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如何理解Mybatis初始化

发表于：2025-01-31 作者：千家信息网编辑

千家信息网最后更新 2025年01月31日，这篇文章主要讲解了"如何理解Mybatis初始化"，文中的讲解内容简单清晰，易于学习与理解，下面请大家跟着小编的思路慢慢深入，一起来研究和学习"如何理解Mybatis初始化"吧！Mybatis 初始化

千家信息网最后更新 2025年01月31日如何理解Mybatis初始化

这篇文章主要讲解了"如何理解Mybatis初始化"，文中的讲解内容简单清晰，易于学习与理解，下面请大家跟着小编的思路慢慢深入，一起来研究和学习"如何理解Mybatis初始化"吧！

Mybatis 初始化是由SqlSessionFactoryBuilder来完成的，主要的工作解析XML文件，并将解析的类容封装到Configuration类中，最后将Configuration类封装到SqlSessionFactory中并返回，自此初始化完成。

完成对XML文件解析的是XMLConfigBuilder、XMLMapperBuilder、XMLStatementBuilder三个类来完成：

XMLConfigBuilder：负责全局配置文件（mybatis-config.xml）中除了mappers节点的解析。
XMLMapperBuilder：负责解析xxxMapper.xml映射文件中cache-ref、cache、parameterMap、resultMap、sql节点；根据 namespace 将Mapper接口的动态代理工厂注册到 MapperRegistry 中。
XMLStatementBuilder：负责解析xxxMapper.xml映射文件中SQL语句节点，如：select、insert、update、delete。
XMLScriptBuilder：负责解析SQL脚本，然后封装成SqlSource。

Mybatis 初始化流程

SqlSessionFactoryBuilder

SqlSessionFactoryBuilder会将解析任务托给XMLConfigBuilder类，源码如下：

public SqlSessionFactory build(InputStream inputStream, String environment, Properties properties) {  try {    // 委托给XMLConfigBuilder去解析配置文件    XMLConfigBuilder parser = new XMLConfigBuilder(inputStream, environment, properties);    // 开始解析    return build(parser.parse());  }   ...}public SqlSessionFactory build(Configuration config) {  return new DefaultSqlSessionFactory(config);}

XMLConfigBuilder

负责全局配置文件（mybatis-config.xml）中除了mappers节点的解析。解析节点委托给XMLMapperBuilder解析器。

private void parseConfiguration(XNode root) {  try {    //issue #117 read properties first    // 解析节点    propertiesElement(root.evalNode("properties"));    // 解析节点    Properties settings = settingsAsProperties(root.evalNode("settings"));    loadCustomVfs(settings);    loadCustomLogImpl(settings);    // 解析节点    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 #631    environmentsElement(root.evalNode("environments"));    databaseIdProviderElement(root.evalNode("databaseIdProvider"));    typeHandlerElement(root.evalNode("typeHandlers"));    // 解析节点    mapperElement(root.evalNode("mappers"));  } catch (Exception e) {    throw new BuilderException("Error parsing SQL Mapper Configuration. Cause: " + e, e);  }}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);          // 委托XMLMapperBuilder来解析映射文件          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);          // 委托XMLMapperBuilder来解析映射文件          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.");        }      }    }  }}

XMLMapperBuilder

负责解析xxxMapper.xml映射文件中cache-ref、cache、parameterMap、resultMap、sql节点；根据 namespace 将Mapper接口的动态代理工厂（MapperProxyFactory）注册到 MapperRegistry 中。

public void parse() {  // 防止重复解析  if (!configuration.isResourceLoaded(resource)) {    // 解析xxxMapper.xml 映射文件中的 mapper节点    configurationElement(parser.evalNode("/mapper"));    // 标记为已经加载过    configuration.addLoadedResource(resource);    // 根据 namespace 将Mapper接口的动态代理工厂注册到 MapperRegistry 中    bindMapperForNamespace();  }  // 兜底  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);    // 解析节点    cacheRefElement(context.evalNode("cache-ref"));    // 解析节点    cacheElement(context.evalNode("cache"));    // 解析节点    parameterMapElement(context.evalNodes("/mapper/parameterMap"));    // 解析节点    resultMapElements(context.evalNodes("/mapper/resultMap"));    sqlElement(context.evalNodes("/mapper/sql"));    // 解析节点    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 buildStatementFromContext(List list) {  if (configuration.getDatabaseId() != null) {    buildStatementFromContext(list, configuration.getDatabaseId());  }  buildStatementFromContext(list, null);}private void buildStatementFromContext(List list, String requiredDatabaseId) {  for (XNode context : list) {    // 解析节点委托给 XMLStatementBuilder    final XMLStatementBuilder statementParser = new XMLStatementBuilder(configuration, builderAssistant, context, requiredDatabaseId);    try {      statementParser.parseStatementNode();    } catch (IncompleteElementException e) {      configuration.addIncompleteStatement(statementParser);    }  }}

