MyBatis3源码解析(7)TypeHandler注册与获取

简介

在上篇文章中，我们介绍了TypeHandler的简单使用和解析了TypeHandler的处理核心，这篇文章中我们接着看到TypeHandler是如注册和获取使用的

源码解析

TypeHandler注册

typeHandler注册的函数代码如下：

根据JavaType放入第一层Map
根据jdbcType放入第二层Map

  configuration.getTypeHandlerRegistry().register(String[].class, JdbcType.VARCHAR, StringArrayTypeHandler.class);private void register(Type javaType, JdbcType jdbcType, TypeHandler<?> handler) {if (javaType != null) {Map<JdbcType, TypeHandler<?>> map = typeHandlerMap.get(javaType);if (map == null || map == NULL_TYPE_HANDLER_MAP) {map = new HashMap<>();}map.put(jdbcType, handler);typeHandlerMap.put(javaType, map);}allTypeHandlersMap.put(handler.getClass(), handler);}

TypeHandler获取

在探索中，我们发现是在Mapper初始化的过程就会去获取TypeHandler了，在示例代码中我们调用了函数：addMapper

在该函数中，我们看到了我们熟悉的（前面文章分析过，Sql执行其实就是从Mapper代理类开始的）MapperProxy相关的东西

  public <T> void addMapper(Class<T> type) {if (type.isInterface()) {if (hasMapper(type)) {throw new BindingException("Type " + type + " is already known to the MapperRegistry.");}boolean loadCompleted = false;try {// 生成我们熟悉的Mapper代理类knownMappers.put(type, new MapperProxyFactory<>(type));// It's important that the type is added before the parser is run// otherwise the binding may automatically be attempted by the// mapper parser. If the type is already known, it won't try.MapperAnnotationBuilder parser = new MapperAnnotationBuilder(config, type);// 进行解析parser.parse();loadCompleted = true;} finally {if (!loadCompleted) {knownMappers.remove(type);}}}}

跟踪下面，我们看到SQLSource生成的相关代码，ParameterMapper就是从SQLSource带下去的

  void parseStatement(Method method) {......getAnnotationWrapper(method, true, statementAnnotationTypes).ifPresent(statementAnnotation -> {final SqlSource sqlSource = buildSqlSource(statementAnnotation.getAnnotation(), parameterTypeClass, languageDriver, method);......});}public SqlSource createSqlSource(Configuration configuration, String script, Class<?> parameterType) {// issue #3if (script.startsWith("<script>")) {XPathParser parser = new XPathParser(script, false, configuration.getVariables(), new XMLMapperEntityResolver());return createSqlSource(configuration, parser.evalNode("/script"), parameterType);} else {// issue #127script = PropertyParser.parse(script, configuration.getVariables());TextSqlNode textSqlNode = new TextSqlNode(script);if (textSqlNode.isDynamic()) {// 这个暂时不理解return new DynamicSqlSource(configuration, textSqlNode);} else {// 目前走的这个return new RawSqlSource(configuration, script, parameterType);}}}public SqlSource parse(String originalSql, Class<?> parameterType, Map<String, Object> additionalParameters) {ParameterMappingTokenHandler handler = new ParameterMappingTokenHandler(configuration, parameterType, additionalParameters);GenericTokenParser parser = new GenericTokenParser("#{", "}", handler);String sql;if (configuration.isShrinkWhitespacesInSql()) {sql = parser.parse(removeExtraWhitespaces(originalSql));} else {// 走的这个sql = parser.parse(originalSql);}return new StaticSqlSource(configuration, sql, handler.getParameterMappings());}

下面是对SQL语句进行了解析，最终的效果是遍历了我们示例SQL中的id和name，对其找到对应的TypeHandler

细节部分没怎么看到，暂时跳过

public class GenericTokenParser {public String parse(String text) {if (text == null || text.isEmpty()) {return "";}// search open tokenint start = text.indexOf(openToken);if (start == -1) {return text;}char[] src = text.toCharArray();int offset = 0;final StringBuilder builder = new StringBuilder();StringBuilder expression = null;do {if (start > 0 && src[start - 1] == '\\') {// this open token is escaped. remove the backslash and continue.builder.append(src, offset, start - offset - 1).append(openToken);offset = start + openToken.length();} else {// found open token. let's search close token.if (expression == null) {expression = new StringBuilder();} else {expression.setLength(0);}builder.append(src, offset, start - offset);offset = start + openToken.length();int end = text.indexOf(closeToken, offset);while (end > -1) {if (end > offset && src[end - 1] == '\\') {// this close token is escaped. remove the backslash and continue.expression.append(src, offset, end - offset - 1).append(closeToken);offset = end + closeToken.length();end = text.indexOf(closeToken, offset);} else {expression.append(src, offset, end - offset);break;}}if (end == -1) {// close token was not found.builder.append(src, start, src.length - start);offset = src.length;} else {builder.append(handler.handleToken(expression.toString()));offset = end + closeToken.length();}}start = text.indexOf(openToken, offset);} while (start > -1);if (offset < src.length) {builder.append(src, offset, src.length - offset);}return builder.toString();}
}

