mybatis3源码1-初始化

青旅半醒 2022-02-20 04:53 286阅读 0赞

## 项目 ##

mybatis配置文件mybatis.xml  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L21pbmd3dWxpcG8_size_16_color_FFFFFF_t_70]  
mapper.xml

<?xml version="1.0" encoding="UTF-8"?>
    <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
    <mapper namespace="com.geely.cep.aso.statement.dao.StatementDao">
        <resultMap id="BaseResultMap" type="com.geely.cep.aso.statement.model.SvcStatement">
            <id column="Id" jdbcType="BIGINT" property="id"/>
            <result column="StatementNo" jdbcType="NVARCHAR" property="statementNo"/>
            <result column="ServiceProxyCode" jdbcType="NVARCHAR" property="serviceProxyCode"/>
    
        </resultMap>
        <sql id="Base_Column_List">
            Id, StatementNo, ServiceProxyCode, SystemOrder, StatementType, DealerId, DealerName,
            NextMaintainMileage, NextMaintainAt, AccountType, StatementTime, StatementerId, StatementerName
        </sql>
    
        <select id="selectStatementClmStatusByStatementNo" parameterType="String" resultType="Integer">
            SELECT clmstatus
            FROM SvcStatement
            WHERE statementNo = #{value}
            AND isnull(IsDeleted,0) = 0
        </select>
    
    </mapper>

main函数

public class Main {
        public static void main(String[] args) throws IOException {
    
            String resource = "mybatis.xml";
            InputStream inputStream = Resources.getResourceAsStream(resource);
            SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
    
            SqlSession sqlSession = sqlSessionFactory.openSession();
            try {
                ProductMapper productMapper = sqlSession.getMapper(ProductMapper.class);
                List<Product> productList = productMapper.selectProductList();
                for (Product product : productList) {
                    System.out.printf(product.toString());
                }
            } finally {
                sqlSession.close();
            }
        }
    }

初始化过程

## 1.读取配置文件 ##

InputStream inputStream = Resources.getResourceAsStream(resource);

## 2.创建SqlSessionFactory对象 ##

SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);

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.
          }
        }
      }

## 2.1创建XMLConfigBuilder ##

XMLxxxBuilder是用来解析XML配置文件的，不同类型XMLxxxBuilder用来解析MyBatis配置文件的不同部位。比如：XMLConfigBuilder用来解析MyBatis的配置文件，XMLMapperBuilder用来解析MyBatis中的映射文件（如上文提到的ProductMapper.xml），XMLStatementBuilder用来解析映射文件中的SQL语句。  
这些XMLxxxBuilder都有一个共同的父类——BaseBuilder。这个父类维护了一个全局的Configuration对象，MyBatis的配置文件解析后就以Configuration对象的形式存储。  
当创建XMLConfigBuilder对象时，就会初始化Configuration对象，并且在初始化Configuration对象的时候，一些别名会被注册到Configuration的typeAliasRegistry容器中。

XMLConfigBuilder创建，先解析xml文件输入流成XPathParser，然后创建一个Configuration对象属性

public XMLConfigBuilder(InputStream inputStream, String environment, Properties props) {
        this(new XPathParser(inputStream, true, props, new XMLMapperEntityResolver()), environment, props);
      }
    
      private XMLConfigBuilder(XPathParser parser, String environment, Properties props) {
        super(new Configuration());
        ErrorContext.instance().resource("SQL Mapper Configuration");
        this.configuration.setVariables(props);
        this.parsed = false;
        this.environment = environment;
        this.parser = parser;
      }

Configuration初始化变量，创建很多对象属性。创建时，注册很多别名

protected final TypeHandlerRegistry typeHandlerRegistry = new TypeHandlerRegistry();
      protected final TypeAliasRegistry typeAliasRegistry = new TypeAliasRegistry();
      public Configuration() {
        typeAliasRegistry.registerAlias("JDBC", JdbcTransactionFactory.class);
        typeAliasRegistry.registerAlias("MANAGED", ManagedTransactionFactory.class);
        ...
      }

TypeAliasRegistry创建时，注册很多基本类型的别名，存到hashmap中，

private final Map<String, Class<?>> TYPE_ALIASES = new HashMap<String, Class<?>>();
      
      public TypeAliasRegistry() {
        registerAlias("string", String.class);
        registerAlias("byte", Byte.class);
    
