public class AutoConstructorTest {private static SqlSessionFactory sqlSessionFactory;@BeforeClasspublic static void setUp() throws Exception {// create a SqlSessionFactorytry (Reader reader = Resources.getResourceAsReader("org/apache/ibatis/autoconstructor/mybatis-config.xml")) {sqlSessionFactory = new SqlSessionFactoryBuilder().build(reader);}// populate in-memory database
    BaseDataTest.runScript(sqlSessionFactory.getConfiguration().getEnvironment().getDataSource(),"org/apache/ibatis/autoconstructor/CreateDB.sql");}@Testpublic void fullyPopulatedSubject() {try (SqlSession sqlSession = sqlSessionFactory.openSession()) {final AutoConstructorMapper mapper = sqlSession.getMapper(AutoConstructorMapper.class);final Object subject = mapper.getSubject(1);assertNotNull(subject);}}@Test(expected = PersistenceException.class)public void primitiveSubjects() {try (SqlSession sqlSession = sqlSessionFactory.openSession()) {final AutoConstructorMapper mapper = sqlSession.getMapper(AutoConstructorMapper.class);mapper.getSubjects();}}@Testpublic void annotatedSubject() {try (SqlSession sqlSession = sqlSessionFactory.openSession()) {final AutoConstructorMapper mapper = sqlSession.getMapper(AutoConstructorMapper.class);verifySubjects(mapper.getAnnotatedSubjects());}}@Test(expected = PersistenceException.class)public void badSubject() {try (SqlSession sqlSession = sqlSessionFactory.openSession()) {final AutoConstructorMapper mapper = sqlSession.getMapper(AutoConstructorMapper.class);mapper.getBadSubjects();}}@Testpublic void extensiveSubject() {try (SqlSession sqlSession = sqlSessionFactory.openSession()) {final AutoConstructorMapper mapper = sqlSession.getMapper(AutoConstructorMapper.class);verifySubjects(mapper.getExtensiveSubject());}}private void verifySubjects(final List<?> subjects) {assertNotNull(subjects);Assertions.assertThat(subjects.size()).isEqualTo(3);}
}

SELECT * FROM subject WHERE id = #{id}

   try (Reader reader = Resources.getResourceAsReader("org/apache/ibatis/autoconstructor/mybatis-config.xml")) {sqlSessionFactory = new SqlSessionFactoryBuilder().build(reader);}// SqlSessionFactoryBuilder.build(reader) -> XMLConfigBuilder.parse()
// org.apache.ibatis.session.SqlSessionFactoryBuilderpublic SqlSessionFactory build(Reader reader) {return build(reader, null, null);}// 建立factorypublic SqlSessionFactory build(Reader reader, String environment, Properties properties) {try {XMLConfigBuilder parser = new XMLConfigBuilder(reader, environment, properties);return build(parser.parse());} catch (Exception e) {throw ExceptionFactory.wrapException("Error building SqlSession.", e);} finally {// 加载完成后，上下文管理器重置
      ErrorContext.instance().reset();try {reader.close();} catch (IOException e) {// Intentionally ignore. Prefer previous error.
      }}}

/*** Offline entity resolver for the MyBatis DTDs* * @author Clinton Begin* @author Eduardo Macarron*/
public class XMLMapperEntityResolver implements EntityResolver {private static final String IBATIS_CONFIG_SYSTEM = "ibatis-3-config.dtd";private static final String IBATIS_MAPPER_SYSTEM = "ibatis-3-mapper.dtd";private static final String MYBATIS_CONFIG_SYSTEM = "mybatis-3-config.dtd";private static final String MYBATIS_MAPPER_SYSTEM = "mybatis-3-mapper.dtd";private static final String MYBATIS_CONFIG_DTD = "org/apache/ibatis/builder/xml/mybatis-3-config.dtd";private static final String MYBATIS_MAPPER_DTD = "org/apache/ibatis/builder/xml/mybatis-3-mapper.dtd";/*** Converts a public DTD into a local one* * @param publicId The public id that is what comes after "PUBLIC"* @param systemId The system id that is what comes after the public id.* @return The InputSource for the DTD* * @throws org.xml.sax.SAXException If anything goes wrong*/@Overridepublic InputSource resolveEntity(String publicId, String systemId) throws SAXException {try {if (systemId != null) {String lowerCaseSystemId = systemId.toLowerCase(Locale.ENGLISH);if (lowerCaseSystemId.contains(MYBATIS_CONFIG_SYSTEM) || lowerCaseSystemId.contains(IBATIS_CONFIG_SYSTEM)) {return getInputSource(MYBATIS_CONFIG_DTD, publicId, systemId);} else if (lowerCaseSystemId.contains(MYBATIS_MAPPER_SYSTEM) || lowerCaseSystemId.contains(IBATIS_MAPPER_SYSTEM)) {return getInputSource(MYBATIS_MAPPER_DTD, publicId, systemId);}}return null;} catch (Exception e) {throw new SAXException(e.toString());}}private InputSource getInputSource(String path, String publicId, String systemId) {InputSource source = null;if (path != null) {try {InputStream in = Resources.getResourceAsStream(path);source = new InputSource(in);source.setPublicId(publicId);source.setSystemId(systemId);        } catch (IOException e) {// ignore, null is ok
      }}return source;}}

// org.apache.ibatis.parsing.XPathParser.XPathParser(), 设备一些必要参数public XPathParser(Reader reader, boolean validation, Properties variables, EntityResolver entityResolver) {commonConstructor(validation, variables, entityResolver);this.document = createDocument(new InputSource(reader));}private Document createDocument(InputSource inputSource) {// important: this must only be called AFTER common constructortry {DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();factory.setValidating(validation);factory.setNamespaceAware(false);factory.setIgnoringComments(true);factory.setIgnoringElementContentWhitespace(false);factory.setCoalescing(false);factory.setExpandEntityReferences(true);DocumentBuilder builder = factory.newDocumentBuilder();builder.setEntityResolver(entityResolver);builder.setErrorHandler(new ErrorHandler() {@Overridepublic void error(SAXParseException exception) throws SAXException {throw exception;}@Overridepublic void fatalError(SAXParseException exception) throws SAXException {throw exception;}@Overridepublic void warning(SAXParseException exception) throws SAXException {}});return builder.parse(inputSource);} catch (Exception e) {throw new BuilderException("Error creating document instance.  Cause: " + e, e);}}

// 在返回fatory的时候调用 return build(parser.parse());  将 config.xml 的配置全部解析到 configuration 实例中
// org.apache.ibatis.builder.xml.XMLConfigBuilder.parse()public Configuration parse() {if (parsed) {throw new BuilderException("Each XMLConfigBuilder can only be used once.");}parsed = true;// 根元素为 /configuration, 依次向下解析parseConfiguration(parser.evalNode("/configuration"));return configuration;}// org.apache.ibatis.parsing.XPathParser.evalNode() 映射 xml 属性到 bean public XNode evalNode(Object root, String expression) {Node node = (Node) evaluate(expression, root, XPathConstants.NODE);if (node == null) {return null;}return new XNode(this, node, variables);}private Object evaluate(String expression, Object root, QName returnType) {try {return xpath.evaluate(expression, root, returnType);} catch (Exception e) {throw new BuilderException("Error evaluating XPath.  Cause: " + e, e);}}

