Mybatis 的初始化與建造者模式

建造者模式

建造者模式（Builder Pattern）指的是將一個複雜的構建與其表示相分離，使得同樣的構建過程可以創建不同的表示。它使用多個簡單的對象一步一步構建成一個複雜的對象。這種類型的設計模式屬於創建型模式，它提供了一種創建對象的最佳方式。

結構

角色

• Product：要創建的複雜對象
• Builder：給出一個抽象接口，以規範產品對象的各個組成成分的建造。這個接口規定要實現複雜對象的哪些部分的創建，並不涉及具體的對象部件的創建
• ConcreteBuilder：實現 Builder 接口，針對不同的商業邏輯，具體化複雜對象的各部分的創建。 在建造過程完成後，提供產品的實例
• Director：調用具體建造者來創建複雜對象的各個部分，在指導者中不涉及具體產品的信息，只負責保證對象各部分完整創建或按某種順序創建

使用場景

• 需要生成的對象具有複雜的內部結構，實例化對象時要屏蔽掉對象內部的細節，讓上層代碼與複雜對象的實例化過程解耦，可以使用建造者模式；簡而言之，如果“遇到多個構造器參數時要考慮用構建器”
• 對象的實例化是依賴各個組件的產生以及裝配順序，關注的是一步一步地組裝出目標對象，可以使用建造器模式

與工廠模式的區別

建造者模式在Mybatis裏的應用

Mybatis 的初始化

• Configuration ： Mybatis 啓動初始化的核心就是將所有 xml 配置文件信息加載到 Configuration 對象中， Configuration是單例的，生命週期是應用級的。
• XMLConfigBuilder： 主要負責解析 mybatis-config.xml
• XMLMapperBuilder： 主要負責解析映射配置文件（各個Mapper.xml）
• XMLStatementBuilder： 主要負責解析映射配置文件中的SQL節點
• MapperBuilderAssistant：輔助XMLMapperBuilder解析mapper.xml文件，完善屬性信息，並註冊到configuration對象（單一職責原則）

• BaseBuilder：所有解析器的父類，包含配置文件實例，爲解析文件提供的一些通用的方法

入口

當我們創建了一個 SqlSessionFactory，其實就完成了初始化，所以入口是 build 方法。

private SqlSessionFactory sqlSessionFactory;
//讀取mybatis配置文件創SqlSessionFactory
String resource = "mybatis-config.xml";
InputStream inputStream = Resources.getResourceAsStream(resource);
//讀取mybatis配置文件創SqlSessionFactory
sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
inputStream.close();

跟 build：
這就是一個建造者模式的簡單實現。屏蔽了創建對象的複雜過程，但並沒有流式編程的思想。並不是建造者模式的最佳實現。

public class SqlSessionFactoryBuilder {

public SqlSessionFactory build(InputStream inputStream) {
    return build(inputStream, null, null);
  }
  
public SqlSessionFactory build(InputStream inputStream, String environment, Properties properties) {
    try {
      XMLConfigBuilder parser = new XMLConfigBuilder(inputStream, environment, properties);
      return build(parser.parse());
    } catch (Exception e) {
      throw ExceptionFactory.wrapException("Error building SqlSession.", e);
    } finally {
      ErrorContext.instance().reset();
      try {
        inputStream.close();
      } catch (IOException e) {
        // Intentionally ignore. Prefer previous error.
      }
    }
  }

public SqlSessionFactory build(Configuration config) {
  return new DefaultSqlSessionFactory(config);
}
  //省略了一些代碼

XMLConfigBuilder

public class XMLConfigBuilder extends BaseBuilder {
  //是否解析過mybatis-config.xml文件
  private boolean parsed;
  //xml文件的解析器
  private final XPathParser parser;
  //讀取默認的environment
  private String environment;
  //負責創建和緩存Reflector對象
  private final ReflectorFactory localReflectorFactory = new DefaultReflectorFactory();
  
  public Configuration parse() {
    if (parsed) {
      throw new BuilderException("Each XMLConfigBuilder can only be used once.");
    }
    parsed = true;
    parseConfiguration(parser.evalNode("/configuration"));
    return configuration;
  }

