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本文主要研究一下如果mybatis mapper定义了多个同名方法会不会有问题

MybatisConfiguration

com/baomidou/mybatisplus/core/MybatisConfiguration.java

    /*** MybatisPlus 加载 SQL 顺序：* <p> 1、加载 XML中的 SQL </p>* <p> 2、加载 SqlProvider 中的 SQL </p>* <p> 3、XmlSql 与 SqlProvider不能包含相同的 SQL </p>* <p>调整后的 SQL优先级：XmlSql > sqlProvider > CurdSql </p>*/@Overridepublic void addMappedStatement(MappedStatement ms) {if (mappedStatements.containsKey(ms.getId())) {/** 说明已加载了xml中的节点； 忽略mapper中的 SqlProvider 数据*/logger.error("mapper[" + ms.getId() + "] is ignored, because it exists, maybe from xml file");return;}mappedStatements.put(ms.getId(), ms);}

MybatisSqlSessionFactoryBean

com/baomidou/mybatisplus/extension/spring/MybatisSqlSessionFactoryBean.java

    /*** Build a {@code SqlSessionFactory} instance.* <p>* The default implementation uses the standard MyBatis {@code XMLConfigBuilder} API to build a* {@code SqlSessionFactory} instance based on an Reader. Since 1.3.0, it can be specified a* {@link Configuration} instance directly(without config file).* </p>** @return SqlSessionFactory* @throws IOException if loading the config file failed*/protected SqlSessionFactory buildSqlSessionFactory() throws Exception {//......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 {XMLMapperBuilder xmlMapperBuilder = new XMLMapperBuilder(mapperLocation.getInputStream(),targetConfiguration, mapperLocation.toString(), targetConfiguration.getSqlFragments());xmlMapperBuilder.parse();} catch (Exception e) {throw new IOException("Failed to parse mapping resource: '" + mapperLocation + "'", e);} finally {ErrorContext.instance().reset();}LOGGER.debug(() -> "Parsed mapper file: '" + mapperLocation + "'");}}}}

MybatisSqlSessionFactoryBean的buildSqlSessionFactory方法会根据mapperLocations的配置取加载xml配置，即加载xml的mapper信息

XMLMapperBuilder

org/apache/ibatis/builder/xml/XMLMapperBuilder.java

  public void parse() {if (!configuration.isResourceLoaded(resource)) {configurationElement(parser.evalNode("/mapper"));configuration.addLoadedResource(resource);bindMapperForNamespace();}parsePendingResultMaps();parsePendingCacheRefs();parsePendingStatements();}private void bindMapperForNamespace() {String namespace = builderAssistant.getCurrentNamespace();if (namespace != null) {Class<?> boundType = null;try {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#loadXmlResourceconfiguration.addLoadedResource("namespace:" + namespace);configuration.addMapper(boundType);}}}

XMLMapperBuilder的parse方法会执行configurationElement，即加载xml的mapper方法，之后执行bindMapperForNamespace，加载对应java mapper的方法

MybatisMapperRegistry

com/baomidou/mybatisplus/core/MybatisMapperRegistry.java

    @Overridepublic <T> void addMapper(Class<T> type) {if (type.isInterface()) {if (hasMapper(type)) {// TODO 如果之前注入 直接返回return;// TODO 这里就不抛异常了
//                throw new BindingException("Type " + type + " is already known to the MapperRegistry.");}boolean loadCompleted = false;try {// TODO 这里也换成 MybatisMapperProxyFactory 而不是 MapperProxyFactoryknownMappers.put(type, new MybatisMapperProxyFactory<>(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.// TODO 这里也换成 MybatisMapperAnnotationBuilder 而不是 MapperAnnotationBuilderMybatisMapperAnnotationBuilder parser = new MybatisMapperAnnotationBuilder(config, type);parser.parse();loadCompleted = true;} finally {if (!loadCompleted) {knownMappers.remove(type);}}}}

