作为公司的技术保障部，一直承担着技术方向的把控，最近公司准备全面转入spring boot的开发。所以我们部门也一直在调研相关的技术知识点；

使用springboot开发应用已经有一段时间了，我们都沉醉于它简洁的配置和平滑的上手曲线。

在springboot的开发中，starter是一个核心的配置，只需要引入对应模块的starter，然后在application.properties中引入对应的配置项，就可以开发业务逻辑了。

这一切都归功于springboot的自动配置的能力。

本文会从一个mybatis与spring boot结合的starter开始学习，该框架是我们提供出来，需要使用mybatis的团队只需要引入这个starter的jar包即可使用

新建原型项目

完整的pom.xml如下

<?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>cn.caijiajia</groupId>

        <artifactId>springboot-parent</artifactId>

        <version>1.0.0.RELEASE</version>

    </parent>

    <groupId>cn.caijiajia</groupId>

    <artifactId>mybatis-starter</artifactId>

    <version>${project.release.version}</version>

    <packaging>jar</packaging>

    <dependencies>

        <dependency>

            <groupId>cn.caijiajia</groupId>

            <artifactId>framework-starter</artifactId>

            <version>${project.release.version}</version>

        </dependency>

        <dependency>

            <groupId>org.springframework.boot</groupId>

            <artifactId>spring-boot-starter-jdbc</artifactId>

        </dependency>

        <dependency>

            <groupId>org.mybatis</groupId>

            <artifactId>mybatis</artifactId>

        </dependency>

        <dependency>

            <groupId>org.mybatis</groupId>

            <artifactId>mybatis-spring</artifactId>

        </dependency>

        <dependency>

            <groupId>org.apache.tomcat</groupId>

            <artifactId>tomcat-jdbc</artifactId>

        </dependency>

        <dependency>

            <groupId>com.alibaba</groupId>

            <artifactId>fastjson</artifactId>

        </dependency>

        <dependency>

            <groupId>com.github.pagehelper</groupId>

            <artifactId>pagehelper</artifactId>

        </dependency>

        <dependency>

            <groupId>mysql</groupId>

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

            <scope>runtime</scope>

        </dependency>

    </dependencies>

</project>

开发阶段

1.配置类 DatabaseAutoConfiguration DbProperties

@EnableConfigurationProperties({DbProperties.class})

public class DatabaseAutoConfiguration

        implements BeanDefinitionRegistryPostProcessor, EnvironmentAware {

    private static Logger log = LoggerFactory.getLogger(DatabaseAutoConfiguration.class);

    private Environment environment;

    @Override

    public void setEnvironment(Environment environment) {

        this.environment = environment;

    }

    @Override

    public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {

    }

    @Override

    public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) throws BeansException {

        DbProperties dbProperties = ConfigUtil.getDbConfig(environment, DbProperties.PROPERTY_PREFIX,

                DbProperties.class);

        // TODO 检查参数

        if (dbProperties.getDatabase() == null && dbProperties.getDatabases() != null && dbProperties

                .getDatabases().size() == 1) {

            dbProperties.setDatabase(dbProperties.getDatabases().get(0));

        }

        initAllDataAccessBean(dbProperties, registry);

    }

    protected void initAllDataAccessBean(DbProperties dbProperties, BeanDefinitionRegistry registry) {

        // 单数据源

        if (dbProperties.getDatabase() != null) {

            initDataAccessBean(dbProperties.getDatabase(), null, registry);

        }

        // 多数据源

        else if (dbProperties.getDatabases() != null && dbProperties.getDatabases().size() > 0) {

            for (int i = 0; i < dbProperties.getDatabases().size(); i++) {

                initDataAccessBean(dbProperties.getDatabases().get(i), i, registry);

            }

        }

    }

    /**

     * 注册一个datasource的所有bean 信息

     *

     * @param databaseConfig

     * @param index

     * @param registry

     */

    protected void initDataAccessBean(DatabaseConfig databaseConfig, Integer index, BeanDefinitionRegistry registry) {

        DataSourceConfig dataSourceConfig = databaseConfig.getDataSource();

        TransactionConfig transactionConfig = databaseConfig.getTransaction();

        MyBatisConfig myBatisConfig = databaseConfig.getMybatis();

        LogConfig logConfig = databaseConfig.getLog();

        // 给与默认 dataSource bean id: dataSource${index}

        if (StringUtils.isEmpty(dataSourceConfig.getName())) {

            if (index == null) {

                dataSourceConfig.setName("dataSource");

            } else {

                dataSourceConfig.setName("dataSource" + index);

            }

        }

        // 注册datasource

        registry.registerBeanDefinition(dataSourceConfig

                .getName(), getTomcatJdbcDataSourceBeanDefinition(dataSourceConfig, logConfig));

        // 注册事务

        if (transactionConfig != null && transactionConfig.isEnable()) {

            if (index == null) {

                registry.registerBeanDefinition("transactionManager", getTransactionManagerBeanDefinition(dataSourceConfig));

            } else {

                registry.registerBeanDefinition("transactionManager" + index, getTransactionManagerBeanDefinition(dataSourceConfig));

