Spring Boot中parent标签的作用
葛炯
在Spring Boot的官方示例中，都是让我们继承一个spring的 spring-boot-starter-parent作为parent标签
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>2.1.6.RELEASE</version>
<relativePath/> <!-- lookup parent from repository -->
</parent>
这个parent标签有一个最常用的功能，就是定义子标签的依赖版本号，然而它的功能却不仅仅如此
parent 源码
<?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>
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-dependencies</artifactId>
<version>2.1.6.RELEASE</version>
<relativePath>../../spring-boot-dependencies</relativePath>
</parent>
<artifactId>spring-boot-starter-parent</artifactId>
<packaging>pom</packaging>
<name>Spring Boot Starter Parent</name>
<description>Parent pom providing dependency and plugin management for applications
built with Maven</description>
<url>https://projects.spring.io/spring-boot/#/spring-boot-starter-parent</url>
<properties>
<project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
<java.version>1.8</java.version>
<resource.delimiter>@</resource.delimiter>
<maven.compiler.source>${java.version}</maven.compiler.source>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
<maven.compiler.target>${java.version}</maven.compiler.target>
</properties>
<build>
<resources>
<resource>
<filtering>true</filtering>
<directory>${basedir}/src/main/resources</directory>
<includes>
<include>**/application*.yml</include>
<include>**/application*.yaml</include>
<include>**/application*.properties</include>
</includes>
</resource>
<resource>
<directory>${basedir}/src/main/resources</directory>
<excludes>
<exclude>**/application*.yml</exclude>
<exclude>**/application*.yaml</exclude>
<exclude>**/application*.properties</exclude>
</excludes>
</resource>
</resources>
<pluginManagement>
<plugins>
<plugin>
<groupId>org.jetbrains.kotlin</groupId>
<artifactId>kotlin-maven-plugin</artifactId>
<version>${kotlin.version}</version>
<executions>
<execution>
<id>compile</id>
<phase>compile</phase>
<goals>
<goal>compile</goal>
</goals>
</execution>
<execution>
<id>test-compile</id>
<phase>test-compile</phase>
<goals>
<goal>test-compile</goal>
</goals>
</execution>
</executions>
<configuration>
<jvmTarget>${java.version}</jvmTarget>
<javaParameters>true</javaParameters>
</configuration>
</plugin>
<plugin>
<artifactId>maven-compiler-plugin</artifactId>
<configuration>
<parameters>true</parameters>
</configuration>
</plugin>
<plugin>
<artifactId>maven-failsafe-plugin</artifactId>
<executions>
<execution>
<goals>
<goal>integration-test</goal>
<goal>verify</goal>
</goals>
</execution>
</executions>
<configuration>
<classesDirectory>${project.build.outputDirectory}</classesDirectory>
</configuration>
</plugin>
<plugin>
<artifactId>maven-jar-plugin</artifactId>
<configuration>
<archive>
<manifest>
<mainClass>${start-class}</mainClass>
<addDefaultImplementationEntries>true</addDefaultImplementationEntries>
</manifest>
</archive>
</configuration>
</plugin>
<plugin>
<artifactId>maven-war-plugin</artifactId>
<configuration>
<archive>
<manifest>
<mainClass>${start-class}</mainClass>
<addDefaultImplementationEntries>true</addDefaultImplementationEntries>
</manifest>
</archive>
</configuration>
</plugin>
<plugin>
<groupId>org.codehaus.mojo</groupId>
<artifactId>exec-maven-plugin</artifactId>
<configuration>
<mainClass>${start-class}</mainClass>
</configuration>
</plugin>
<plugin>
<artifactId>maven-resources-plugin</artifactId>
<configuration>
<delimiters>
<delimiter>${resource.delimiter}</delimiter>
</delimiters>
<useDefaultDelimiters>false</useDefaultDelimiters>
</configuration>
</plugin>
<plugin>
<groupId>pl.project13.maven</groupId>
<artifactId>git-commit-id-plugin</artifactId>
<executions>
<execution>
<goals>
<goal>revision</goal>
