mybatis配置文件解析原理简略时序图

配置文件解析主要用到XMLConfigBuilder(解析mybatis-config.xml) -->  XMLMapperBuilder(解析mapper.xml) --> XMLStatementBuilder(解析mapper.xml中cache, resultMap等配置信息，包括处理sql语句中的include标签) -->XMLScriptBuilder(解析mapper.xml中insert update select delete等sql语句节点)

1. 每个SQL语句节点都会生成一个SqlSource，每个SqlSource中都会保存一个SqlNode，SqlNode中又有子的SqlNode(包括普通sql语句也是一个文本SqlNode(StaticTextSqlNode))

2. 对于每个SQL语句节点，不同Node的解析会使用不同的NodeHandler，XMLScriptBuilder中有一个内部接口NodeHandler，有多个实现类(IfNodeHandler, WhereNodeHandler, ChooseNodeHandler等)， 这些实现类的作用就是处理SQL语句节点内部的每种不同的节点标签（如<if></if> <where></where>等）

3. 对于上边红色标示的处理include标签，是在XMLStatementBuilder中来做的，源码：

/**
* XMLStatmentBuilder
*/
public void parseStatementNode() {
    //...处理属性

    // Include Fragments before parsing 处理include标签
    XMLIncludeTransformer includeParser = new XMLIncludeTransformer(configuration, builderAssistant);
    includeParser.applyIncludes(context.getNode());

    // Parse selectKey after includes and remove them. 处理<selectKey>标签
    processSelectKeyNodes(id, parameterTypeClass, langDriver);
    
    // Parse the SQL (pre: <selectKey> and <include> were parsed and removed) 处理SQL语句和内部标签
    //...
  }

 

/**
* XMLIncludeTransformer
*/
public void applyIncludes(Node source) {
    if (source.getNodeName().equals("include")) {
      Node toInclude = findSqlFragment(getStringAttribute(source, "refid"));
      applyIncludes(toInclude);
      if (toInclude.getOwnerDocument() != source.getOwnerDocument()) {
        toInclude = source.getOwnerDocument().importNode(toInclude, true);
      }
      source.getParentNode().replaceChild(toInclude, source);
      while (toInclude.hasChildNodes()) {
        toInclude.getParentNode().insertBefore(toInclude.getFirstChild(), toInclude);
      }
      toInclude.getParentNode().removeChild(toInclude);
    } else if (source.getNodeType() == Node.ELEMENT_NODE) {
      NodeList children = source.getChildNodes();
      for (int i=0; i<children.getLength(); i++) {
        applyIncludes(children.item(i));
      }
    }
  }

 

/**
* XMLStatmentBuilder
*/
private void processSelectKeyNodes(String id, Class<?> parameterTypeClass, LanguageDriver langDriver) {
    List<XNode> selectKeyNodes = context.evalNodes("selectKey");
    if (configuration.getDatabaseId() != null) {
      parseSelectKeyNodes(id, selectKeyNodes, parameterTypeClass, langDriver, configuration.getDatabaseId());
    }
    parseSelectKeyNodes(id, selectKeyNodes, parameterTypeClass, langDriver, null);
    removeSelectKeyNodes(selectKeyNodes);
  }