概述

Statement是我们平时sql的载体，一条sql代表一个Statement，来看下mybatis如何解析Statement。

接着上篇最后的入口

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) {//解析异常的，记录下来configuration.addIncompleteStatement(statementParser);}}
}

XMLStatementBuilder

public class XMLStatementBuilder extends BaseBuilder {/*** mapper构造助手*/private final MapperBuilderAssistant builderAssistant;/*** statement节点*/private final XNode context;/*** 要求的数据库id（忽略）*/private final String requiredDatabaseId;public XMLStatementBuilder(Configuration configuration, MapperBuilderAssistant builderAssistant, XNode context, String databaseId) {super(configuration);this.builderAssistant = builderAssistant;this.context = context;this.requiredDatabaseId = databaseId;}

这里元数据是，mapper构造助手、statement节点。

parseStatementNode 解析xml

public void parseStatementNode() {String id = context.getStringAttribute("id");String databaseId = context.getStringAttribute("databaseId");if (!databaseIdMatchesCurrent(id, databaseId, this.requiredDatabaseId)) {return;}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// ①include sql片段解析，替换<include />XMLIncludeTransformer includeParser = new XMLIncludeTransformer(configuration, builderAssistant);includeParser.applyIncludes(context.getNode());String parameterType = context.getStringAttribute("parameterType");Class<?> parameterTypeClass = resolveClass(parameterType);String lang = context.getStringAttribute("lang");LanguageDriver langDriver = getLanguageDriver(lang);// Parse selectKey after includes and remove them.// 解析<selectKey />processSelectKeyNodes(id, parameterTypeClass, langDriver);// Parse the SQL (pre: <selectKey> and <include> were parsed and removed)// 获取主键生成器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;}// 创建sqlSource，sql载体SqlSource sqlSource = langDriver.createSqlSource(configuration, context, parameterTypeClass);StatementType statementType = StatementType.valueOf(context.getStringAttribute("statementType", StatementType.PREPARED.toString()));// 属性解析Integer fetchSize = context.getIntAttribute("fetchSize");Integer timeout = context.getIntAttribute("timeout");String parameterMap = context.getStringAttribute("parameterMap");String resultType = context.getStringAttribute("resultType");Class<?> resultTypeClass = resolveClass(resultType);String resultMap = context.getStringAttribute("resultMap");String resultSetType = context.getStringAttribute("resultSetType");ResultSetType resultSetTypeEnum = resolveResultSetType(resultSetType);if (resultSetTypeEnum == null) {resultSetTypeEnum = configuration.getDefaultResultSetType();}String keyProperty = context.getStringAttribute("keyProperty");String keyColumn = context.getStringAttribute("keyColumn");String resultSets = context.getStringAttribute("resultSets");// ②使用xml构造助手生成MappedStatementbuilderAssistant.addMappedStatement(id, sqlSource, statementType, sqlCommandType,fetchSize, timeout, parameterMap, parameterTypeClass, resultMap, resultTypeClass,resultSetTypeEnum, flushCache, useCache, resultOrdered,keyGenerator, keyProperty, keyColumn, databaseId, langDriver, resultSets);
}

statement标签上定义的属性比较多，一些简单的属性解析之后，直接保存结果。

对某些标签会做稍复杂一点的处理。

include解析

XMLIncludeTransformer includeParser = new XMLIncludeTransformer(configuration, builderAssistant);
// 应用include标签
includeParser.applyIncludes(context.getNode());

public void applyIncludes(Node source) {// properties读取Properties variablesContext = new Properties();Properties configurationVariables = configuration.getVariables();Optional.ofNullable(configurationVariables).ifPresent(variablesContext::putAll);// 应用applyIncludes(source, variablesContext, false);
}

