springboot-mybatis 整合了 mybatis 对数据库的拜访操，其为我做了很好的封装，开箱即用。只有在我的项目中引入 maven 的依赖，打上 MapperScan 的注解就能够进入咱们的业务开发。
咱们从注解 MapperScan 动手查看，可知在这个注解用 @Import 在容器中注册了一个 MapperScannerRegistrar 的 bean。该类实现了 ImportBeanDefinitionRegistrar 接口，重写了 registerBeanDefinitions 办法：
**1.**
@Override
public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {
// 获取打了 MapperScan 注解的类上的注解信息，包含 basePackages 等信息，这里即便 dao 包里的接口没有打 Component 注解也会被注入到容器中。AnnotationAttributes mapperScanAttrs = AnnotationAttributes
.fromMap(importingClassMetadata.getAnnotationAttributes(MapperScan.class.getName()));
if (mapperScanAttrs != null) {
registerBeanDefinitions(importingClassMetadata, mapperScanAttrs, registry,
generateBaseBeanName(importingClassMetadata, 0));
}
}获取到注解信息之后，进入其本身的 registerBeanDefinitions 办法：
**2.**
void registerBeanDefinitions(AnnotationMetadata annoMeta, AnnotationAttributes annoAttrs,
BeanDefinitionRegistry registry, String beanName) {
// new 了一个 BeanDefinitionBuilder 对象并将其 beanClass 设置为 MapperScannerConfigurer.class。BeanDefinitionBuilder builder = BeanDefinitionBuilder.genericBeanDefinition(MapperScannerConfigurer.class);
builder.addPropertyValue("processPropertyPlaceHolders", true);
// 上面都是一些属性的设置
Class<? extends Annotation> annotationClass = annoAttrs.getClass("annotationClass");
if (!Annotation.class.equals(annotationClass)) {builder.addPropertyValue("annotationClass", annotationClass);
}
Class<?> markerInterface = annoAttrs.getClass("markerInterface");
if (!Class.class.equals(markerInterface)) {builder.addPropertyValue("markerInterface", markerInterface);
}
Class<? extends BeanNameGenerator> generatorClass = annoAttrs.getClass("nameGenerator");
if (!BeanNameGenerator.class.equals(generatorClass)) {builder.addPropertyValue("nameGenerator", BeanUtils.instantiateClass(generatorClass));
}
Class<? extends MapperFactoryBean> mapperFactoryBeanClass = annoAttrs.getClass("factoryBean");
if (!MapperFactoryBean.class.equals(mapperFactoryBeanClass)) {builder.addPropertyValue("mapperFactoryBeanClass", mapperFactoryBeanClass);
}
String sqlSessionTemplateRef = annoAttrs.getString("sqlSessionTemplateRef");
if (StringUtils.hasText(sqlSessionTemplateRef)) {builder.addPropertyValue("sqlSessionTemplateBeanName", annoAttrs.getString("sqlSessionTemplateRef"));
}
String sqlSessionFactoryRef = annoAttrs.getString("sqlSessionFactoryRef");
if (StringUtils.hasText(sqlSessionFactoryRef)) {builder.addPropertyValue("sqlSessionFactoryBeanName", annoAttrs.getString("sqlSessionFactoryRef"));
}
List<String> basePackages = new ArrayList<>();
basePackages.addAll(Arrays.stream(annoAttrs.getStringArray("value")).filter(StringUtils::hasText).collect(Collectors.toList()));
basePackages.addAll(Arrays.stream(annoAttrs.getStringArray("basePackages")).filter(StringUtils::hasText)
.collect(Collectors.toList()));
basePackages.addAll(Arrays.stream(annoAttrs.getClassArray("basePackageClasses")).map(ClassUtils::getPackageName)
.collect(Collectors.toList()));
if (basePackages.isEmpty()) {basePackages.add(getDefaultBasePackage(annoMeta));
}
String lazyInitialization = annoAttrs.getString("lazyInitialization");
if (StringUtils.hasText(lazyInitialization)) {builder.addPropertyValue("lazyInitialization", lazyInitialization);
}
// 在 builder 中设置 basePackage 属性
builder.addPropertyValue("basePackage", StringUtils.collectionToCommaDelimitedString(basePackages));