      }
    
      public void registerAlias(String alias, Class<?> value) {
        if (alias == null) {
          throw new TypeException("The parameter alias cannot be null");
        }
        // issue #748
        String 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);
      }

XMLConfigBuilder调用父类BaseBuilder的构造器，赋值Configuration 对象

public BaseBuilder(Configuration configuration) {
        this.configuration = configuration;
        this.typeAliasRegistry = this.configuration.getTypeAliasRegistry();
        this.typeHandlerRegistry = this.configuration.getTypeHandlerRegistry();
      }

## 2.2 XMLConfigBuilder解析xml配置文件，存储到Configuration 对象属性中 ##

XMLConfigBuilder

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 {
        // 解析<properties>节点
        propertiesElement(root.evalNode("properties"));
        // 解析<settings>节点
        Properties settings = settingsAsProperties(root.evalNode("settings"));
        loadCustomVfs(settings);
        // 解析<typeAliases>节点
        typeAliasesElement(root.evalNode("typeAliases"));
        // 解析<plugins>节点
        pluginElement(root.evalNode("plugins"));
        // 解析<objectFactory>节点
        objectFactoryElement(root.evalNode("objectFactory"));
        objectWrapperFactoryElement(root.evalNode("objectWrapperFactory"));
        // 解析<reflectorFactory>节点
        reflectorFactoryElement(root.evalNode("reflectorFactory"));
        settingsElement(settings);
        // 解析<environments>节点
        environmentsElement(root.evalNode("environments"));
        databaseIdProviderElement(root.evalNode("databaseIdProvider"));
        typeHandlerElement(root.evalNode("typeHandlers"));
        // 解析<mappers>节点
        mapperElement(root.evalNode("mappers"));
      } catch (Exception e) {
        throw new BuilderException("Error parsing SQL Mapper Configuration. Cause: " + e, e);
      }
    }

XMLConfigBuilder会依次解析配置文件中的、< settings >、< environments>、< typeAliases >、< plugins >、< mappers >等属性。

## 2.2.1 节点的解析过程 ##

private void propertiesElement(XNode context) throws Exception {
      if (context != null) {
        // 获取<properties>节点的所有子节点
        Properties defaults = context.getChildrenAsProperties();
        // 获取<properties>节点上的resource属性
        String resource = context.getStringAttribute("resource");
        // 获取<properties>节点上的url属性
        String url = context.getStringAttribute("url");
        // resource和url不能同时存在
        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) {
          // 获取resource属性值对应的properties文件中的键值对，并添加至defaults容器中        
          defaults.putAll(Resources.getResourceAsProperties(resource));
        } else if (url != null) {
          // 获取url属性值对应的properties文件中的键值对，并添加至defaults容器中
          defaults.putAll(Resources.getUrlAsProperties(url));
        }
        // 获取configuration中原本的属性，并添加至defaults容器中
        Properties vars = configuration.getVariables();
        if (vars != null) {
          defaults.putAll(vars);
        }
        parser.setVariables(defaults);
        // 将defaults容器添加至configuration中
        configuration.setVariables(defaults);
      }
    }

首先读取节点下的所有节点，并将每个节点的name和value属性存入Properties中。  
然后读取节点上的resource、url属性，并获取指定配置文件中的name和value，也存入Properties中。（PS：由此可知，如果resource节点上定义的属性和properties文件中的属性重名，那么properties文件中的属性值会覆盖resource节点上定义的属性值。）  
最终，携带所有属性的Properties对象会被存储在Configuration对象中。

## 节点的解析过程 ##

## 属性的解析过程 ##

MyBatis会为指定包下的所有类起一个别名，该别名为首字母小写的类名。

private void typeAliasesElement(XNode parent) {
      if (parent != null) {
        // 遍历<typeAliases>下的所有子节点
        for (XNode child : parent.getChildren()) {
          // 若当前结点为<package>
          if ("package".equals(child.getName())) {
            // 获取<package>上的name属性（包名）
            String typeAliasPackage = child.getStringAttribute("name");
            // 为该包下的所有类起个别名，并注册进configuration的typeAliasRegistry中          
            configuration.getTypeAliasRegistry().registerAliases(typeAliasPackage);
          } 
          // 如果当前结点为< typeAlias >
          else {
            // 获取alias和type属性
            String alias = child.getStringAttribute("alias");
            String type = child.getStringAttribute("type");
            // 注册进configuration的typeAliasRegistry中
            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);
            }
          }
        }
      }
    }

