mybatis-初始化(三)statement解析

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MappedStatement builderAssistant.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 values NamedNodeMap 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ParameterMap ParameterMap 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。