下面就是根据对应的JavaType和jdbcType,获取对应的TypeHandler

    public String handleToken(String content) {parameterMappings.add(buildParameterMapping(content));return "?";}// 在其中设置JavaType和jdbcTypeprivate ParameterMapping buildParameterMapping(String content) {Map<String, String> propertiesMap = parseParameterMapping(content);String property = propertiesMap.get("property");Class<?> propertyType;if (metaParameters.hasGetter(property)) { // issue #448 get type from additional paramspropertyType = metaParameters.getGetterType(property);} else if (typeHandlerRegistry.hasTypeHandler(parameterType)) {propertyType = parameterType;} else if (JdbcType.CURSOR.name().equals(propertiesMap.get("jdbcType"))) {propertyType = java.sql.ResultSet.class;} else if (property == null || Map.class.isAssignableFrom(parameterType)) {propertyType = Object.class;} else {MetaClass metaClass = MetaClass.forClass(parameterType, configuration.getReflectorFactory());if (metaClass.hasGetter(property)) {propertyType = metaClass.getGetterType(property);} else {propertyType = Object.class;}}ParameterMapping.Builder builder = new ParameterMapping.Builder(configuration, property, propertyType);Class<?> javaType = propertyType;String typeHandlerAlias = null;for (Map.Entry<String, String> entry : propertiesMap.entrySet()) {String name = entry.getKey();String value = entry.getValue();if ("javaType".equals(name)) {javaType = resolveClass(value);builder.javaType(javaType);} else if ("jdbcType".equals(name)) {builder.jdbcType(resolveJdbcType(value));} else if ("mode".equals(name)) {builder.mode(resolveParameterMode(value));} else if ("numericScale".equals(name)) {builder.numericScale(Integer.valueOf(value));} else if ("resultMap".equals(name)) {builder.resultMapId(value);} else if ("typeHandler".equals(name)) {typeHandlerAlias = value;} else if ("jdbcTypeName".equals(name)) {builder.jdbcTypeName(value);} else if ("property".equals(name)) {// Do Nothing} else if ("expression".equals(name)) {throw new BuilderException("Expression based parameters are not supported yet");} else {throw new BuilderException("An invalid property '" + name + "' was found in mapping #{" + content + "}.  Valid properties are " + PARAMETER_PROPERTIES);}}if (typeHandlerAlias != null) {builder.typeHandler(resolveTypeHandler(javaType, typeHandlerAlias));}return builder.build();}public ParameterMapping build() {resolveTypeHandler();validate();return parameterMapping;}private void resolveTypeHandler() {if (parameterMapping.typeHandler == null && parameterMapping.javaType != null) {Configuration configuration = parameterMapping.configuration;TypeHandlerRegistry typeHandlerRegistry = configuration.getTypeHandlerRegistry();// 从Map中获取对应的TypeHandler，以javaType和jdbcType为标识parameterMapping.typeHandler = typeHandlerRegistry.getTypeHandler(parameterMapping.javaType, parameterMapping.jdbcType);}}private <T> TypeHandler<T> getTypeHandler(Type type, JdbcType jdbcType) {if (ParamMap.class.equals(type)) {return null;}// 根据javaType获取MapMap<JdbcType, TypeHandler<?>> jdbcHandlerMap = getJdbcHandlerMap(type);TypeHandler<?> handler = null;if (jdbcHandlerMap != null) {// 根据jdbcType获取handler = jdbcHandlerMap.get(jdbcType);if (handler == null) {handler = jdbcHandlerMap.get(null);}if (handler == null) {// #591handler = pickSoleHandler(jdbcHandlerMap);}}// type drives generics herereturn (TypeHandler<T>) handler;}

总结

在本篇文章中，我们初步探索了Mapper初始化的一部分，着重解析了TypeHandler相关的注册和MapperProxy生成时TypeHandler对应的获取

核心流程如下：

1.注册TypeHandler：放入Map中
2.MapperProxy生成，字段的TypeHandler是在SQLSource中，生成SQLSource
3.解析SQL语句，得到对应参数和返回字段的TypeHandler：这部分没细研究，但后面如果遇到问题，可以回来参考参考
4.根据JavaType和jdbcType得到对应的TypeHandler

这部分还有很多的细节没来得及去细看，但如果遇到问题，还是能提供方向性的指导