  // 解析各配置参数到实例中private void parseConfiguration(XNode root) {try {//issue #117 read properties firstpropertiesElement(root.evalNode("properties"));Properties settings = settingsAsProperties(root.evalNode("settings"));// 这个配置没有用过吧
      loadCustomVfs(settings);// 解析别名设置typeAliasesElement(root.evalNode("typeAliases"));pluginElement(root.evalNode("plugins"));objectFactoryElement(root.evalNode("objectFactory"));objectWrapperFactoryElement(root.evalNode("objectWrapperFactory"));reflectorFactoryElement(root.evalNode("reflectorFactory"));settingsElement(settings);// read it after objectFactory and objectWrapperFactory issue #631environmentsElement(root.evalNode("environments"));databaseIdProviderElement(root.evalNode("databaseIdProvider"));typeHandlerElement(root.evalNode("typeHandlers"));// 重要节点，解析 mappermapperElement(root.evalNode("mappers"));} catch (Exception e) {throw new BuilderException("Error parsing SQL Mapper Configuration. Cause: " + e, e);}}

  // propertiesElement(root.evalNode("properties"));  url, resource 解析private void propertiesElement(XNode context) throws Exception {if (context != null) {Properties defaults = context.getChildrenAsProperties();String resource = context.getStringAttribute("resource");String url = context.getStringAttribute("url");if (resource != null && url != null) {throw new BuilderException("The properties element cannot specify both a URL and a resource based property file reference.  Please specify one or the other.");}if (resource != null) {defaults.putAll(Resources.getResourceAsProperties(resource));} else if (url != null) {defaults.putAll(Resources.getUrlAsProperties(url));}Properties vars = configuration.getVariables();if (vars != null) {defaults.putAll(vars);}// 解析完成后，放到 parser 和 configuration 实例中
      parser.setVariables(defaults);configuration.setVariables(defaults);}}

  // Properties settings = settingsAsProperties(root.evalNode("settings"));private Properties settingsAsProperties(XNode context) {if (context == null) {return new Properties();}Properties props = context.getChildrenAsProperties();// Check that all settings are known to the configuration classMetaClass metaConfig = MetaClass.forClass(Configuration.class, localReflectorFactory);for (Object key : props.keySet()) {if (!metaConfig.hasSetter(String.valueOf(key))) {throw new BuilderException("The setting " + key + " is not known.  Make sure you spelled it correctly (case sensitive).");}}return props;}// loadCustomVfs(settings);  这个...private void loadCustomVfs(Properties props) throws ClassNotFoundException {String value = props.getProperty("vfsImpl");if (value != null) {String[] clazzes = value.split(",");for (String clazz : clazzes) {if (!clazz.isEmpty()) {@SuppressWarnings("unchecked")Class<? extends VFS> vfsImpl = (Class<? extends VFS>)Resources.classForName(clazz);configuration.setVfsImpl(vfsImpl);}}}}

  // typeAliasesElement(root.evalNode("typeAliases"));private void typeAliasesElement(XNode parent) {if (parent != null) {for (XNode child : parent.getChildren()) {if ("package".equals(child.getName())) {// 针对package配置，需注册一系列别名，以 simpleName 代替String typeAliasPackage = child.getStringAttribute("name");configuration.getTypeAliasRegistry().registerAliases(typeAliasPackage);} else {String alias = child.getStringAttribute("alias");String type = child.getStringAttribute("type");try {Class<?> clazz = Resources.classForName(type);if (alias == null) {typeAliasRegistry.registerAlias(clazz);} else {typeAliasRegistry.registerAlias(alias, clazz);}} catch (ClassNotFoundException e) {throw new BuilderException("Error registering typeAlias for '" + alias + "'. Cause: " + e, e);}}}}}// org.apache.ibatis.type.TypeAliasRegistry.registerAlias(), 具体数据结构为 map 封装public void registerAlias(Class<?> type) {String alias = type.getSimpleName();Alias aliasAnnotation = type.getAnnotation(Alias.class);if (aliasAnnotation != null) {alias = aliasAnnotation.value();} registerAlias(alias, type);}public void registerAlias(String alias, Class<?> value) {if (alias == null) {throw new TypeException("The parameter alias cannot be null");}// issue #748String key = alias.toLowerCase(Locale.ENGLISH);if (TYPE_ALIASES.containsKey(key) && TYPE_ALIASES.get(key) != null && !TYPE_ALIASES.get(key).equals(value)) {throw new TypeException("The alias '" + alias + "' is already mapped to the value '" + TYPE_ALIASES.get(key).getName() + "'.");}TYPE_ALIASES.put(key, value);}

  // pluginElement(root.evalNode("plugins"));private void pluginElement(XNode parent) throws Exception {if (parent != null) {for (XNode child : parent.getChildren()) {String interceptor = child.getStringAttribute("interceptor");Properties properties = child.getChildrenAsProperties();// 先创建一个plugin实例，备用Interceptor interceptorInstance = (Interceptor) resolveClass(interceptor).newInstance();// 配置属性的注入，回调
        interceptorInstance.setProperties(properties);// 添加到 configuration
        configuration.addInterceptor(interceptorInstance);}}}
public class InterceptorChain {private final List<Interceptor> interceptors = new ArrayList<>();public Object pluginAll(Object target) {for (Interceptor interceptor : interceptors) {target = interceptor.plugin(target);}return target;}public void addInterceptor(Interceptor interceptor) {interceptors.add(interceptor);}public List<Interceptor> getInterceptors() {return Collections.unmodifiableList(interceptors);}}

  // objectFactoryElement(root.evalNode("objectFactory"));private void objectFactoryElement(XNode context) throws Exception {if (context != null) {String type = context.getStringAttribute("type");Properties properties = context.getChildrenAsProperties();ObjectFactory factory = (ObjectFactory) resolveClass(type).newInstance();factory.setProperties(properties);configuration.setObjectFactory(factory);}}// objectWrapperFactoryElement(root.evalNode("objectWrapperFactory")); 没什么特别private void objectWrapperFactoryElement(XNode context) throws Exception {if (context != null) {String type = context.getStringAttribute("type");ObjectWrapperFactory factory = (ObjectWrapperFactory) resolveClass(type).newInstance();configuration.setObjectWrapperFactory(factory);}}

  // reflectorFactoryElement(root.evalNode("reflectorFactory"));private void reflectorFactoryElement(XNode context) throws Exception {if (context != null) {String type = context.getStringAttribute("type");ReflectorFactory factory = (ReflectorFactory) resolveClass(type).newInstance();configuration.setReflectorFactory(factory);}}