            }

        }

        // 注册mybatis

        if (myBatisConfig != null) {

            final String sqlSessionFactoryBeanName = "sqlSessionFactory" + dataSourceConfig.getName();

            registry.registerBeanDefinition(sqlSessionFactoryBeanName, getSqlSessionFactoryBeanDefinition(myBatisConfig, dataSourceConfig));

            registry.registerBeanDefinition("mapperScannerConfigurer" + dataSourceConfig

                    .getName(), getMapperScannerConfigurerBeanDefinition(myBatisConfig, sqlSessionFactoryBeanName));

            // 给与默认 dataSource bean id: sqlSession${index}

            if (StringUtils.isEmpty(myBatisConfig.getSqlSessionBeanName())) {

                if (index == null) {

                    myBatisConfig.setSqlSessionBeanName("sqlSession");

                } else {

                    myBatisConfig.setSqlSessionBeanName("sqlSession" + index);

                }

            }

            registry.registerBeanDefinition(myBatisConfig

                    .getSqlSessionBeanName(), getSqlSessionBeanDefinition(sqlSessionFactoryBeanName));

        }

    }

    /**

     * 获取 tomcat jdbc datasource bean 定义

     *

     * @param dataSourceConfig

     * @return

     */

    protected AbstractBeanDefinition getTomcatJdbcDataSourceBeanDefinition(DataSourceConfig dataSourceConfig, LogConfig logConfig) {

        if (dataSourceConfig.getMinIdle() == null) {

            dataSourceConfig.setMinIdle(dataSourceConfig.getInitialSize());

        }

        if (dataSourceConfig.getMaxIdle() == null) {

            dataSourceConfig.setMaxIdle(dataSourceConfig.getMaxActive());

        }

        BeanDefinitionBuilder definitionBuilder = BeanDefinitionBuilder

                .rootBeanDefinition("org.apache.tomcat.jdbc.pool.DataSource");

        definitionBuilder.setDestroyMethodName("close");

        // add filter

        definitionBuilder

                .addPropertyValue("jdbcInterceptors", "cn.caijiajia.framework.db.log.TomcatJdbcLogFilter(slowLogOn=" + logConfig

                        .isSlowSqlOn() + ",slowSqlThreshold=" + logConfig.getSlowSqlThreshold() + ")");

        // if not set, use default value in jdbc driver

        if (dataSourceConfig.getDefaultAutoCommit() != null) {

            definitionBuilder

                    .addPropertyValue("defaultAutoCommit", dataSourceConfig.getDefaultAutoCommit());

        }

        if (dataSourceConfig.getDefaultReadOnly() != null) {

            definitionBuilder

                    .addPropertyValue("defaultReadOnly", dataSourceConfig.getDefaultReadOnly());

        }

        if (dataSourceConfig.getDefaultTransactionIsolation() != null) {

            definitionBuilder

                    .addPropertyValue("defaultTransactionIsolation", dataSourceConfig.getDefaultTransactionIsolation());

        }

        definitionBuilder.addPropertyValue("url", dataSourceConfig.getUrl());

        definitionBuilder.addPropertyValue("username", dataSourceConfig.getUsername());

        definitionBuilder.addPropertyValue("password", dataSourceConfig.getPassword());

        definitionBuilder.addPropertyValue("driverClassName", dataSourceConfig.getDriverClassName());

        // 配置初始化大小、最小、最大

        definitionBuilder.addPropertyValue("initialSize", dataSourceConfig.getInitialSize());

        definitionBuilder.addPropertyValue("minIdle", dataSourceConfig.getMinIdle());

        definitionBuilder.addPropertyValue("maxActive", dataSourceConfig.getMaxActive());

        definitionBuilder.addPropertyValue("maxIdle", dataSourceConfig.getMaxIdle());

        // 配置获取连接等待超时的时间

        definitionBuilder.addPropertyValue("maxWait", dataSourceConfig.getMaxWait());

        // 配置间隔多久才进行一次检测，检测需要关闭的空闲连接，单位是毫

        definitionBuilder

                .addPropertyValue("timeBetweenEvictionRunsMillis", dataSourceConfig.getTimeBetweenEvictionRunsMillis());

        // 配置一个连接在池中最小生存的时间，单位是毫秒

        definitionBuilder

                .addPropertyValue("minEvictableIdleTimeMillis", dataSourceConfig.getMinEvictableIdleTimeMillis());

        definitionBuilder.addPropertyValue("validationQuery", "select 1");

        definitionBuilder.addPropertyValue("testOnConnect", dataSourceConfig.isTestOnConnect());

        definitionBuilder.addPropertyValue("testWhileIdle", dataSourceConfig.isTestWhileIdle());

        definitionBuilder.addPropertyValue("testOnBorrow", dataSourceConfig.isTestOnBorrow());

        definitionBuilder.addPropertyValue("testOnReturn", dataSourceConfig.isTestOnReturn());

        definitionBuilder.addPropertyValue("removeAbandoned", dataSourceConfig.isRemoveAbandoned());

        definitionBuilder.addPropertyValue("removeAbandonedTimeout", dataSourceConfig.getRemoveAbandonedTimeout());

