绑定Mapper接口
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quanhengf
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@ -442,14 +442,257 @@ public class ResultMap {
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private Boolean autoMapping;
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}
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```
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了解了ResultMapping 和ResultMap 记录的信息之后，下面开始介绍<resultMap>节点的解析过程。在XMLMapperBuilder中通过resultMapElements()方法解析映射配置文件中的全部<resultMap>节点，该方法会循环调用resultMapElement()方法处理每个＜resultMap＞节点。
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```java
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private ResultMap resultMapElement(XNode resultMapNode) throws Exception {
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return resultMapElement(resultMapNode, Collections.<ResultMapping> emptyList());
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}
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private ResultMap resultMapElement(XNode resultMapNode, List<ResultMapping> additionalResultMappings) throws Exception {
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ErrorContext.instance().activity("processing " + resultMapNode.getValueBasedIdentifier());
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// <resultMap>的id属性，默认值会拼装所有父节点的id 或value或property属性值
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String id = resultMapNode.getStringAttribute("id",
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resultMapNode.getValueBasedIdentifier());
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// <resultMap>的type属性，表示结果集将被映射成type指定类型的对象
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String type = resultMapNode.getStringAttribute("type",
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resultMapNode.getStringAttribute("ofType",
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resultMapNode.getStringAttribute("resultType",
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resultMapNode.getStringAttribute("javaType"))));
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// 该属性指定了该<resultMap>节点的继承关系
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String extend = resultMapNode.getStringAttribute("extends");
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// 为true则启动自动映射功能，该功能会自动查找与列明相同的属性名，并调用setter方法，
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// 为false，则需要在<resultMap>节点内注明映射关系才会调用对应的setter方法
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Boolean autoMapping = resultMapNode.getBooleanAttribute("autoMapping");
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// 解析type类型
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Class<?> typeClass = resolveClass(type);
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Discriminator discriminator = null;
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// 该集合用来记录解析结果
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List<ResultMapping> resultMappings = new ArrayList<ResultMapping>();
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resultMappings.addAll(additionalResultMappings);
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// 获取并处理<resultMap>的子节点
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List<XNode> resultChildren = resultMapNode.getChildren();
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// child单数形式，children复数形式
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for (XNode resultChild : resultChildren) {
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// 处理<constructor>节点
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if ("constructor".equals(resultChild.getName())) {
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processConstructorElement(resultChild, typeClass, resultMappings);
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// 处理<discriminator>节点
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} else if ("discriminator".equals(resultChild.getName())) {
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discriminator = processDiscriminatorElement(resultChild, typeClass, resultMappings);
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} else {
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// 处理<id>,<result>,<association>,<collection>等节点
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List<ResultFlag> flags = new ArrayList<ResultFlag>();
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if ("id".equals(resultChild.getName())) {
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flags.add(ResultFlag.ID);
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}
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// 创建ResultMapping对象，并添加到resultMappings集合
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resultMappings.add(buildResultMappingFromContext(resultChild, typeClass, flags));
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}
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}
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ResultMapResolver resultMapResolver = new ResultMapResolver(builderAssistant, id, typeClass, extend, discriminator, resultMappings, autoMapping);
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try {
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return resultMapResolver.resolve();
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} catch (IncompleteElementException e) {
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configuration.addIncompleteResultMap(resultMapResolver);
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throw e;
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}
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}
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```
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从上面的代码我们可以看到，mybatis从<resultMap>节点获取到id属性和type属性值之后，就会通过XMLMapperBuilder的buildResultMappingFromContext()方法为<result>节点创建对应的ResultMapping 对象。
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```java
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/**
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* 根据上下文环境构建ResultMapping
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*/
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private ResultMapping buildResultMappingFromContext(XNode context, Class<?> resultType, List<ResultFlag> flags) throws Exception {
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// 获取各个节点的属性，见文知意
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String property;
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if (flags.contains(ResultFlag.CONSTRUCTOR)) {
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property = context.getStringAttribute("name");
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} else {
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property = context.getStringAttribute("property");
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}
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String column = context.getStringAttribute("column");
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String javaType = context.getStringAttribute("javaType");
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String jdbcType = context.getStringAttribute("jdbcType");
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String nestedSelect = context.getStringAttribute("select");
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String nestedResultMap = context.getStringAttribute("resultMap",
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processNestedResultMappings(context, Collections.<ResultMapping> emptyList()));
