springboot之場景啟動器

為什么springboot不需要我們去配置那么繁瑣的東西?

我們直接看pom.xml

<?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>

    <groupId>com.gong</groupId>
    <artifactId>myspringboot</artifactId>
    <version>1.0-SNAPSHOT</version>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>1.5.9.RELEASE</version>
    </parent>

    <dependencies>
        <!--引入springboot的web支持，幫你封裝好了很多個依賴-->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
    </dependencies>
    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>

</project>

首先看spring-boot-starter-parent，spring-boot-start就是場景啟動器，這是所有項目的父項目，我們ctrl+鼠標左鍵點進去：

新文件的開頭部分：

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-dependencies</artifactId>
        <version>1.5.9.RELEASE</version>
        <relativePath>../../spring-boot-dependencies</relativePath>
    </parent>

它的父項目是spring-boot-dependencies，用於管理依賴包的版本號。也就是說spring-boot-start-parent是版本仲裁中心。

再來看spring-boot-starter-web，我們來查看其中有什么：

<?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-starters</artifactId>
        <version>1.5.9.RELEASE</version>
    </parent>
    <artifactId>spring-boot-starter-web</artifactId>
    <name>Spring Boot Web Starter</name>
    <description>Starter for building web, including RESTful, applications using Spring
        MVC. Uses Tomcat as the default embedded container</description>
    <url>http://projects.spring.io/spring-boot/</url>
    <organization>
        <name>Pivotal Software, Inc.</name>
        <url>http://www.spring.io</url>
    </organization>
    <properties>
        <main.basedir>${basedir}/../..</main.basedir>
    </properties>
    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-tomcat</artifactId>
        </dependency>
        <dependency>
            <groupId>org.hibernate</groupId>
            <artifactId>hibernate-validator</artifactId>
        </dependency>
        <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-databind</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-web</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-webmvc</artifactId>
        </dependency>
    </dependencies>
</project>

這里面才是幫我們導入了真正所需的依賴包。

springboot還有許多場景啟動器，例如AOP、郵件開發等等。我們只需要在項目里面引用這些starter，這些場景的相關依賴包就會自動導入出來。