上一篇，我们这只是粗略的说了一下Mybatis的配置文件解析的大体流程。而这一篇针对上一篇进行补充。

1. <sql> 是如何解析的

我们经常会把一些公用的，重复出现的字段写在<sql>标签中，而通过上图，我们知道sqlElement是负责解析sql中公用字段的。

 其实，它就是拿到xml中的 id值，然后把nameSpace和id进行拼接，形成一个全局唯一的id值。id为key，整个<sql>为value。放入map中

2. <ResultMap> 是如何解析与封装的

在mybatis中有个ResultMap对象和ResultMapping对象。而他们分别对象xml文件中的<ResultMap> 和 <result>、<collection> 、<association>、<id>等

在我们解析的过程中，就是找到<ResultMap>已经下面的子元素，逐个解析。而如果遇到了<collection> 、<association>，就递归解析。把他们分别分装成子的ResultMap对象。最后把这些子对象的id返回到上一层的ResultMap中，继续充当ResultMapping对象

private ResultMap resultMapElement(XNode resultMapNode, List<ResultMapping> additionalResultMappings) throws Exception {
    ErrorContext.instance().activity("processing " + resultMapNode.getValueBasedIdentifier());
    //获取resultmap节点的id属性
    String id = resultMapNode.getStringAttribute("id",
        resultMapNode.getValueBasedIdentifier());
    //获取resultmap节点的type属性
    String type = resultMapNode.getStringAttribute("type",
        resultMapNode.getStringAttribute("ofType",
            resultMapNode.getStringAttribute("resultType",
                resultMapNode.getStringAttribute("javaType"))));
    //获取resultmap节点的extends属性，描述继承关系
    String extend = resultMapNode.getStringAttribute("extends");
    //获取resultmap节点的autoMapping属性，是否开启自动映射
    Boolean autoMapping = resultMapNode.getBooleanAttribute("autoMapping");
    //从别名注册中心获取entity的class对象
    Class<?> typeClass = resolveClass(type);
    Discriminator discriminator = null;
    //记录子节点中的映射结果集合
    List<ResultMapping> resultMappings = new ArrayList<>();
    resultMappings.addAll(additionalResultMappings);
    //从xml文件中获取当前resultmap中的所有子节点，并开始遍历
    List<XNode> resultChildren = resultMapNode.getChildren();
    for (XNode resultChild : resultChildren) {
      if ("constructor".equals(resultChild.getName())) {//处理<constructor>节点
        processConstructorElement(resultChild, typeClass, resultMappings);
      } else if ("discriminator".equals(resultChild.getName())) {//处理<discriminator>节点
        discriminator = processDiscriminatorElement(resultChild, typeClass, resultMappings);
      } else {//处理<id> <result> <association> <collection>节点
        List<ResultFlag> flags = new ArrayList<>();
        if ("id".equals(resultChild.getName())) {
          flags.add(ResultFlag.ID);//如果是id节点，向flags中添加元素
        }
        //创建ResultMapping对象并加入resultMappings集合中
        resultMappings.add(buildResultMappingFromContext(resultChild, typeClass, flags));
      }
    }
    //实例化resultMap解析器
    ResultMapResolver resultMapResolver = new ResultMapResolver(builderAssistant, id, typeClass, extend, discriminator, resultMappings, autoMapping);
    try {
      //通过resultMap解析器实例化resultMap并将其注册到configuration对象
      return resultMapResolver.resolve();
    } catch (IncompleteElementException  e) {
      configuration.addIncompleteResultMap(resultMapResolver);
      throw e;
    }
  }

这里的buildResultMappingFromContext方法，是具体创建ResultMapping对象的。它使用到MapperBuilderAssistant这个助手类进行创建。

/根据resultmap中的子节点信息，创建resultMapping对象
  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);
    //使用建造者模式创建resultMapping对象
    return builderAssistant.buildResultMapping(resultType, property, column, javaTypeClass, jdbcTypeEnum, nestedSelect, nestedResultMap, notNullColumn, columnPrefix, typeHandlerClass, flags, resultSet, foreignColumn, lazy);
  }

下面简单看一下这个助手类 MapperBuilderAssistant。一眼看上去，好像全是使用的建造者模式创建对象的。像缓存、ResultMapping、ResultMap、ParameterMapping等好多信息，都是由它创建对象的。而封装增删改查的类 MappedStatement 也是由它创建的。

