<!-- DAO接口所在包名，Spring会自动查找其下的类 -->
<bean class="org.mybatis.spring.mapper.MapperScannerConfigurer"><!--basePackage指定要扫描的包，在此包之下的映射器都会被搜索到。可指定多个包，包与包之间用逗号或分号分隔--><property name="basePackage" value="com.joonwhee.open.mapper"/><property name="sqlSessionFactoryBeanName" value="sqlSessionFactory"/>
</bean><!-- spring和MyBatis完美整合，不需要mybatis的配置映射文件 -->
<bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean"><property name="dataSource" ref="dataSource"/><!-- 自动扫描mapping.xml文件 --><property name="mapperLocations" value="classpath:config/mapper/*.xml"/><property name="configLocation" value="classpath:config/mybatis/mybatis-config.xml"/><!--Entity package --><property name="typeAliasesPackage" value="com.joonwhee.open.po"/>
</bean><!-- dataSource -->
<bean id="dataSource" class="com.alibaba.druid.pool.DruidDataSource" init-method="init" destroy-method="close"><property name="driverClassName" value="${driver}"/><property name="url" value="${url}"/><property name="username" value="${username}"/><property name="password" value="${password}"/>
</bean>

package com.joonwhee.open.mapper;import com.joonwhee.open.po.UserPO;public interface UserPOMapper {UserPO queryByPrimaryKey(Integer id);
}
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd" >
<mapper namespace="com.joonwhee.open.mapper.UserPOMapper" ><resultMap id="BaseResultMap" type="com.joonwhee.open.po.UserPO"><result column="id" property="id" jdbcType="INTEGER" /><result column="name" property="name" jdbcType="VARCHAR" /></resultMap><select id="queryByPrimaryKey" resultMap="BaseResultMap"parameterType="java.lang.Integer">select id, namefrom userwhere id = #{id,jdbcType=INTEGER}</select>
</mapper>

@Override
public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) {if (this.processPropertyPlaceHolders) {processPropertyPlaceHolders();}// 1.新建一个ClassPathMapperScanner，并填充相应属性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)) {// 2.设置mapper bean是否需要懒加载scanner.setLazyInitialization(Boolean.valueOf(lazyInitialization));}// 3.注册Filter，因为上面构造函数我们没有使用默认的Filter，// 有两种Filter，includeFilters：要扫描的；excludeFilters：要排除的scanner.registerFilters();// 4.扫描basePackage，basePackage可通过",; tn"来填写多个，// ClassPathMapperScanner重写了doScan方法scanner.scan(StringUtils.tokenizeToStringArray(this.basePackage, ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS));
}

public void registerFilters() {boolean acceptAllInterfaces = true;// if specified, use the given annotation and / or marker interface// 1.如果指定了注解，则将注解添加到includeFiltersif (this.annotationClass != null) {addIncludeFilter(new AnnotationTypeFilter(this.annotationClass));acceptAllInterfaces = false;}// override AssignableTypeFilter to ignore matches on the actual marker interface// 2.如果指定了标记接口，则将标记接口添加到includeFilters，// 但这边重写了matchClassName方法，并返回了false，// 相当于忽略了标记接口上的匹配项，所以该参数目前相当于没有任何作用if (this.markerInterface != null) {addIncludeFilter(new AssignableTypeFilter(this.markerInterface) {@Overrideprotected boolean matchClassName(String className) {return false;}});acceptAllInterfaces = false;}// 3.如果没有指定annotationClass和markerInterface，则// 添加默认的includeFilters，直接返回true，接受所有类if (acceptAllInterfaces) {// default include filter that accepts all classesaddIncludeFilter((metadataReader, metadataReaderFactory) -> true);}// exclude package-info.java// 4.添加默认的excludeFilters，排除以package-info结尾的类addExcludeFilter((metadataReader, metadataReaderFactory) -> {String className = metadataReader.getClassMetadata().getClassName();return className.endsWith("package-info");});
}

@Override
public Set<BeanDefinitionHolder> doScan(String... basePackages) {// 1.直接使用父类的方法扫描和注册bean定义，// 之前在spring中已经介绍过：Spring IoC源码学习：context:component-scan 节点详解 代码块5Set<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 {// 2.对扫描到的beanDefinitions进行处理，主要4件事：// 1）将bean的真正接口类添加到通用构造函数参数中// 2）将beanClass直接设置为MapperFactoryBean.class，//  结合1，相当于要使用的构造函数是MapperFactoryBean(java.lang.Class<T>)// 3）添加sqlSessionFactory属性，sqlSessionFactoryBeanName和//  sqlSessionFactory中，优先使用sqlSessionFactoryBeanName// 4）添加sqlSessionTemplate属性，同样的，sqlSessionTemplateBeanName//  优先于sqlSessionTemplate，processBeanDefinitions(beanDefinitions);}return beanDefinitions;
}