如果节点下定义了节点，那么MyBatis会给该包下的所有类起一个别名（以类名首字母小写作为别名）  
如果节点下定义了节点，那么MyBatis就会给指定的类起指定的别名。  
这些别名都会被存入configuration的typeAliasRegistry容器中

## 节点的解析过程 ##

mappers有4种方式

MyBatis会遍历下所有的子节点，如果当前遍历到的节点是，则MyBatis会将该包下的所有Mapper Class注册到configuration的mapperRegistry容器中。  
如果当前节点为，则会依次获取resource、url、class属性，解析映射文件，并将映射文件对应的Mapper Class注册到configuration的mapperRegistry容器中。

private void mapperElement(XNode parent) throws Exception {
      if (parent != null) {
        // 遍历<mappers>下所有子节点
        for (XNode child : parent.getChildren()) {
          // 如果当前节点为<package>
          if ("package".equals(child.getName())) {
            // 获取<package>的name属性（该属性值为mapper class所在的包名）
            String mapperPackage = child.getStringAttribute("name");
            // 将该包下的所有Mapper Class注册到configuration的mapperRegistry容器中
            configuration.addMappers(mapperPackage);
          } 
          // 如果当前节点为<mapper>
          else {
            // 依次获取resource、url、class属性
            String resource = child.getStringAttribute("resource");
            String url = child.getStringAttribute("url");
            String mapperClass = child.getStringAttribute("class");
            // 解析resource属性（Mapper.xml文件的路径）
            if (resource != null && url == null && mapperClass == null) {
              ErrorContext.instance().resource(resource);
              // 将Mapper.xml文件解析成输入流
              InputStream inputStream = Resources.getResourceAsStream(resource);
              // 使用XMLMapperBuilder解析Mapper.xml，并将Mapper Class注册进configuration对象的mapperRegistry容器中
              XMLMapperBuilder mapperParser = new XMLMapperBuilder(inputStream, configuration, resource, configuration.getSqlFragments());
              mapperParser.parse();
            } 
            // 解析url属性（Mapper.xml文件的路径）
            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();
            } 
            // 解析class属性（Mapper Class的全限定名）
            else if (resource == null && url == null && mapperClass != null) {
              // 将Mapper Class的权限定名转化成Class对象
              Class<?> mapperInterface = Resources.classForName(mapperClass);
              // 注册进configuration对象的mapperRegistry容器中
              configuration.addMapper(mapperInterface);
            } else {
              throw new BuilderException("A mapper element may only specify a url, resource or class, but not more than one.");
            }
          }
        }
      }
    }

## 节点的解析过程 ##

XMLMapperBuilder mapperParser = new XMLMapperBuilder(inputStream, configuration, resource, configuration.getSqlFragments());
    mapperParser.parse();

创建XMLMapperBuilder，首先会初始化父类BaseBuilder，并将configuration赋给BaseBuilder；  
然后创建MapperBuilderAssistant对象，该对象为XMLMapperBuilder的协助者，用来协助XMLMapperBuilder完成一些解析映射文件的动作。

private XMLMapperBuilder(XPathParser parser, Configuration configuration, String resource, Map<String, XNode> sqlFragments) {
      // 将configuration赋给BaseBuilder
      super(configuration);
      // 创建MapperBuilderAssistant对象（该对象为MapperBuilder的协助者）
      this.builderAssistant = new  MapperBuilderAssistant(configuration, resource);
      this.parser = parser;
      this.sqlFragments = sqlFragments;
      this.resource = resource;
    }
    
    //判断是否解析过
    public void parse() {
      // 若当前的Mapper.xml尚未被解析，则开始解析
      // PS：若<mappers>节点下有相同的<mapper>节点，那么就无需再次解析了
      if (!configuration.isResourceLoaded(resource)) {
        // 解析<mapper>节点
        configurationElement(parser.evalNode("/mapper"));
        // 将该Mapper.xml添加至configuration的LoadedResource容器中，下回无需再解析
        configuration.addLoadedResource(resource);
        // 将该Mapper.xml对应的Mapper Class注册进configuration的mapperRegistry容器中
        bindMapperForNamespace();
      }
    
      parsePendingResultMaps();
      parsePendingCacheRefs();
      parsePendingStatements();
    }
    
