mybatis-spring-boot-starter自动装配原理与源码分析

在springboot项目中使用mybatis只需要引入mybatis-spring-boot-starter即可使用，从源码的角度分析其自动装配原理

1.引入依赖

 	   <dependency>
            <groupId>org.mybatis.spring.boot</groupId>
            <artifactId>mybatis-spring-boot-starter</artifactId>
            <version>2.1.2</version>
        </dependency>

2.导入mybatis与mybatis-spring依赖

1.在maven库中找到mybatis-spring-boot-autoconfigure=》MATA-INF-spring.factories文件，文件

# springboot会扫描spring.factories文件中EnableAutoConfiguration指定类
#注入到IOC容器中
org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
org.mybatis.spring.boot.autoconfigure.MybatisLanguageDriverAutoConfiguration,\
org.mybatis.spring.boot.autoconfigure.MybatisAutoConfiguration

a）第一个类MybatisLanguageDriverAutoConfiguration，当存在LanguageDriver时生效

b）MybatisAutoConfiguration，此类为springboot整合mybatis核心类

//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by Fernflower decompiler)
//

package org.mybatis.spring.boot.autoconfigure;

import java.beans.FeatureDescriptor;
import java.util.Iterator;
import java.util.List;
import java.util.Set;
import java.util.stream.Collectors;
import java.util.stream.Stream;
import javax.sql.DataSource;
import org.apache.ibatis.annotations.Mapper;
import org.apache.ibatis.mapping.DatabaseIdProvider;
import org.apache.ibatis.plugin.Interceptor;
import org.apache.ibatis.scripting.LanguageDriver;
import org.apache.ibatis.session.ExecutorType;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.type.TypeHandler;
import org.mybatis.spring.SqlSessionFactoryBean;
import org.mybatis.spring.SqlSessionTemplate;
import org.mybatis.spring.mapper.MapperFactoryBean;
import org.mybatis.spring.mapper.MapperScannerConfigurer;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.BeanWrapper;
import org.springframework.beans.BeanWrapperImpl;
import org.springframework.beans.factory.BeanFactory;
import org.springframework.beans.factory.BeanFactoryAware;
import org.springframework.beans.factory.InitializingBean;
import org.springframework.beans.factory.ObjectProvider;
import org.springframework.beans.factory.support.BeanDefinitionBuilder;
import org.springframework.beans.factory.support.BeanDefinitionRegistry;
import org.springframework.boot.autoconfigure.AutoConfigurationPackages;
import org.springframework.boot.autoconfigure.AutoConfigureAfter;
import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
import org.springframework.boot.autoconfigure.condition.ConditionalOnSingleCandidate;
import org.springframework.boot.autoconfigure.jdbc.DataSourceAutoConfiguration;
import org.springframework.boot.context.properties.EnableConfigurationProperties;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Import;
import org.springframework.context.annotation.ImportBeanDefinitionRegistrar;
import org.springframework.core.io.Resource;
import org.springframework.core.io.ResourceLoader;
import org.springframework.core.type.AnnotationMetadata;
import org.springframework.util.Assert;
import org.springframework.util.CollectionUtils;
import org.springframework.util.ObjectUtils;
import org.springframework.util.StringUtils;

//指定配置类
@Configuration
//当存在SqlSessionFactory.class，SqlSessionFactoryBean.class时生效
@ConditionalOnClass({SqlSessionFactory.class, SqlSessionFactoryBean.class})
//当只有一个单例的DataSource或者指定了首选DataSource时生效
@ConditionalOnSingleCandidate(DataSource.class)
//启用Mybatis属性配置
@EnableConfigurationProperties({MybatisProperties.class})
//在DataSourceAutoConfiguration，MybatisLanguageDriverAutoConfiguration配置完后才咸亨小
@AutoConfigureAfter({DataSourceAutoConfiguration.class, MybatisLanguageDriverAutoConfiguration.class})
public class MybatisAutoConfiguration implements InitializingBean {
    private static final Logger logger = LoggerFactory.getLogger(MybatisAutoConfiguration.class);
    private final MybatisProperties properties;
    private final Interceptor[] interceptors;
    private final TypeHandler[] typeHandlers;
    private final LanguageDriver[] languageDrivers;
    private final ResourceLoader resourceLoader;
    private final DatabaseIdProvider databaseIdProvider;
    private final List<ConfigurationCustomizer> configurationCustomizers;