// 向容器中注册了一个 MapperScannerConfigurer 的 bean。registry.registerBeanDefinition(beanName, builder.getBeanDefinition());
}通过下面的代码逻辑咱们可知，MapperScannerRegistrar 向容器中注册了一个 MapperScannerConfigurer 的 bean。而该类实现了 BeanDefinitionRegistryPostProcessor 接口，查看其 postProcessBeanDefinitionRegistry 办法，在该办法中实现了对 basePackages 包下的 dao 接口文件的解析包装成 bean。
**3.**
public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) {if (this.processPropertyPlaceHolders) {processPropertyPlaceHolders();
}
// 创立了一个 ClassPathMapperScanner 用于解析 mapper.xml 文件，上面是一些属性设置。ClassPathMapperScanner scanner = new ClassPathMapperScanner(registry);
scanner.setAddToConfig(this.addToConfig);
scanner.setAnnotationClass(this.annotationClass);
scanner.setMarkerInterface(this.markerInterface);
scanner.setSqlSessionFactory(this.sqlSessionFactory);
scanner.setSqlSessionTemplate(this.sqlSessionTemplate);
scanner.setSqlSessionFactoryBeanName(this.sqlSessionFactoryBeanName);
scanner.setSqlSessionTemplateBeanName(this.sqlSessionTemplateBeanName);
scanner.setResourceLoader(this.applicationContext);
scanner.setBeanNameGenerator(this.nameGenerator);
scanner.setMapperFactoryBeanClass(this.mapperFactoryBeanClass);
if (StringUtils.hasText(lazyInitialization)) {scanner.setLazyInitialization(Boolean.valueOf(lazyInitialization));
}
// scanner 外面设置过滤器，增加默认的 includeFilters 和 excludeFilters
scanner.registerFilters();
// 这里是真正的解析 mapper.xml 文件，生成各个 MapperedStatement 对象保留至 Configuration 中。scanner.scan(StringUtils.tokenizeToStringArray(this.basePackage, ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS));
}
跟进 scanner 的 scan 办法到 ClassPathMapperScanner 的 doScan 办法：
**4.**
public Set<BeanDefinitionHolder> doScan(String... basePackages) {
// 调用父类的 doScan 办法，父类是 spring 的类，和 mybatis 没有关系，返回的是一个类型为 BeanDefinition 的 set。Set<BeanDefinitionHolder> beanDefinitions = super.doScan(basePackages);
if (beanDefinitions.isEmpty()) {LOGGER.warn(() -> "No MyBatis mapper was found in'" + Arrays.toString(basePackages)
+ "'package. Please check your configuration.");
} else {
// 这里为 beanDefinition 设置属性相干的信息。（**5.**）processBeanDefinitions(beanDefinitions);
}
return beanDefinitions;
}**5.**
private void processBeanDefinitions(Set<BeanDefinitionHolder> beanDefinitions) {
GenericBeanDefinition definition;
for (BeanDefinitionHolder holder : beanDefinitions) {definition = (GenericBeanDefinition) holder.getBeanDefinition();
String beanClassName = definition.getBeanClassName();
LOGGER.debug(() -> "Creating MapperFactoryBean with name'" + holder.getBeanName() + "'and'" + beanClassName
+ "'mapperInterface");
definition.getConstructorArgumentValues().addGenericArgumentValue(beanClassName);
// 这里设置 beanClass 为 MapperFactoryBean，之后实例化调用的是这个类的结构器。这个很要害 -。-
definition.setBeanClass(this.mapperFactoryBeanClass);
definition.getPropertyValues().add("addToConfig", this.addToConfig);
boolean explicitFactoryUsed = false;
if (StringUtils.hasText(this.sqlSessionFactoryBeanName)) {definition.getPropertyValues().add("sqlSessionFactory",
new RuntimeBeanReference(this.sqlSessionFactoryBeanName));
explicitFactoryUsed = true;
} else if (this.sqlSessionFactory != null) {definition.getPropertyValues().add("sqlSessionFactory", this.sqlSessionFactory);
explicitFactoryUsed = true;
}
if (StringUtils.hasText(this.sqlSessionTemplateBeanName)) {if (explicitFactoryUsed) {
LOGGER.warn(() -> "Cannot use both: sqlSessionTemplate and sqlSessionFactory together. sqlSessionFactory is ignored.");