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String notNullColumn = context.getStringAttribute("notNullColumn");
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String columnPrefix = context.getStringAttribute("columnPrefix");
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String typeHandler = context.getStringAttribute("typeHandler");
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String resultSet = context.getStringAttribute("resultSet");
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String foreignColumn = context.getStringAttribute("foreignColumn");
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boolean lazy = "lazy".equals(context.getStringAttribute("fetchType", configuration.isLazyLoadingEnabled() ? "lazy" : "eager"));
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Class<?> javaTypeClass = resolveClass(javaType);
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@SuppressWarnings("unchecked")
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Class<? extends TypeHandler<?>> typeHandlerClass = (Class<? extends TypeHandler<?>>) resolveClass(typeHandler);
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JdbcType jdbcTypeEnum = resolveJdbcType(jdbcType);
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// 创建ResultMapping对象并返回
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return builderAssistant.buildResultMapping(resultType, property, column, javaTypeClass, jdbcTypeEnum, nestedSelect, nestedResultMap, notNullColumn, columnPrefix, typeHandlerClass, flags, resultSet, foreignColumn, lazy);
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}
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```
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得到ResultMapping对象集合之后，会调用ResultMapResolver的resolve()方法，该方法会调用MapperBuilderAssistant的addResultMap()方法创建ResultMap对象，并将ResultMap对象添加到Configuration的resultMaps集合中保存。
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```java
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public class MapperBuilderAssistant extends BaseBuilder {
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public ResultMap addResultMap(String id, Class<?> type, String extend,
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Discriminator discriminator, List<ResultMapping> resultMappings, Boolean autoMapping) {
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// ResultMap的完整id是"namespace.id"的格式
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id = applyCurrentNamespace(id, false);
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// 获取 父ResultMap的完整id
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extend = applyCurrentNamespace(extend, true);
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// 针对extend属性进行的处理
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if (extend != null) {
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if (!configuration.hasResultMap(extend)) {
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throw new IncompleteElementException("Could not find a parent resultmap with id '" + extend + "'");
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}
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// 父ResultMap对象
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ResultMap resultMap = configuration.getResultMap(extend);
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// 父ResultMap对象的ResultMapping集合
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List<ResultMapping> extendedResultMappings = new ArrayList<ResultMapping>(resultMap.getResultMappings());
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// 删除需要覆盖的ResultMapping集合
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extendedResultMappings.removeAll(resultMappings);
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// Remove parent constructor if this resultMap declares a constructor.
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boolean declaresConstructor = false;
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for (ResultMapping resultMapping : resultMappings) {
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if (resultMapping.getFlags().contains(ResultFlag.CONSTRUCTOR)) {
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declaresConstructor = true;
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break;
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}
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}
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if (declaresConstructor) {
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Iterator<ResultMapping> extendedResultMappingsIter = extendedResultMappings.iterator();
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while (extendedResultMappingsIter.hasNext()) {
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if (extendedResultMappingsIter.next().getFlags().contains(ResultFlag.CONSTRUCTOR)) {
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extendedResultMappingsIter.remove();
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}
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}
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}
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// 添加需要被继承下来的ResultMapping集合
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resultMappings.addAll(extendedResultMappings);
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}
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ResultMap resultMap = new ResultMap.Builder(configuration, id, type, resultMappings, autoMapping)
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.discriminator(discriminator)
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.build();
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configuration.addResultMap(resultMap);
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return resultMap;
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}
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}
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```
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### 3.2 解析<sql>节点
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在映射配置文件中，可以使用<sql>节点定义可重用的SQL语句片段，当需要重用<sql>节点中定义的SQL语句片段时，只需要使用<include>节点引入相应的片段即可，这样，在编写SQL语句以及维护这些SQL语句时，都会比较方便。XMLMapperBuilder的sqlElement()方法负责解析映射配置文件中定义的全部<sql>节点。
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```java
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private void sqlElement(List<XNode> list) throws Exception {
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if (configuration.getDatabaseId() != null) {
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sqlElement(list, configuration.getDatabaseId());
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}
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sqlElement(list, null);
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}
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private void sqlElement(List<XNode> list, String requiredDatabaseId) throws Exception {
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// 遍历<sql>节点
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for (XNode context : list) {
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String databaseId = context.getStringAttribute("databaseId");
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String id = context.getStringAttribute("id");
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// 为id添加命名空间
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id = builderAssistant.applyCurrentNamespace(id, false);
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// 检测<sql>的databaseId与当前Configuration中记录的databaseId是否一致