/*
 *    Copyright ${license.git.copyrightYears} the original author or authors.
 *
 *    Licensed under the Apache License, Version 2.0 (the "License");
 *    you may not use this file except in compliance with the License.
 *    You may obtain a copy of the License at
 *
 *       http://www.apache.org/licenses/LICENSE-2.0
 *
 *    Unless required by applicable law or agreed to in writing, software
 *    distributed under the License is distributed on an "AS IS" BASIS,
 *    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *    See the License for the specific language governing permissions and
 *    limitations under the License.
 */
package org.apache.ibatis.builder;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Properties;
import java.util.Set;
import java.util.StringTokenizer;

import org.apache.ibatis.cache.Cache;
import org.apache.ibatis.cache.decorators.LruCache;
import org.apache.ibatis.cache.impl.PerpetualCache;
import org.apache.ibatis.executor.ErrorContext;
import org.apache.ibatis.executor.keygen.KeyGenerator;
import org.apache.ibatis.mapping.CacheBuilder;
import org.apache.ibatis.mapping.Discriminator;
import org.apache.ibatis.mapping.MappedStatement;
import org.apache.ibatis.mapping.ParameterMap;
import org.apache.ibatis.mapping.ParameterMapping;
import org.apache.ibatis.mapping.ParameterMode;
import org.apache.ibatis.mapping.ResultFlag;
import org.apache.ibatis.mapping.ResultMap;
import org.apache.ibatis.mapping.ResultMapping;
import org.apache.ibatis.mapping.ResultSetType;
import org.apache.ibatis.mapping.SqlCommandType;
import org.apache.ibatis.mapping.SqlSource;
import org.apache.ibatis.mapping.StatementType;
import org.apache.ibatis.reflection.MetaClass;
import org.apache.ibatis.scripting.LanguageDriver;
import org.apache.ibatis.session.Configuration;
import org.apache.ibatis.type.JdbcType;
import org.apache.ibatis.type.TypeHandler;

/**
 * 辅助XMLMapperBuilder解析mapper.xml文件，完善属性信息，并注册到configuration对象
 * @author Clinton Begin
 */
public class MapperBuilderAssistant extends BaseBuilder {

  private String currentNamespace;
  private final String resource;
  private Cache currentCache;
  private boolean unresolvedCacheRef; // issue #676

  public MapperBuilderAssistant(Configuration configuration, String resource) {
    super(configuration);
    ErrorContext.instance().resource(resource);
    this.resource = resource;
  }

  public String getCurrentNamespace() {
    return currentNamespace;
  }

  public void setCurrentNamespace(String currentNamespace) {
    if (currentNamespace == null) {
      throw new BuilderException("The mapper element requires a namespace attribute to be specified.");
    }

    if (this.currentNamespace != null && !this.currentNamespace.equals(currentNamespace)) {
      throw new BuilderException("Wrong namespace. Expected '"
          + this.currentNamespace + "' but found '" + currentNamespace + "'.");
    }

    this.currentNamespace = currentNamespace;
  }

  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;
  }

  public Cache useCacheRef(String namespace) {
    if (namespace == null) {
      throw new BuilderException("cache-ref element requires a namespace attribute.");
    }
    try {
      unresolvedCacheRef = true;
      Cache cache = configuration.getCache(namespace);
      if (cache == null) {
        throw new IncompleteElementException("No cache for namespace '" + namespace + "' could be found.");
      }
      currentCache = cache;
      unresolvedCacheRef = false;
      return cache;
    } catch (IllegalArgumentException e) {
      throw new IncompleteElementException("No cache for namespace '" + namespace + "' could be found.", e);
    }
  }

 //通过builderAssistant创建缓存对象，并添加至configuration
  public Cache useNewCache(Class<? extends Cache> typeClass,
      Class<? extends Cache> evictionClass,
      Long flushInterval,
      Integer size,
      boolean readWrite,
      boolean blocking,
      Properties props) {
	//经典的建造起模式，创建一个cache对象
    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();
    //将缓存添加至configuration，注意二级缓存以命名空间为单位进行划分
    configuration.addCache(cache);
    currentCache = cache;
    return cache;
  }

  public ParameterMap addParameterMap(String id, Class<?> parameterClass, List<ParameterMapping> parameterMappings) {
    id = applyCurrentNamespace(id, false);
    ParameterMap parameterMap = new ParameterMap.Builder(configuration, id, parameterClass, parameterMappings).build();
    configuration.addParameterMap(parameterMap);
    return parameterMap;
  }

  public ParameterMapping buildParameterMapping(
      Class<?> parameterType,
      String property,
      Class<?> javaType,
      JdbcType jdbcType,
      String resultMap,
      ParameterMode parameterMode,
      Class<? extends TypeHandler<?>> typeHandler,
      Integer numericScale) {
    resultMap = applyCurrentNamespace(resultMap, true);

