第三章-Mybatis源码解析-以xml方式走流程-mapper解析（四）

3.2.2.7 selectKey解析

回到 XMLStatementBuilder.processSelectKeyNodes 的方法

private void processSelectKeyNodes(String id, Class<?> parameterTypeClass, LanguageDriver langDriver) {// 拿到所有 selectKey 节点List<XNode> selectKeyNodes = context.evalNodes("selectKey");if (configuration.getDatabaseId() != null) {parseSelectKeyNodes(id, selectKeyNodes, parameterTypeClass, langDriver, configuration.getDatabaseId());}// 解析selectKey节点parseSelectKeyNodes(id, selectKeyNodes, parameterTypeClass, langDriver, null);// 遍历并移除selectKey节点，防止干扰<insert>主节点后续解析流程removeSelectKeyNodes(selectKeyNodes);
}/** 
parentId 就是上级节点id，其实就是<insert id={parentId}>标签的id；
parameterTypeClass 也是<insert>标签上设置的参数类型
langDriver 就是 XMLLanguageDriver
skRequiredDatabaseId 一般情况下为 null
*/
private void parseSelectKeyNodes(String parentId, List<XNode> list, Class<?> parameterTypeClass, LanguageDriver langDriver, String skRequiredDatabaseId) {for (XNode nodeToHandle : list) {// 给selectKey 语句生成一个以“!selectKey”结尾的idString id = parentId + SelectKeyGenerator.SELECT_KEY_SUFFIX;// databaseId, skRequiredDatabaseId 这两个值一般为null，实际生产也基本为nullString databaseId = nodeToHandle.getStringAttribute("databaseId");if (databaseIdMatchesCurrent(id, databaseId, skRequiredDatabaseId)) {// 两种情况会走到这里：1.如果configuration 中没有当前 id 的statement；2.如果有 statement，但是databaseId 为  nullparseSelectKeyNode(id, nodeToHandle, parameterTypeClass, langDriver, databaseId);}}
}private void parseSelectKeyNode(String id, XNode nodeToHandle, Class<?> parameterTypeClass, LanguageDriver langDriver, String databaseId) {// 下面这一段都是获取开发时对selectKey配置的几个属性，各属性的值前面也有介绍，或者自己去官网捞出来看String resultType = nodeToHandle.getStringAttribute("resultType");Class<?> resultTypeClass = resolveClass(resultType);StatementType statementType = StatementType.valueOf(nodeToHandle.getStringAttribute("statementType", StatementType.PREPARED.toString()));String keyProperty = nodeToHandle.getStringAttribute("keyProperty");String keyColumn = nodeToHandle.getStringAttribute("keyColumn");boolean executeBefore = "BEFORE".equals(nodeToHandle.getStringAttribute("order", "AFTER"));//defaultsboolean useCache = false;boolean resultOrdered = false;KeyGenerator keyGenerator = NoKeyGenerator.INSTANCE;Integer fetchSize = null;Integer timeout = null;boolean flushCache = false;String parameterMap = null;String resultMap = null;ResultSetType resultSetTypeEnum = null;// 创建 sqlSource，看章节`3.2.2.6`SqlSource sqlSource = .createSqlSource(configuration, nodeToHandle, parameterTypeClass);SqlCommandType sqlCommandType = SqlCommandType.SELECT;// 创建 MappedStatement 并添加到 configuration 中，看章节`3.2.2.6`builderAssistant.addMappedStatement(id, sqlSource, statementType, sqlCommandType,fetchSize, timeout, parameterMap, parameterTypeClass, resultMap, resultTypeClass,resultSetTypeEnum, flushCache, useCache, resultOrdered,keyGenerator, keyProperty, keyColumn, databaseId, langDriver, null);id = builderAssistant.applyCurrentNamespace(id, false);// 再从 configuration 中把 刚创建的 MappedStatement 对象取出来MappedStatement keyStatement = configuration.getMappedStatement(id, false);// 生成 SelectKeyGenerator 并存放到 configuration 的相应 HashMap 中configuration.addKeyGenerator(id, new SelectKeyGenerator(keyStatement, executeBefore));
}private void removeSelectKeyNodes(List<XNode> selectKeyNodes) {for (XNode nodeToHandle : selectKeyNodes) {// 遍历并移除selectKey节点nodeToHandle.getParent().getNode().removeChild(nodeToHandle.getNode());}
}