开启Spring Boot

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本文介绍了如何使用http://start.spring.io/创建Spring Boot项目，从生成项目文件、简单演示、打包发布到解析pom.xml文件，特别是讨论了spring-boot-maven-plugin的作用。

Spring Boot是在Spring框架上创建的一个全新的框架，其设计目的是简化Spring应用的搭建和开发过程。开启Spring Boot有许多种方法可供选择，这里仅介绍使用http://start.spring.io/来构建一个简单的Spring Boot项目。

生成项目文件

访问http://start.spring.io/，页面显示如下：

这里选择以Maven构建，语言选择Java，Spring Boot版本为2.3.2。

在项目信息里选择以jar包的方式部署，Java版本为8。

最后点击页面的按钮生成项目文件。文件下载后是一个压缩包，进行解压然后使用IDEA打开。项目目录如下所示：

简单演示

项目根目录下生成了一个artifactId+Application命名规则的入口类，为了演示简单，不再新建控制器，直接在入口类中编写代码：

然后在IDEA中点击运行启动入口：

访问http://localhost:8080，页面显示如下：

打包发布

在IDEA中右击项目，选择Maven模块，勾选跳过测试按钮，如下图所示：

然后双击package就将项目打包成jar包（初次打包会自动下载一些依赖）。

看到BUILD SUCCESS即表示打包完成。

打包完毕后可看到项目目录target文件夹下生成了一个jar文件：

生成jar包后，cd到target目录下，执行以下命令：

访问http://localhost:8080，效果如上。

聊聊pom.xml

打开pom.xml可看到配置如下：

<?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>2.3.2.RELEASE</version>
		<relativePath/> <!-- lookup parent from repository -->
	</parent>
	<groupId>com.example</groupId>
	<artifactId>demo</artifactId>
	<version>0.0.1-SNAPSHOT</version>
	<name>demo</name>
	<description>Demo project for Spring Boot</description>

	<properties>
		<java.version>1.8</java.version>
	</properties>

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

		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-test</artifactId>
			<scope>test</scope>
			<exclusions>
				<exclusion>
					<groupId>org.junit.vintage</groupId>
					<artifactId>junit-vintage-engine</artifactId>
				</exclusion>
			</exclusions>
		</dependency>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-web</artifactId>
			<version>RELEASE</version>
			<scope>compile</scope>
		</dependency>
	</dependencies>

	<build>
		<plugins>
			<plugin>
				<groupId>org.springframework.boot</groupId>
				<artifactId>spring-boot-maven-plugin</artifactId>
			</plugin>
		</plugins>
	</build>

</project>

spring-boot-starter-parent

spring-boot-starter-parent指定了当前项目为一个Spring Boot项目，它提供了诸多的默认Maven依赖，具体可查看目录C:\.m2\repository\org\springframework\boot\spring-boot-dependencies\2.3.2.RELEASE下的spring-boot-dependencies-2.3.2.RELEASE.pom文件，这里仅截取一小部分：

<properties>
    ...
    <spring-amqp.version>2.2.9.RELEASE</spring-amqp.version>
    <spring-batch.version>4.2.4.RELEASE</spring-batch.version>
    <spring-data-releasetrain.version>Neumann-SR2</spring-data-releasetrain.version>
    <spring-framework.version>5.2.8.RELEASE</spring-framework.version>
    <spring-hateoas.version>1.1.0.RELEASE</spring-hateoas.version>
    <spring-integration.version>5.3.2.RELEASE</spring-integration.version>
    <spring-kafka.version>2.5.4.RELEASE</spring-kafka.version>
    <spring-ldap.version>2.3.3.RELEASE</spring-ldap.version>
    <spring-restdocs.version>2.0.4.RELEASE</spring-restdocs.version>
    <spring-retry.version>1.2.5.RELEASE</spring-retry.version>
    <spring-security.version>5.3.3.RELEASE</spring-security.version>
    <spring-session-bom.version>Dragonfruit-RELEASE</spring-session-bom.version>
    <spring-ws.version>3.0.9.RELEASE</spring-ws.version>
    <sqlite-jdbc.version>3.31.1</sqlite-jdbc.version>
    <sun-mail.version>1.6.5</sun-mail.version>
    <thymeleaf.version>3.0.11.RELEASE</thymeleaf.version>
    <thymeleaf-extras-data-attribute.version>2.0.1</thymeleaf-extras-data-attribute.version>
    <thymeleaf-extras-java8time.version>3.0.4.RELEASE</thymeleaf-extras-java8time.version>
    <thymeleaf-extras-springsecurity.version>3.0.4.RELEASE</thymeleaf-extras-springsecurity.version>
    <thymeleaf-layout-dialect.version>2.4.1</thymeleaf-layout-dialect.version>
    <tomcat.version>9.0.37</tomcat.version>
    ...
</properties>