  // settingsElement(settings);  设置各种开关, 如缓存private void settingsElement(Properties props) throws Exception {configuration.setAutoMappingBehavior(AutoMappingBehavior.valueOf(props.getProperty("autoMappingBehavior", "PARTIAL")));configuration.setAutoMappingUnknownColumnBehavior(AutoMappingUnknownColumnBehavior.valueOf(props.getProperty("autoMappingUnknownColumnBehavior", "NONE")));configuration.setCacheEnabled(booleanValueOf(props.getProperty("cacheEnabled"), true));configuration.setProxyFactory((ProxyFactory) createInstance(props.getProperty("proxyFactory")));configuration.setLazyLoadingEnabled(booleanValueOf(props.getProperty("lazyLoadingEnabled"), false));configuration.setAggressiveLazyLoading(booleanValueOf(props.getProperty("aggressiveLazyLoading"), false));configuration.setMultipleResultSetsEnabled(booleanValueOf(props.getProperty("multipleResultSetsEnabled"), true));configuration.setUseColumnLabel(booleanValueOf(props.getProperty("useColumnLabel"), true));configuration.setUseGeneratedKeys(booleanValueOf(props.getProperty("useGeneratedKeys"), false));configuration.setDefaultExecutorType(ExecutorType.valueOf(props.getProperty("defaultExecutorType", "SIMPLE")));configuration.setDefaultStatementTimeout(integerValueOf(props.getProperty("defaultStatementTimeout"), null));configuration.setDefaultFetchSize(integerValueOf(props.getProperty("defaultFetchSize"), null));configuration.setMapUnderscoreToCamelCase(booleanValueOf(props.getProperty("mapUnderscoreToCamelCase"), false));configuration.setSafeRowBoundsEnabled(booleanValueOf(props.getProperty("safeRowBoundsEnabled"), false));configuration.setLocalCacheScope(LocalCacheScope.valueOf(props.getProperty("localCacheScope", "SESSION")));configuration.setJdbcTypeForNull(JdbcType.valueOf(props.getProperty("jdbcTypeForNull", "OTHER")));configuration.setLazyLoadTriggerMethods(stringSetValueOf(props.getProperty("lazyLoadTriggerMethods"), "equals,clone,hashCode,toString"));configuration.setSafeResultHandlerEnabled(booleanValueOf(props.getProperty("safeResultHandlerEnabled"), true));configuration.setDefaultScriptingLanguage(resolveClass(props.getProperty("defaultScriptingLanguage")));@SuppressWarnings("unchecked")Class<? extends TypeHandler> typeHandler = (Class<? extends TypeHandler>)resolveClass(props.getProperty("defaultEnumTypeHandler"));configuration.setDefaultEnumTypeHandler(typeHandler);configuration.setCallSettersOnNulls(booleanValueOf(props.getProperty("callSettersOnNulls"), false));configuration.setUseActualParamName(booleanValueOf(props.getProperty("useActualParamName"), true));configuration.setReturnInstanceForEmptyRow(booleanValueOf(props.getProperty("returnInstanceForEmptyRow"), false));configuration.setLogPrefix(props.getProperty("logPrefix"));@SuppressWarnings("unchecked")Class<? extends Log> logImpl = (Class<? extends Log>)resolveClass(props.getProperty("logImpl"));configuration.setLogImpl(logImpl);configuration.setConfigurationFactory(resolveClass(props.getProperty("configurationFactory")));}

  // environmentsElement(root.evalNode("environments")); 环境配置private void environmentsElement(XNode context) throws Exception {if (context != null) {if (environment == null) {// 默认为 developmentenvironment = context.getStringAttribute("default");}for (XNode child : context.getChildren()) {String id = child.getStringAttribute("id");// 查找当前环境配置，指定加载if (isSpecifiedEnvironment(id)) {// 事务管理、数据源TransactionFactory txFactory = transactionManagerElement(child.evalNode("transactionManager"));DataSourceFactory dsFactory = dataSourceElement(child.evalNode("dataSource"));DataSource dataSource = dsFactory.getDataSource();Environment.Builder environmentBuilder = new Environment.Builder(id).transactionFactory(txFactory).dataSource(dataSource);configuration.setEnvironment(environmentBuilder.build());}}}}// 环境配置包含， id, 事务管理, 数据源public Environment build() {return new Environment(this.id, this.transactionFactory, this.dataSource);}

  // databaseIdProviderElement(root.evalNode("databaseIdProvider")); private void databaseIdProviderElement(XNode context) throws Exception {DatabaseIdProvider databaseIdProvider = null;if (context != null) {String type = context.getStringAttribute("type");// awful patch to keep backward compatibilityif ("VENDOR".equals(type)) {type = "DB_VENDOR";}Properties properties = context.getChildrenAsProperties();databaseIdProvider = (DatabaseIdProvider) resolveClass(type).newInstance();databaseIdProvider.setProperties(properties);}Environment environment = configuration.getEnvironment();if (environment != null && databaseIdProvider != null) {String databaseId = databaseIdProvider.getDatabaseId(environment.getDataSource());configuration.setDatabaseId(databaseId);}}

  // typeHandlerElement(root.evalNode("typeHandlers")); 自定义 typeHandlerprivate void typeHandlerElement(XNode parent) throws Exception {if (parent != null) {for (XNode child : parent.getChildren()) {if ("package".equals(child.getName())) {String typeHandlerPackage = child.getStringAttribute("name");typeHandlerRegistry.register(typeHandlerPackage);} else {String javaTypeName = child.getStringAttribute("javaType");String jdbcTypeName = child.getStringAttribute("jdbcType");String handlerTypeName = child.getStringAttribute("handler");Class<?> javaTypeClass = resolveClass(javaTypeName);JdbcType jdbcType = resolveJdbcType(jdbcTypeName);Class<?> typeHandlerClass = resolveClass(handlerTypeName);if (javaTypeClass != null) {if (jdbcType == null) {typeHandlerRegistry.register(javaTypeClass, typeHandlerClass);} else {typeHandlerRegistry.register(javaTypeClass, jdbcType, typeHandlerClass);}} else {typeHandlerRegistry.register(typeHandlerClass);}}}}}// org.apache.ibatis.type.TypeHandlerRegistry.register(), 以map保存映射private void register(Type javaType, JdbcType jdbcType, TypeHandler<?> handler) {if (javaType != null) {Map<JdbcType, TypeHandler<?>> map = TYPE_HANDLER_MAP.get(javaType);if (map == null || map == NULL_TYPE_HANDLER_MAP) {map = new HashMap<>();TYPE_HANDLER_MAP.put(javaType, map);}map.put(jdbcType, handler);}ALL_TYPE_HANDLERS_MAP.put(handler.getClass(), handler);}

  // mapperElement(root.evalNode("mappers"));private void mapperElement(XNode parent) throws Exception {if (parent != null) {for (XNode child : parent.getChildren()) {if ("package".equals(child.getName())) {String mapperPackage = child.getStringAttribute("name");configuration.addMappers(mapperPackage);} else {String resource = child.getStringAttribute("resource");String url = child.getStringAttribute("url");String mapperClass = child.getStringAttribute("class");if (resource != null && url == null && mapperClass == null) {ErrorContext.instance().resource(resource);InputStream inputStream = Resources.getResourceAsStream(resource);XMLMapperBuilder mapperParser = new XMLMapperBuilder(inputStream, configuration, resource, configuration.getSqlFragments());mapperParser.parse();} else if (resource == null && url != null && mapperClass == null) {ErrorContext.instance().resource(url);InputStream inputStream = Resources.getUrlAsStream(url);XMLMapperBuilder mapperParser = new XMLMapperBuilder(inputStream, configuration, url, configuration.getSqlFragments());mapperParser.parse();} else if (resource == null && url == null && mapperClass != null) {Class<?> mapperInterface = Resources.classForName(mapperClass);configuration.addMapper(mapperInterface);} else {throw new BuilderException("A mapper element may only specify a url, resource or class, but not more than one.");}}}}}