}
definition.getPropertyValues().add("sqlSessionTemplate",
new RuntimeBeanReference(this.sqlSessionTemplateBeanName));
explicitFactoryUsed = true;
} else if (this.sqlSessionTemplate != null) {if (explicitFactoryUsed) {
LOGGER.warn(() -> "Cannot use both: sqlSessionTemplate and sqlSessionFactory together. sqlSessionFactory is ignored.");
}
definition.getPropertyValues().add("sqlSessionTemplate", this.sqlSessionTemplate);
explicitFactoryUsed = true;
}
if (!explicitFactoryUsed) {LOGGER.debug(() -> "Enabling autowire by type for MapperFactoryBean with name'" + holder.getBeanName() + "'.");
definition.setAutowireMode(AbstractBeanDefinition.AUTOWIRE_BY_TYPE);
}
definition.setLazyInit(lazyInitialization);
}
}
到这里的 beanDefinition 的创立及属性设置根本结束，接下来是 bean 的创立。spring bean 实例化之后，调用 populateBean 办法设置属性，其中有个 autowireByType 办法 对属性从新获取，并通过 setter 办法，将 sqlSessionTemplate 作为属性注入。而这个 sqlSessionTemplate 蕴含了 mapper.xml 文件的解析后果，前期须要执行的 sql 都在这里。接下来咱们须要晓得这个 sqlSessionTemplate bean 是如何被创立的。
咱们查看 mybatis 的主动配置类 MybatisAutoConfiguration 其的两个办法：sqlSessionFactory 和 sqlSessionTemplate 别离向容器中注入了 sqlSessionFactory 和 SqlSessionTemplate 的 bean。提供了咱们自定义的 dao 中这两个属性的注入。咱们先看 sqlSessionFactory 办法，SqlSessionTemplate 办法只不过是将 sqlSessionFactory 作为参数传入并 new 了一个 SqlSessionTemplate 的 bean。
**6.**
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()));
}
// 这里其实是新建了一个 Configuration 对象，前面的代码都是一些属性的设置。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())) {
// 设置 mapper.xml 文件的地位。factory.setMapperLocations(this.properties.resolveMapperLocations());
}
Set<String> factoryPropertyNames = Stream
.of(new BeanWrapperImpl(SqlSessionFactoryBean.class).getPropertyDescriptors()).map(PropertyDescriptor::getName)
.collect(Collectors.toSet());
Class<? extends LanguageDriver> defaultLanguageDriver = this.properties.getDefaultScriptingLanguageDriver();
if (factoryPropertyNames.contains("scriptingLanguageDrivers") && !ObjectUtils.isEmpty(this.languageDrivers)) {
// Need to mybatis-spring 2.0.2+
factory.setScriptingLanguageDrivers(this.languageDrivers);
if (defaultLanguageDriver == null && this.languageDrivers.length == 1) {defaultLanguageDriver = this.languageDrivers[0].getClass();}
}
if (factoryPropertyNames.contains("defaultScriptingLanguageDriver")) {
// Need to mybatis-spring 2.0.2+
factory.setDefaultScriptingLanguageDriver(defaultLanguageDriver);
}
// 要害办法，进入：**7**
return factory.getObject();}咱们跟进步骤 6 中的 factory.getObject() 办法会进入到 SqlSessionFactory 的 buildSqlSessionFactory 办法：
**7.**
protected SqlSessionFactory buildSqlSessionFactory() throws Exception {
final Configuration targetConfiguration;
// 后面的操作都是一些属性的设置
XMLConfigBuilder xmlConfigBuilder = null;
if (this.configuration != null) {
targetConfiguration = this.configuration;
if (targetConfiguration.getVariables() == null) {targetConfiguration.setVariables(this.configurationProperties);
} else if (this.configurationProperties != null) {targetConfiguration.getVariables().putAll(this.configurationProperties);
}
} else if (this.configLocation != null) {xmlConfigBuilder = new XMLConfigBuilder(this.configLocation.getInputStream(), null, this.configurationProperties);
targetConfiguration = xmlConfigBuilder.getConfiguration();} else {
LOGGER.debug(() -> "Property'configuration'or'configLocation'not specified, using default MyBatis Configuration");