  private void parseConfiguration(XNode root) {
    try {
      //issue #117 read properties first
      //解析<properties>節點
      propertiesElement(root.evalNode("properties"));
      //解析<settings>節點
      Properties settings = settingsAsProperties(root.evalNode("settings"));
      loadCustomVfs(settings);
      //解析<typeAliases>節點
      typeAliasesElement(root.evalNode("typeAliases"));
      //解析<plugins>節點
      pluginElement(root.evalNode("plugins"));
      //解析<objectFactory>節點
      objectFactoryElement(root.evalNode("objectFactory"));
      //解析<objectWrapperFactory>節點
      objectWrapperFactoryElement(root.evalNode("objectWrapperFactory"));
      //解析<reflectorFactory>節點
      reflectorFactoryElement(root.evalNode("reflectorFactory"));
      settingsElement(settings);//將settings填充到configuration
      // read it after objectFactory and objectWrapperFactory issue #631
      //解析<environments>節點
      environmentsElement(root.evalNode("environments"));
      //解析<databaseIdProvider>節點
      databaseIdProviderElement(root.evalNode("databaseIdProvider"));
      //解析<typeHandlers>節點
      typeHandlerElement(root.evalNode("typeHandlers"));
      //解析<mappers>節點
      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()) {//處理mapper子節點
        if ("package".equals(child.getName())) {//package子節點
          String mapperPackage = child.getStringAttribute("name");
          configuration.addMappers(mapperPackage);
        } else {//獲取<mapper>節點的resource、url或mapperClass屬性這三個屬性互斥
          String resource = child.getStringAttribute("resource");
          String url = child.getStringAttribute("url");
          String mapperClass = child.getStringAttribute("class");
          if (resource != null && url == null && mapperClass == null) {//如果resource不爲空
            ErrorContext.instance().resource(resource);
            InputStream inputStream = Resources.getResourceAsStream(resource);//加載mapper文件
            //實例化XMLMapperBuilder解析mapper映射文件
            XMLMapperBuilder mapperParser = new XMLMapperBuilder(inputStream, configuration, resource, configuration.getSqlFragments());
            mapperParser.parse();
          } else if (resource == null && url != null && mapperClass == null) {//如果url不爲空
            ErrorContext.instance().resource(url);
            InputStream inputStream = Resources.getUrlAsStream(url);//加載mapper文件
            //實例化XMLMapperBuilder解析mapper映射文件
            XMLMapperBuilder mapperParser = new XMLMapperBuilder(inputStream, configuration, url, configuration.getSqlFragments());
            mapperParser.parse();
          } else if (resource == null && url == null && mapperClass != null) {//如果class不爲空
            Class<?> mapperInterface = Resources.classForName(mapperClass);//加載class對象
            configuration.addMapper(mapperInterface);//向代理中心註冊mapper
          } else {
            throw new BuilderException("A mapper element may only specify a url, resource or class, but not more than one.");
          }
        }
      }
    }
  }
  //省略了一些方法
}

XMLMapperBuilder

public class XMLMapperBuilder extends BaseBuilder {

  private final XPathParser parser;
  private final MapperBuilderAssistant builderAssistant;
  private final Map<String, XNode> sqlFragments;
  private final String resource;
  
  public void parse() {
	//判斷是否已經加載該配置文件
    if (!configuration.isResourceLoaded(resource)) {
      configurationElement(parser.evalNode("/mapper"));//處理mapper節點
      configuration.addLoadedResource(resource);//將mapper文件添加到configuration.loadedResources中
      bindMapperForNamespace();//註冊mapper接口
    }
    //處理解析失敗的ResultMap節點
    parsePendingResultMaps();
    //處理解析失敗的CacheRef節點
    parsePendingCacheRefs();
    //處理解析失敗的Sql語句節點
    parsePendingStatements();
  }
  