当然，我们可以手动改变这些依赖的版本。比如我想把kafka的版本改为2.5.5.RELEASE，我们可以在pom.xml中进行如下配置：

<properties>
    <spring-kafka.version>2.5.5.RELEASE</spring-kafka.version>
</properties>

需要说明的是，并非所有在<properties>标签中配置了版本号的依赖都有被启用，其启用与否取决于您是否配置了相应的starter。比如tomcat这个依赖就是spring-boot-starter-web的传递性依赖（下面将会描述到）。

spring-boot-starter-web

Spring Boot提供了许多开箱即用的依赖模块，这些模块都是以spring-boot-starter-XX命名的。比如要开启Spring Boot的web功能，只需要在pom.xml中配置spring-boot-starter-web即可：

因为其依赖于spring-boot-starter-parent，所以这里可以不用配置version。保存后Maven会自动帮我们下载spring-boot-starter-web模块所包含的jar文件。如果需要具体查看spring-boot-starter-web包含了哪些依赖，我们可以选择Maven Goals，输入命令dependency:tree

然后点击Execute即可在IDEA控制台查看到如下信息：

[INFO] com.example:demo:jar:0.0.1-SNAPSHOT
[INFO] +- org.springframework.boot:spring-boot-starter:jar:2.3.2.RELEASE:compile
[INFO] |  +- org.springframework.boot:spring-boot:jar:2.3.2.RELEASE:compile
[INFO] |  |  \- org.springframework:spring-context:jar:5.2.8.RELEASE:compile
[INFO] |  +- org.springframework.boot:spring-boot-autoconfigure:jar:2.3.2.RELEASE:compile
[INFO] |  +- org.springframework.boot:spring-boot-starter-logging:jar:2.3.2.RELEASE:compile
[INFO] |  |  +- ch.qos.logback:logback-classic:jar:1.2.3:compile
[INFO] |  |  |  \- ch.qos.logback:logback-core:jar:1.2.3:compile
[INFO] |  |  +- org.apache.logging.log4j:log4j-to-slf4j:jar:2.13.3:compile
[INFO] |  |  |  \- org.apache.logging.log4j:log4j-api:jar:2.13.3:compile
[INFO] |  |  \- org.slf4j:jul-to-slf4j:jar:1.7.30:compile
[INFO] |  +- jakarta.annotation:jakarta.annotation-api:jar:1.3.5:compile
[INFO] |  +- org.springframework:spring-core:jar:5.2.8.RELEASE:compile
[INFO] |  |  \- org.springframework:spring-jcl:jar:5.2.8.RELEASE:compile
[INFO] |  \- org.yaml:snakeyaml:jar:1.26:compile
[INFO] +- org.springframework.boot:spring-boot-starter-test:jar:2.3.2.RELEASE:test
[INFO] |  +- org.springframework.boot:spring-boot-test:jar:2.3.2.RELEASE:test
[INFO] |  +- org.springframework.boot:spring-boot-test-autoconfigure:jar:2.3.2.RELEASE:test
[INFO] |  +- com.jayway.jsonpath:json-path:jar:2.4.0:test
[INFO] |  |  +- net.minidev:json-smart:jar:2.3:test
[INFO] |  |  |  \- net.minidev:accessors-smart:jar:1.2:test
[INFO] |  |  |     \- org.ow2.asm:asm:jar:5.0.4:test
[INFO] |  |  \- org.slf4j:slf4j-api:jar:1.7.30:compile
[INFO] |  +- jakarta.xml.bind:jakarta.xml.bind-api:jar:2.3.3:test
[INFO] |  |  \- jakarta.activation:jakarta.activation-api:jar:1.2.2:test
[INFO] |  +- org.assertj:assertj-core:jar:3.16.1:test
[INFO] |  +- org.hamcrest:hamcrest:jar:2.2:test
[INFO] |  +- org.junit.jupiter:junit-jupiter:jar:5.6.2:test
[INFO] |  |  +- org.junit.jupiter:junit-jupiter-api:jar:5.6.2:test
[INFO] |  |  |  +- org.apiguardian:apiguardian-api:jar:1.1.0:test
[INFO] |  |  |  +- org.opentest4j:opentest4j:jar:1.2.0:test
