1，mybatis流程跟踪，原理理解
基本思路： 从SqlSessionFactory的初始化出发，观察资源的准备和环境的准备，以及实现持久层的一些过程；
进入SqlSessionFactoryBean类，发现先执行的是
然后是：
在初始化类之后，做的准备工作如下：
public void afterPropertiesSet() throws Exception {
notNull(dataSource, "Property 'dataSource' is required");//1，检查spring准备的datasource是否ok
notNull(sqlSessionFactoryBuilder, "Property 'sqlSessionFactoryBuilder' is required");//2,检查空构造方法的sqlSessionFactoryBuilder是否准备好this.sqlSessionFactory = buildSqlSessionFactory();//3，利用配置的属性，构造sqlSessionFactory
}构造细节如下：方法有点长，注意注释这个是流程，之后我画一个图来加深理解；
protected SqlSessionFactory buildSqlSessionFactory() throws IOException {
Configuration configuration;
XMLConfigBuilder xmlConfigBuilder = null;
if (this.configLocation != null) {//1，检查是否有配置configLocation，即mybatis的整体配置文件，非mapper文件，如果有加载进去，没有，构造一个空的
xmlConfigBuilder = new XMLConfigBuilder(this.configLocation.getInputStream(), null, this.configurationProperties);
configuration = xmlConfigBuilder.getConfiguration();
} else {
if (logger.isDebugEnabled()) {
logger.debug("Property 'configLocation' not specified, using default MyBatis Configuration");
}
configuration = new Configuration();
configuration.setVariables(this.configurationProperties);
}if (this.objectFactory != null) {//2,检查对象工厂，如果有设置进去，没有留空
configuration.setObjectFactory(this.objectFactory);
}if (this.objectWrapperFactory != null) {//3,检查对象装饰工厂，如果有设置进去，没有留空
configuration.setObjectWrapperFactory(this.objectWrapperFactory);
}if (hasLength(this.typeAliasesPackage)) {//4,检查包的简称，如果有注册进去
String[] typeAliasPackageArray = tokenizeToStringArray(this.typeAliasesPackage,
ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS);
for (String packageToScan : typeAliasPackageArray) {
configuration.getTypeAliasRegistry().registerAliases(packageToScan,
typeAliasesSuperType == null ? Object.class : typeAliasesSuperType);
if (logger.isDebugEnabled()) {
logger.debug("Scanned package: '" + packageToScan + "' for aliases");
}
}
}if (!isEmpty(this.typeAliases)) {//5,检查类的简称，如果有注册进去
for (Class<?> typeAlias : this.typeAliases) {
configuration.getTypeAliasRegistry().registerAlias(typeAlias);
if (logger.isDebugEnabled()) {
logger.debug("Registered type alias: '" + typeAlias + "'");
}
}
}if (!isEmpty(this.plugins)) {//6，检查插件，如果有注册进去
for (Interceptor plugin : this.plugins) {
configuration.addInterceptor(plugin);
if (logger.isDebugEnabled()) {
logger.debug("Registered plugin: '" + plugin + "'");
}
}
}if (hasLength(this.typeHandlersPackage)) {//7,检查类型转换类包，如果有注册进去
String[] typeHandlersPackageArray = tokenizeToStringArray(this.typeHandlersPackage,
ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS);
for (String packageToScan : typeHandlersPackageArray) {
configuration.getTypeHandlerRegistry().register(packageToScan);
if (logger.isDebugEnabled()) {
logger.debug("Scanned package: '" + packageToScan + "' for type handlers");
}
}
}if (!isEmpty(this.typeHandlers)) {//8,检查类型转换类，如果有注册进去
for (TypeHandler<?> typeHandler : this.typeHandlers) {
configuration.getTypeHandlerRegistry().register(typeHandler);
if (logger.isDebugEnabled()) {
logger.debug("Registered type handler: '" + typeHandler + "'");
}
}
}if (xmlConfigBuilder != null) {//9,检查是否有xml的构造器，如果有，直接使用构造器构造
try {
xmlConfigBuilder.parse();if (logger.isDebugEnabled()) {
logger.debug("Parsed configuration file: '" + this.configLocation + "'");
}
} catch (Exception ex) {
throw new NestedIOException("Failed to parse config resource: " + this.configLocation, ex);
} finally {
ErrorContext.instance().reset();
}
}if (this.transactionFactory == null) {//10,检查事物工厂，如果没有，构造一个spring管理的事物工厂
this.transactionFactory = new SpringManagedTransactionFactory();
}//11，构造环境变量
Environment environment = new Environment(this.environment, this.transactionFactory, this.dataSource);
configuration.setEnvironment(environment);if (this.databaseIdProvider != null) {
try {//12，检查是否配置了db id，如果有，设置到配置的类中
configuration.setDatabaseId(this.databaseIdProvider.getDatabaseId(this.dataSource));
} catch (SQLException e) {
throw new NestedIOException("Failed getting a databaseId", e);
}
}if (!isEmpty(this.mapperLocations)) {//13，把配置的mapper弄进来总配置文件里
for (Resource mapperLocation : this.mapperLocations) {
if (mapperLocation == null) {
continue;
}try {
XMLMapperBuilder xmlMapperBuilder = new XMLMapperBuilder(mapperLocation.getInputStream(),
configuration, mapperLocation.toString(), configuration.getSqlFragments());
xmlMapperBuilder.parse();
} catch (Exception e) {
throw new NestedIOException("Failed to parse mapping resource: '" + mapperLocation + "'", e);
} 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);//14，最后通过得到的配置类来构造一个sqlsessionFactory工厂
}设置好属性之后，执行
得到factory构造的bean，即sqlSessionFactory,
最后容器启动成功的事件监控
public void onApplicationEvent(ApplicationEvent event) {
if (failFast && event instanceof ContextRefreshedEvent) {
// fail-fast -> check all statements are completed
this.sqlSessionFactory.getConfiguration().getMappedStatementNames();
}
}以上是资源的准备，下面来一次增删改查的跟踪，观察内部的工作原理；
查询单条记录的过程：
public <E> List<E> selectList(String statement, Object parameter, RowBounds rowBounds) {
try {
MappedStatement ms = configuration.getMappedStatement(statement);//1，通过转换，得到存储的mapperedStatement
List<E> result = executor.query(ms, wrapCollection(parameter), rowBounds, Executor.NO_RESULT_HANDLER);//2，转换成jdbc代码执行
return result;
} catch (Exception e) {
throw ExceptionFactory.wrapException("Error querying database. Cause: " + e, e);
} finally {
ErrorContext.instance().reset();
}
}内部就像是一台精密的仪器，去除了大量的模版jdbc代码；