private void configurationElement(XNode context) {
    try {
    	//獲取mapper節點的namespace屬性
      String namespace = context.getStringAttribute("namespace");
      if (namespace == null || namespace.equals("")) {
        throw new BuilderException("Mapper's namespace cannot be empty");
      }
      //設置builderAssistant的namespace屬性
      builderAssistant.setCurrentNamespace(namespace);
      //解析cache-ref節點
      cacheRefElement(context.evalNode("cache-ref"));
      //重點分析 ：解析cache節點----------------1-------------------
      cacheElement(context.evalNode("cache"));
      //解析parameterMap節點（已廢棄）
      parameterMapElement(context.evalNodes("/mapper/parameterMap"));
      //重點分析 ：解析resultMap節點（基於數據結果去理解）----------------2-------------------
      resultMapElements(context.evalNodes("/mapper/resultMap"));
      //解析sql節點
      sqlElement(context.evalNodes("/mapper/sql"));
      //重點分析 ：解析select、insert、update、delete節點 ----------------3-------------------
      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);
    }
  }
  
  //重點分析 ：解析cache節點----------------1-------------------
  private void cacheElement(XNode context) throws Exception {
    if (context != null) {
      //獲取cache節點的type屬性，默認爲PERPETUAL
      String type = context.getStringAttribute("type", "PERPETUAL");
      //找到type對應的cache接口的實現
      Class<? extends Cache> typeClass = typeAliasRegistry.resolveAlias(type);
      //讀取eviction屬性，既緩存的淘汰策略，默認LRU
      String eviction = context.getStringAttribute("eviction", "LRU");
      //根據eviction屬性，找到裝飾器
      Class<? extends Cache> evictionClass = typeAliasRegistry.resolveAlias(eviction);
      //讀取flushInterval屬性，既緩存的刷新週期
      Long flushInterval = context.getLongAttribute("flushInterval");
      //讀取size屬性，既緩存的容量大小
      Integer size = context.getIntAttribute("size");
     //讀取readOnly屬性，既緩存的是否只讀
      boolean readWrite = !context.getBooleanAttribute("readOnly", false);
      //讀取blocking屬性，既緩存的是否阻塞
      boolean blocking = context.getBooleanAttribute("blocking", false);
      Properties props = context.getChildrenAsProperties();
      //通過builderAssistant創建緩存對象，並添加至configuration
      builderAssistant.useNewCache(typeClass, evictionClass, flushInterval, size, readWrite, blocking, props);
    }
  }
  
  //重點分析 ：解析resultMap節點（基於數據結果去理解）----------------2-------------------
  //解析resultMap節點,實際就是解析sql查詢的字段與pojo屬性之間的轉化規則
  private void resultMapElements(List<XNode> list) throws Exception {
	//遍歷所有的resultmap節點
    for (XNode resultMapNode : list) {
      try {
    	 //解析具體某一個resultMap節點
        resultMapElement(resultMapNode);
      } catch (IncompleteElementException e) {
        // ignore, it will be retried
      }
    }
  }

  private ResultMap resultMapElement(XNode resultMapNode) throws Exception {
    return resultMapElement(resultMapNode, Collections.<ResultMapping> emptyList());
  }
  
  private ResultMap resultMapElement(XNode resultMapNode, List<ResultMapping> additionalResultMappings) throws Exception {
    ErrorContext.instance().activity("processing " + resultMapNode.getValueBasedIdentifier());
    //獲取resultmap節點的id屬性
    String id = resultMapNode.getStringAttribute("id",
        resultMapNode.getValueBasedIdentifier());
    //獲取resultmap節點的type屬性
    String type = resultMapNode.getStringAttribute("type",
        resultMapNode.getStringAttribute("ofType",
            resultMapNode.getStringAttribute("resultType",
                resultMapNode.getStringAttribute("javaType"))));
    //獲取resultmap節點的extends屬性，描述繼承關係
    String extend = resultMapNode.getStringAttribute("extends");
    //獲取resultmap節點的autoMapping屬性，是否開啓自動映射
    Boolean autoMapping = resultMapNode.getBooleanAttribute("autoMapping");
    //從別名註冊中心獲取entity的class對象
    Class<?> typeClass = resolveClass(type);
    Discriminator discriminator = null;
    //記錄子節點中的映射結果集合
    List<ResultMapping> resultMappings = new ArrayList<>();
    resultMappings.addAll(additionalResultMappings);
    //從xml文件中獲取當前resultmap中的所有子節點，並開始遍歷
    List<XNode> resultChildren = resultMapNode.getChildren();
    for (XNode resultChild : resultChildren) {
      if ("constructor".equals(resultChild.getName())) {//處理<constructor>節點
        processConstructorElement(resultChild, typeClass, resultMappings);
      } else if ("discriminator".equals(resultChild.getName())) {//處理<discriminator>節點
        discriminator = processDiscriminatorElement(resultChild, typeClass, resultMappings);
      } else {//處理<id> <result> <association> <collection>節點
        List<ResultFlag> flags = new ArrayList<>();
        if ("id".equals(resultChild.getName())) {
          flags.add(ResultFlag.ID);//如果是id節點，向flags中添加元素
        }
        //重點看：創建ResultMapping對象並加入resultMappings集合中
        resultMappings.add(buildResultMappingFromContext(resultChild, typeClass, flags));
      }
    }
    //實例化resultMap解析器
    ResultMapResolver resultMapResolver = new ResultMapResolver(builderAssistant, id, typeClass, extend, discriminator, resultMappings, autoMapping);
    try {
      //通過resultMap解析器實例化resultMap並將其註冊到configuration對象（也是交給MapperBuilderAssistant去做）
      //return assistant.addResultMap(this.id, this.type, this.extend, this.discriminator, this.resultMappings, this.autoMapping);
      return resultMapResolver.resolve();
    } catch (IncompleteElementException  e) {
      configuration.addIncompleteResultMap(resultMapResolver);
      throw e;
    }
  }
  