[INFO] |  |  |  \- org.junit.platform:junit-platform-commons:jar:1.6.2:test
[INFO] |  |  +- org.junit.jupiter:junit-jupiter-params:jar:5.6.2:test
[INFO] |  |  \- org.junit.jupiter:junit-jupiter-engine:jar:5.6.2:test
[INFO] |  |     \- org.junit.platform:junit-platform-engine:jar:1.6.2:test
[INFO] |  +- org.mockito:mockito-core:jar:3.3.3:test
[INFO] |  |  +- net.bytebuddy:byte-buddy:jar:1.10.13:test
[INFO] |  |  +- net.bytebuddy:byte-buddy-agent:jar:1.10.13:test
[INFO] |  |  \- org.objenesis:objenesis:jar:2.6:test
[INFO] |  +- org.mockito:mockito-junit-jupiter:jar:3.3.3:test
[INFO] |  +- org.skyscreamer:jsonassert:jar:1.5.0:test
[INFO] |  |  \- com.vaadin.external.google:android-json:jar:0.0.20131108.vaadin1:test
[INFO] |  +- org.springframework:spring-test:jar:5.2.8.RELEASE:test
[INFO] |  \- org.xmlunit:xmlunit-core:jar:2.7.0:test
[INFO] \- org.springframework.boot:spring-boot-starter-web:jar:2.3.2.RELEASE:compile
[INFO]    +- org.springframework.boot:spring-boot-starter-json:jar:2.3.2.RELEASE:compile
[INFO]    |  +- com.fasterxml.jackson.core:jackson-databind:jar:2.11.1:compile
[INFO]    |  |  +- com.fasterxml.jackson.core:jackson-annotations:jar:2.11.1:compile
[INFO]    |  |  \- com.fasterxml.jackson.core:jackson-core:jar:2.11.1:compile
[INFO]    |  +- com.fasterxml.jackson.datatype:jackson-datatype-jdk8:jar:2.11.1:compile
[INFO]    |  +- com.fasterxml.jackson.datatype:jackson-datatype-jsr310:jar:2.11.1:compile
[INFO]    |  \- com.fasterxml.jackson.module:jackson-module-parameter-names:jar:2.11.1:compile
[INFO]    +- org.springframework.boot:spring-boot-starter-tomcat:jar:2.3.2.RELEASE:compile
[INFO]    |  +- org.apache.tomcat.embed:tomcat-embed-core:jar:9.0.37:compile
[INFO]    |  +- org.glassfish:jakarta.el:jar:3.0.3:compile
[INFO]    |  \- org.apache.tomcat.embed:tomcat-embed-websocket:jar:9.0.37:compile
[INFO]    +- org.springframework:spring-web:jar:5.2.8.RELEASE:compile
[INFO]    |  \- org.springframework:spring-beans:jar:5.2.8.RELEASE:compile
[INFO]    \- org.springframework:spring-webmvc:jar:5.2.8.RELEASE:compile
[INFO]       +- org.springframework:spring-aop:jar:5.2.8.RELEASE:compile
[INFO]       \- org.springframework:spring-expression:jar:5.2.8.RELEASE:compile
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 35.623 s
[INFO] Finished at: 2020-08-13T16:46:20+08:00
[INFO] Final Memory: 26M/222M
[INFO] ------------------------------------------------------------------------

上述这些依赖都是隐式依赖于spring-boot-starter-web，我们也可以手动排除一些我们不需要的依赖。

比如spring-boot-starter-web默认集成了tomcat，假如我们想把它换为jetty，可以在pom.xml中spring-boot-starter-web下排除tomcat依赖，然后手动引入jetty依赖：

tips：依赖的坐标可以到上述的spring-boot-dependencies-2.3.2.RELEASE.pom文件里查找。再次运行dependency:tree：

