SpringBoot2系列教程（一）简介及HelloWorld项目

Spring Boot 2.0.0.RELEASE 需要Java 8 or 9 and Spring Framework 5.0.4.RELEASE 或者更高版本. 支持Maven 3.2+和Gradle 4 版本

支持的Servlet容器

Tomcat 8.5、Jetty 9.4、Jetty 9.4

官方版本迁移wiki

https://github.com/spring-projects/spring-boot/wiki

HelloWorld异同项目分析

1. 修改 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>springboot-mybatis</groupId>
    <artifactId>springboot-mybatis</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <packaging>jar</packaging>

    <name>springboot-mybatis</name>
    <description>Demo project for Spring Boot</description>

  <parent>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-parent</artifactId>
    <version>2.0.0.RELEASE</version>
  </parent>

    <!-- Add typical dependencies for a web application -->
    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-test</artifactId>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-test</artifactId>
            <version>5.0.4.RELEASE</version>
        </dependency>
    </dependencies>

    <!-- Package as an executable jar -->
    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>
</project>

2. 修改启动类

package springbootmybatis.springbootmybatis;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
@EnableAutoConfiguration
public class MybatisApplication {

    public static void main(String[] args) {
        SpringApplication.run(MybatisApplication.class, args);
    }

    @RequestMapping("/")
    String home() {
        return "Hello World!";
    }

}

运行结果

代码中三个注解分析

两个MVC注解：

1. @RestController 是Spring处理web请求时用到的注解。告诉Spring将结果字符串直接呈现给调用者。
2. @RequestMapping 提供了“路由”信息，将/请求映射给home()方法。

SpringBoot注解：

1. @EnableAutoConfiguration 这个注解告诉Springboot 根据你添加的jar包来猜测配置Spring 。@SpringBootApplication一样，也可以使用exclude属性来禁用不需要自动配置的应用。例子：@EnableAutoConfiguration（exclude = {DataSourceAutoConfiguration.class}） 那么，它和@SpringBootApplication注解有什么关系呢？

我们来看下@SpringBootApplication注解源码

通俗的讲：@SpringBootApplication = @Configuration+@EnableAutoConfiguration+@ComponentScan 。前提是默认配置，当然，如果你想要覆盖默认配置，你就需要重写该注解了，重写也很简单，给注解加上参数就好。