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if (databaseIdMatchesCurrent(id, databaseId, requiredDatabaseId)) {
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// 记录到sqlFragments(Map<String, XNode>)中保存
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sqlFragments.put(id, context);
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}
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}
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}
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```
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## 4 XMLStatementBuilder
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这一部分看的不是很懂，暂时保留，日后深入理解了再写。
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## 5 绑定Mapper接口
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通过之前对binding模块的解析可知，每个映射配置文件的命名空间可以绑定一个Mapper接口，并注册到MapperRegistry中。XMLMapperBuilder的bindMapperForNamespace()方法中，完成了映射配置文件与对应Mapper 接
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口的绑定。
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```java
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public class XMLMapperBuilder extends BaseBuilder {
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private void bindMapperForNamespace() {
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// 获取映射配置文件的命名空间
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String namespace = builderAssistant.getCurrentNamespace();
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if (namespace != null) {
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Class<?> boundType = null;
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try {
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// 解析命名空间对应的类型
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boundType = Resources.classForName(namespace);
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} catch (ClassNotFoundException e) {
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//ignore, bound type is not required
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}
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if (boundType != null) {
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// 是否已加载boundType接口
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if (!configuration.hasMapper(boundType)) {
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// 追加个"namespace:"的前缀，并添加到Configuration的loadedResources集合中
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configuration.addLoadedResource("namespace:" + namespace);
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// 添加到Configuration的mapperRegistry集合中，另外，往这个方法栈的更深处看 会发现
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// 其创建了MapperAnnotationBuilder对象，并调用了该对象的parse()方法解析Mapper接口
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configuration.addMapper(boundType);
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}
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}
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}
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}
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}
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public class MapperRegistry {
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public <T> void addMapper(Class<T> type) {
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if (type.isInterface()) {
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if (hasMapper(type)) {
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throw new BindingException("Type " + type + " is already known to the MapperRegistry.");
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}
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boolean loadCompleted = false;
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try {
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knownMappers.put(type, new MapperProxyFactory<T>(type));
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// 解析Mapper接口type中的信息
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MapperAnnotationBuilder parser = new MapperAnnotationBuilder(config, type);
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parser.parse();
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loadCompleted = true;
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} finally {
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if (!loadCompleted) {
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knownMappers.remove(type);
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}
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}
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}
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}
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}
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public class MapperAnnotationBuilder {
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public void parse() {
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String resource = type.toString();
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// 是否已经加载过该接口
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if (!configuration.isResourceLoaded(resource)) {
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// 检查是否加载过该接口对应的映射文件，如果未加载，则创建XMLMapperBuilder对象
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// 解析对应的映射文件，该过程就是前面介绍的映射配置文件解析过程
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loadXmlResource();
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configuration.addLoadedResource(resource);
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assistant.setCurrentNamespace(type.getName());
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// 解析@CacheNamespace注解
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parseCache();
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// 解析@CacheNamespaceRef注解
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parseCacheRef();
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// type接口的所有方法
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Method[] methods = type.getMethods();
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for (Method method : methods) {
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try {
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if (!method.isBridge()) {
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// 解析SelectKey、ResultMap等注解，并创建MappedStatement对象
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parseStatement(method);
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}
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} catch (IncompleteElementException e) {
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// 如果解析过程出现IncompleteElementException异常，可能是因为引用了
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// 未解析的注解，这里将出现异常的方法记录下来，后面提供补偿机制，重新进行解析
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configuration.addIncompleteMethod(new MethodResolver(this, method));
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}
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}
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}
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// 遍历configuration中的incompleteMethods集合，集合中记录了未解析的方法
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// 重新调用这些方法进行解析
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parsePendingMethods();
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}
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}
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```
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另外，在MapperAnnotationBuilder的parse()方法中解析的注解，都能在映射配置文件中找到与之对应的XML节点，且两者的解析过程也非常相似。
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