  // org.apache.ibatis.builder.xml.XMLMapperBuilder.parse() mapper解析细节public void parse() {// 只解析一次 namespaceif (!configuration.isResourceLoaded(resource)) {configurationElement(parser.evalNode("/mapper"));configuration.addLoadedResource(resource);bindMapperForNamespace();}// 解析 resultMaps
    parsePendingResultMaps();parsePendingCacheRefs();parsePendingStatements();}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");}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);}}private void parsePendingResultMaps() {Collection<ResultMapResolver> incompleteResultMaps = configuration.getIncompleteResultMaps();synchronized (incompleteResultMaps) {Iterator<ResultMapResolver> iter = incompleteResultMaps.iterator();while (iter.hasNext()) {try {iter.next().resolve();iter.remove();} catch (IncompleteElementException e) {// ResultMap is still missing a resource...
        }}}}private void parsePendingCacheRefs() {Collection<CacheRefResolver> incompleteCacheRefs = configuration.getIncompleteCacheRefs();synchronized (incompleteCacheRefs) {Iterator<CacheRefResolver> iter = incompleteCacheRefs.iterator();while (iter.hasNext()) {try {iter.next().resolveCacheRef();iter.remove();} catch (IncompleteElementException e) {// Cache ref is still missing a resource...
        }}}}private void parsePendingStatements() {Collection<XMLStatementBuilder> incompleteStatements = configuration.getIncompleteStatements();synchronized (incompleteStatements) {Iterator<XMLStatementBuilder> iter = incompleteStatements.iterator();while (iter.hasNext()) {try {iter.next().parseStatementNode();iter.remove();} catch (IncompleteElementException e) {// Statement is still missing a resource...
        }}}}

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  public SqlSessionFactory build(Configuration config) {return new DefaultSqlSessionFactory(config);}

  public void fullyPopulatedSubject() {// 打开一个连接，使用完成后关闭try (SqlSession sqlSession = sqlSessionFactory.openSession()) {final AutoConstructorMapper mapper = sqlSession.getMapper(AutoConstructorMapper.class);final Object subject = mapper.getSubject(1);assertNotNull(subject);}}

// org.apache.ibatis.session.defaults.SqlSession.openSession(); 打开一个数据库连接
@Overridepublic SqlSession openSession() {return openSessionFromDataSource(configuration.getDefaultExecutorType(), null, false);}private SqlSession openSessionFromDataSource(ExecutorType execType, TransactionIsolationLevel level, boolean autoCommit) {Transaction tx = null;try {// 运行环境获取final Environment environment = configuration.getEnvironment();// 事务管理工厂获取final TransactionFactory transactionFactory = getTransactionFactoryFromEnvironment(environment);// 创建新事务tx = transactionFactory.newTransaction(environment.getDataSource(), level, autoCommit);// new Executorfinal Executor executor = configuration.newExecutor(tx, execType);// 最后返回 DefaultSqlSession 使用return new DefaultSqlSession(configuration, executor, autoCommit);} catch (Exception e) {closeTransaction(tx); // may have fetched a connection so lets call close()throw ExceptionFactory.wrapException("Error opening session.  Cause: " + e, e);} finally {// 关闭上下文监控
      ErrorContext.instance().reset();}}

  // org.apache.ibatis.session.Configuration.newExecutor()public Executor newExecutor(Transaction transaction, ExecutorType executorType) {executorType = executorType == null ? defaultExecutorType : executorType;executorType = executorType == null ? ExecutorType.SIMPLE : executorType;Executor executor;// 根据不同请求类型创建不同的 executorif (ExecutorType.BATCH == executorType) {executor = new BatchExecutor(this, transaction);} else if (ExecutorType.REUSE == executorType) {executor = new ReuseExecutor(this, transaction);} else {// 默认为 SIMPLEexecutor = new SimpleExecutor(this, transaction);}if (cacheEnabled) {// 创建缓存管理，将缓存请求委托给 executor 处理executor = new CachingExecutor(executor);}// 处理plugin 请求executor = (Executor) interceptorChain.pluginAll(executor);return executor;}// org.apache.ibatis.executor.CachingExecutorpublic CachingExecutor(Executor delegate) {this.delegate = delegate;delegate.setExecutorWrapper(this);}// 最后将加载好的各种配置和实际处理，由 DefaultSqlSession 包装好后返回public DefaultSqlSession(Configuration configuration, Executor executor, boolean autoCommit) {this.configuration = configuration;this.executor = executor;this.dirty = false;this.autoCommit = autoCommit;}

  // org.apache.ibatis.session.defaults.DefaultSqlSession.getMapper()
  @Overridepublic <T> T getMapper(Class<T> type) {return configuration.<T>getMapper(type, this);}// org.apache.ibatis.binding.MapperRegistry.getMapper()@SuppressWarnings("unchecked")public <T> T getMapper(Class<T> type, SqlSession sqlSession) {// 获取 MapperProxyFactoryfinal MapperProxyFactory<T> mapperProxyFactory = (MapperProxyFactory<T>) knownMappers.get(type);if (mapperProxyFactory == null) {throw new BindingException("Type " + type + " is not known to the MapperRegistry.");}try {// 创建 mapper 实例 return mapperProxyFactory.newInstance(sqlSession);} catch (Exception e) {throw new BindingException("Error getting mapper instance. Cause: " + e, e);}}// org.apache.ibatis.binding.newInstance(); public T newInstance(SqlSession sqlSession) {final MapperProxy<T> mapperProxy = new MapperProxy<>(sqlSession, mapperInterface, methodCache);return newInstance(mapperProxy);}

  //mapper.getSubject(1); 查询数据
  @Overridepublic Object invoke(Object proxy, Method method, Object[] args) throws Throwable {try {if (Object.class.equals(method.getDeclaringClass())) {return method.invoke(this, args);} else if (isDefaultMethod(method)) {return invokeDefaultMethod(proxy, method, args);}} catch (Throwable t) {throw ExceptionUtil.unwrapThrowable(t);}// 加载缓存包装方法final MapperMethod mapperMethod = cachedMapperMethod(method);// 执行查询return mapperMethod.execute(sqlSession, args);}private MapperMethod cachedMapperMethod(Method method) {return methodCache.computeIfAbsent(method, k -> new MapperMethod(mapperInterface, method, sqlSession.getConfiguration()));}// org.apache.ibatis.binding.MapperMethod.execute(sqlSession, args); 针对不同类型语句，做不同调用public Object execute(SqlSession sqlSession, Object[] args) {Object result;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 {// 转换参数Object param = method.convertArgsToSqlCommandParam(args);// 执行单条查询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;}

