录下找到它。在我们的例子中，它位于E: > Dev > demo > target > demo-0.0.1-SNAPSHOT.jar.

现在，使用命令java –jar <JARFILE>运行 JAR 文件。观察在上述示例中，JAR 文件名为demo-0.0.1-SNAPSHOT.jar

E:\dev\demo\target>java -jar demo-0.0.1-SNAPSHOT.jar

运行 jar 文件后，您可以在控制台窗口中看到输出，如下所示：

  .   ____          _            __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/

 :: Spring Boot ::                (v3.3.3)

2024-09-02T17:42:38.623+05:30  INFO 4712 --- [demo] [           main] c.tutorialspoint.demo.DemoApplication    : Starting DemoApplication v0.0.1-SNAPSHOT using Java 21.0.2 with PID 4712 (E:\Dev\demo\target\demo-0.0.1-SNAPSHOT.jar started by Tutorialspoint in E:\Dev\demo\target)
2024-09-02T17:42:38.626+05:30  INFO 4712 --- [demo] [           main] c.tutorialspoint.demo.DemoApplication    : No active profile set, falling back to 1 default profile: "default"
2024-09-02T17:42:40.250+05:30  INFO 4712 --- [demo] [           main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat initialized with port 8080 (http)
2024-09-02T17:42:40.266+05:30  INFO 4712 --- [demo] [           main] o.apache.catalina.core.StandardService   : Starting service [Tomcat]
2024-09-02T17:42:40.266+05:30  INFO 4712 --- [demo] [           main] o.apache.catalina.core.StandardEngine    : Starting Servlet engine: [Apache Tomcat/10.1.28]
2024-09-02T17:42:40.320+05:30  INFO 4712 --- [demo] [           main] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring embedded WebApplicationContext
2024-09-02T17:42:40.322+05:30  INFO 4712 --- [demo] [           main] w.s.c.ServletWebServerApplicationContext : Root WebApplicationContext: initialization completed in 1574 ms
2024-09-02T17:42:40.943+05:30  INFO 4712 --- [demo] [           main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat started on port 8080 (http) with context path '/'
2024-09-02T17:42:40.969+05:30  INFO 4712 --- [demo] [           main] c.tutorialspoint.demo.DemoApplication    : Started DemoApplication in 3.122 seconds (process running for 3.902)

现在，查看控制台，Tomcat 在端口 8080 (http) 上启动。现在，转到 Web 浏览器并访问 URL https://127.0.0.1:8080/，您将看到如下所示的输出：

Tomcat Started on Port 8080 (http).
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