  //根據resultmap中的子節點信息，創建resultMapping對象
  private ResultMapping buildResultMappingFromContext(XNode context, Class<?> resultType, List<ResultFlag> flags) throws Exception {
    String property;
    if (flags.contains(ResultFlag.CONSTRUCTOR)) {
      property = context.getStringAttribute("name");
    } else {
      property = context.getStringAttribute("property");
    }
    String column = context.getStringAttribute("column");
    String javaType = context.getStringAttribute("javaType");
    String jdbcType = context.getStringAttribute("jdbcType");
    String nestedSelect = context.getStringAttribute("select");
    String nestedResultMap = context.getStringAttribute("resultMap",
        processNestedResultMappings(context, Collections.<ResultMapping> emptyList()));
    String notNullColumn = context.getStringAttribute("notNullColumn");
    String columnPrefix = context.getStringAttribute("columnPrefix");
    String typeHandler = context.getStringAttribute("typeHandler");
    String resultSet = context.getStringAttribute("resultSet");
    String foreignColumn = context.getStringAttribute("foreignColumn");
    boolean lazy = "lazy".equals(context.getStringAttribute("fetchType", configuration.isLazyLoadingEnabled() ? "lazy" : "eager"));
    Class<?> javaTypeClass = resolveClass(javaType);
    @SuppressWarnings("unchecked")
    Class<? extends TypeHandler<?>> typeHandlerClass = (Class<? extends TypeHandler<?>>) resolveClass(typeHandler);
    JdbcType jdbcTypeEnum = resolveJdbcType(jdbcType);
    //使用建造者模式創建resultMapping對象
    return builderAssistant.buildResultMapping(resultType, property, column, javaTypeClass, jdbcTypeEnum, nestedSelect, nestedResultMap, notNullColumn, columnPrefix, typeHandlerClass, flags, resultSet, foreignColumn, lazy);
  }
  
  //重點分析 ：解析select、insert、update、delete節點 ----------------3-------------------
  private void buildStatementFromContext(List<XNode> list) {
    if (configuration.getDatabaseId() != null) {
      buildStatementFromContext(list, configuration.getDatabaseId());
    }
    buildStatementFromContext(list, null);
  }

  //處理所有的sql語句節點並註冊至configuration對象
  private void buildStatementFromContext(List<XNode> list, String requiredDatabaseId) {
    for (XNode context : list) {
      //創建XMLStatementBuilder 專門用於解析sql語句節點
      final XMLStatementBuilder statementParser = new XMLStatementBuilder(configuration, builderAssistant, context, requiredDatabaseId);
      try {
    	//解析sql語句節點
        statementParser.parseStatementNode();
      } catch (IncompleteElementException e) {
        configuration.addIncompleteStatement(statementParser);
      }
    }
  }
  