  // org.apache.ibatis.reflection.ParamNameResolver.getNamedParams() 返回参数，如果是单个参数，直接返回参数值//  如果是多个参数，则以 map 形式返回public Object getNamedParams(Object[] args) {final int paramCount = names.size();if (args == null || paramCount == 0) {return null;} else if (!hasParamAnnotation && paramCount == 1) {return args[names.firstKey()];} else {final Map<String, Object> param = new ParamMap<>();int i = 0;for (Map.Entry<Integer, String> entry : names.entrySet()) {param.put(entry.getValue(), args[entry.getKey()]);// add generic param names (param1, param2, ...)final String genericParamName = GENERIC_NAME_PREFIX + String.valueOf(i + 1);// ensure not to overwrite parameter named with @Paramif (!names.containsValue(genericParamName)) {param.put(genericParamName, args[entry.getKey()]);}i++;}return param;}}

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  // org.apache.ibatis.session.defaults.DefaultSqlSession.selectOne(command.getName(), param);
  @Overridepublic <T> T selectOne(String statement, Object parameter) {// Popular vote was to return null on 0 results and throw exception on too many.// 查询单条记录时，默认也是先查询list,然后取第一条List<T> list = this.<T>selectList(statement, parameter);if (list.size() == 1) {return list.get(0);} else if (list.size() > 1) {throw new TooManyResultsException("Expected one result (or null) to be returned by selectOne(), but found: " + list.size());} else {return null;}}// 查询列表
  @Overridepublic <E> List<E> selectList(String statement, Object parameter, RowBounds rowBounds) {try {// 先获取执行语句，此处 statement 为 idMappedStatement 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();}}// org.apache.ibatis.session.Configuration.getMappedStatement(id), 获取初始化解析出来的语句public MappedStatement getMappedStatement(String id) {return this.getMappedStatement(id, true);}public MappedStatement getMappedStatement(String id, boolean validateIncompleteStatements) {if (validateIncompleteStatements) {buildAllStatements();}return mappedStatements.get(id);}

  // executor.query(ms, wrapCollection(parameter), rowBounds, Executor.NO_RESULT_HANDLER);// org.apache.ibatis.executor.CachingExecutor.query()
  @Overridepublic <E> List<E> query(MappedStatement ms, Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler) throws SQLException {// 获取sqlBoundSql boundSql = ms.getBoundSql(parameterObject);CacheKey key = createCacheKey(ms, parameterObject, rowBounds, boundSql);return query(ms, parameterObject, rowBounds, resultHandler, key, boundSql);}// org.apache.ibatis.mapping.MappedStatement.getBoundSql()public BoundSql getBoundSql(Object parameterObject) {BoundSql boundSql = sqlSource.getBoundSql(parameterObject);// 字段映射List<ParameterMapping> parameterMappings = boundSql.getParameterMappings();if (parameterMappings == null || parameterMappings.isEmpty()) {boundSql = new BoundSql(configuration, boundSql.getSql(), parameterMap.getParameterMappings(), parameterObject);}// check for nested result maps in parameter mappings (issue #30)for (ParameterMapping pm : boundSql.getParameterMappings()) {String rmId = pm.getResultMapId();if (rmId != null) {ResultMap rm = configuration.getResultMap(rmId);if (rm != null) {hasNestedResultMaps |= rm.hasNestedResultMaps();}}}return boundSql;}// CacheKey key = createCacheKey(ms, parameterObject, rowBounds, boundSql);// return query(ms, parameterObject, rowBounds, resultHandler, key, boundSql);// org.apache.ibatis.executor.CachingExecutor.query()
  @Overridepublic <E> List<E> query(MappedStatement ms, Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler, CacheKey key, BoundSql boundSql)throws SQLException {Cache cache = ms.getCache();if (cache != null) {flushCacheIfRequired(ms);if (ms.isUseCache() && resultHandler == null) {ensureNoOutParams(ms, boundSql);@SuppressWarnings("unchecked")List<E> list = (List<E>) tcm.getObject(cache, key);if (list == null) {list = delegate.<E> query(ms, parameterObject, rowBounds, resultHandler, key, boundSql);tcm.putObject(cache, key, list); // issue #578 and #116
        }return list;}}return delegate.<E> query(ms, parameterObject, rowBounds, resultHandler, key, boundSql);}

  // org.apache.ibatis.executor.SimpleExecutor.query() / BaseExecutor@SuppressWarnings("unchecked")@Overridepublic <E> List<E> query(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, CacheKey key, BoundSql boundSql) throws SQLException {ErrorContext.instance().resource(ms.getResource()).activity("executing a query").object(ms.getId());if (closed) {throw new ExecutorException("Executor was closed.");}// 缓存刷新if (queryStack == 0 && ms.isFlushCacheRequired()) {clearLocalCache();}List<E> list;try {queryStack++;list = resultHandler == null ? (List<E>) localCache.getObject(key) : null;if (list != null) {handleLocallyCachedOutputParameters(ms, key, parameter, boundSql);} else {// 没有缓存，走dblist = queryFromDatabase(ms, parameter, rowBounds, resultHandler, key, boundSql);}} finally {queryStack--;}if (queryStack == 0) {for (DeferredLoad deferredLoad : deferredLoads) {deferredLoad.load();}// issue #601
      deferredLoads.clear();if (configuration.getLocalCacheScope() == LocalCacheScope.STATEMENT) {// issue #482
        clearLocalCache();}}return list;}// BaseExecutorprivate <E> List<E> queryFromDatabase(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, CacheKey key, BoundSql boundSql) throws SQLException {List<E> list;// 缓存占位符
    localCache.putObject(key, EXECUTION_PLACEHOLDER);try {list = doQuery(ms, parameter, rowBounds, resultHandler, boundSql);} finally {// 防止异常情况，保证将占位缓存删除
      localCache.removeObject(key);}// 操作完成后，重新放入缓存
    localCache.putObject(key, list);if (ms.getStatementType() == StatementType.CALLABLE) {localOutputParameterCache.putObject(key, parameter);}return list;}

  @Overridepublic <E> List<E> doQuery(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) throws SQLException {Statement stmt = null;try {// 获取全局配置Configuration configuration = ms.getConfiguration();// 获取statement, 处理 JDBC 接口StatementHandler handler = configuration.newStatementHandler(wrapper, ms, parameter, rowBounds, resultHandler, boundSql);stmt = prepareStatement(handler, ms.getStatementLog());return handler.<E>query(stmt, resultHandler);} finally {closeStatement(stmt);}}// org.apache.ibatis.session.Configuration.newStatementHandler(), 兼顾 plugins, public StatementHandler newStatementHandler(Executor executor, MappedStatement mappedStatement, Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) {StatementHandler statementHandler = new RoutingStatementHandler(executor, mappedStatement, parameterObject, rowBounds, resultHandler, boundSql);statementHandler = (StatementHandler) interceptorChain.pluginAll(statementHandler);return statementHandler;}