@Override
public SqlSessionFactory getObject() throws Exception {if (this.sqlSessionFactory == null) {// 如果之前没有构建，则这边也会调用afterPropertiesSet进行构建操作afterPropertiesSet();}return this.sqlSessionFactory;
}@Override
public void afterPropertiesSet() throws Exception {// 省略部分代码// 构建sqlSessionFactorythis.sqlSessionFactory = buildSqlSessionFactory();
}

protected SqlSessionFactory buildSqlSessionFactory() throws Exception {// 省略部分代码// 5.mapper处理（最重要）if (this.mapperLocations != null) {if (this.mapperLocations.length == 0) {LOGGER.warn(() -> "Property 'mapperLocations' was specified but matching resources are not found.");} else {for (Resource mapperLocation : this.mapperLocations) {if (mapperLocation == null) {continue;}try {// 5.1 新建XMLMapperBuilderXMLMapperBuilder xmlMapperBuilder = new XMLMapperBuilder(mapperLocation.getInputStream(),targetConfiguration, mapperLocation.toString(), targetConfiguration.getSqlFragments());// 5.2 解析mapper文件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.");}// 6.使用targetConfiguration构建DefaultSqlSessionFactoryreturn this.sqlSessionFactoryBuilder.build(targetConfiguration);
}

public void parse() {// 1.如果resource没被加载过才进行加载if (!configuration.isResourceLoaded(resource)) {// 1.1 解析mapper文件configurationElement(parser.evalNode("/mapper"));// 1.2 将resource添加到已加载列表configuration.addLoadedResource(resource);// 1.3 绑定namespace的mapperbindMapperForNamespace();}parsePendingResultMaps();parsePendingCacheRefs();parsePendingStatements();
}

private void configurationElement(XNode context) {try {// 1.获取namespace属性String namespace = context.getStringAttribute("namespace");if (namespace == null || namespace.isEmpty()) {throw new BuilderException("Mapper's namespace cannot be empty");}// 2.设置currentNamespace属性builderAssistant.setCurrentNamespace(namespace);// 3.解析parameterMap、resultMap、sql等节点cacheRefElement(context.evalNode("cache-ref"));cacheElement(context.evalNode("cache"));parameterMapElement(context.evalNodes("/mapper/parameterMap"));resultMapElements(context.evalNodes("/mapper/resultMap"));sqlElement(context.evalNodes("/mapper/sql"));// 4.解析增删改查节点，封装成StatementbuildStatementFromContext(context.evalNodes("select|insert|update|delete"));} catch (Exception e) {throw new BuilderException("Error parsing Mapper XML. The XML location is '" + resource + "'. Cause: " + e, e);}
}private void buildStatementFromContext(List<XNode> list) {if (configuration.getDatabaseId() != null) {buildStatementFromContext(list, configuration.getDatabaseId());}// 解析增删改查节点，封装成StatementbuildStatementFromContext(list, null);
}private void buildStatementFromContext(List<XNode> list, String requiredDatabaseId) {for (XNode context : list) {// 1.构建XMLStatementBuilderfinal XMLStatementBuilder statementParser = new XMLStatementBuilder(configuration, builderAssistant, context, requiredDatabaseId);try {// 2.解析节点statementParser.parseStatementNode();} catch (IncompleteElementException e) {configuration.addIncompleteStatement(statementParser);}}
}

<select id="queryByPrimaryKey" resultMap="BaseResultMap"parameterType="java.lang.Integer">select id, name, password, agefrom userwhere id = #{id,jdbcType=INTEGER}
</select>

