sqlSessionFactory创建

 前言

分析上篇文章的整合的配置文件，我们可以知道配置的bean是成树状结构的，而在树的最顶层是类型为org.mybatis.Spring.SqlSessionFactoryBean的bean，它将其他相关的bean组装在了一起，那么我们的分析就从此类开始。

sqlSessionFactory创建

 对于配置文件的读取，Spring是通过org.mybatis.Spring.SqlSessionFactoryBean封装了MyBatis中的实现。首先来看一下这个类的类图：

根据上图对两个感兴趣的接口FactoryBean和InitializingBean。

　　❤ InitializingBean：实现此接口的bean会在初始化时调用其afterPropertiesSet方法来进行bean的逻辑初始化。

　　❤ FactoryBean：一旦某个bean实现此接口，那么通过getBean方法获取bean时其实是获取此类的getObject返回的实例。

1.sqlSessionFactoryBean的初始化

 查看org.mybatis.Spring.SqlSessionFactoryBean类型的bean在初始化时做了哪些逻辑实现。

public void afterPropertiesSet() throws Exception {
        Assert.notNull(this.dataSource, "Property 'dataSource' is required");
        Assert.notNull(this.sqlSessionFactoryBuilder, "Property 'sqlSessionFactoryBuilder' is required");
        Assert.state(this.configuration == null && this.configLocation == null || this.configuration == null || this.configLocation == null, "Property 'configuration' and 'configLocation' can not specified with together");
        this.sqlSessionFactory = this.buildSqlSessionFactory();
    }

很显然，此函数的主要目的是对于sqlSessionFactory的初始化，sqlSessionFactory是所有MyBatis功能的基础。

protected SqlSessionFactory buildSqlSessionFactory() throws IOException {
        XMLConfigBuilder xmlConfigBuilder = null;
        Configuration configuration;
        if (this.configuration != null) {
            configuration = this.configuration;
            if (configuration.getVariables() == null) {
                configuration.setVariables(this.configurationProperties);
            } else if (this.configurationProperties != null) {
                configuration.getVariables().putAll(this.configurationProperties);
            }
        } else if (this.configLocation != null) {
            xmlConfigBuilder = new XMLConfigBuilder(this.configLocation.getInputStream(), (String)null, this.configurationProperties);
            configuration = xmlConfigBuilder.getConfiguration();
        } else {
            if (LOGGER.isDebugEnabled()) {
                LOGGER.debug("Property 'configuration' or 'configLocation' not specified, using default MyBatis Configuration");
            }

            configuration = new Configuration();
            if (this.configurationProperties != null) {
                configuration.setVariables(this.configurationProperties);
            }
        }

        if (this.objectFactory != null) {
            configuration.setObjectFactory(this.objectFactory);
        }

        if (this.objectWrapperFactory != null) {
            configuration.setObjectWrapperFactory(this.objectWrapperFactory);
        }

        if (this.vfs != null) {
            configuration.setVfsImpl(this.vfs);
        }

        String[] typeHandlersPackageArray;
        String[] var4;
        int var5;
        int var6;
        String packageToScan;
        if (StringUtils.hasLength(this.typeAliasesPackage)) {
            typeHandlersPackageArray = StringUtils.tokenizeToStringArray(this.typeAliasesPackage, ",; \t\n");
            var4 = typeHandlersPackageArray;
            var5 = typeHandlersPackageArray.length;

            for(var6 = 0; var6 < var5; ++var6) {
                packageToScan = var4[var6];
                configuration.getTypeAliasRegistry().registerAliases(packageToScan, this.typeAliasesSuperType == null ? Object.class : this.typeAliasesSuperType);
                if (LOGGER.isDebugEnabled()) {
                    LOGGER.debug("Scanned package: '" + packageToScan + "' for aliases");
                }
            }
        }

        int var27;
        if (!ObjectUtils.isEmpty(this.typeAliases)) {
            Class[] var25 = this.typeAliases;
            var27 = var25.length;

            for(var5 = 0; var5 < var27; ++var5) {
                Class<?> typeAlias = var25[var5];
                configuration.getTypeAliasRegistry().registerAlias(typeAlias);
                if (LOGGER.isDebugEnabled()) {
                    LOGGER.debug("Registered type alias: '" + typeAlias + "'");
                }
            }
        }

        if (!ObjectUtils.isEmpty(this.plugins)) {
            Interceptor[] var26 = this.plugins;
            var27 = var26.length;

            for(var5 = 0; var5 < var27; ++var5) {
                Interceptor plugin = var26[var5];
                configuration.addInterceptor(plugin);
                if (LOGGER.isDebugEnabled()) {
                    LOGGER.debug("Registered plugin: '" + plugin + "'");
                }
            }
        }