XMLStatementBuilder

负责解析xxxMapper.xml映射文件中SQL语句节点，如：select、insert、update、delete。解析节点委托给XMLStatementBuilder解析器。

public void parseStatementNode() {  String id = context.getStringAttribute("id");  String databaseId = context.getStringAttribute("databaseId");  if (!databaseIdMatchesCurrent(id, databaseId, this.requiredDatabaseId)) {    return;  }  // 根据节点的名称来判断SQL语句的类型（select|insert|update|delete）  String nodeName = context.getNode().getNodeName();  SqlCommandType sqlCommandType = SqlCommandType.valueOf(nodeName.toUpperCase(Locale.ENGLISH));  boolean isSelect = sqlCommandType == SqlCommandType.SELECT;  boolean flushCache = context.getBooleanAttribute("flushCache", !isSelect);  boolean useCache = context.getBooleanAttribute("useCache", isSelect);  boolean resultOrdered = context.getBooleanAttribute("resultOrdered", false);  // Include Fragments before parsing  // 解析节点  XMLIncludeTransformer includeParser = new XMLIncludeTransformer(configuration, builderAssistant);  includeParser.applyIncludes(context.getNode());  String parameterType = context.getStringAttribute("parameterType");  Class parameterTypeClass = resolveClass(parameterType);  String lang = context.getStringAttribute("lang");  LanguageDriver langDriver = getLanguageDriver(lang);  // Parse selectKey after includes and remove them.  // 解析节点，并在XML中删除节点  processSelectKeyNodes(id, parameterTypeClass, langDriver);  // Parse the SQL (pre:  and  were parsed and removed)  KeyGenerator keyGenerator;  String keyStatementId = id + SelectKeyGenerator.SELECT_KEY_SUFFIX;  keyStatementId = builderAssistant.applyCurrentNamespace(keyStatementId, true);  if (configuration.hasKeyGenerator(keyStatementId)) {    keyGenerator = configuration.getKeyGenerator(keyStatementId);  } else {    keyGenerator = context.getBooleanAttribute("useGeneratedKeys",        configuration.isUseGeneratedKeys() && SqlCommandType.INSERT.equals(sqlCommandType))        ? Jdbc3KeyGenerator.INSTANCE : NoKeyGenerator.INSTANCE;  }  // 解析SQL语句，然后封装成SqlSource  SqlSource sqlSource = langDriver.createSqlSource(configuration, context, parameterTypeClass);  StatementType statementType = StatementType.valueOf(context.getStringAttribute("statementType", StatementType.PREPARED.toString()));  Integer fetchSize = context.getIntAttribute("fetchSize");  Integer timeout = context.getIntAttribute("timeout");  String parameterMap = context.getStringAttribute("parameterMap");  String resultType = context.getStringAttribute("resultType");  Class resultTypeClass = resolveClass(resultType);  String resultMap = context.getStringAttribute("resultMap");  String resultSetType = context.getStringAttribute("resultSetType");  ResultSetType resultSetTypeEnum = resolveResultSetType(resultSetType);  if (resultSetTypeEnum == null) {    resultSetTypeEnum = configuration.getDefaultResultSetType();  }  String keyProperty = context.getStringAttribute("keyProperty");  String keyColumn = context.getStringAttribute("keyColumn");  String resultSets = context.getStringAttribute("resultSets");  // 使用建造者模式构建MappedStatement对象  builderAssistant.addMappedStatement(id, sqlSource, statementType, sqlCommandType,      fetchSize, timeout, parameterMap, parameterTypeClass, resultMap, resultTypeClass,      resultSetTypeEnum, flushCache, useCache, resultOrdered,      keyGenerator, keyProperty, keyColumn, databaseId, langDriver, resultSets);}

Mybatis 初始化流程图

核心数据结构类

Configuration

Configuration其实就是XML配置文件的Java形态，Configuration是单例的，生命周期是应用级的；

ResultMap

对应xxxMapper.xml映射文件中的resultMap节点。节点中的子节点使用ResultMapping来封装，如：、等节点。

MappedStatement

对应xxxMapper.xml映射文件中的