spring-boot-starter-parent简介

　　本指南将帮助您了解Spring Boot Starter Parent如何帮助管理依赖项版本，所有Spring Boot项目通常使用spring-boot-starter-parent作为pom.xml中的父项：

<parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>1.4.0.RELEASE</version>
    </parent>

Parent Poms为多个子项目和模块管理以下内容：

• 配置 - Java版本和其他属性
• Depedency Management - 依赖项的版本
• 默认插件配置

内部原理

首先 启动器Spring Boot Starter Parent将spring-boot-dependencies定义为父pom。它从spring-boot-dependencies继承了依赖关系管理。

<parent>
   <groupId>org.springframework.boot</groupId>
   <artifactId>spring-boot-dependencies</artifactId>
   <version>1.4.0.RELEASE</version>
   <relativePath>../../spring-boot-dependencies</relativePath>
</parent>

默认的java版本是1.6。项目可以通过<java.version>1.8</java.version>在项目pom中指定属性来覆盖它。还有一些与编码和源相关的其他设置，目标版本也在父pom中设置。

<java.version>1.6</java.version>
<resource.delimiter>@</resource.delimiter> <!-- delimiter that doesn't clash with Spring ${} placeholders -->
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
<project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
<maven.compiler.source>${java.version}</maven.compiler.source>
<maven.compiler.target>${java.version}</maven.compiler.target>

Spring Boot Starter Parent指定了一系列插件的默认配置，包括maven-failsafe-plugin，maven-jar-plugin和maven-surefire-plugin。

<plugin>
   <groupId>org.apache.maven.plugins</groupId>
   <artifactId>maven-failsafe-plugin</artifactId>
   <executions>
      <execution>
         <goals>
            <goal>integration-test</goal>
            <goal>verify</goal>
         </goals>
      </execution>
   </executions>
</plugin>
<plugin>
   <groupId>org.apache.maven.plugins</groupId>
   <artifactId>maven-jar-plugin</artifactId>
   <configuration>
      <archive>
         <manifest>
            <mainClass>${start-class}</mainClass>
            <addDefaultImplementationEntries>true</addDefaultImplementationEntries>
         </manifest>
      </archive>
   </configuration>
</plugin>
<plugin>
   <groupId>org.apache.maven.plugins</groupId>
   <artifactId>maven-surefire-plugin</artifactId>
   <configuration>
      <includes>
         <include>**/*Tests.java</include>
         <include>**/*Test.java</include>
      </includes>
      <excludes>
         <exclude>**/Abstract*.java</exclude>
      </excludes>
   </configuration>
</plugin>

Spring Boot Starter Parent从spring-boot-dependencies继承了什么？

Spring Boot Dependencies定义了所有Spring Boot项目的默认依赖关系管理。如果我们想要使用特定依赖项的新版本，我们可以通过在项目pom中指定新属性来覆盖该版本。下面的摘录显示了由Spring Boot Dependencies父pom管理的一些重要依赖项。由于Spring Boot Starter Parent继承自spring-boot-dependencies，因此它也共享所有这些特性。

<properties>
   <activemq.version>5.13.4</activemq.version>
         ...
   <ehcache.version>2.10.2.2.21</ehcache.version>
   <ehcache3.version>3.1.1</ehcache3.version>
         ...
   <h2.version>1.4.192</h2.version>
   <hamcrest.version>1.3</hamcrest.version>
   <hazelcast.version>3.6.4</hazelcast.version>
   <hibernate.version>5.0.9.Final</hibernate.version>
   <hibernate-validator.version>5.2.4.Final</hibernate-validator.version>
   <hikaricp.version>2.4.7</hikaricp.version>
   <hikaricp-java6.version>2.3.13</hikaricp-java6.version>
   <hornetq.version>2.4.7.Final</hornetq.version>
   <hsqldb.version>2.3.3</hsqldb.version>
   <htmlunit.version>2.21</htmlunit.version>
   <httpasyncclient.version>4.1.2</httpasyncclient.version>
   <httpclient.version>4.5.2</httpclient.version>
   <httpcore.version>4.4.5</httpcore.version>
   <infinispan.version>8.2.2.Final</infinispan.version>
   <jackson.version>2.8.1</jackson.version>
         ....
   <jersey.version>2.23.1</jersey.version>
   <jest.version>2.0.3</jest.version>
   <jetty.version>9.3.11.v20160721</jetty.version>
   <jetty-jsp.version>2.2.0.v201112011158</jetty-jsp.version>
   <spring-security.version>4.1.1.RELEASE</spring-security.version>
   <tomcat.version>8.5.4</tomcat.version>
   <undertow.version>1.3.23.Final</undertow.version>
   <velocity.version>1.7</velocity.version>
   <velocity-tools.version>2.0</velocity-tools.version>
   <webjars-hal-browser.version>9f96c74</webjars-hal-browser.version>
   <webjars-locator.version>0.32</webjars-locator.version>
   <wsdl4j.version>1.6.3</wsdl4j.version>
   <xml-apis.version>1.4.01</xml-apis.version>
</properties>

将Maven 3.2.1定义为所需的最低版本：

<prerequisites>
   <maven>3.2.1</maven>
</prerequisites>

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