使用过SSM的框架的都知道mybatis这个持久层框架，今天小编就来简单说说这个框架的核心工厂类sqlSessionFactory的加载过程，一般的SSM框架我们都会在spring的application.xml中引入如下的配置：

其中的SqlSessionFactoryBean便是加载sqlSessionFactory的入口，首先我们来看看这个类的源代码：

public class SqlSessionFactoryBean implements FactoryBean
     
      , InitializingBean, ApplicationListener
      
        {  private static final Log logger = LogFactory.getLog(SqlSessionFactoryBean.class);  private Resource configLocation; private Resource[] mapperLocations;  private DataSource dataSource; private TransactionFactory transactionFactory;  private Properties configurationProperties;  private SqlSessionFactoryBuilder sqlSessionFactoryBuilder = new SqlSessionFactoryBuilder();  private SqlSessionFactory sqlSessionFactory;
      
     

其中标红的两处，就是我们在application.xml中注入的两个属性，从源码中我们可以看出该类实现了InitializingBean接口，实现了其afterPropertiesSet（）方法，

该方法是在当前bean的所有属性被初始化完成之后再执行，也就是其中的datasource和configurationProperties等属性，接下来我们看看这个方法主要干什么了？

1 public void afterPropertiesSet() throws Exception {2     notNull(dataSource, "Property 'dataSource' is required");3     notNull(sqlSessionFactoryBuilder, "Property 'sqlSessionFactoryBuilder' is required");4 5     this.sqlSessionFactory = buildSqlSessionFactory();6   }

其中第5行很明显的buildSqlSessionFactory（）方法初始化了sqlSessionFactory ，接下来我们看看这个方法的主要行为：

1 Configuration configuration;  2   3     XMLConfigBuilder xmlConfigBuilder = null;  4     if (this.configLocation != null) {  5       xmlConfigBuilder = new XMLConfigBuilder(this.configLocation.getInputStream(), null, this.configurationProperties);  6       configuration = xmlConfigBuilder.getConfiguration();  7     } else {  8       if (logger.isDebugEnabled()) {  9         logger.debug("Property 'configLocation' not specified, using default MyBatis Configuration"); 10       } 11       configuration = new Configuration(); 12       configuration.setVariables(this.configurationProperties); 13     } 14  15     if (this.objectFactory != null) { 16       configuration.setObjectFactory(this.objectFactory); 17     } 18  19     if (this.objectWrapperFactory != null) { 20       configuration.setObjectWrapperFactory(this.objectWrapperFactory); 21     } 22  23     if (hasLength(this.typeAliasesPackage)) { 24       String[] typeAliasPackageArray = tokenizeToStringArray(this.typeAliasesPackage, 25           ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS); 26       for (String packageToScan : typeAliasPackageArray) { 27         configuration.getTypeAliasRegistry().registerAliases(packageToScan, 28                 typeAliasesSuperType == null ? Object.class : typeAliasesSuperType); 29         if (logger.isDebugEnabled()) { 30           logger.debug("Scanned package: '" + packageToScan + "' for aliases"); 31         } 32       } 33     } 34  35     if (!isEmpty(this.typeAliases)) { 36       for (Class
       typeAlias : this.typeAliases) { 37         configuration.getTypeAliasRegistry().registerAlias(typeAlias); 38         if (logger.isDebugEnabled()) { 39           logger.debug("Registered type alias: '" + typeAlias + "'"); 40         } 41       } 42     } 43  44     if (!isEmpty(this.plugins)) { 45       for (Interceptor plugin : this.plugins) { 46         configuration.addInterceptor(plugin); 47         if (logger.isDebugEnabled()) { 48           logger.debug("Registered plugin: '" + plugin + "'"); 49         } 50       } 51     } 52  53     if (hasLength(this.typeHandlersPackage)) { 54       String[] typeHandlersPackageArray = tokenizeToStringArray(this.typeHandlersPackage, 55           ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS); 56       for (String packageToScan : typeHandlersPackageArray) { 57         configuration.getTypeHandlerRegistry().register(packageToScan); 58         if (logger.isDebugEnabled()) { 59           logger.debug("Scanned package: '" + packageToScan + "' for type handlers"); 60         } 61       } 62     } 63  64     if (!isEmpty(this.typeHandlers)) { 65       for (TypeHandler
       typeHandler : this.typeHandlers) { 66         configuration.getTypeHandlerRegistry().register(typeHandler); 67         if (logger.isDebugEnabled()) { 68           logger.debug("Registered type handler: '" + typeHandler + "'"); 69         } 70       } 71     } 72  73     if (xmlConfigBuilder != null) { 74       try { 75         xmlConfigBuilder.parse(); 76  77         if (logger.isDebugEnabled()) { 78           logger.debug("Parsed configuration file: '" + this.configLocation + "'"); 79         } 80       } catch (Exception ex) { 81         throw new NestedIOException("Failed to parse config resource: " + this.configLocation, ex); 82       } finally { 83         ErrorContext.instance().reset(); 84       } 85     } 86  87     if (this.transactionFactory == null) { 88       this.transactionFactory = new SpringManagedTransactionFactory(); 89     } 90  91     Environment environment = new Environment(this.environment, this.transactionFactory, this.dataSource); 92     configuration.setEnvironment(environment); 93  94     if (this.databaseIdProvider != null) { 95       try { 96         configuration.setDatabaseId(this.databaseIdProvider.getDatabaseId(this.dataSource)); 97       } catch (SQLException e) { 98         throw new NestedIOException("Failed getting a databaseId", e); 99       }100     }101 102     if (!isEmpty(this.mapperLocations)) {103       for (Resource mapperLocation : this.mapperLocations) {104         if (mapperLocation == null) {105           continue;106         }107 108         try {109           XMLMapperBuilder xmlMapperBuilder = new XMLMapperBuilder(mapperLocation.getInputStream(),110               configuration, mapperLocation.toString(), configuration.getSqlFragments());111           xmlMapperBuilder.parse();112         } catch (Exception e) {113           throw new NestedIOException("Failed to parse mapping resource: '" + mapperLocation + "'", e);114         } finally {115           ErrorContext.instance().reset();116         }117 118         if (logger.isDebugEnabled()) {119           logger.debug("Parsed mapper file: '" + mapperLocation + "'");120         }121       }122     } else {123       if (logger.isDebugEnabled()) {124         logger.debug("Property 'mapperLocations' was not specified or no matching resources found");125       }126     }

该方法主要就是设置configuration参数，首先是从mybatis-config.xml中获取对应的配置信息，然后再从spring的注入属性中获取所有的配置信息，从后调用

sqlSessionFactoryBuilder.build(configuration)方法获取sqlSessionFactory的实例。

由于整个加载过程没有过多的难点，所以就介绍到这里，感兴趣的朋友可以自己去源码，了解更多知识。