    // Class parameterType = parameterMapBuilder.type();
    Class<?> javaTypeClass = resolveParameterJavaType(parameterType, property, javaType, jdbcType);
    TypeHandler<?> typeHandlerInstance = resolveTypeHandler(javaTypeClass, typeHandler);

    return new ParameterMapping.Builder(configuration, property, javaTypeClass)
        .jdbcType(jdbcType)
        .resultMapId(resultMap)
        .mode(parameterMode)
        .numericScale(numericScale)
        .typeHandler(typeHandlerInstance)
        .build();
  }
  //实例化resultMap并将其注册到configuration对象
  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);
    //获得父类resultMap的完整id
    extend = applyCurrentNamespace(extend, true);

    //针对extend属性的处理
    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();
          }
        }
      }
      //添加需要被继承下来的resultMapping对象结合
      resultMappings.addAll(extendedResultMappings);
    }
    //通过建造者模式实例化resultMap,并注册到configuration.resultMaps中
    ResultMap resultMap = new ResultMap.Builder(configuration, id, type, resultMappings, autoMapping)
        .discriminator(discriminator)
        .build();
    configuration.addResultMap(resultMap);
    return resultMap;
  }

  public Discriminator buildDiscriminator(
      Class<?> resultType,
      String column,
      Class<?> javaType,
      JdbcType jdbcType,
      Class<? extends TypeHandler<?>> typeHandler,
      Map<String, String> discriminatorMap) {
    ResultMapping resultMapping = buildResultMapping(
        resultType,
        null,
        column,
        javaType,
        jdbcType,
        null,
        null,
        null,
        null,
        typeHandler,
        new ArrayList<ResultFlag>(),
        null,
        null,
        false);
    Map<String, String> namespaceDiscriminatorMap = new HashMap<>();
    for (Map.Entry<String, String> e : discriminatorMap.entrySet()) {
      String resultMap = e.getValue();
      resultMap = applyCurrentNamespace(resultMap, true);
      namespaceDiscriminatorMap.put(e.getKey(), resultMap);
    }
    return new Discriminator.Builder(configuration, resultMapping, namespaceDiscriminatorMap).build();
  }

  //添加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;

    //使用建造者模式创建一个mappedStatment
    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();//使用建造者模式创建一个mappedStatment
    configuration.addMappedStatement(statement);//将mappedStatment注册到configuration
    return statement;
  }

  private <T> T valueOrDefault(T value, T defaultValue) {
    return value == null ? defaultValue : value;
  }

  private ParameterMap getStatementParameterMap(
      String parameterMapName,
      Class<?> parameterTypeClass,
      String statementId) {
    parameterMapName = applyCurrentNamespace(parameterMapName, true);
    ParameterMap parameterMap = null;
    if (parameterMapName != null) {
      try {
        parameterMap = configuration.getParameterMap(parameterMapName);
      } catch (IllegalArgumentException e) {
        throw new IncompleteElementException("Could not find parameter map " + parameterMapName, e);
      }
    } else if (parameterTypeClass != null) {
      List<ParameterMapping> parameterMappings = new ArrayList<>();
      parameterMap = new ParameterMap.Builder(
          configuration,
          statementId + "-Inline",
          parameterTypeClass,
          parameterMappings).build();
    }
    return parameterMap;
  }

  private List<ResultMap> getStatementResultMaps(
      String resultMap,
      Class<?> resultType,
      String statementId) {
    resultMap = applyCurrentNamespace(resultMap, true);

