Spring Boot(一)开发自己的starter

这里将开发一个spring boot starter，它用于连接mysql并自动生成一个mysql数据库连接池的datasource。

一、环境
jdk:13
spring boot:2.1.0.RELEASE
mysql jdbc驱动使用mysql-connector-java
数据库连接池采用HikariCP

二、创建spring-boot-start-mysql工程
1.新建pom.xml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>

	<parent>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starters</artifactId>
		<version>2.1.0.RELEASE</version>
	</parent>

	<groupId>com.bry.springboot</groupId>
	<artifactId>spring-boot-start-mysql</artifactId>
	<version>2.1.0.RELEASE</version>
	<name>spring-boot-start-mysql</name>

	<properties>
		<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
		<project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
		<java.version>1.8</java.version>
	</properties>

	<dependencies>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-autoconfigure</artifactId>
		</dependency>

		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-configuration-processor</artifactId>
			<optional>true</optional>
		</dependency>

		<dependency>
			<groupId>mysql</groupId>
			<artifactId>mysql-connector-java</artifactId>
		</dependency>

		<dependency>
			<groupId>com.zaxxer</groupId>
			<artifactId>HikariCP</artifactId>
		</dependency>
	</dependencies>

</project>

2.建立数据库连接属性类MysqlProperties.java

package com.bruce.mysqlstart;

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

@ConfigurationProperties(prefix = "mysql")
public class MysqlProperties {
	private String driverURL;
	private String user;
	private String password;
	public String getDriverURL() {
		return driverURL;
	}
	public void setDriverURL(String driverURL) {
		this.driverURL = driverURL;
	}
	public String getUser() {
		return user;
	}
	public void setUser(String user) {
		this.user = user;
	}
	public String getPassword() {
		return password;
	}
	public void setPassword(String password) {
		this.password = password;
	}
}

@ConfigurationProperties(prefix = “mysql”)： 数据库配置以mysql开头，如 msyql.driverURL,msyql.driverURL,mysql.user,mysql.password

3.创建mysql连接池自动配置类MysqlAutoConfiguration.java

package com.bruce.mysqlstart;

import javax.sql.DataSource;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
import org.springframework.boot.context.properties.EnableConfigurationProperties;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

import com.zaxxer.hikari.HikariConfig;
import com.zaxxer.hikari.HikariDataSource;

@Configuration
@EnableConfigurationProperties(MysqlProperties.class)
@ConditionalOnClass({ com.zaxxer.hikari.HikariDataSource.class, com.mysql.jdbc.Driver.class })
public class MysqlAutoConfiguration {

	@Autowired
	MysqlProperties mysqlProperties;

	@Bean(destroyMethod = "close")
	@ConditionalOnMissingBean(DataSource.class)
	public DataSource getPhoneService() {

		HikariConfig hikariConfig = new HikariConfig();
		hikariConfig.setJdbcUrl(mysqlProperties.getDriverURL());
		hikariConfig.setUsername(mysqlProperties.getUser());
		hikariConfig.setPassword(mysqlProperties.getPassword());
		// In case we're using MySQL, these settings are recommended by HikariCP:
		hikariConfig.addDataSourceProperty("cachePrepStmts", "true");
		hikariConfig.addDataSourceProperty("prepStmtCacheSize", "250");
		hikariConfig.addDataSourceProperty("prepStmtCacheSqlLimit", "2048");
		hikariConfig.addDataSourceProperty("useServerPrepStmts", "true");
		hikariConfig.setConnectionTestQuery("select CURRENT_DATE");

		HikariDataSource hikariDataSource = new HikariDataSource(hikariConfig);

		return hikariDataSource;

	}
}

@EnableConfigurationProperties(MysqlProperties.class): 加载属性文件到MysqlProperitest.claa中
@ConditionalOnClass({ com.zaxxer.hikari.HikariDataSource.class, com.mysql.jdbc.Driver.class }): 类加载路径中必须有HikariDataSource类和com.mysql.jdbc.Driver才自动配置数据源
@Bean(destroyMethod = “close”): spring容器结束时调用数据源的close方法关闭数据源
@ConditionalOnMissingBean(DataSource.class): spring上下文中没有DataSource实例时才自动配置数据源

三、根据期望的使用方式进行不同配置

1. 如果只是通过在启动类中增加 @Import(MysqlAutoConfiguration.class) 使用该starter，那么只需要做前面的工作就可以了。

2. 通过在启动类中增加 @EnableMysql 的方式使用。
   需要定义一个名为EnableMysql的注解，EnableMysql.java

package com.bruce.mysqlstart;

import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

import org.springframework.context.annotation.Import;

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Import(MysqlAutoConfiguration.class)
public @interface EnableMysql {
}

3. 希望在启动类中不增加任何额外配置，只将jar包放在classpath中。
   新增META-INF/spring.factories文件内容如下：

org.springframework.boot.autoconfigure.EnableAutoConfiguration=com.bruce.mysqlstart.MysqlAutoConfiguration

参考
SpringBoot 自定义starter
自定义starter
Creating Your Own Starter

最后

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