SpringBoot自动配置的演示

1. 需求说明：
    当加入redis客户端的坐标的时候，自动配置jedis的bean 加载到spring容器中；
    
2. 实现步骤：
    1.创建工程 it-redis-springboot-starter 用作起步依赖
        
    2.添加依赖
        1. pom文件
        <?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.it</groupId>
            <artifactId>it-redis-springboot-starter</artifactId>
            <version>1.0-SNAPSHOT</version>
            <description>自定义起步依赖，给别人用，需要在这个项目中进行自动配置</description>

            <parent>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-starter-parent</artifactId>
                <version>2.1.4.RELEASE</version>
            </parent>

            <dependencies>
                <!--springboot的starter-->
                <dependency>
                    <groupId>org.springframework.boot</groupId>
                    <artifactId>spring-boot-starter</artifactId>
                </dependency>
                <!--redis的依赖jedis-->
                <dependency>
                    <groupId>redis.clients</groupId>
                    <artifactId>jedis</artifactId>
                    <version>3.2.0</version>
                </dependency>
            </dependencies>


        </project>
    3.创建自动配置类和POJO
        1. 创建pojo，并在配置类中使用注解@EnableConfigurationProperties(value = RedisProperties.class)建立映射：
        package com.it.redis.config;

        import org.springframework.boot.context.properties.ConfigurationProperties;
        import org.springframework.boot.context.properties.EnableConfigurationProperties;

        import java.io.Serializable;

        /**
         * ToDo
         *
         * @author Lyle
         * @date 2020/4/2
         */
        @ConfigurationProperties(prefix = "redis")
        public class RedisProperties implements Serializable {
            private String host = "localhost";//给与默认值
            private Integer port = 6379;//给与默认值

            public String getHost() {
                return host;
            }

            public void setHost(String host) {
                this.host = host;
            }

            public Integer getPort() {
                return port;
            }

            public void setPort(Integer port) {
                this.port = port;
            }
        }
        
        2. 创建配置类：
            package com.it.redis.config;

            import org.springframework.beans.factory.annotation.Autowired;
            import org.springframework.boot.context.properties.EnableConfigurationProperties;
            import org.springframework.context.annotation.Bean;
            import org.springframework.context.annotation.Configuration;
            import redis.clients.jedis.Jedis;

            /**
             * ToDo
             *
             * @author Lyle
             * @date 2020/4/2
             */
            @Configuration//表是这是一个配置类
            @EnableConfigurationProperties(value = RedisProperties.class)
            public class RedisAutoConfiguration {

                @Autowired
                private RedisProperties redisProperties;

                //注册类，交给spring容器
                @Bean
                public Jedis jedis(){
                    System.out.println("该方法已经执行。。。。");
                    System.out.println(redisProperties.getHost()+"<=======>"+redisProperties.getPort());
                    return new Jedis(redisProperties.getHost(),redisProperties.getPort());
                }
            }
        
        3. 在resources下创建文件夹：META-INF，并在META-INF下创建文件spring.factories，文件中设置如下信息：
            第一行信息为EnableAutoConfiguration的全限定路径名；
            第二行为RedisAutoConfiguration的全限定路径；
            \：表示换行；
            org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
            com.it.redis.config.RedisAutoConfiguration
            


    4.创建工程 it-test-starter 用于测试使用：
        4.1 测试类的pom文件：
        <?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.it</groupId>
            <artifactId>it-test-starter</artifactId>
            <version>1.0-SNAPSHOT</version>
            <description>依赖自定义的starter，可以直接使用jedis</description>

            <parent>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-starter-parent</artifactId>
                <version>2.1.4.RELEASE</version>
            </parent>

            <dependencies>
                <dependency>
                    <groupId>com.it</groupId>
                    <artifactId>it-redis-springboot-starter</artifactId>
                    <version>1.0-SNAPSHOT</version>
                </dependency>
            </dependencies>


        </project>
        
        4.2 创建启动类；
            package com.it;

            import org.springframework.boot.SpringApplication;
            import org.springframework.boot.autoconfigure.SpringBootApplication;
            import org.springframework.context.ConfigurableApplicationContext;
            import redis.clients.jedis.Jedis;

            /**
             * ToDo
             *
             * @author Lyle
             * @date 2020/4/2
             */
            @SpringBootApplication
            public class JedisStarterApplication {
                public static void main(String[] args) {
                    ConfigurableApplicationContext context = SpringApplication.run(JedisStarterApplication.class, args);
                    Jedis jedis = context.getBean(Jedis.class);
                    System.out.println(jedis);
                }
            }
            
        4.3 配置文件application.properties（可以不配置，使用pojo中的默认配置）
            redis.host=localhost
            redis.port=666