  // 为不同处理类型，建立不同的 handlerpublic RoutingStatementHandler(Executor executor, MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) {switch (ms.getStatementType()) {case STATEMENT:delegate = new SimpleStatementHandler(executor, ms, parameter, rowBounds, resultHandler, boundSql);break;case PREPARED:delegate = new PreparedStatementHandler(executor, ms, parameter, rowBounds, resultHandler, boundSql);break;case CALLABLE:delegate = new CallableStatementHandler(executor, ms, parameter, rowBounds, resultHandler, boundSql);break;default:throw new ExecutorException("Unknown statement type: " + ms.getStatementType());}}//stmt = prepareStatement(handler, ms.getStatementLog());// org.apache.ibatis.executor.SimpleExecutor.prepareStatement(), 获取 statement, JDBCprivate Statement prepareStatement(StatementHandler handler, Log statementLog) throws SQLException {Statement stmt;Connection connection = getConnection(statementLog);// sql录入stmt = handler.prepare(connection, transaction.getTimeout());// 参数绑定
    handler.parameterize(stmt);return stmt;}// BaseExecutorprotected Connection getConnection(Log statementLog) throws SQLException {Connection connection = transaction.getConnection();if (statementLog.isDebugEnabled()) {return ConnectionLogger.newInstance(connection, statementLog, queryStack);} else {return connection;}}// org.apache.ibatis.transaction.jdbc.JdbcTransaction.getConnection()
  @Overridepublic Connection getConnection() throws SQLException {if (connection == null) {// 为空时新建 connection
      openConnection();}return connection;}protected void openConnection() throws SQLException {if (log.isDebugEnabled()) {log.debug("Opening JDBC Connection");}connection = dataSource.getConnection();if (level != null) {connection.setTransactionIsolation(level.getLevel());}setDesiredAutoCommit(autoCommit);}// org.apache.ibatis.datasource.unpooled.getConnection()
  @Overridepublic Connection getConnection() throws SQLException {return doGetConnection(username, password);}private Connection doGetConnection(String username, String password) throws SQLException {Properties props = new Properties();if (driverProperties != null) {props.putAll(driverProperties);}if (username != null) {props.setProperty("user", username);}if (password != null) {props.setProperty("password", password);}return doGetConnection(props);}private Connection doGetConnection(Properties properties) throws SQLException {// 如果没有初始化驱动，初始化
    initializeDriver();// Connection connection = DriverManager.getConnection(url, properties);configureConnection(connection);return connection;}private synchronized void initializeDriver() throws SQLException {if (!registeredDrivers.containsKey(driver)) {Class<?> driverType;try {// 加载驱动if (driverClassLoader != null) {driverType = Class.forName(driver, true, driverClassLoader);} else {driverType = Resources.classForName(driver);}// DriverManager requires the driver to be loaded via the system ClassLoader.// http://www.kfu.com/~nsayer/Java/dyn-jdbc.htmlDriver driverInstance = (Driver)driverType.newInstance();DriverManager.registerDriver(new DriverProxy(driverInstance));registeredDrivers.put(driver, driverInstance);} catch (Exception e) {throw new SQLException("Error setting driver on UnpooledDataSource. Cause: " + e);}}}private void configureConnection(Connection conn) throws SQLException {if (autoCommit != null && autoCommit != conn.getAutoCommit()) {conn.setAutoCommit(autoCommit);}if (defaultTransactionIsolationLevel != null) {conn.setTransactionIsolation(defaultTransactionIsolationLevel);}}// stmt = handler.prepare(connection, transaction.getTimeout()); 组装sql
// org.apache.ibatis.executor.statement.RoutingStatementHandler.prepare()
  @Overridepublic Statement prepare(Connection connection, Integer transactionTimeout) throws SQLException {return delegate.prepare(connection, transactionTimeout);}// org.apache.ibatis.executor.statement.PreparedStatementHandler.
  @Overridepublic Statement prepare(Connection connection, Integer transactionTimeout) throws SQLException {ErrorContext.instance().sql(boundSql.getSql());Statement statement = null;try {// select * from tab where id = ?statement = instantiateStatement(connection);// 设置超时
      setStatementTimeout(statement, transactionTimeout);// 设置查询大小，默认不限制
      setFetchSize(statement);return statement;} catch (SQLException e) {closeStatement(statement);throw e;} catch (Exception e) {closeStatement(statement);throw new ExecutorException("Error preparing statement.  Cause: " + e, e);}}// 调用jdbc connection.prepareStatement(sql), 初始化语句
  @Overrideprotected Statement instantiateStatement(Connection connection) throws SQLException {String sql = boundSql.getSql();if (mappedStatement.getKeyGenerator() instanceof Jdbc3KeyGenerator) {String[] keyColumnNames = mappedStatement.getKeyColumns();if (keyColumnNames == null) {return connection.prepareStatement(sql, PreparedStatement.RETURN_GENERATED_KEYS);} else {return connection.prepareStatement(sql, keyColumnNames);}} else if (mappedStatement.getResultSetType() == ResultSetType.DEFAULT) {return connection.prepareStatement(sql);} else {return connection.prepareStatement(sql, mappedStatement.getResultSetType().getValue(), ResultSet.CONCUR_READ_ONLY);}}// PreparedStatementHandler handler.parameterize(stmt);
  @Overridepublic void parameterize(Statement statement) throws SQLException {parameterHandler.setParameters((PreparedStatement) statement);}// org.apache.ibatis.scripting.defaults.DefaultParameterHandler.setParameters()
  @Overridepublic void setParameters(PreparedStatement ps) {ErrorContext.instance().activity("setting parameters").object(mappedStatement.getParameterMap().getId());List<ParameterMapping> parameterMappings = boundSql.getParameterMappings();if (parameterMappings != null) {for (int i = 0; i < parameterMappings.size(); i++) {ParameterMapping parameterMapping = parameterMappings.get(i);if (parameterMapping.getMode() != ParameterMode.OUT) {Object value;String propertyName = parameterMapping.getProperty();if (boundSql.hasAdditionalParameter(propertyName)) { // issue #448 ask first for additional paramsvalue = boundSql.getAdditionalParameter(propertyName);} else if (parameterObject == null) {value = null;} else if (typeHandlerRegistry.hasTypeHandler(parameterObject.getClass())) {value = parameterObject;} else {MetaObject metaObject = configuration.newMetaObject(parameterObject);value = metaObject.getValue(propertyName);}// TypeHandler 处理参数类型TypeHandler typeHandler = parameterMapping.getTypeHandler();JdbcType jdbcType = parameterMapping.getJdbcType();if (value == null && jdbcType == null) {jdbcType = configuration.getJdbcTypeForNull();}try {typeHandler.setParameter(ps, i + 1, value, jdbcType);} catch (TypeException e) {throw new TypeException("Could not set parameters for mapping: " + parameterMapping + ". Cause: " + e, e);} catch (SQLException e) {throw new TypeException("Could not set parameters for mapping: " + parameterMapping + ". Cause: " + e, e);}}}}}// return handler.<E>query(stmt, resultHandler);// org.apache.ibatis.executor.statement.RoutingStatementHandler.query()
  @Overridepublic <E> List<E> query(Statement statement, ResultHandler resultHandler) throws SQLException {return delegate.<E>query(statement, resultHandler);}// PreparedStatementHandler.query()
  @Overridepublic <E> List<E> query(Statement statement, ResultHandler resultHandler) throws SQLException {PreparedStatement ps = (PreparedStatement) statement;// 调用驱动程序执行 execute
    ps.execute();// 处理结果集映射return resultSetHandler.<E> handleResultSets(ps);}// org.apache.ibatis.executor.resultset.DefaultResultSetHandler.handleResultSets(), 处理结果集映射
  @Overridepublic List<Object> handleResultSets(Statement stmt) throws SQLException {ErrorContext.instance().activity("handling results").object(mappedStatement.getId());final List<Object> multipleResults = new ArrayList<>();int resultSetCount = 0;// 获取第一个结果集（开始偏移的地方）ResultSetWrapper rsw = getFirstResultSet(stmt);List<ResultMap> resultMaps = mappedStatement.getResultMaps();int resultMapCount = resultMaps.size();validateResultMapsCount(rsw, resultMapCount);while (rsw != null && resultMapCount > resultSetCount) {ResultMap resultMap = resultMaps.get(resultSetCount);handleResultSet(rsw, resultMap, multipleResults, null);rsw = getNextResultSet(stmt);cleanUpAfterHandlingResultSet();resultSetCount++;}String[] resultSets = mappedStatement.getResultSets();if (resultSets != null) {while (rsw != null && resultSetCount < resultSets.length) {ResultMapping parentMapping = nextResultMaps.get(resultSets[resultSetCount]);if (parentMapping != null) {String nestedResultMapId = parentMapping.getNestedResultMapId();ResultMap resultMap = configuration.getResultMap(nestedResultMapId);handleResultSet(rsw, resultMap, null, parentMapping);}rsw = getNextResultSet(stmt);cleanUpAfterHandlingResultSet();resultSetCount++;}}return collapseSingleResultList(multipleResults);}// org.apache.ibatis.executor.resultset.ResultSetWrapper, 根据第一行返回数据集，初始化字段名及字段类型public ResultSetWrapper(ResultSet rs, Configuration configuration) throws SQLException {super();this.typeHandlerRegistry = configuration.getTypeHandlerRegistry();this.resultSet = rs;final ResultSetMetaData metaData = rs.getMetaData();final int columnCount = metaData.getColumnCount();for (int i = 1; i <= columnCount; i++) {columnNames.add(configuration.isUseColumnLabel() ? metaData.getColumnLabel(i) : metaData.getColumnName(i));// java.sql.Types, 处理返回的类型为具体的java类型映射到 org.apache.ibatis.type.JdbcType
      jdbcTypes.add(JdbcType.forCode(metaData.getColumnType(i)));// java 类型全名
      classNames.add(metaData.getColumnClassName(i));}}

