springboot集成mybatis源码分析-启动加载mybatis过程（二）

1、springboot项目最核心的就是自动加载配置，该功能则依赖的是一个注解@SpringBootApplication中的@EnableAutoConfiguration

2、EnableAutoConfiguration主要是通过AutoConfigurationImportSelector类来加载

　　以mybatis为例，*selector通过反射加载spring.factories中指定的java类，也就是加载MybatisAutoConfiguration类（该类有Configuration注解，属于配置类）

 16 package org.mybatis.spring.boot.autoconfigure; 60 重点：SqlSessionFactory 和 SqlSessionTemplate 两个类
 61 /**
 62  * {@link EnableAutoConfiguration Auto-Configuration} for Mybatis. Contributes a
 63  * {@link SqlSessionFactory} and a {@link SqlSessionTemplate}.
 64  *
 65  * If {@link org.mybatis.spring.annotation.MapperScan} is used, or a
 66  * configuration file is specified as a property, those will be considered,
 67  * otherwise this auto-configuration will attempt to register mappers based on
 68  * the interface definitions in or under the root auto-configuration package.
 69  *
 70  * @author Eddú Meléndez
 71  * @author Josh Long
 72  * @author Kazuki Shimizu
 73  * @author Eduardo Macarrón
 74  */
 75 @org.springframework.context.annotation.Configuration
 76 @ConditionalOnClass({ SqlSessionFactory.class, SqlSessionFactoryBean.class })
 77 @ConditionalOnBean(DataSource.class)
 78 @EnableConfigurationProperties(MybatisProperties.class)
 79 @AutoConfigureAfter(DataSourceAutoConfiguration.class)
 80 public class MybatisAutoConfiguration {
 81 
 82   private static final Logger logger = LoggerFactory.getLogger(MybatisAutoConfiguration.class);
 83 　//与mybatis配置文件对应
 84   private final MybatisProperties properties;
 85 
 86   private final Interceptor[] interceptors;
 87 
 88   private final ResourceLoader resourceLoader;
 89 
 90   private final DatabaseIdProvider databaseIdProvider;
 91 
 92   private final List<ConfigurationCustomizer> configurationCustomizers;
 93 
 94   public MybatisAutoConfiguration(MybatisProperties properties,
 95                                   ObjectProvider<Interceptor[]> interceptorsProvider,
 96                                   ResourceLoader resourceLoader,
 97                                   ObjectProvider<DatabaseIdProvider> databaseIdProvider,
 98                                   ObjectProvider<List<ConfigurationCustomizer>> configurationCustomizersProvider) {
 99     this.properties = properties;
100     this.interceptors = interceptorsProvider.getIfAvailable();
101     this.resourceLoader = resourceLoader;
102     this.databaseIdProvider = databaseIdProvider.getIfAvailable();
103     this.configurationCustomizers = configurationCustomizersProvider.getIfAvailable();
104   }
105 　//postConstruct作用是在创建类的时候先调用，  校验配置文件是否存在
106   @PostConstruct
107   public void checkConfigFileExists() {
108     if (this.properties.isCheckConfigLocation() && StringUtils.hasText(this.properties.getConfigLocation())) {
109       Resource resource = this.resourceLoader.getResource(this.properties.getConfigLocation());
110       Assert.state(resource.exists(), "Cannot find config location: " + resource
111           + " (please add config file or check your Mybatis configuration)");
112     }
113   }
114   //conditionalOnMissingBean作用：在没有类的时候调用，创建sqlsessionFactory  sqlsessionfactory最主要的是创建并保存了Configuration类
115   @Bean
116   @ConditionalOnMissingBean
117   public SqlSessionFactory sqlSessionFactory(DataSource dataSource) throws Exception {
118     SqlSessionFactoryBean factory = new SqlSessionFactoryBean();
119     factory.setDataSource(dataSource);
120     factory.setVfs(SpringBootVFS.class);
121     if (StringUtils.hasText(this.properties.getConfigLocation())) {
122       factory.setConfigLocation(this.resourceLoader.getResource(this.properties.getConfigLocation()));
123     }
124     Configuration configuration = this.properties.getConfiguration();
125     if (configuration == null && !StringUtils.hasText(this.properties.getConfigLocation())) {
126       configuration = new Configuration();
127     }
128     if (configuration != null && !CollectionUtils.isEmpty(this.configurationCustomizers)) {
129       for (ConfigurationCustomizer customizer : this.configurationCustomizers) {
130         customizer.customize(configuration);
131       }
132     }
133     factory.setConfiguration(configuration);
134     if (this.properties.getConfigurationProperties() != null) {
135       factory.setConfigurationProperties(this.properties.getConfigurationProperties());
136     }
137     if (!ObjectUtils.isEmpty(this.interceptors)) {
138       factory.setPlugins(this.interceptors);
139     }
140     if (this.databaseIdProvider != null) {
141       factory.setDatabaseIdProvider(this.databaseIdProvider);
142     }
143     if (StringUtils.hasLength(this.properties.getTypeAliasesPackage())) {
144       factory.setTypeAliasesPackage(this.properties.getTypeAliasesPackage());
145     }
146     if (StringUtils.hasLength(this.properties.getTypeHandlersPackage())) {
147       factory.setTypeHandlersPackage(this.properties.getTypeHandlersPackage());
148     }
149     if (!ObjectUtils.isEmpty(this.properties.resolveMapperLocations())) {
150       factory.setMapperLocations(this.properties.resolveMapperLocations());
151     }
152 
153     return factory.getObject();
154   }
155 
156   @Bean
157   @ConditionalOnMissingBean
158   public SqlSessionTemplate sqlSessionTemplate(SqlSessionFactory sqlSessionFactory) {
159     ExecutorType executorType = this.properties.getExecutorType();
160     if (executorType != null) {
161       return new SqlSessionTemplate(sqlSessionFactory, executorType);
162     } else {
163       return new SqlSessionTemplate(sqlSessionFactory);
164     }
165   }
238 }