targetConfiguration = new Configuration();
Optional.ofNullable(this.configurationProperties).ifPresent(targetConfiguration::setVariables);
}
Optional.ofNullable(this.objectFactory).ifPresent(targetConfiguration::setObjectFactory);
Optional.ofNullable(this.objectWrapperFactory).ifPresent(targetConfiguration::setObjectWrapperFactory);
Optional.ofNullable(this.vfs).ifPresent(targetConfiguration::setVfsImpl);
if (hasLength(this.typeAliasesPackage)) {scanClasses(this.typeAliasesPackage, this.typeAliasesSuperType).stream()
.filter(clazz -> !clazz.isAnonymousClass()).filter(clazz -> !clazz.isInterface())
.filter(clazz -> !clazz.isMemberClass()).forEach(targetConfiguration.getTypeAliasRegistry()::registerAlias);
}
if (!isEmpty(this.typeAliases)) {Stream.of(this.typeAliases).forEach(typeAlias -> {targetConfiguration.getTypeAliasRegistry().registerAlias(typeAlias);
LOGGER.debug(() -> "Registered type alias:'" + typeAlias + "'");
});
}
if (!isEmpty(this.plugins)) {Stream.of(this.plugins).forEach(plugin -> {targetConfiguration.addInterceptor(plugin);
LOGGER.debug(() -> "Registered plugin:'" + plugin + "'");
});
}
if (hasLength(this.typeHandlersPackage)) {scanClasses(this.typeHandlersPackage, TypeHandler.class).stream().filter(clazz -> !clazz.isAnonymousClass())
.filter(clazz -> !clazz.isInterface()).filter(clazz -> !Modifier.isAbstract(clazz.getModifiers()))
.forEach(targetConfiguration.getTypeHandlerRegistry()::register);
}
if (!isEmpty(this.typeHandlers)) {Stream.of(this.typeHandlers).forEach(typeHandler -> {targetConfiguration.getTypeHandlerRegistry().register(typeHandler);
LOGGER.debug(() -> "Registered type handler:'" + typeHandler + "'");
});
}
targetConfiguration.setDefaultEnumTypeHandler(defaultEnumTypeHandler);
if (!isEmpty(this.scriptingLanguageDrivers)) {Stream.of(this.scriptingLanguageDrivers).forEach(languageDriver -> {targetConfiguration.getLanguageRegistry().register(languageDriver);
LOGGER.debug(() -> "Registered scripting language driver:'" + languageDriver + "'");
});
}
Optional.ofNullable(this.defaultScriptingLanguageDriver)
.ifPresent(targetConfiguration::setDefaultScriptingLanguage);
if (this.databaseIdProvider != null) {// fix #64 set databaseId before parse mapper xmls
try {targetConfiguration.setDatabaseId(this.databaseIdProvider.getDatabaseId(this.dataSource));
} catch (SQLException e) {throw new NestedIOException("Failed getting a databaseId", e);
}
}
Optional.ofNullable(this.cache).ifPresent(targetConfiguration::addCache);
if (xmlConfigBuilder != null) {
try {xmlConfigBuilder.parse();
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();}
}
targetConfiguration.setEnvironment(new Environment(this.environment,
this.transactionFactory == null ? new SpringManagedTransactionFactory() : this.transactionFactory,
this.dataSource));
if (this.mapperLocations != null) {if (this.mapperLocations.length == 0) {LOGGER.warn(() -> "Property'mapperLocations'was specified but matching resources are not found.");
} else {
// 从这里开始解析 mapper.xml 文件
for (Resource mapperLocation : this.mapperLocations) {if (mapperLocation == null) {continue;}
try {XMLMapperBuilder xmlMapperBuilder = new XMLMapperBuilder(mapperLocation.getInputStream(),
targetConfiguration, mapperLocation.toString(), targetConfiguration.getSqlFragments());
// XMLMapperBuilder 解析，跟进之 **8.**