    //解析配置文件
    private void configurationElement(XNode context) {
    try {
      // 获取<mapper>节点上的namespace属性，该属性必须存在，表示当前映射文件对应的Mapper Class是谁
      String namespace = context.getStringAttribute("namespace");
      if (namespace == null || namespace.equals("")) {
        throw new BuilderException("Mapper's namespace cannot be empty");
      }
      // 将namespace属性值赋给builderAssistant
      builderAssistant.setCurrentNamespace(namespace);
      // 解析<cache-ref>节点
      cacheRefElement(context.evalNode("cache-ref"));
      // 解析<cache>节点
      cacheElement(context.evalNode("cache"));
      // 解析<parameterMap>节点
      parameterMapElement(context.evalNodes("/mapper/parameterMap"));
      // 解析<resultMap>节点
      resultMapElements(context.evalNodes("/mapper/resultMap"));
      // 解析<sql>节点
      sqlElement(context.evalNodes("/mapper/sql"));
      // 解析sql语句      
      buildStatementFromContext(context.evalNodes("select|insert|update|delete"));
    } catch (Exception e) {
      throw new BuilderException("Error parsing Mapper XML. Cause: " + e, e);
    }
    }

resultMapElements函数解析resultMap节点

//解析resultMap节点
    private ResultMap resultMapElement(XNode resultMapNode, List<ResultMapping> additionalResultMappings) throws Exception {
      ErrorContext.instance().activity("processing " + resultMapNode.getValueBasedIdentifier());
      // 获取<ResultMap>上的id属性
      String id = resultMapNode.getStringAttribute("id",
        resultMapNode.getValueBasedIdentifier());
      // 获取<ResultMap>上的type属性（即resultMap的返回值类型）
      String type = resultMapNode.getStringAttribute("type",
        resultMapNode.getStringAttribute("ofType",
            resultMapNode.getStringAttribute("resultType",
                resultMapNode.getStringAttribute("javaType"))));
      // 获取extends属性
      String extend = resultMapNode.getStringAttribute("extends");
      // 获取autoMapping属性
      Boolean autoMapping = resultMapNode.getBooleanAttribute("autoMapping");
      // 将resultMap的返回值类型转换成Class对象
      Class<?> typeClass = resolveClass(type);
      Discriminator discriminator = null;
      // resultMappings用于存储<resultMap>下所有的子节点
      List<ResultMapping> resultMappings = new ArrayList<ResultMapping>();
      resultMappings.addAll(additionalResultMappings);
      // 获取并遍历<resultMap>下所有的子节点
      List<XNode> resultChildren = resultMapNode.getChildren();
      for (XNode resultChild : resultChildren) {
        // 若当前节点为<constructor>，则将它的子节点们添加到resultMappings中去
        if ("constructor".equals(resultChild.getName())) {
          processConstructorElement(resultChild, typeClass, resultMappings);
        }
        // 若当前节点为<discriminator>，则进行条件判断，并将命中的子节点添加到resultMappings中去
        else if ("discriminator".equals(resultChild.getName())) {
          discriminator = processDiscriminatorElement(resultChild, typeClass, resultMappings);
        }
        // 若当前节点为<result>、<association>、<collection>，则将其添加到resultMappings中去
        else {
          // PS:flags仅用于区分当前节点是否是<id>或<idArg>，因为这两个节点的属性名为name，而其他节点的属性名为property
          List<ResultFlag> flags = new ArrayList<ResultFlag>();
          if ("id".equals(resultChild.getName())) {
            flags.add(ResultFlag.ID);
          }
          resultMappings.add(buildResultMappingFromContext(resultChild, typeClass, flags));
        }
      }
      ResultMapResolver resultMapResolver = new ResultMapResolver(builderAssistant, id, typeClass, extend, discriminator, resultMappings, autoMapping);
      try {
        return resultMapResolver.resolve();
      } catch (IncompleteElementException  e) {
        configuration.addIncompleteResultMap(resultMapResolver);
        throw e;
      }
    }