public void parseStatementNode() {// 省略所有的属性解析// 将解析出来的所有参数添加到 mappedStatements 缓存builderAssistant.addMappedStatement(id, sqlSource, statementType, sqlCommandType,fetchSize, timeout, parameterMap, parameterTypeClass, resultMap, resultTypeClass,resultSetTypeEnum, flushCache, useCache, resultOrdered,keyGenerator, keyProperty, keyColumn, databaseId, langDriver, resultSets);
}// MapperBuilderAssistant.java
public MappedStatement addMappedStatement(String id,SqlSource sqlSource,StatementType statementType,SqlCommandType sqlCommandType,Integer fetchSize,Integer timeout,String parameterMap,Class<?> parameterType,String resultMap,Class<?> resultType,ResultSetType resultSetType,boolean flushCache,boolean useCache,boolean resultOrdered,KeyGenerator keyGenerator,String keyProperty,String keyColumn,String databaseId,LanguageDriver lang,String resultSets) {if (unresolvedCacheRef) {throw new IncompleteElementException("Cache-ref not yet resolved");}// 1.将id填充上namespace，例如：queryByPrimaryKey变成// com.joonwhee.open.mapper.UserPOMapper.queryByPrimaryKeyid = applyCurrentNamespace(id, false);boolean isSelect = sqlCommandType == SqlCommandType.SELECT;// 2.使用参数构建MappedStatement.BuilderMappedStatement.Builder statementBuilder = new MappedStatement.Builder(configuration, id, sqlSource, sqlCommandType).resource(resource).fetchSize(fetchSize).timeout(timeout).statementType(statementType).keyGenerator(keyGenerator).keyProperty(keyProperty).keyColumn(keyColumn).databaseId(databaseId).lang(lang).resultOrdered(resultOrdered).resultSets(resultSets).resultMaps(getStatementResultMaps(resultMap, resultType, id)).resultSetType(resultSetType).flushCacheRequired(valueOrDefault(flushCache, !isSelect)).useCache(valueOrDefault(useCache, isSelect)).cache(currentCache);ParameterMap statementParameterMap = getStatementParameterMap(parameterMap, parameterType, id);if (statementParameterMap != null) {statementBuilder.parameterMap(statementParameterMap);}// 3.使用MappedStatement.Builder构建MappedStatementMappedStatement statement = statementBuilder.build();// 4.将MappedStatement 添加到缓存configuration.addMappedStatement(statement);return statement;
}

private void bindMapperForNamespace() {String namespace = builderAssistant.getCurrentNamespace();if (namespace != null) {Class<?> boundType = null;try {// 1.解析namespace对应的绑定类型boundType = Resources.classForName(namespace);} catch (ClassNotFoundException e) {// ignore, bound type is not required}if (boundType != null && !configuration.hasMapper(boundType)) {// Spring may not know the real resource name so we set a flag// to prevent loading again this resource from the mapper interface// look at MapperAnnotationBuilder#loadXmlResource// 2.boundType不为空，并且configuration还没有添加boundType，// 则将namespace添加到已加载列表，将boundType添加到knownMappers缓存configuration.addLoadedResource("namespace:" + namespace);configuration.addMapper(boundType);}}
}public <T> void addMapper(Class<T> type) {mapperRegistry.addMapper(type);
}public <T> void addMapper(Class<T> type) {if (type.isInterface()) {if (hasMapper(type)) {throw new BindingException("Type " + type + " is already known to the MapperRegistry.");}boolean loadCompleted = false;try {// 将type和以该type为参数构建的MapperProxyFactory作为键值对，// 放到knownMappers缓存中去knownMappers.put(type, new MapperProxyFactory<>(type));// It's important that the type is added before the parser is run// otherwise the binding may automatically be attempted by the// mapper parser. If the type is already known, it won't try.MapperAnnotationBuilder parser = new MapperAnnotationBuilder(config, type);parser.parse();loadCompleted = true;} finally {if (!loadCompleted) {knownMappers.remove(type);}}}
}

@Override
public T getObject() throws Exception {// 1.从父类中拿到sqlSessionTemplate，这边的sqlSessionTemplate也是doScan中添加的属性// 2.通过mapperInterface获取mapperreturn getSqlSession().getMapper(this.mapperInterface);
}// SqlSessionTemplate
@Override
public <T> T getMapper(Class<T> type) {return getConfiguration().getMapper(type, this);
}// Configuration.java
public <T> T getMapper(Class<T> type, SqlSession sqlSession) {return mapperRegistry.getMapper(type, sqlSession);
}// MapperRegistry.java
public <T> T getMapper(Class<T> type, SqlSession sqlSession) {// 1.从knownMappers缓存中获取final MapperProxyFactory<T> mapperProxyFactory = (MapperProxyFactory<T>) knownMappers.get(type);if (mapperProxyFactory == null) {throw new BindingException("Type " + type + " is not known to the MapperRegistry.");}try {// 2.新建实例return mapperProxyFactory.newInstance(sqlSession);} catch (Exception e) {throw new BindingException("Error getting mapper instance. Cause: " + e, e);}
}// MapperProxyFactory.java
public T newInstance(SqlSession sqlSession) {// 1.构造一个MapperProxyfinal MapperProxy<T> mapperProxy = new MapperProxy<>(sqlSession, mapperInterface, methodCache);// 2.使用MapperProxy来构建实例对象return newInstance(mapperProxy);
}protected T newInstance(MapperProxy<T> mapperProxy) {// 使用JDK动态代理来代理要创建的实例对象，InvocationHandler为mapperProxy，// 因此当我们真正调用时，会走到mapperProxy的invoke方法return (T) Proxy.newProxyInstance(mapperInterface.getClassLoader(), new Class[] { mapperInterface }, mapperProxy);
}

@Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {try {if (Object.class.equals(method.getDeclaringClass())) {return method.invoke(this, args);} else {// 1.创建MapperMethodInvoker// 2.将method -> MapperMethodInvoker放到methodCache缓存// 3.调用MapperMethodInvoker的invoke方法return cachedInvoker(method).invoke(proxy, method, args, sqlSession);}} catch (Throwable t) {throw ExceptionUtil.unwrapThrowable(t);}
}// MapperProxy.java
private MapperMethodInvoker cachedInvoker(Method method) throws Throwable {try {// 1.放到methodCache缓存，key为method，value为MapperMethodInvokerreturn methodCache.computeIfAbsent(method, m -> {if (m.isDefault()) {// 2.方法为默认方法，Java8之后，接口允许有默认方法try {if (privateLookupInMethod == null) {return new DefaultMethodInvoker(getMethodHandleJava8(method));} else {return new DefaultMethodInvoker(getMethodHandleJava9(method));}} catch (IllegalAccessException | InstantiationException | InvocationTargetException| NoSuchMethodException e) {throw new RuntimeException(e);}} else {// 3.正常接口会走这边，使用mapperInterface、method、configuration// 构建一个MapperMethod，封装成PlainMethodInvokerreturn new PlainMethodInvoker(new MapperMethod(mapperInterface, method, sqlSession.getConfiguration()));}});} catch (RuntimeException re) {Throwable cause = re.getCause();throw cause == null ? re : cause;}
}

@Override
public Object invoke(Object proxy, Method method, Object[] args, SqlSession sqlSession) throws Throwable {return mapperMethod.execute(sqlSession, args);
}// MapperMethod.java
public Object execute(SqlSession sqlSession, Object[] args) {Object result;// 1.根据命令类型执行来进行相应操作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;
}

// 1.insert
@Override
public int insert(String statement, Object parameter) {return update(statement, parameter);
}// 2.update
@Override
public int update(String statement, Object parameter) {try {dirty = true;// 从mappedStatements缓存拿到对应的MappedStatement对象，执行更新操作MappedStatement ms = configuration.getMappedStatement(statement);return executor.update(ms, wrapCollection(parameter));} catch (Exception e) {throw ExceptionFactory.wrapException("Error updating database.  Cause: " + e, e);} finally {ErrorContext.instance().reset();}
}// 3.delete
@Override
public int delete(String statement, Object parameter) {return update(statement, parameter);
}// 4.select，以executeForMany为例
private <E> Object executeForMany(SqlSession sqlSession, Object[] args) {List<E> result;// 1.参数转换成sql命令参数Object param = method.convertArgsToSqlCommandParam(args);if (method.hasRowBounds()) {RowBounds rowBounds = method.extractRowBounds(args);result = sqlSession.selectList(command.getName(), param, rowBounds);} else {// 2.执行查询操作result = sqlSession.selectList(command.getName(), param);}// 3.处理返回结果// issue #510 Collections & arrays supportif (!method.getReturnType().isAssignableFrom(result.getClass())) {if (method.getReturnType().isArray()) {return convertToArray(result);} else {return convertToDeclaredCollection(sqlSession.getConfiguration(), result);}}return result;
}@Override
public <E> List<E> selectList(String statement, Object parameter) {return this.selectList(statement, parameter, RowBounds.DEFAULT);
}@Override
public <E> List<E> selectList(String statement, Object parameter, RowBounds rowBounds) {try {//从mappedStatements缓存中拿到对应的MappedStatement对象，执行查询操作MappedStatement ms = configuration.getMappedStatement(statement);return executor.query(ms, wrapCollection(parameter), rowBounds, Executor.NO_RESULT_HANDLER);} catch (Exception e) {throw ExceptionFactory.wrapException("Error querying database.  Cause: " + e, e);} finally {ErrorContext.instance().reset();}
}