xmlMapperBuilder.parse();} catch (Exception e) {throw new NestedIOException("Failed to parse mapping resource:'" + mapperLocation + "'", e);
} finally {ErrorContext.instance().reset();}
LOGGER.debug(() -> "Parsed mapper file:'" + mapperLocation + "'");
}
}
} else {LOGGER.debug(() -> "Property'mapperLocations'was not specified.");
}
return this.sqlSessionFactoryBuilder.build(targetConfiguration);
}咱们持续跟进 XMLMapperBuilder 的 parse 办法：
**8.**
public void parse() {if (!configuration.isResourceLoaded(resource)) {
// 从 mapper 文件的根节点开始解析（**9.**）configurationElement(parser.evalNode("/mapper"));
configuration.addLoadedResource(resource);
bindMapperForNamespace();}
parsePendingResultMaps();
parsePendingCacheRefs();
parsePendingStatements();}查看 configurationElement 办法：
**9.**
private void configurationElement(XNode context) {
try {String namespace = context.getStringAttribute("namespace");
if (namespace == null || namespace.equals("")) {throw new BuilderException("Mapper's namespace cannot be empty");
}
// 此处开始依据 xml 的各个节点解析，并将后果存储到 Configuration 对象中，ResultMap 节点解析并存储在 resultMaps 中，增删改查的 sql 封装成一个个 MappedStatement 对象中。builderAssistant.setCurrentNamespace(namespace);
cacheRefElement(context.evalNode("cache-ref"));
cacheElement(context.evalNode("cache"));
parameterMapElement(context.evalNodes("/mapper/parameterMap"));
resultMapElements(context.evalNodes("/mapper/resultMap"));
sqlElement(context.evalNodes("/mapper/sql"));
buildStatementFromContext(context.evalNodes("select|insert|update|delete"));
} catch (Exception e) {throw new BuilderException("Error parsing Mapper XML. The XML location is'" + resource + "'. Cause:" + e, e); 测
}
}到此为止，mybatis 对于配置文件的解析，封装 sql 的工作根本做好了，接下来的工作是如何调用。
当咱们调用咱们写好的 dao 上的业务办法时，最里面的一层是 jdk 的动静代理，接着往里面一层是 mybaits 的 MapperProxy 代理。查看 MapperProxy 的 invoke 办法：
**10.**
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
try {if (Object.class.equals(method.getDeclaringClass())) {return method.invoke(this, args);
} else if (method.isDefault()) {if (privateLookupInMethod == null) {return invokeDefaultMethodJava8(proxy, method, args);
} else {return invokeDefaultMethodJava9(proxy, method, args);
}
}
} catch (Throwable t) {throw ExceptionUtil.unwrapThrowable(t);
}
// 下面的办法略过，间接看上面的 execute 办法，这里的 MapperMethod 做了一层缓存
final MapperMethod mapperMethod = cachedMapperMethod(method);
// 正真执行 sql。跟进 MapperMethod 的 execute 办法（**11.**）return mapperMethod.execute(sqlSession, args);
}**11.**
public Object execute(SqlSession sqlSession, Object[] args) {
Object result;
// 判断 sql 的类型，增删改查。switch (command.getType()) {
case INSERT: {Object param = method.convertArgsToSqlCommandParam(args);
result = rowCountResult(sqlSession.insert(command.getName(), param));
break;
}
case UPDATE: {Object param = method.convertArgsToSqlCommandParam(args);
result = rowCountResult(sqlSession.update(command.getName(), param));
break;
}
case DELETE: {Object param = method.convertArgsToSqlCommandParam(args);
result = rowCountResult(sqlSession.delete(command.getName(), param));
break;
}
case SELECT:
if (method.returnsVoid() && method.hasResultHandler()) {executeWithResultHandler(sqlSession, args);
result = null;
} else if (method.returnsMany()) {result = executeForMany(sqlSession, args);
} else if (method.returnsMap()) {result = executeForMap(sqlSession, args);
} else if (method.returnsCursor()) {result = executeForCursor(sqlSession, args);
} else {Object param = method.convertArgsToSqlCommandParam(args);