ResultMapResolver的作用是生成ResultMap对象，并将其加入到Configuration对象的resultMaps容器中（具体过程见下）  
ResultMapResolver

public ResultMap resolve() {
        return assistant.addResultMap(this.id, this.type, this.extend, this.discriminator, this.resultMappings, this.autoMapping);
      }
    
    
      public ResultMap addResultMap(
          String id,
          Class<?> type,
          String extend,
          Discriminator discriminator,
          List<ResultMapping> resultMappings,
          Boolean autoMapping) {
        id = applyCurrentNamespace(id, false);
        extend = applyCurrentNamespace(extend, true);
    	//继承的父ResultMap
        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<ResultMapping>(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();
              }
            }
          }
          resultMappings.addAll(extendedResultMappings);
        }
        ResultMap resultMap = new ResultMap.Builder(configuration, id, type, resultMappings, autoMapping)
            .discriminator(discriminator)
            .build();
        configuration.addResultMap(resultMap);
        return resultMap;
      }

## sqlElement函数 ##

XMLMapperBuilder解析映射文件中所有的节点，并将这些节点存储在当前映射文件所对应的XMLMapperBuilder对象的sqlFragments容器中，已sql的id为key，XNode为key，供解析sql语句时使用

private void sqlElement(List<XNode> list) throws Exception {
        if (configuration.getDatabaseId() != null) {
          sqlElement(list, configuration.getDatabaseId());
        }
        sqlElement(list, null);
      }
    
      private void sqlElement(List<XNode> list, String requiredDatabaseId) throws Exception {
        for (XNode context : list) {
          String databaseId = context.getStringAttribute("databaseId");
          String id = context.getStringAttribute("id");
          id = builderAssistant.applyCurrentNamespace(id, false);
          if (databaseIdMatchesCurrent(id, databaseId, requiredDatabaseId)) {
            sqlFragments.put(id, context);
          }
        }
      }

## buildStatementFromContext函数 ##

XMLMapperBuilder将映射文件中的sql语句解析成MappedStatement对象，并存在configuration的mappedStatements容器中。

private void buildStatementFromContext(List<XNode> list) {
        if (configuration.getDatabaseId() != null) {
          buildStatementFromContext(list, configuration.getDatabaseId());
        }
        buildStatementFromContext(list, null);
      }
    
      private void buildStatementFromContext(List<XNode> list, String requiredDatabaseId) {
        for (XNode context : list) {
          final XMLStatementBuilder statementParser = new XMLStatementBuilder(configuration, builderAssistant, context, requiredDatabaseId);
          try {
            statementParser.parseStatementNode();
          } catch (IncompleteElementException e) {
            configuration.addIncompleteStatement(statementParser);
          }
        }
      }

XMLStatementBuilder解析xml的insert等节点

public void parseStatementNode() {
        String id = context.getStringAttribute("id");
        String databaseId = context.getStringAttribute("databaseId");
    
        if (!databaseIdMatchesCurrent(id, databaseId, this.requiredDatabaseId)) {
          return;
        }
    
        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);
    
        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
        XMLIncludeTransformer includeParser = new XMLIncludeTransformer(configuration, builderAssistant);
        includeParser.applyIncludes(context.getNode());
    
        // Parse selectKey after includes and remove them.
        processSelectKeyNodes(id, parameterTypeClass, langDriver);
        
        // Parse the SQL (pre: <selectKey> and <include> were parsed and removed)
        SqlSource sqlSource = langDriver.createSqlSource(configuration, context, parameterTypeClass);
        String resultSets = context.getStringAttribute("resultSets");
        String keyProperty = context.getStringAttribute("keyProperty");
        String keyColumn = context.getStringAttribute("keyColumn");
        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;
        }
    
        builderAssistant.addMappedStatement(id, sqlSource, statementType, sqlCommandType,
            fetchSize, timeout, parameterMap, parameterTypeClass, resultMap, resultTypeClass,
            resultSetTypeEnum, flushCache, useCache, resultOrdered, 
            keyGenerator, keyProperty, keyColumn, databaseId, langDriver, resultSets);
      }

MapperBuilderAssistant根据insert节点解析后的元素构建MappedStatement 对象

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;
      }

## 创建SqlSessionFactory对象 ##

看一下SqlSessionFactory的build函数，刚才说了半天，介绍了XMLConfigBuilder解析映射文件的过程，解析完成之后parser.parse()函数会返回一个包含了映射文件解析结果的configuration对象，紧接着，这个对象将作为参数传递给另一个build函数

SqlSessionFactoryBuilder

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);
      }

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