    public MybatisAutoConfiguration(MybatisProperties properties, ObjectProvider<Interceptor[]> interceptorsProvider, ObjectProvider<TypeHandler[]> typeHandlersProvider, ObjectProvider<LanguageDriver[]> languageDriversProvider, ResourceLoader resourceLoader, ObjectProvider<DatabaseIdProvider> databaseIdProvider, ObjectProvider<List<ConfigurationCustomizer>> configurationCustomizersProvider) {
        this.properties = properties;
        this.interceptors = (Interceptor[])interceptorsProvider.getIfAvailable();
        this.typeHandlers = (TypeHandler[])typeHandlersProvider.getIfAvailable();
        this.languageDrivers = (LanguageDriver[])languageDriversProvider.getIfAvailable();
        this.resourceLoader = resourceLoader;
        this.databaseIdProvider = (DatabaseIdProvider)databaseIdProvider.getIfAvailable();
        this.configurationCustomizers = (List)configurationCustomizersProvider.getIfAvailable();
    }

    public void afterPropertiesSet() {
        this.checkConfigFileExists();
    }

    private void checkConfigFileExists() {
        if (this.properties.isCheckConfigLocation() && StringUtils.hasText(this.properties.getConfigLocation())) {
            Resource resource = this.resourceLoader.getResource(this.properties.getConfigLocation());
            Assert.state(resource.exists(), "Cannot find config location: " + resource + " (please add config file or check your Mybatis configuration)");
        }

    }

	//当IOC容器中没有sqlSessionFactory时创建bean实例
    @Bean
    @ConditionalOnMissingBean
    public SqlSessionFactory sqlSessionFactory(DataSource dataSource) throws Exception {
        SqlSessionFactoryBean factory = new SqlSessionFactoryBean();
        factory.setDataSource(dataSource);
        factory.setVfs(SpringBootVFS.class);
        if (StringUtils.hasText(this.properties.getConfigLocation())) {
            factory.setConfigLocation(this.resourceLoader.getResource(this.properties.getConfigLocation()));
        }

        this.applyConfiguration(factory);
        if (this.properties.getConfigurationProperties() != null) {
            factory.setConfigurationProperties(this.properties.getConfigurationProperties());
        }

        if (!ObjectUtils.isEmpty(this.interceptors)) {
            factory.setPlugins(this.interceptors);
        }

        if (this.databaseIdProvider != null) {
            factory.setDatabaseIdProvider(this.databaseIdProvider);
        }

        if (StringUtils.hasLength(this.properties.getTypeAliasesPackage())) {
            factory.setTypeAliasesPackage(this.properties.getTypeAliasesPackage());
        }

        if (this.properties.getTypeAliasesSuperType() != null) {
            factory.setTypeAliasesSuperType(this.properties.getTypeAliasesSuperType());
        }

        if (StringUtils.hasLength(this.properties.getTypeHandlersPackage())) {
            factory.setTypeHandlersPackage(this.properties.getTypeHandlersPackage());
        }

        if (!ObjectUtils.isEmpty(this.typeHandlers)) {
            factory.setTypeHandlers(this.typeHandlers);
        }

        if (!ObjectUtils.isEmpty(this.properties.resolveMapperLocations())) {
            factory.setMapperLocations(this.properties.resolveMapperLocations());
        }

        Set<String> factoryPropertyNames = (Set)Stream.of((new BeanWrapperImpl(SqlSessionFactoryBean.class)).getPropertyDescriptors()).map(FeatureDescriptor::getName).collect(Collectors.toSet());
        Class<? extends LanguageDriver> defaultLanguageDriver = this.properties.getDefaultScriptingLanguageDriver();
        if (factoryPropertyNames.contains("scriptingLanguageDrivers") && !ObjectUtils.isEmpty(this.languageDrivers)) {
            factory.setScriptingLanguageDrivers(this.languageDrivers);
            if (defaultLanguageDriver == null && this.languageDrivers.length == 1) {
                defaultLanguageDriver = this.languageDrivers[0].getClass();
            }
        }

        if (factoryPropertyNames.contains("defaultScriptingLanguageDriver")) {
            factory.setDefaultScriptingLanguageDriver(defaultLanguageDriver);
        }

        return factory.getObject();
    }

    private void applyConfiguration(SqlSessionFactoryBean factory) {
        org.apache.ibatis.session.Configuration configuration = this.properties.getConfiguration();
        if (configuration == null && !StringUtils.hasText(this.properties.getConfigLocation())) {
            configuration = new org.apache.ibatis.session.Configuration();
        }

        if (configuration != null && !CollectionUtils.isEmpty(this.configurationCustomizers)) {
            Iterator var3 = this.configurationCustomizers.iterator();

            while(var3.hasNext()) {
                ConfigurationCustomizer customizer = (ConfigurationCustomizer)var3.next();
                customizer.customize(configuration);
            }
        }