MybatisMapperRegistry通过MybatisMapperAnnotationBuilder进行parse

MybatisMapperAnnotationBuilder

com/baomidou/mybatisplus/core/MybatisMapperAnnotationBuilder.java

    public void parse() {String resource = type.toString();if (!configuration.isResourceLoaded(resource)) {loadXmlResource();configuration.addLoadedResource(resource);String mapperName = type.getName();assistant.setCurrentNamespace(mapperName);parseCache();parseCacheRef();IgnoreStrategy ignoreStrategy = InterceptorIgnoreHelper.initSqlParserInfoCache(type);for (Method method : type.getMethods()) {if (!canHaveStatement(method)) {continue;}if (getAnnotationWrapper(method, false, Select.class, SelectProvider.class).isPresent()&& method.getAnnotation(ResultMap.class) == null) {parseResultMap(method);}try {// TODO 加入 注解过滤缓存InterceptorIgnoreHelper.initSqlParserInfoCache(ignoreStrategy, mapperName, method);parseStatement(method);} catch (IncompleteElementException e) {// TODO 使用 MybatisMethodResolver 而不是 MethodResolverconfiguration.addIncompleteMethod(new MybatisMethodResolver(this, method));}}// TODO 注入 CURD 动态 SQL , 放在在最后, because 可能会有人会用注解重写sqltry {// https://github.com/baomidou/mybatis-plus/issues/3038if (GlobalConfigUtils.isSupperMapperChildren(configuration, type)) {parserInjector();}} catch (IncompleteElementException e) {configuration.addIncompleteMethod(new InjectorResolver(this));}}parsePendingMethods();}

这里通过反射获取对应java mapper的方法(这里的顺序是先接口本身定义的方法，然后是逐层继承的接口定义的方法)，然后挨个执行parseStatement，接着执行parserInjector来处理内置的通过SqlMethod提供的内置方法

parseStatement

    private static final Set<Class<? extends Annotation>> statementAnnotationTypes = Stream.of(Select.class, Update.class, Insert.class, Delete.class, SelectProvider.class, UpdateProvider.class,InsertProvider.class, DeleteProvider.class).collect(Collectors.toSet());void parseStatement(Method method) {final Class<?> parameterTypeClass = getParameterType(method);final LanguageDriver languageDriver = getLanguageDriver(method);getAnnotationWrapper(method, true, statementAnnotationTypes).ifPresent(statementAnnotation -> {final SqlSource sqlSource = buildSqlSource(statementAnnotation.getAnnotation(), parameterTypeClass, languageDriver, method);final SqlCommandType sqlCommandType = statementAnnotation.getSqlCommandType();final Options options = getAnnotationWrapper(method, false, Options.class).map(x -> (Options) x.getAnnotation()).orElse(null);final String mappedStatementId = type.getName() + StringPool.DOT + method.getName();final KeyGenerator keyGenerator;String keyProperty = null;String keyColumn = null;if (SqlCommandType.INSERT.equals(sqlCommandType) || SqlCommandType.UPDATE.equals(sqlCommandType)) {// first check for SelectKey annotation - that overrides everything elseSelectKey selectKey = getAnnotationWrapper(method, false, SelectKey.class).map(x -> (SelectKey) x.getAnnotation()).orElse(null);if (selectKey != null) {keyGenerator = handleSelectKeyAnnotation(selectKey, mappedStatementId, getParameterType(method), languageDriver);keyProperty = selectKey.keyProperty();} else if (options == null) {keyGenerator = configuration.isUseGeneratedKeys() ? Jdbc3KeyGenerator.INSTANCE : NoKeyGenerator.INSTANCE;} else {keyGenerator = options.useGeneratedKeys() ? Jdbc3KeyGenerator.INSTANCE : NoKeyGenerator.INSTANCE;keyProperty = options.keyProperty();keyColumn = options.keyColumn();}} else {keyGenerator = NoKeyGenerator.INSTANCE;}Integer fetchSize = null;Integer timeout = null;StatementType statementType = StatementType.PREPARED;ResultSetType resultSetType = configuration.getDefaultResultSetType();boolean isSelect = sqlCommandType == SqlCommandType.SELECT;boolean flushCache = !isSelect;boolean useCache = isSelect;if (options != null) {if (FlushCachePolicy.TRUE.equals(options.flushCache())) {flushCache = true;} else if (FlushCachePolicy.FALSE.equals(options.flushCache())) {flushCache = false;}useCache = options.useCache();fetchSize = options.fetchSize() > -1 || options.fetchSize() == Integer.MIN_VALUE ? options.fetchSize() : null; //issue #348timeout = options.timeout() > -1 ? options.timeout() : null;statementType = options.statementType();if (options.resultSetType() != ResultSetType.DEFAULT) {resultSetType = options.resultSetType();}}String resultMapId = null;if (isSelect) {ResultMap resultMapAnnotation = method.getAnnotation(ResultMap.class);if (resultMapAnnotation != null) {resultMapId = String.join(StringPool.COMMA, resultMapAnnotation.value());} else {resultMapId = generateResultMapName(method);}}assistant.addMappedStatement(mappedStatementId,sqlSource,statementType,sqlCommandType,fetchSize,timeout,// ParameterMapIDnull,parameterTypeClass,resultMapId,getReturnType(method),resultSetType,flushCache,useCache,// TODO gcode issue #577false,keyGenerator,keyProperty,keyColumn,statementAnnotation.getDatabaseId(),languageDriver,// ResultSetsoptions != null ? nullOrEmpty(options.resultSets()) : null);});}