        if (StringUtils.hasLength(this.typeHandlersPackage)) {
            typeHandlersPackageArray = StringUtils.tokenizeToStringArray(this.typeHandlersPackage, ",; \t\n");
            var4 = typeHandlersPackageArray;
            var5 = typeHandlersPackageArray.length;

            for(var6 = 0; var6 < var5; ++var6) {
                packageToScan = var4[var6];
                configuration.getTypeHandlerRegistry().register(packageToScan);
                if (LOGGER.isDebugEnabled()) {
                    LOGGER.debug("Scanned package: '" + packageToScan + "' for type handlers");
                }
            }
        }

        if (!ObjectUtils.isEmpty(this.typeHandlers)) {
            TypeHandler[] var28 = this.typeHandlers;
            var27 = var28.length;

            for(var5 = 0; var5 < var27; ++var5) {
                TypeHandler<?> typeHandler = var28[var5];
                configuration.getTypeHandlerRegistry().register(typeHandler);
                if (LOGGER.isDebugEnabled()) {
                    LOGGER.debug("Registered type handler: '" + typeHandler + "'");
                }
            }
        }

        if (this.databaseIdProvider != null) {
            try {
                configuration.setDatabaseId(this.databaseIdProvider.getDatabaseId(this.dataSource));
            } catch (SQLException var24) {
                throw new NestedIOException("Failed getting a databaseId", var24);
            }
        }

        if (this.cache != null) {
            configuration.addCache(this.cache);
        }

        if (xmlConfigBuilder != null) {
            try {
                xmlConfigBuilder.parse();
                if (LOGGER.isDebugEnabled()) {
                    LOGGER.debug("Parsed configuration file: '" + this.configLocation + "'");
                }
            } catch (Exception var22) {
                throw new NestedIOException("Failed to parse config resource: " + this.configLocation, var22);
            } finally {
                ErrorContext.instance().reset();
            }
        }

        if (this.transactionFactory == null) {
            this.transactionFactory = new SpringManagedTransactionFactory();
        }

        configuration.setEnvironment(new Environment(this.environment, this.transactionFactory, this.dataSource));
        if (!ObjectUtils.isEmpty(this.mapperLocations)) {
            Resource[] var29 = this.mapperLocations;
            var27 = var29.length;

            for(var5 = 0; var5 < var27; ++var5) {
                Resource mapperLocation = var29[var5];
                if (mapperLocation != null) {
                    try {
                        XMLMapperBuilder xmlMapperBuilder = new XMLMapperBuilder(mapperLocation.getInputStream(), configuration, mapperLocation.toString(), configuration.getSqlFragments());
                        xmlMapperBuilder.parse();
                    } catch (Exception var20) {
                        throw new NestedIOException("Failed to parse mapping resource: '" + mapperLocation + "'", var20);
                    } finally {
                        ErrorContext.instance().reset();
                    }

                    if (LOGGER.isDebugEnabled()) {
                        LOGGER.debug("Parsed mapper file: '" + mapperLocation + "'");
                    }
                }
            }
        } else if (LOGGER.isDebugEnabled()) {
            LOGGER.debug("Property 'mapperLocations' was not specified or no matching resources found");
        }

        return this.sqlSessionFactoryBuilder.build(configuration);
    }

从函数中可以看到，尽管我们还是习惯于将MyBatis的配置和Spring的配置独立出来，但是，这并不代表Spring中的配置不支持直接配置。也就是说，在上篇文章的示例中，完全裤取消配置中的configLocation属性，而把其中的属性直接写在sqlSessionFactoryBean中。

从这个函数中还可以得知，配置文件还可以支持其他多种属性的配置，如configLocation、objectFactory、objectWrapperFactory、typeAliasesPackage、typeAliases、typeHandlersPackage、plugins、typeHandlers、transactionFactory、databaseIdProvider、mapperLocations。

其实，如果只按照常用的配置，那么我们只需要在函数最开始按照如下方式处理configLocation：

　　 xmlConfigBuilder = new XMLConfigBuilder(this.configLocation.getInputStream(),null,this.configurationProperties);
    configuration = xmlConfigBuilder.getConfiguration();

 根据configLocation构造XMLConfigBuilder并进行解析，但是，为了体现Spring更强大的兼容性，Spring还整合了MyBatis中其他属性的注入，并通过实例configuration来承载每一步所获取的信息并最终使用sqlSessionFactoryBuilder实例根据解析到的configuration创建sqlSessionFactory实例。

2.获取SqlSessionFactoryBean实例

 由于sqlSessionFactoryBean实现了FactoryBean接口，所以当通过getBean方法获取对应实例时，其实是获取该类的getObject函数返回的实例，也就是获得初始化后的sqlSessionFactory属性。

public SqlSessionFactory getObject() throws Exception {
        if (this.sqlSessionFactory == null) {
            this.afterPropertiesSet();
        }

        return this.sqlSessionFactory;
    }

 参考：《Spring源码深度解析》 郝佳 编著：