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  // DefaultResultSetHandler.handleResultSet() 处理单条记录映射关系private void handleResultSet(ResultSetWrapper rsw, ResultMap resultMap, List<Object> multipleResults, ResultMapping parentMapping) throws SQLException {try {if (parentMapping != null) {handleRowValues(rsw, resultMap, null, RowBounds.DEFAULT, parentMapping);} else {if (resultHandler == null) {DefaultResultHandler defaultResultHandler = new DefaultResultHandler(objectFactory);handleRowValues(rsw, resultMap, defaultResultHandler, rowBounds, null);multipleResults.add(defaultResultHandler.getResultList());} else {handleRowValues(rsw, resultMap, resultHandler, rowBounds, null);}}} finally {// issue #228 (close resultsets)
      closeResultSet(rsw.getResultSet());}}// handleRowValues(rsw, resultMap, defaultResultHandler, rowBounds, null);public void handleRowValues(ResultSetWrapper rsw, ResultMap resultMap, ResultHandler<?> resultHandler, RowBounds rowBounds, ResultMapping parentMapping) throws SQLException {if (resultMap.hasNestedResultMaps()) {// 嵌套数据的映射
      ensureNoRowBounds();checkResultHandler();handleRowValuesForNestedResultMap(rsw, resultMap, resultHandler, rowBounds, parentMapping);} else {// 简单数据映射
      handleRowValuesForSimpleResultMap(rsw, resultMap, resultHandler, rowBounds, parentMapping);}}// 简单数据映射private void handleRowValuesForSimpleResultMap(ResultSetWrapper rsw, ResultMap resultMap, ResultHandler<?> resultHandler, RowBounds rowBounds, ResultMapping parentMapping)throws SQLException {DefaultResultContext<Object> resultContext = new DefaultResultContext<>();ResultSet resultSet = rsw.getResultSet();// 跳过行偏移，难道不是在数据sql中添加 limit 进行数据筛选的？
    skipRows(resultSet, rowBounds);while (shouldProcessMoreRows(resultContext, rowBounds) && !resultSet.isClosed() && resultSet.next()) {// 1. Discriminated 鉴别器ResultMap discriminatedResultMap = resolveDiscriminatedResultMap(resultSet, resultMap, null);// Object rowValue = getRowValue(rsw, discriminatedResultMap, null);storeObject(resultHandler, resultContext, rowValue, parentMapping, resultSet);}}// 检测超过 limit 后，不再继续获取结果private boolean shouldProcessMoreRows(ResultContext<?> context, RowBounds rowBounds) {return !context.isStopped() && context.getResultCount() < rowBounds.getLimit();}// Discriminatedpublic ResultMap resolveDiscriminatedResultMap(ResultSet rs, ResultMap resultMap, String columnPrefix) throws SQLException {Set<String> pastDiscriminators = new HashSet<>();Discriminator discriminator = resultMap.getDiscriminator();while (discriminator != null) {final Object value = getDiscriminatorValue(rs, discriminator, columnPrefix);final String discriminatedMapId = discriminator.getMapIdFor(String.valueOf(value));if (configuration.hasResultMap(discriminatedMapId)) {resultMap = configuration.getResultMap(discriminatedMapId);Discriminator lastDiscriminator = discriminator;discriminator = resultMap.getDiscriminator();if (discriminator == lastDiscriminator || !pastDiscriminators.add(discriminatedMapId)) {break;}} else {break;}}return resultMap;}// 从结果set中获取值private Object getRowValue(ResultSetWrapper rsw, ResultMap resultMap, String columnPrefix) throws SQLException {final ResultLoaderMap lazyLoader = new ResultLoaderMap();Object rowValue = createResultObject(rsw, resultMap, lazyLoader, columnPrefix);if (rowValue != null && !hasTypeHandlerForResultObject(rsw, resultMap.getType())) {final MetaObject metaObject = configuration.newMetaObject(rowValue);boolean foundValues = this.useConstructorMappings;if (shouldApplyAutomaticMappings(resultMap, false)) {foundValues = applyAutomaticMappings(rsw, resultMap, metaObject, columnPrefix) || foundValues;}foundValues = applyPropertyMappings(rsw, resultMap, metaObject, lazyLoader, columnPrefix) || foundValues;foundValues = lazyLoader.size() > 0 || foundValues;rowValue = foundValues || configuration.isReturnInstanceForEmptyRow() ? rowValue : null;}return rowValue;}// DefaultResultSetHandlerprivate Object createResultObject(ResultSetWrapper rsw, ResultMap resultMap, List<Class<?>> constructorArgTypes, List<Object> constructorArgs, String columnPrefix)throws SQLException {final Class<?> resultType = resultMap.getType();final MetaClass metaType = MetaClass.forClass(resultType, reflectorFactory);final List<ResultMapping> constructorMappings = resultMap.getConstructorResultMappings();if (hasTypeHandlerForResultObject(rsw, resultType)) {return createPrimitiveResultObject(rsw, resultMap, columnPrefix);} else if (!constructorMappings.isEmpty()) {return createParameterizedResultObject(rsw, resultType, constructorMappings, constructorArgTypes, constructorArgs, columnPrefix);} else if (resultType.isInterface() || metaType.hasDefaultConstructor()) {return objectFactory.create(resultType);} else if (shouldApplyAutomaticMappings(resultMap, false)) {return createByConstructorSignature(rsw, resultType, constructorArgTypes, constructorArgs, columnPrefix);}throw new ExecutorException("Do not know how to create an instance of " + resultType);}// 构造器注入方式private Object createByConstructorSignature(ResultSetWrapper rsw, Class<?> resultType, List<Class<?>> constructorArgTypes, List<Object> constructorArgs,String columnPrefix) throws SQLException {final Constructor<?>[] constructors = resultType.getDeclaredConstructors();final Constructor<?> defaultConstructor = findDefaultConstructor(constructors);if (defaultConstructor != null) {return createUsingConstructor(rsw, resultType, constructorArgTypes, constructorArgs, columnPrefix, defaultConstructor);} else {for (Constructor<?> constructor : constructors) {if (allowedConstructorUsingTypeHandlers(constructor, rsw.getJdbcTypes())) {return createUsingConstructor(rsw, resultType, constructorArgTypes, constructorArgs, columnPrefix, constructor);}}}throw new ExecutorException("No constructor found in " + resultType.getName() + " matching " + rsw.getClassNames());}private Object createUsingConstructor(ResultSetWrapper rsw, Class<?> resultType, List<Class<?>> constructorArgTypes, List<Object> constructorArgs, String columnPrefix, Constructor<?> constructor) throws SQLException {boolean foundValues = false;for (int i = 0; i < constructor.getParameterTypes().length; i++) {Class<?> parameterType = constructor.getParameterTypes()[i];String columnName = rsw.getColumnNames().get(i);TypeHandler<?> typeHandler = rsw.getTypeHandler(parameterType, columnName);Object value = typeHandler.getResult(rsw.getResultSet(), prependPrefix(columnName, columnPrefix));constructorArgTypes.add(parameterType);constructorArgs.add(value);foundValues = value != null || foundValues;}// 调用构造方法注入值return foundValues ? objectFactory.create(resultType, constructorArgTypes, constructorArgs) : null;}