  //省略了一些方法
}

XMLStatementBuilder

public class XMLStatementBuilder extends BaseBuilder {

  private final MapperBuilderAssistant builderAssistant;
  private final XNode context;
  private final String requiredDatabaseId;

  public void parseStatementNode() {
	//獲取sql節點的id
    String id = context.getStringAttribute("id");
    String databaseId = context.getStringAttribute("databaseId");

    if (!databaseIdMatchesCurrent(id, databaseId, this.requiredDatabaseId)) {
      return;
    }
    /*獲取sql節點的各種屬性*/
    Integer fetchSize = context.getIntAttribute("fetchSize");
    Integer timeout = context.getIntAttribute("timeout");
    String parameterMap = context.getStringAttribute("parameterMap");
    String parameterType = context.getStringAttribute("parameterType");
    Class<?> parameterTypeClass = resolveClass(parameterType);
    String resultMap = context.getStringAttribute("resultMap");
    String resultType = context.getStringAttribute("resultType");
    String lang = context.getStringAttribute("lang");
    LanguageDriver langDriver = getLanguageDriver(lang);

    Class<?> resultTypeClass = resolveClass(resultType);
    String resultSetType = context.getStringAttribute("resultSetType");
    StatementType statementType = StatementType.valueOf(context.getStringAttribute("statementType", StatementType.PREPARED.toString()));
    ResultSetType resultSetTypeEnum = resolveResultSetType(resultSetType);



    //根據sql節點的名稱獲取SqlCommandType（INSERT, UPDATE, DELETE, SELECT）
    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
    //在解析sql語句之前先解析<include>節點
    XMLIncludeTransformer includeParser = new XMLIncludeTransformer(configuration, builderAssistant);
    includeParser.applyIncludes(context.getNode());

    // Parse selectKey after includes and remove them.
    //在解析sql語句之前，處理<selectKey>子節點，並在xml節點中刪除
    processSelectKeyNodes(id, parameterTypeClass, langDriver);

    // Parse the SQL (pre: <selectKey> and <include> were parsed and removed)
    //解析sql語句是解析mapper.xml的核心，實例化sqlSource，使用sqlSource封裝sql語句
    SqlSource sqlSource = langDriver.createSqlSource(configuration, context, parameterTypeClass);
    String resultSets = context.getStringAttribute("resultSets");//獲取resultSets屬性
    String keyProperty = context.getStringAttribute("keyProperty");//獲取主鍵信息keyProperty
    String keyColumn = context.getStringAttribute("keyColumn");///獲取主鍵信息keyColumn

    //根據<selectKey>獲取對應的SelectKeyGenerator的id
    KeyGenerator keyGenerator;
    String keyStatementId = id + SelectKeyGenerator.SELECT_KEY_SUFFIX;
    keyStatementId = builderAssistant.applyCurrentNamespace(keyStatementId, true);


    //獲取keyGenerator對象，如果是insert類型的sql語句，會使用KeyGenerator接口獲取數據庫生產的id；
    if (configuration.hasKeyGenerator(keyStatementId)) {
      keyGenerator = configuration.getKeyGenerator(keyStatementId);
    } else {
      keyGenerator = context.getBooleanAttribute("useGeneratedKeys",
          configuration.isUseGeneratedKeys() && SqlCommandType.INSERT.equals(sqlCommandType))
          ? Jdbc3KeyGenerator.INSTANCE : NoKeyGenerator.INSTANCE;
    }

    //通過builderAssistant實例化MappedStatement，並註冊至configuration對象
    builderAssistant.addMappedStatement(id, sqlSource, statementType, sqlCommandType,
        fetchSize, timeout, parameterMap, parameterTypeClass, resultMap, resultTypeClass,
        resultSetTypeEnum, flushCache, useCache, resultOrdered,
        keyGenerator, keyProperty, keyColumn, databaseId, langDriver, resultSets);
  }
  //省略了一些方法
}

MapperBuilderAssistant

public class MapperBuilderAssistant extends BaseBuilder {

  private String currentNamespace;
  private final String resource;
  private Cache currentCache;
  private boolean unresolvedCacheRef; // issue #676
  