result = sqlSession.selectOne(command.getName(), param);
if (method.returnsOptional()
&& (result == null || !method.getReturnType().equals(result.getClass()))) {result = Optional.ofNullable(result);
}
}
break;
case FLUSH:
result = sqlSession.flushStatements();
break;
default:
throw new BindingException("Unknown execution method for:" + command.getName());
}
if (result == null && method.getReturnType().isPrimitive() && !method.returnsVoid()) {throw new BindingException("Mapper method'" + command.getName()
+ "attempted to return null from a method with a primitive return type (" + method.getReturnType() + ").");
}
return result;
}步骤 11 中依据 sql 的类型来判断执行什么流程，以下以 insert 为例：
**12.**
public int insert(String statement, Object parameter) {
**11.** 中的 sqlSession 为 SqlSessionTemplate，这里的 qlSessionProxy 又是一层代理，代理了 DefaultSqlSession 的 update 办法。return this.sqlSessionProxy.insert(statement, parameter);
}**13.**
public int update(String statement, Object parameter) {
try {
dirty = true;
// 从 Configuration 对象中获取 MappedStatement 对象。MappedStatement ms = configuration.getMappedStatement(statement);
// sql 的是 executor。return executor.update(ms, wrapCollection(parameter));
} catch (Exception e) {throw ExceptionFactory.wrapException("Error updating database. Cause:" + e, e);
} finally {ErrorContext.instance().reset();}
}持续跟进进入到了 SimpleExecutor 的 doUpdate 办法：
**14.**
public int doUpdate(MappedStatement ms, Object parameter) throws SQLException {
Statement stmt = null;
try {Configuration configuration = ms.getConfiguration();
StatementHandler handler = configuration.newStatementHandler(this, ms, parameter, RowBounds.DEFAULT, null, null);
// 连贯数据库创立 prepareStatement，并应用 handler 为 sql 设置参数。stmt = prepareStatement(handler, ms.getStatementLog());
// 执行封装好的 sql。return handler.update(stmt);
} finally {closeStatement(stmt);
}
}在 SimpleExecutor 中，对于增删改的操作执行的是 doUpdate 办法，而查问走的是 doQuery 办法。
**15.**
public <E> List<E> doQuery(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) throws SQLException {
Statement stmt = null;
try {Configuration configuration = ms.getConfiguration();
StatementHandler handler = configuration.newStatementHandler(wrapper, ms, parameter, rowBounds, resultHandler, boundSql);
stmt = prepareStatement(handler, ms.getStatementLog());
// 这里的 resultHandler 对数据库查问后果做了封装，封装成 resultMap 对应的 java 类型，再看下 handler.query 办法（**16.**）return handler.query(stmt, resultHandler);
} finally {closeStatement(stmt);
}
}handler.query 会进入到 PreparedStatementHandler 的 query 办法里：
**16.**
public <E> List<E> query(Statement statement, ResultHandler resultHandler) throws SQLException {
// preparedStatement 的执行，该逻辑属于 jdbc，不属于 mybatis 的领域。PreparedStatement ps = (PreparedStatement) statement;
ps.execute();
// resultHandler 对查问的后果进行封装成咱们想要的 java 类型。return resultSetHandler.handleResultSets(ps);
} 小结
次要从两个方面讲述了 springboot-mybatis 的基本功能：MapperScan 应用 @Import 在容器中注册了一个 MapperScannerRegistrar，实现了对 basePackages 的接口文件的解析，并替换掉 bean 的类型为 MapperFactoryBean。而 MybatisAutoConfiguration 则创立了 SqlSessionFactory 的 bean，创立过程中实现了对 mapper.xml 文件的解析，并寄存于 SqlSessionFactory 的 Confuguration 属性当中。而在自定义 dao 的 bean 实例化之后，通过属性注入，将 SqlSessionFactory 注入到各个 dao 的 bean 中。在 dao 办法的执行中，jdk 代理的是 MapperProxy，理论通过执行 MapperMethod 办法。sql 语句的执行由 Executor 执行，在获取数据的的 preparedStatment 之后，通过 ParameterHandler 对预编译语句参数设置。ResultHandler 对数据查问后果封装成咱们须要的 java 类型。