  // org.apache.ibatis.reflection.factory.DefaultObjectFactory.create(), 调用构造器返回 bean 实例@SuppressWarnings("unchecked")@Overridepublic <T> T create(Class<T> type, List<Class<?>> constructorArgTypes, List<Object> constructorArgs) {Class<?> classToCreate = resolveInterface(type);// we know types are assignablereturn (T) instantiateClass(classToCreate, constructorArgTypes, constructorArgs);}private  <T> T instantiateClass(Class<T> type, List<Class<?>> constructorArgTypes, List<Object> constructorArgs) {try {Constructor<T> constructor;if (constructorArgTypes == null || constructorArgs == null) {constructor = type.getDeclaredConstructor();try {return constructor.newInstance();} catch (IllegalAccessException e) {if (Reflector.canControlMemberAccessible()) {constructor.setAccessible(true);return constructor.newInstance();} else {throw e;}}}constructor = type.getDeclaredConstructor(constructorArgTypes.toArray(new Class[constructorArgTypes.size()]));try {return constructor.newInstance(constructorArgs.toArray(new Object[constructorArgs.size()]));} catch (IllegalAccessException e) {if (Reflector.canControlMemberAccessible()) {constructor.setAccessible(true);return constructor.newInstance(constructorArgs.toArray(new Object[constructorArgs.size()]));} else {throw e;}}} catch (Exception e) {StringBuilder argTypes = new StringBuilder();if (constructorArgTypes != null && !constructorArgTypes.isEmpty()) {for (Class<?> argType : constructorArgTypes) {argTypes.append(argType.getSimpleName());argTypes.append(",");}argTypes.deleteCharAt(argTypes.length() - 1); // remove trailing ,
      }StringBuilder argValues = new StringBuilder();if (constructorArgs != null && !constructorArgs.isEmpty()) {for (Object argValue : constructorArgs) {argValues.append(String.valueOf(argValue));argValues.append(",");}argValues.deleteCharAt(argValues.length() - 1); // remove trailing ,
      }throw new ReflectionException("Error instantiating " + type + " with invalid types (" + argTypes + ") or values (" + argValues + "). Cause: " + e, e);}}

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  // 保存结果private void storeObject(ResultHandler<?> resultHandler, DefaultResultContext<Object> resultContext, Object rowValue, ResultMapping parentMapping, ResultSet rs) throws SQLException {if (parentMapping != null) {linkToParents(rs, parentMapping, rowValue);} else {callResultHandler(resultHandler, resultContext, rowValue);}}@SuppressWarnings("unchecked" /* because ResultHandler<?> is always ResultHandler<Object>*/)private void callResultHandler(ResultHandler<?> resultHandler, DefaultResultContext<Object> resultContext, Object rowValue) {resultContext.nextResultObject(rowValue);((ResultHandler<Object>) resultHandler).handleResult(resultContext);}// private boolean applyPropertyMappings(ResultSetWrapper rsw, ResultMap resultMap, MetaObject metaObject, ResultLoaderMap lazyLoader, String columnPrefix)throws SQLException {final List<String> mappedColumnNames = rsw.getMappedColumnNames(resultMap, columnPrefix);boolean foundValues = false;final List<ResultMapping> propertyMappings = resultMap.getPropertyResultMappings();for (ResultMapping propertyMapping : propertyMappings) {String column = prependPrefix(propertyMapping.getColumn(), columnPrefix);if (propertyMapping.getNestedResultMapId() != null) {// the user added a column attribute to a nested result map, ignore itcolumn = null;}if (propertyMapping.isCompositeResult()|| (column != null && mappedColumnNames.contains(column.toUpperCase(Locale.ENGLISH)))|| propertyMapping.getResultSet() != null) {Object value = getPropertyMappingValue(rsw.getResultSet(), metaObject, propertyMapping, lazyLoader, columnPrefix);// issue #541 make property optionalfinal String property = propertyMapping.getProperty();if (property == null) {continue;} else if (value == DEFERED) {foundValues = true;continue;}if (value != null) {foundValues = true;}if (value != null || (configuration.isCallSettersOnNulls() && !metaObject.getSetterType(property).isPrimitive())) {// gcode issue #377, call setter on nulls (value is not 'found')
          metaObject.setValue(property, value);}}}return foundValues;}// collapseSingleResultList(multipleResults);  转换多级 list 为1级list@SuppressWarnings("unchecked")private List<Object> collapseSingleResultList(List<Object> multipleResults) {return multipleResults.size() == 1 ? (List<Object>) multipleResults.get(0) : multipleResults;}