</goals>
</execution>
</executions>
<configuration>
<verbose>true</verbose>
<dateFormat>yyyy-MM-dd'T'HH:mm:ssZ</dateFormat>
<generateGitPropertiesFile>true</generateGitPropertiesFile>
<generateGitPropertiesFilename>${project.build.outputDirectory}/git.properties</generateGitPropertiesFilename>
</configuration>
</plugin>
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
<executions>
<execution>
<id>repackage</id>
<goals>
<goal>repackage</goal>
</goals>
</execution>
</executions>
<configuration>
<mainClass>${start-class}</mainClass>
</configuration>
</plugin>
<plugin>
<artifactId>maven-shade-plugin</artifactId>
<executions>
<execution>
<phase>package</phase>
<goals>
<goal>shade</goal>
</goals>
<configuration>
<transformers>
<transformer implementation="org.apache.maven.plugins.shade.resource.AppendingTransformer">
<resource>META-INF/spring.handlers</resource>
</transformer>
<transformer implementation="org.springframework.boot.maven.PropertiesMergingResourceTransformer">
<resource>META-INF/spring.factories</resource>
</transformer>
<transformer implementation="org.apache.maven.plugins.shade.resource.AppendingTransformer">
<resource>META-INF/spring.schemas</resource>
</transformer>
<transformer implementation="org.apache.maven.plugins.shade.resource.ServicesResourceTransformer"/>
<transformer implementation="org.apache.maven.plugins.shade.resource.ManifestResourceTransformer">
<mainClass>${start-class}</mainClass>
</transformer>
</transformers>
</configuration>
</execution>
</executions>
<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
<version>2.1.6.RELEASE</version>
</dependency>
</dependencies>
<configuration>
<keepDependenciesWithProvidedScope>true</keepDependenciesWithProvidedScope>
<createDependencyReducedPom>true</createDependencyReducedPom>
<filters>
<filter>
<artifact>*:*</artifact>
<excludes>
<exclude>META-INF/*.SF</exclude>
<exclude>META-INF/*.DSA</exclude>
<exclude>META-INF/*.RSA</exclude>
</excludes>
</filter>
</filters>
</configuration>
</plugin>
<plugin>
<groupId>org.eclipse.m2e</groupId>
<artifactId>lifecycle-mapping</artifactId>
<version>1.0.0</version>
<configuration>
<lifecycleMappingMetadata>
<pluginExecutions>
<pluginExecution>
<pluginExecutionFilter>
<groupId>org.codehaus.mojo</groupId>
<artifactId>flatten-maven-plugin</artifactId>
<versionRange>[1.0.0,)</versionRange>
<goals>
<goal>flatten</goal>
</goals>
</pluginExecutionFilter>
<action>
<ignore/>
</action>
</pluginExecution>
<pluginExecution>
<pluginExecutionFilter>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-checkstyle-plugin</artifactId>
<versionRange>[3.0.0,)</versionRange>
<goals>
<goal>check</goal>
</goals>
</pluginExecutionFilter>
<action>
<ignore/>
</action>
</pluginExecution>
</pluginExecutions>
</lifecycleMappingMetadata>
</configuration>
</plugin>
</plugins>
</pluginManagement>
</build>
</project>
parent基本功能
从上面的源码中我们可以看到parent主要有如下功能：
定义了一个父标签spring-boot-dependencies，这个里边定义了依赖的版本，也正是因为继承了这个依赖，所以我们在写依赖时才不需要写版本号
使用默认编码格式为 UTF-8
定义了 Java 编译版本为 1.8
定义了针对 application.properties 和 application.yml 的资源过滤，包括通过 profile 定义的不同环境的配置文件，例如 application-dev.properties 和 application-dev.yml
执行打包操作的配置
自动化的资源过滤
自动化的插件配置
使用自定义的parent
当我们需要使用自己定义的 parent ，我们的 Spring Boot 项目要继承自公司内部的 parent ，这个时候可以这么做。
一个简单的办法就是我们自行定义 dependencyManagement 节点，然后在里边定义好版本号，再接下来在引用依赖时也就不用写版本号了，像下面这样：
<dependencyManagement>
<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-dependencies</artifactId>
<version>2.1.6.RELEASE</version>
<type>pom</type>
<scope>import</scope>
</dependency>
</dependencies>
</dependencyManagement>
但这种方式只能解决依赖的版本号问题，如果我们仍然需要关于打包的插件、编译的 JDK 版本、文件的编码格式等等这些配置，在没有 parent 的时候，这些统统要自己去配置。
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