[INFO] Scanning for projects...
[INFO]                                                                         
[INFO] ------------------------------------------------------------------------
[INFO] Building demo 0.0.1-SNAPSHOT
[INFO] ------------------------------------------------------------------------
[INFO] 
[INFO] --- maven-dependency-plugin:3.1.2:tree (default-cli) @ demo ---
[INFO] com.example:demo:jar:0.0.1-SNAPSHOT
[INFO] +- org.springframework.boot:spring-boot-starter:jar:2.3.2.RELEASE:compile
[INFO] |  +- org.springframework.boot:spring-boot:jar:2.3.2.RELEASE:compile
[INFO] |  |  \- org.springframework:spring-context:jar:5.2.8.RELEASE:compile
[INFO] |  +- org.springframework.boot:spring-boot-autoconfigure:jar:2.3.2.RELEASE:compile
[INFO] |  +- org.springframework.boot:spring-boot-starter-logging:jar:2.3.2.RELEASE:compile
[INFO] |  |  +- ch.qos.logback:logback-classic:jar:1.2.3:compile
[INFO] |  |  |  \- ch.qos.logback:logback-core:jar:1.2.3:compile
[INFO] |  |  +- org.apache.logging.log4j:log4j-to-slf4j:jar:2.13.3:compile
[INFO] |  |  |  \- org.apache.logging.log4j:log4j-api:jar:2.13.3:compile
[INFO] |  |  \- org.slf4j:jul-to-slf4j:jar:1.7.30:compile
[INFO] |  +- jakarta.annotation:jakarta.annotation-api:jar:1.3.5:compile
[INFO] |  +- org.springframework:spring-core:jar:5.2.8.RELEASE:compile
[INFO] |  |  \- org.springframework:spring-jcl:jar:5.2.8.RELEASE:compile
[INFO] |  \- org.yaml:snakeyaml:jar:1.26:compile
[INFO] +- org.springframework.boot:spring-boot-starter-test:jar:2.3.2.RELEASE:test
[INFO] |  +- org.springframework.boot:spring-boot-test:jar:2.3.2.RELEASE:test
[INFO] |  +- org.springframework.boot:spring-boot-test-autoconfigure:jar:2.3.2.RELEASE:test
[INFO] |  +- com.jayway.jsonpath:json-path:jar:2.4.0:test
[INFO] |  |  +- net.minidev:json-smart:jar:2.3:test
[INFO] |  |  |  \- net.minidev:accessors-smart:jar:1.2:test
[INFO] |  |  \- org.slf4j:slf4j-api:jar:1.7.30:compile
[INFO] |  +- jakarta.xml.bind:jakarta.xml.bind-api:jar:2.3.3:test
[INFO] |  |  \- jakarta.activation:jakarta.activation-api:jar:1.2.2:test
[INFO] |  +- org.assertj:assertj-core:jar:3.16.1:test
[INFO] |  +- org.hamcrest:hamcrest:jar:2.2:test
[INFO] |  +- org.junit.jupiter:junit-jupiter:jar:5.6.2:test
[INFO] |  |  +- org.junit.jupiter:junit-jupiter-api:jar:5.6.2:test
[INFO] |  |  |  +- org.apiguardian:apiguardian-api:jar:1.1.0:test
[INFO] |  |  |  +- org.opentest4j:opentest4j:jar:1.2.0:test
[INFO] |  |  |  \- org.junit.platform:junit-platform-commons:jar:1.6.2:test
[INFO] |  |  +- org.junit.jupiter:junit-jupiter-params:jar:5.6.2:test
[INFO] |  |  \- org.junit.jupiter:junit-jupiter-engine:jar:5.6.2:test
[INFO] |  |     \- org.junit.platform:junit-platform-engine:jar:1.6.2:test
[INFO] |  +- org.mockito:mockito-core:jar:3.3.3:test
[INFO] |  |  +- net.bytebuddy:byte-buddy:jar:1.10.13:test
[INFO] |  |  +- net.bytebuddy:byte-buddy-agent:jar:1.10.13:test
[INFO] |  |  \- org.objenesis:objenesis:jar:2.6:test
[INFO] |  +- org.mockito:mockito-junit-jupiter:jar:3.3.3:test
[INFO] |  +- org.skyscreamer:jsonassert:jar:1.5.0:test
[INFO] |  |  \- com.vaadin.external.google:android-json:jar:0.0.20131108.vaadin1:test
[INFO] |  +- org.springframework:spring-test:jar:5.2.8.RELEASE:test
[INFO] |  \- org.xmlunit:xmlunit-core:jar:2.7.0:test
[INFO] +- org.springframework.boot:spring-boot-starter-web:jar:2.3.2.RELEASE:compile