parseStatement这里解析带有Select.class, Update.class, Insert.class, Delete.class, SelectProvider.class, UpdateProvider.class, InsertProvider.class, DeleteProvider.class注解的方法，然后通过assistant.addMappedStatement注册到configuration的mappedStatements中，key为statementId(type.getName() + StringPool.DOT + method.getName())

parserInjector

com/baomidou/mybatisplus/core/MybatisMapperAnnotationBuilder.java

    void parserInjector() {GlobalConfigUtils.getSqlInjector(configuration).inspectInject(assistant, type);}

com/baomidou/mybatisplus/core/injector/AbstractSqlInjector.java

    @Overridepublic void inspectInject(MapperBuilderAssistant builderAssistant, Class<?> mapperClass) {Class<?> modelClass = ReflectionKit.getSuperClassGenericType(mapperClass, Mapper.class, 0);if (modelClass != null) {String className = mapperClass.toString();Set<String> mapperRegistryCache = GlobalConfigUtils.getMapperRegistryCache(builderAssistant.getConfiguration());if (!mapperRegistryCache.contains(className)) {TableInfo tableInfo = TableInfoHelper.initTableInfo(builderAssistant, modelClass);List<AbstractMethod> methodList = this.getMethodList(mapperClass, tableInfo);if (CollectionUtils.isNotEmpty(methodList)) {// 循环注入自定义方法methodList.forEach(m -> m.inject(builderAssistant, mapperClass, modelClass, tableInfo));} else {logger.debug(mapperClass.toString() + ", No effective injection method was found.");}mapperRegistryCache.add(className);}}}

com/baomidou/mybatisplus/core/injector/AbstractMethod.java

    public void inject(MapperBuilderAssistant builderAssistant, Class<?> mapperClass, Class<?> modelClass, TableInfo tableInfo) {this.configuration = builderAssistant.getConfiguration();this.builderAssistant = builderAssistant;this.languageDriver = configuration.getDefaultScriptingLanguageInstance();/* 注入自定义方法 */injectMappedStatement(mapperClass, modelClass, tableInfo);}protected MappedStatement addInsertMappedStatement(Class<?> mapperClass, Class<?> parameterType, String id,SqlSource sqlSource, KeyGenerator keyGenerator,String keyProperty, String keyColumn) {return addMappedStatement(mapperClass, id, sqlSource, SqlCommandType.INSERT, parameterType, null,Integer.class, keyGenerator, keyProperty, keyColumn);}protected MappedStatement addMappedStatement(Class<?> mapperClass, String id, SqlSource sqlSource,SqlCommandType sqlCommandType, Class<?> parameterType,String resultMap, Class<?> resultType, KeyGenerator keyGenerator,String keyProperty, String keyColumn) {String statementName = mapperClass.getName() + DOT + id;if (hasMappedStatement(statementName)) {logger.warn(LEFT_SQ_BRACKET + statementName + "] Has been loaded by XML or SqlProvider or Mybatis's Annotation, so ignoring this injection for [" + getClass() + RIGHT_SQ_BRACKET);return null;}/* 缓存逻辑处理 */boolean isSelect = sqlCommandType == SqlCommandType.SELECT;return builderAssistant.addMappedStatement(id, sqlSource, StatementType.PREPARED, sqlCommandType,null, null, null, parameterType, resultMap, resultType,null, !isSelect, isSelect, false, keyGenerator, keyProperty, keyColumn,configuration.getDatabaseId(), languageDriver, null);}

这里会通过statementName(mapperClass.getName() + DOT + id)j检测是否存在，如果不存在则添加

org/apache/ibatis/builder/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");}id = applyCurrentNamespace(id, false);boolean isSelect = sqlCommandType == SqlCommandType.SELECT;MappedStatement.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);}MappedStatement statement = statementBuilder.build();configuration.addMappedStatement(statement);return statement;}public String applyCurrentNamespace(String base, boolean isReference) {if (base == null) {return null;}if (isReference) {// is it qualified with any namespace yet?if (base.contains(".")) {return base;}} else {// is it qualified with this namespace yet?if (base.startsWith(currentNamespace + ".")) {return base;}if (base.contains(".")) {throw new BuilderException("Dots are not allowed in element names, please remove it from " + base);}}return currentNamespace + "." + base;}