  //通過builderAssistant創建緩存對象，並添加至configuration
  public Cache useNewCache(Class<? extends Cache> typeClass,
      Class<? extends Cache> evictionClass,
      Long flushInterval,
      Integer size,
      boolean readWrite,
      boolean blocking,
      Properties props) {
	//經典的建造起模式，創建一個cache對象
    Cache cache = new CacheBuilder(currentNamespace)
        .implementation(valueOrDefault(typeClass, PerpetualCache.class))
        .addDecorator(valueOrDefault(evictionClass, LruCache.class))
        .clearInterval(flushInterval)
        .size(size)
        .readWrite(readWrite)
        .blocking(blocking)
        .properties(props)
        .build();
    //將緩存添加至configuration，注意二級緩存以命名空間爲單位進行劃分
    configuration.addCache(cache);
    currentCache = cache;
    return cache;
  }

  public ResultMapping buildResultMapping(
      Class<?> resultType,
      String property,
      String column,
      Class<?> javaType,
      JdbcType jdbcType,
      String nestedSelect,
      String nestedResultMap,
      String notNullColumn,
      String columnPrefix,
      Class<? extends TypeHandler<?>> typeHandler,
      List<ResultFlag> flags,
      String resultSet,
      String foreignColumn,
      boolean lazy) {
    Class<?> javaTypeClass = resolveResultJavaType(resultType, property, javaType);
    TypeHandler<?> typeHandlerInstance = resolveTypeHandler(javaTypeClass, typeHandler);
    List<ResultMapping> composites = parseCompositeColumnName(column);
    return new ResultMapping.Builder(configuration, property, column, javaTypeClass)
        .jdbcType(jdbcType)
        .nestedQueryId(applyCurrentNamespace(nestedSelect, true))
        .nestedResultMapId(applyCurrentNamespace(nestedResultMap, true))
        .resultSet(resultSet)
        .typeHandler(typeHandlerInstance)
        .flags(flags == null ? new ArrayList<ResultFlag>() : flags)
        .composites(composites)
        .notNullColumns(parseMultipleColumnNames(notNullColumn))
        .columnPrefix(columnPrefix)
        .foreignColumn(foreignColumn)
        .lazy(lazy)
        .build();
  }
  
  //實例化ResultMap並將其註冊到Configuration對象
  public ResultMap addResultMap(
      String id,
      Class<?> type,
      String extend,
      Discriminator discriminator,
      List<ResultMapping> resultMappings,
      Boolean autoMapping) {
	 //完善id，id的完整格式是"namespace.id"
    id = applyCurrentNamespace(id, false);
    //獲得父類resultMap的完整id
    extend = applyCurrentNamespace(extend, true);

    //針對extend屬性的處理
    if (extend != null) {
      if (!configuration.hasResultMap(extend)) {
        throw new IncompleteElementException("Could not find a parent resultmap with id '" + extend + "'");
      }
      ResultMap resultMap = configuration.getResultMap(extend);
      List<ResultMapping> extendedResultMappings = new ArrayList<>(resultMap.getResultMappings());
      extendedResultMappings.removeAll(resultMappings);
      // Remove parent constructor if this resultMap declares a constructor.
      boolean declaresConstructor = false;
      for (ResultMapping resultMapping : resultMappings) {
        if (resultMapping.getFlags().contains(ResultFlag.CONSTRUCTOR)) {
          declaresConstructor = true;
          break;
        }
      }
      if (declaresConstructor) {
        Iterator<ResultMapping> extendedResultMappingsIter = extendedResultMappings.iterator();
        while (extendedResultMappingsIter.hasNext()) {
          if (extendedResultMappingsIter.next().getFlags().contains(ResultFlag.CONSTRUCTOR)) {
            extendedResultMappingsIter.remove();
          }
        }
      }
      //添加需要被繼承下來的resultMapping對象結合
      resultMappings.addAll(extendedResultMappings);
    }
    //通過建造者模式實例化resultMap,並註冊到configuration.resultMaps中
    ResultMap resultMap = new ResultMap.Builder(configuration, id, type, resultMappings, autoMapping)
        .discriminator(discriminator)
        .build();
    configuration.addResultMap(resultMap);
    return resultMap;
  }

  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;
  }
  //省略了一些方法
}