Spring Boot - 引導啟動

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本章將向您解釋如何在 Spring Boot 應用程式上執行引導啟動。

Spring Initializer

引導啟動 Spring Boot 應用程式的一種方法是使用 Spring Initializer。為此，您需要訪問 Spring Initializer 網頁 www.start.spring.io 並選擇您的構建、Spring Boot 版本和平臺。此外，您需要提供一個組、工件和執行應用程式所需的依賴項。

觀察以下螢幕截圖，其中顯示了一個示例，我們在其中添加了spring-boot-starter-web依賴項以編寫 REST 端點。

Spring Initializer

提供完組、工件、依賴項、構建專案、平臺和版本後，單擊生成專案按鈕。zip 檔案將下載，並且檔案將被提取。

本節將透過使用 Maven 和 Gradle 來解釋示例。

Maven

下載專案後，解壓縮檔案。現在，您的pom.xml檔案如下所示：

<?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

對於 Gradle，您可以檢查 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')
}

類路徑依賴項

Spring Boot 提供了許多啟動器以將 jar 新增到我們的類路徑中。例如，要編寫 Rest 端點，我們需要在類路徑中新增spring-boot-starter-web依賴項。觀察下面顯示的程式碼以更好地理解：

Maven 依賴項

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

Gradle 依賴項

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

主方法

主方法應該編寫 Spring Boot 應用程式類。此類應使用@SpringBootApplication進行註釋。這是啟動 Spring Boot 應用程式的入口點。您可以在src/java/main目錄下找到預設包的主類檔案。

在此示例中，主類檔案位於src/java/main目錄下，預設包為com.tutorialspoint.demo。觀察此處顯示的程式碼以更好地理解：

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);
   }
}

編寫 Rest 端點

要在 Spring Boot 應用程式的主類檔案中編寫一個簡單的 Hello World Rest 端點，請按照以下步驟操作：

  • 首先，在類的頂部新增@RestController註釋。

  • 現在，使用@GetMapping註釋編寫一個請求 URI 方法。

  • 然後，請求 URI 方法應返回Hello World字串。

現在，您的 Spring Boot 應用程式主類檔案將如下所示：

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";
   }
}

建立可執行 JAR

讓我們使用命令提示符中的 Maven 命令建立一個可執行 JAR 檔案以執行 Spring Boot 應用程式，如下所示：

使用 Maven 命令 mvn clean install，如下所示：

E:\dev\demo>mvn clean install

您將看到類似於以下的結果

[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

同樣，對於 Gradle，您可以執行以下命令來構建 jar。

gradle clean build

使用 Java 執行 Hello World

建立可執行 JAR 檔案後，您可以在 target 目錄下找到它。在我們的例子中，它位於E: > Dev > demo > target > demo-0.0.1-SNAPSHOT.jar.

現在，使用命令java –jar <JARFILE>執行 JAR 檔案。觀察在上述示例中，JAR 檔名為demo-0.0.1-SNAPSHOT.jar

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

執行 jar 檔案後，您可以在控制檯視窗中看到輸出，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)

現在，檢視控制檯，Tomcat 在埠 8080 (http) 上啟動。現在，轉到 Web 瀏覽器並訪問 URL https://:8080/，您將看到如下所示的輸出：

Tomcat Started on Port 8080 (http).
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