    List<ResultMap> resultMaps = new ArrayList<>();
    if (resultMap != null) {
      String[] resultMapNames = resultMap.split(",");
      for (String resultMapName : resultMapNames) {
        try {
          resultMaps.add(configuration.getResultMap(resultMapName.trim()));
        } catch (IllegalArgumentException e) {
          throw new IncompleteElementException("Could not find result map " + resultMapName, e);
        }
      }
    } else if (resultType != null) {
      ResultMap inlineResultMap = new ResultMap.Builder(
          configuration,
          statementId + "-Inline",
          resultType,
          new ArrayList<ResultMapping>(),
          null).build();
      resultMaps.add(inlineResultMap);
    }
    return resultMaps;
  }

  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();
  }

  private Set<String> parseMultipleColumnNames(String columnName) {
    Set<String> columns = new HashSet<>();
    if (columnName != null) {
      if (columnName.indexOf(',') > -1) {
        StringTokenizer parser = new StringTokenizer(columnName, "{}, ", false);
        while (parser.hasMoreTokens()) {
          String column = parser.nextToken();
          columns.add(column);
        }
      } else {
        columns.add(columnName);
      }
    }
    return columns;
  }

  private List<ResultMapping> parseCompositeColumnName(String columnName) {
    List<ResultMapping> composites = new ArrayList<>();
    if (columnName != null && (columnName.indexOf('=') > -1 || columnName.indexOf(',') > -1)) {
      StringTokenizer parser = new StringTokenizer(columnName, "{}=, ", false);
      while (parser.hasMoreTokens()) {
        String property = parser.nextToken();
        String column = parser.nextToken();
        ResultMapping complexResultMapping = new ResultMapping.Builder(
            configuration, property, column, configuration.getTypeHandlerRegistry().getUnknownTypeHandler()).build();
        composites.add(complexResultMapping);
      }
    }
    return composites;
  }

  private Class<?> resolveResultJavaType(Class<?> resultType, String property, Class<?> javaType) {
    if (javaType == null && property != null) {
      try {
        MetaClass metaResultType = MetaClass.forClass(resultType, configuration.getReflectorFactory());
        javaType = metaResultType.getSetterType(property);
      } catch (Exception e) {
        //ignore, following null check statement will deal with the situation
      }
    }
    if (javaType == null) {
      javaType = Object.class;
    }
    return javaType;
  }

  private Class<?> resolveParameterJavaType(Class<?> resultType, String property, Class<?> javaType, JdbcType jdbcType) {
    if (javaType == null) {
      if (JdbcType.CURSOR.equals(jdbcType)) {
        javaType = java.sql.ResultSet.class;
      } else if (Map.class.isAssignableFrom(resultType)) {
        javaType = Object.class;
      } else {
        MetaClass metaResultType = MetaClass.forClass(resultType, configuration.getReflectorFactory());
        javaType = metaResultType.getGetterType(property);
      }
    }
    if (javaType == null) {
      javaType = Object.class;
    }
    return javaType;
  }

  /** Backward compatibility signature */
  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) {
      return buildResultMapping(
        resultType, property, column, javaType, jdbcType, nestedSelect,
        nestedResultMap, notNullColumn, columnPrefix, typeHandler, flags, null, null, configuration.isLazyLoadingEnabled());
  }

  public LanguageDriver getLanguageDriver(Class<? extends LanguageDriver> langClass) {
    if (langClass != null) {
      configuration.getLanguageRegistry().register(langClass);
    } else {
      langClass = configuration.getLanguageRegistry().getDefaultDriverClass();
    }
    return configuration.getLanguageRegistry().getDriver(langClass);
  }

  /** Backward compatibility signature */
  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) {
    return addMappedStatement(
      id, sqlSource, statementType, sqlCommandType, fetchSize, timeout,
      parameterMap, parameterType, resultMap, resultType, resultSetType,
      flushCache, useCache, resultOrdered, keyGenerator, keyProperty,
      keyColumn, databaseId, lang, null);
  }

}

我个人理解，这体现了单一职责的原则。为什么这么说呢？

XMLMapperBuilder 和 XMLStatementBuilder只负责解析xml文件，而MapperBuilderAssistant只负责对他们解析的对象进行封装，责任非常的清楚。但是，这个MapperBuilderAssistant封装的对象又有点多，硬要往单一职责上说也似乎有点牵强。不过这样设计，确实精简了不少的代码，知道研究

3. 增、删、改、查如何封装

 

 而底层更没有什么好说的，就是单纯的解析当前sql语句的所有属性以及子节点。

 public void parseStatementNode() {
	//获取sql节点的id
    String id = context.getStringAttribute("id");
    String databaseId = context.getStringAttribute("databaseId");

    if (!databaseIdMatchesCurrent(id, databaseId, this.requiredDatabaseId)) {
      return;
    }
    /*获取sql节点的各种属性*/
    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);