[INFO] |  +- org.springframework.boot:spring-boot-starter-json:jar:2.3.2.RELEASE:compile
[INFO] |  |  +- com.fasterxml.jackson.core:jackson-databind:jar:2.11.1:compile
[INFO] |  |  |  +- com.fasterxml.jackson.core:jackson-annotations:jar:2.11.1:compile
[INFO] |  |  |  \- com.fasterxml.jackson.core:jackson-core:jar:2.11.1:compile
[INFO] |  |  +- com.fasterxml.jackson.datatype:jackson-datatype-jdk8:jar:2.11.1:compile
[INFO] |  |  +- com.fasterxml.jackson.datatype:jackson-datatype-jsr310:jar:2.11.1:compile
[INFO] |  |  \- com.fasterxml.jackson.module:jackson-module-parameter-names:jar:2.11.1:compile
[INFO] |  +- org.springframework:spring-web:jar:5.2.8.RELEASE:compile
[INFO] |  |  \- org.springframework:spring-beans:jar:5.2.8.RELEASE:compile
[INFO] |  \- org.springframework:spring-webmvc:jar:5.2.8.RELEASE:compile
[INFO] |     +- org.springframework:spring-aop:jar:5.2.8.RELEASE:compile
[INFO] |     \- org.springframework:spring-expression:jar:5.2.8.RELEASE:compile
[INFO] \- org.springframework.boot:spring-boot-starter-jetty:jar:2.3.2.RELEASE:compile
[INFO]    +- jakarta.servlet:jakarta.servlet-api:jar:4.0.4:compile
[INFO]    +- jakarta.websocket:jakarta.websocket-api:jar:1.1.2:compile
[INFO]    +- org.eclipse.jetty:jetty-servlets:jar:9.4.30.v20200611:compile
[INFO]    |  +- org.eclipse.jetty:jetty-continuation:jar:9.4.30.v20200611:compile
[INFO]    |  +- org.eclipse.jetty:jetty-http:jar:9.4.30.v20200611:compile
[INFO]    |  +- org.eclipse.jetty:jetty-util:jar:9.4.30.v20200611:compile
[INFO]    |  \- org.eclipse.jetty:jetty-io:jar:9.4.30.v20200611:compile
[INFO]    +- org.eclipse.jetty:jetty-webapp:jar:9.4.30.v20200611:compile
[INFO]    |  +- org.eclipse.jetty:jetty-xml:jar:9.4.30.v20200611:compile
[INFO]    |  \- org.eclipse.jetty:jetty-servlet:jar:9.4.30.v20200611:compile
[INFO]    |     \- org.eclipse.jetty:jetty-security:jar:9.4.30.v20200611:compile
[INFO]    |        \- org.eclipse.jetty:jetty-server:jar:9.4.30.v20200611:compile
[INFO]    +- org.eclipse.jetty.websocket:websocket-server:jar:9.4.30.v20200611:compile
[INFO]    |  +- org.eclipse.jetty.websocket:websocket-common:jar:9.4.30.v20200611:compile
[INFO]    |  |  \- org.eclipse.jetty.websocket:websocket-api:jar:9.4.30.v20200611:compile
[INFO]    |  +- org.eclipse.jetty.websocket:websocket-client:jar:9.4.30.v20200611:compile
[INFO]    |  |  \- org.eclipse.jetty:jetty-client:jar:9.4.30.v20200611:compile
[INFO]    |  \- org.eclipse.jetty.websocket:websocket-servlet:jar:9.4.30.v20200611:compile
[INFO]    +- org.eclipse.jetty.websocket:javax-websocket-server-impl:jar:9.4.30.v20200611:compile
[INFO]    |  +- org.eclipse.jetty:jetty-annotations:jar:9.4.30.v20200611:compile
[INFO]    |  |  +- org.eclipse.jetty:jetty-plus:jar:9.4.30.v20200611:compile
[INFO]    |  |  +- org.ow2.asm:asm:jar:7.3.1:compile
[INFO]    |  |  \- org.ow2.asm:asm-commons:jar:7.3.1:compile
[INFO]    |  |     +- org.ow2.asm:asm-tree:jar:7.3.1:compile
[INFO]    |  |     \- org.ow2.asm:asm-analysis:jar:7.3.1:compile
[INFO]    |  \- org.eclipse.jetty.websocket:javax-websocket-client-impl:jar:9.4.30.v20200611:compile
[INFO]    \- org.glassfish:jakarta.el:jar:3.0.3:compile
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 1.511 s
[INFO] Finished at: 2020-08-13T16:51:13+08:00
[INFO] Final Memory: 26M/225M
[INFO] ------------------------------------------------------------------------

可看到tomcat已被替换为了jetty。