        factory.setConfiguration(configuration);
    }

	//当IOC容器中没有sqlSessionTemplate创建实例化bean
    @Bean
    @ConditionalOnMissingBean
    public SqlSessionTemplate sqlSessionTemplate(SqlSessionFactory sqlSessionFactory) {
        ExecutorType executorType = this.properties.getExecutorType();
        return executorType != null ? new SqlSessionTemplate(sqlSessionFactory, executorType) : new SqlSessionTemplate(sqlSessionFactory);
    }
	//配置文件引入MybatisAutoConfiguration与AutoConfiguredMapperScannerRegistrar
	//当容器中没有MapperFactoryBean.class, MapperScannerConfigurer.class
    @Configuration
    @Import({MybatisAutoConfiguration.AutoConfiguredMapperScannerRegistrar.class})
    @ConditionalOnMissingBean({MapperFactoryBean.class, MapperScannerConfigurer.class})
    public static class MapperScannerRegistrarNotFoundConfiguration implements InitializingBean {
        public MapperScannerRegistrarNotFoundConfiguration() {
        }

        public void afterPropertiesSet() {
            MybatisAutoConfiguration.logger.debug("Not found configuration for registering mapper bean using @MapperScan, MapperFactoryBean and MapperScannerConfigurer.");
        }
    }

    public static class AutoConfiguredMapperScannerRegistrar implements BeanFactoryAware, ImportBeanDefinitionRegistrar {
        private BeanFactory beanFactory;

        public AutoConfiguredMapperScannerRegistrar() {
        }

        public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {
            if (!AutoConfigurationPackages.has(this.beanFactory)) {
                MybatisAutoConfiguration.logger.debug("Could not determine auto-configuration package, automatic mapper scanning disabled.");
            } else {
                MybatisAutoConfiguration.logger.debug("Searching for mappers annotated with @Mapper");
                List<String> packages = AutoConfigurationPackages.get(this.beanFactory);
                if (MybatisAutoConfiguration.logger.isDebugEnabled()) {
                    packages.forEach((pkg) -> {
                        MybatisAutoConfiguration.logger.debug("Using auto-configuration base package '{}'", pkg);
                    });
                }

                BeanDefinitionBuilder builder = BeanDefinitionBuilder.genericBeanDefinition(MapperScannerConfigurer.class);
                builder.addPropertyValue("processPropertyPlaceHolders", true);
                builder.addPropertyValue("annotationClass", Mapper.class);
                builder.addPropertyValue("basePackage", StringUtils.collectionToCommaDelimitedString(packages));
                BeanWrapper beanWrapper = new BeanWrapperImpl(MapperScannerConfigurer.class);
                Stream.of(beanWrapper.getPropertyDescriptors()).filter((x) -> {
                    return x.getName().equals("lazyInitialization");
                }).findAny().ifPresent((x) -> {
                    builder.addPropertyValue("lazyInitialization", "${mybatis.lazy-initialization:false}");
                });
                registry.registerBeanDefinition(MapperScannerConfigurer.class.getName(), builder.getBeanDefinition());
            }
        }

        public void setBeanFactory(BeanFactory beanFactory) {
            this.beanFactory = beanFactory;
        }
    }
}

从源码中可以看出，当有SqlSessionFactory.class，SqlSessionFactoryBean.class这个两个类存在，并且指定了DataSource之后，该配置类即可生效，生效时IOC容器中若不存在，则会创建sqlSessionFactory与sqlSessionTemplate实例化bean，若在其他地方应用，则直接注入即可，在注入sqlSessionFactory是需要注入DataSource，DataSource到底从哪里来呢？springboot-autoconfigure-jdbc中有一配置类，该配置类会自动注DataSource

在MybatisAutoConfiguration 有一个这样的配置文件，当容器中缺失这个几个bean时该配置类生效，再次注入MybatisAutoConfiguration 实例，其实在正常情况下是不生效，那个这个到底是什么时候生效的呢？在启动的时候，需要加入一个注解@MapperScan("")，包扫描路径，该注解会向IOC注册MapperScannerRegistrar

//配置文件引入MybatisAutoConfiguration与AutoConfiguredMapperScannerRegistrar
	//当容器中没有MapperFactoryBean.class, MapperScannerConfigurer.class
    @Configuration
    @Import({MybatisAutoConfiguration.AutoConfiguredMapperScannerRegistrar.class})
    @ConditionalOnMissingBean({MapperFactoryBean.class, MapperScannerConfigurer.class})
    public static class MapperScannerRegistrarNotFoundConfiguration implements InitializingBean {
        public MapperScannerRegistrarNotFoundConfiguration() {
        }

        public void afterPropertiesSet() {
            MybatisAutoConfiguration.logger.debug("Not found configuration for registering mapper bean using @MapperScan, MapperFactoryBean and MapperScannerConfigurer.");
        }
    }

@MapperScan会引入MapperScannerRegistrar

springboot自动装配流程
1.mybatis-spring-boot-autoconfigure-2.1.2.jar=》spring.factories文件中扫描
org.mybatis.spring.boot.autoconfigure.MybatisLanguageDriverAutoConfiguration,
org.mybatis.spring.boot.autoconfigure.MybatisAutoConfiguration
2.完成MybatisAutoConfiguration配置文件中bean实例化，在IOC容器中创建SqlSessionFactory与SqlSessionTemplate实例