private void applyIncludes(Node source, final Properties variablesContext, boolean included) {if (source.getNodeName().equals("include")) {//通过refid 查找出sql节点,include实际是引入sql标签Node toInclude = findSqlFragment(getStringAttribute(source, "refid"), variablesContext);Properties toIncludeContext = getVariablesContext(source, variablesContext);// 递归处理嵌套<include />applyIncludes(toInclude, toIncludeContext, true);if (toInclude.getOwnerDocument() != source.getOwnerDocument()) {toInclude = source.getOwnerDocument().importNode(toInclude, true);}// 将<include /> 替换成 <sql />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) {if (included && !variablesContext.isEmpty()) {// replace variables in attribute valuesNamedNodeMap attributes = source.getAttributes();for (int i = 0; i < attributes.getLength(); i++) {Node attr = attributes.item(i);// 占位符替换attr.setNodeValue(PropertyParser.parse(attr.getNodeValue(), variablesContext));}}NodeList children = source.getChildNodes();for (int i = 0; i < children.getLength(); i++) {applyIncludes(children.item(i), variablesContext, included);}} else if (included && (source.getNodeType() == Node.TEXT_NODE || source.getNodeType() == Node.CDATA_SECTION_NODE)&& !variablesContext.isEmpty()) {// 占位符替换source.setNodeValue(PropertyParser.parse(source.getNodeValue(), variablesContext));}
}

include标签解析实际是查找当前namespace下的sql片段，并在真正解析Statement之前，将其替换成Sql标签。

然后会将整个sql，可能是动态的可能是静态的转为SqlSource。

MappedStatement 构造

MappedStatement主要是包含了对Statement标签解析的结果，完完整整的描述个Statement。

public final class MappedStatement {private String resource;private Configuration configuration;private String id;private Integer fetchSize;private Integer timeout;private StatementType statementType;private ResultSetType resultSetType;private SqlSource sqlSource;private Cache cache;private ParameterMap parameterMap;private List<ResultMap> resultMaps;private boolean flushCacheRequired;private boolean useCache;private boolean resultOrdered;private SqlCommandType sqlCommandType;private KeyGenerator keyGenerator;private String[] keyProperties;private String[] keyColumns;private boolean hasNestedResultMaps;private String databaseId;private Log statementLog;private LanguageDriver lang;private String[] resultSets;
}

构造过程：

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;// 属性挨个设置到builder中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)// ①resultMap解析.resultMaps(getStatementResultMaps(resultMap, resultType, id)).resultSetType(resultSetType).flushCacheRequired(valueOrDefault(flushCache, !isSelect)).useCache(valueOrDefault(useCache, isSelect)).cache(currentCache);// ②转换ParameterMapParameterMap statementParameterMap = getStatementParameterMap(parameterMap, parameterType, id);if (statementParameterMap != null) {statementBuilder.parameterMap(statementParameterMap);}// 构造实例MappedStatement statement = statementBuilder.build();//保存到configuration中configuration.addMappedStatement(statement);return statement;
}

其实构造过程也比较单纯，就是将xml的上定义的标签解析并保存下来。

resultMap解析

①处，Statement上ResultMap解析展开一下。

private List<ResultMap> getStatementResultMaps(String resultMap,Class<?> resultType,String statementId) {// 在当前命名空间下查找resultMap = applyCurrentNamespace(resultMap, true);/** 存储ResultMap结果*/List<ResultMap> resultMaps = new ArrayList<>();if (resultMap != null) {/** 支持多个 ，分隔，存储过程才会涉及多个ResultMap* 普通sql考虑一个的情况即可*/String[] resultMapNames = resultMap.split(",");for (String resultMapName : resultMapNames) {try {/** 根据resultMap的id从当初Configuration中获取ResultMap实例* 在解析xml的时候Configuration就已经将所有ResultMap存下来了*/resultMaps.add(configuration.getResultMap(resultMapName.trim()));} catch (IllegalArgumentException e) {throw new IncompleteElementException("Could not find result map '" + resultMapName + "' referenced from '" + statementId + "'", e);}}}/** 如果使用的ResultType，那么会自动生成一个ResultMap**/else if (resultType != null) {ResultMap inlineResultMap = new ResultMap.Builder(configuration,statementId + "-Inline",resultType,new ArrayList<>(),null).build();resultMaps.add(inlineResultMap);}return resultMaps;
}

这里看到当配置了ResultType时也会为其创建一个ResultMap。

ParameterMap解析（由于官方正在渐渐废弃，所以略过）

总结

解析的过程比较简单，其中包含了一些实体的转换，最终解析后构造MappedStatement存储。