    //根据sql节点的名称获取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语句之前先解析<include>节点
    XMLIncludeTransformer includeParser = new XMLIncludeTransformer(configuration, builderAssistant);
    includeParser.applyIncludes(context.getNode());

    // Parse selectKey after includes and remove them.
    //在解析sql语句之前，处理<selectKey>子节点，并在xml节点中删除
    processSelectKeyNodes(id, parameterTypeClass, langDriver);

    // Parse the SQL (pre: <selectKey> and <include> were parsed and removed)
    //解析sql语句是解析mapper.xml的核心，实例化sqlSource，使用sqlSource封装sql语句
    SqlSource sqlSource = langDriver.createSqlSource(configuration, context, parameterTypeClass);
    String resultSets = context.getStringAttribute("resultSets");//获取resultSets属性
    String keyProperty = context.getStringAttribute("keyProperty");//获取主键信息keyProperty
    String keyColumn = context.getStringAttribute("keyColumn");///获取主键信息keyColumn

    //根据<selectKey>获取对应的SelectKeyGenerator的id
    KeyGenerator keyGenerator;
    String keyStatementId = id + SelectKeyGenerator.SELECT_KEY_SUFFIX;
    keyStatementId = builderAssistant.applyCurrentNamespace(keyStatementId, true);


    //获取keyGenerator对象，如果是insert类型的sql语句，会使用KeyGenerator接口获取数据库生产的id；
    if (configuration.hasKeyGenerator(keyStatementId)) {
      keyGenerator = configuration.getKeyGenerator(keyStatementId);
    } else {
      keyGenerator = context.getBooleanAttribute("useGeneratedKeys",
          configuration.isUseGeneratedKeys() && SqlCommandType.INSERT.equals(sqlCommandType))
          ? Jdbc3KeyGenerator.INSTANCE : NoKeyGenerator.INSTANCE;
    }

    //通过builderAssistant实例化MappedStatement，并注册至configuration对象
    builderAssistant.addMappedStatement(id, sqlSource, statementType, sqlCommandType,
        fetchSize, timeout, parameterMap, parameterTypeClass, resultMap, resultTypeClass,
        resultSetTypeEnum, flushCache, useCache, resultOrdered,
        keyGenerator, keyProperty, keyColumn, databaseId, langDriver, resultSets);
  }

缓存我们放在后面说。其实上一篇和本篇都是关于解析配置文件的。单纯看解析，其实都挺简单的。多看看细节，学习一些技巧。

最后，我们来认识一下XMLScriptBuilder

 我们知道，MapperStatement是封装具体的增、删、改、查语句的。但是，除了这些，它还存储了哪些信息呢？

其实，它的数据结构很清晰。所有的sql语句信息都是封装在 SqlSource 中的。而我们进入debug模式查看的时候发现：

SqlSource sqlSource = langDriver.createSqlSource(configuration, context, parameterTypeClass);

他是借助于 XMLScriptBuilder 完成的。

 我们发现，它就是new了一个包装类而已。

 此时，我们又看到了一个类 ： SqlSourceBuilder。而调用这个类的parese方法。我们发现，它就是针对sql语句中传递的参数进行预处理的。我们把sql语句中的具体参数名替换成 ？ 占位符。

替换前：

 替换后：

 替换后，我们就得到了一个比较安全的、预处理的sql语句。最后封装成一个SqlSource对象。

 最后，再把SqlSource对象封装到MapperStatement对象中。

总结：

经常听人说Mybatis解析配置文件的3个小伙伴，其实说的就是XMLConfigBuilder、XMLMapperBuilder 和 XMLStatementBuilder。而秘书指的就是MapperBuilderAssistant

但是，通过如上的UML图，我们可以看到还有SqlSourceBuilder 、XMLScriptBulder。

XMLScriptBuilder 就是负责创建 SqlSource 对象的。在我们实例化SqlSource对象的时候，构造方法会实例化SqlSourceBuilder  对象。

SqlSourceBuilder  就是预处理SQL语句的，会把一些参数名替换成 ？占位符。

大致流程图如下：

而XMLStatementBuilder生成MappedStatement的时候，其实还是可以继续划分更为细致的流程