        AbstractBeanDefinition bd = definitionBuilder.getRawBeanDefinition();

        bd.setScope(BeanDefinition.SCOPE_SINGLETON);

        return bd;

    }

    /**

     * 获取mybaits SqlSessionFactory bean 定义

     *

     * @param dataSourceConfig

     * @return

     */

    protected AbstractBeanDefinition getSqlSessionFactoryBeanDefinition(MyBatisConfig myBatisConfig, DataSourceConfig dataSourceConfig) {

        BeanDefinitionBuilder definitionBuilder = BeanDefinitionBuilder

                .rootBeanDefinition(org.mybatis.spring.SqlSessionFactoryBean.class);

        definitionBuilder.addPropertyReference("dataSource", dataSourceConfig.getName());

        PageInterceptor pageInterceptor = new PageInterceptor();

        if (myBatisConfig.getPage().isSupportMethodsArguments()) {

            Properties pageInterceptorProperties = new Properties();

            pageInterceptorProperties.setProperty("supportMethodsArguments", "true");

            pageInterceptorProperties.setProperty("params", "pageNum=pageNum;pageSize=pageSize");

            pageInterceptor.setProperties(pageInterceptorProperties);

        }

        definitionBuilder

                .addPropertyValue("plugins", new Interceptor[]{new LogInfoInterceptor(), pageInterceptor});

        AbstractBeanDefinition bd = definitionBuilder.getRawBeanDefinition();

        bd.setScope(BeanDefinition.SCOPE_SINGLETON);

        return bd;

    }

    /**

     * 获取mybaits MapperScannerConfigurer bean 定义

     *

     * @param myBatisConfig

     * @param sqlSessionFactoryBeanName

     * @return

     */

    protected AbstractBeanDefinition getMapperScannerConfigurerBeanDefinition(MyBatisConfig myBatisConfig, String sqlSessionFactoryBeanName) {

        BeanDefinitionBuilder definitionBuilder = BeanDefinitionBuilder

                .rootBeanDefinition(org.mybatis.spring.mapper.MapperScannerConfigurer.class);

        definitionBuilder

                .addPropertyValue("sqlSessionFactoryBeanName", sqlSessionFactoryBeanName);

        definitionBuilder.addPropertyValue("basePackage", myBatisConfig.getBasePackage());

        AbstractBeanDefinition bd = definitionBuilder.getRawBeanDefinition();

        bd.setScope(BeanDefinition.SCOPE_SINGLETON);

        return bd;

    }

    /**

     * 获取mybaits SqlSessionTemplate bean 定义

     *

     * @param sqlSessionFactoryBeanName

     * @return

     */

    protected AbstractBeanDefinition getSqlSessionBeanDefinition(String sqlSessionFactoryBeanName) {

        BeanDefinitionBuilder definitionBuilder = BeanDefinitionBuilder

                .rootBeanDefinition(org.mybatis.spring.SqlSessionTemplate.class);

        definitionBuilder.addConstructorArgReference(sqlSessionFactoryBeanName);

        AbstractBeanDefinition bd = definitionBuilder.getRawBeanDefinition();

        bd.setScope(BeanDefinition.SCOPE_SINGLETON);

        return bd;

    }

    /**

     * 获取 DataSourceTransactionManager bean定义

     *

     * @param dataSourceConfig

     * @return

     */

    protected AbstractBeanDefinition getTransactionManagerBeanDefinition(DataSourceConfig dataSourceConfig) {

        BeanDefinitionBuilder definitionBuilder = BeanDefinitionBuilder

                .genericBeanDefinition(DataSourceTransactionManager.class);

        definitionBuilder.addConstructorArgReference(dataSourceConfig.getName());

        AbstractBeanDefinition bd = definitionBuilder.getRawBeanDefinition();

        bd.setScope(BeanDefinition.SCOPE_SINGLETON);

        return bd;

    }

}

　　

@ConfigurationProperties(prefix = DbProperties.PROPERTY_PREFIX)

public class DbProperties {

    public final static String PROPERTY_PREFIX = "caijiajia.db";

    private DatabaseConfig database;

    private List<DatabaseConfig> databases = new ArrayList();

    public DatabaseConfig getDatabase() {

        return database;

    }

    public void setDatabase(DatabaseConfig database) {

        this.database = database;

    }

    public List<DatabaseConfig> getDatabases() {

        return databases;

    }

    public void setDatabases(List<DatabaseConfig> databases) {

        this.databases = databases;

    }

}

　　

这是两段核心配置类，其它还有一些pojo类，这里就不写出来了

自定义spring.factories

自定义spring.factories的步骤很简单，只需要在src/main/resource目录下创建META-INF目录,并在该目录下添加文件spring.factories，文件内容为：

org.springframework.boot.autoconfigure.EnableAutoConfiguration=\

cn.caijiajia.framework.db.autoconfigure.DatabaseAutoConfiguration　　

到这里通过spring boot的自动装配原理实现了配置类的自动装配

一个简单的starter创造就完成了

　　

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