首先说明一下, 我是在Springboot中使用的Mybatis所以并没有使用xml配置

这里我整合了一份脑图, 需要的自取思维导图
正好给我赚点积分下载资源

MapperScan

MapperScan这个注解的作用就是将我们的mapper包中的所有mapper接口注册入mybatis,
所以我从这里开始入手全局搜索这个MapperScan

上图中可以看见MapperScannerRegistrar这个类是唯一一个有使用到这个注解类的类, 这个类的作用很明显就是一个Mapper注册连接器
这个类中只有三个方法和一个内部类

  @Overridepublic void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {// 获取了MapperScan注解中的值, 我们上面的mapper包的位置就在这个注解的value中AnnotationAttributes mapperScanAttrs = AnnotationAttributes.fromMap(importingClassMetadata.getAnnotationAttributes(MapperScan.class.getName()));if (mapperScanAttrs != null) {// 解析注解registerBeanDefinitions(mapperScanAttrs, registry);}}

在解析过程中主要是获取mapper
解析方法中的最后一步就是使用了ClassPathMapperScanner的doScan方法扫描

scanner.doScan(StringUtils.toStringArray(basePackages));

  @Overridepublic Set<BeanDefinitionHolder> doScan(String... basePackages) {// 使用的父类的doScan方法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 {// 扫描到的类在这里做进一步的设置processBeanDefinitions(beanDefinitions);}// 返回设置好的mapperreturn beanDefinitions;}

这里是spring的内容, 粗略看一看

	protected Set<BeanDefinitionHolder> doScan(String... basePackages) {Assert.notEmpty(basePackages, "At least one base package must be specified");// 先new一个结果SetSet<BeanDefinitionHolder> beanDefinitions = new LinkedHashSet<>();// 对传入的packages进行遍历for (String basePackage : basePackages) {// findCandidateComponents这个方法就是扫描我们配置的mapper包, 获得class// 里面将com.nit.lab.mapper转换为classpath*:com/nit/lab/mapper/**/*.classSet<BeanDefinition> candidates = findCandidateComponents(basePackage);// 对获取来的class进行遍历for (BeanDefinition candidate : candidates) {ScopeMetadata scopeMetadata = this.scopeMetadataResolver.resolveScopeMetadata(candidate);// 设置candidate的作用域, 这里的scopeName是singletoncandidate.setScope(scopeMetadata.getScopeName());// 获取class的名称String beanName = this.beanNameGenerator.generateBeanName(candidate, this.registry);// 对这个实例进行更多的设置if (candidate instanceof AbstractBeanDefinition) {postProcessBeanDefinition((AbstractBeanDefinition) candidate, beanName);}if (candidate instanceof AnnotatedBeanDefinition) {AnnotationConfigUtils.processCommonDefinitionAnnotations((AnnotatedBeanDefinition) candidate);}// 检查这个类名是否需要定义或者是否冲突if (checkCandidate(beanName, candidate)) {BeanDefinitionHolder definitionHolder = new BeanDefinitionHolder(candidate, beanName);definitionHolder =AnnotationConfigUtils.applyScopedProxyMode(scopeMetadata, definitionHolder, this.registry);beanDefinitions.add(definitionHolder);registerBeanDefinition(definitionHolder, this.registry);}}}return beanDefinitions;}

上面把mapper类扫描完毕后需要加入mybatis的Configuration中
可以得出一个结论, 一个mapper接口会通过MapperFactoryBean加载进Configuration

  public <T> void addMapper(Class<T> type) {// 判断传入的class是否为接口, 所以我们的mapper必须是接口, 如果是类也不报错, 但是不加载if (type.isInterface()) {// 这里判断这个接口是否已经注册过, 所以返回这是一个已知的mapperif (hasMapper(type)) {throw new BindingException("Type " + type + " is already known to the MapperRegistry.");}boolean loadCompleted = false;try {// 将mapper注入knownMappers, 这是一个hashMap用于存储已经注册过的mapperknownMappers.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);// 进入parse关键步骤parser.parse();loadCompleted = true;} finally {if (!loadCompleted) {knownMappers.remove(type);}}}}

parse解析方法

  public void parse() {// 获取type的名称String resource = type.toString();// 判断Configuration中是否已经加载过这个类名if (!configuration.isResourceLoaded(resource)) {loadXmlResource();// loadedResources中加入这个类configuration.addLoadedResource(resource);// 设置assistant的当前命名空间为type的nameassistant.setCurrentNamespace(type.getName());// 这里判断了是否有CacheNamespace, 也就是是否开启二级缓存// 我们没开二级缓存, 不需要管这里parseCache();// 同上parseCacheRef();// 获取mapper中的方法Method[] methods = type.getMethods();for (Method method : methods) {try {// issue #237if (!method.isBridge()) {// 这里开始解析statementparseStatement(method);}} catch (IncompleteElementException e) {configuration.addIncompleteMethod(new MethodResolver(this, method));}}}parsePendingMethods();}

解析statement

void parseStatement(Method method) {// 这里获取方法的参数类型, 如果是多个参数就返回数组Class<?> parameterTypeClass = getParameterType(method);LanguageDriver languageDriver = getLanguageDriver(method);// 获取sql语句, 我这边使用注解写的sql, 所以这里获得的就是注解中的valueSqlSource sqlSource = getSqlSourceFromAnnotations(method, parameterTypeClass, languageDriver);if (sqlSource != null) {Options options = method.getAnnotation(Options.class);// 生成一个唯一的statementIdfinal String mappedStatementId = type.getName() + "." + method.getName();Integer fetchSize = null;Integer timeout = null;StatementType statementType = StatementType.PREPARED;ResultSetType resultSetType = null;// 这里获取该方法的sql类型(SELECT之类的)SqlCommandType sqlCommandType = getSqlCommandType(method);boolean isSelect = sqlCommandType == SqlCommandType.SELECT;// 如果不是select就更新缓存boolean flushCache = !isSelect;// 如果是select就使用缓存boolean useCache = isSelect;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 = method.getAnnotation(SelectKey.class);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;}// mybatis的@Options注解能够设置缓存时间，能够为对象生成自增的keyif (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();resultSetType = options.resultSetType();}String resultMapId = null;ResultMap resultMapAnnotation = method.getAnnotation(ResultMap.class);// 我这边使用注解sql的时候并没有使用到ResultMapif (resultMapAnnotation != null) {resultMapId = String.join(",", resultMapAnnotation.value());} else if (isSelect) {resultMapId = parseResultMap(method);}// 这里设置了assistant的returnType, 我这边是用自定义的DTO接收的assistant.addMappedStatement(mappedStatementId,sqlSource,statementType,sqlCommandType,fetchSize,timeout,// ParameterMapIDnull,parameterTypeClass,resultMapId,getReturnType(method),resultSetType,flushCache,useCache,// TODO gcode issue #577false,keyGenerator,keyProperty,keyColumn,// DatabaseIDnull,languageDriver,// ResultSetsoptions != null ? nullOrEmpty(options.resultSets()) : null);}}

后记

至此Mybatis的mapper加载流程结束了, 总结一下就是先找到mapper接口, 然后加载注册, 然后扫描mapper接口中的方法, 获取sql, 根据sql的类型来做不同的设置, 并且在assistant中注入一个mapperStatement, 这个statemen中有mapper的各种信息, 后面直接用这个创建Statement对象
因为Mybatis其实就是在JDBC的基础上封装的, 所以流程都基本一致