mybatis对mapper.xml的解析（一)

对于mapper配置文件的解析是通过XMLMapperBuilder来完成的，其主要是解析结点为mapper下的结点

public void parse() {if (!configuration.isResourceLoaded(resource)) {configurationElement(parser.evalNode("/mapper"));configuration.addLoadedResource(resource);bindMapperForNamespace();}parsePendingResultMaps();parsePendingCacheRefs();parsePendingStatements();}private void configurationElement(XNode context) {try {String namespace = context.getStringAttribute("namespace");if (namespace == null || namespace.equals("")) {throw new BuilderException("Mapper's namespace cannot be empty");}builderAssistant.setCurrentNamespace(namespace);cacheRefElement(context.evalNode("cache-ref"));cacheElement(context.evalNode("cache"));parameterMapElement(context.evalNodes("/mapper/parameterMap"));resultMapElements(context.evalNodes("/mapper/resultMap"));sqlElement(context.evalNodes("/mapper/sql"));buildStatementFromContext(context.evalNodes("select|insert|update|delete"));} catch (Exception e) {throw new BuilderException("Error parsing Mapper XML. Cause: " + e, e);}}

1、解析cache-ref节点

设置当前缓存所引用的名字空间对应的缓存，相当于两个名字空间共用一个缓存，会在configuration中添加当前名字空间与引用名字空间的映射关系

private void cacheRefElement(XNode context) {if (context != null) {configuration.addCacheRef(builderAssistant.getCurrentNamespace(), context.getStringAttribute("namespace"));CacheRefResolver cacheRefResolver = new CacheRefResolver(builderAssistant, context.getStringAttribute("namespace"));try {cacheRefResolver.resolveCacheRef();} catch (IncompleteElementException e) {configuration.addIncompleteCacheRef(cacheRefResolver);}}}

2、解析cache节点

缓存的默认实现为PerpetualCache,默认淘汰策略为LRU,可以通过flushInterval设置定刷新间隔，size设置是修改Cache装饰器中有setSize方法的。默认是readWrite为true的，即可序列化。默认blocking为非阻塞的。对于使用第三方缓存，可以通过属性子节点配置来设置。使用MapperBuilderAssistant来创建 Cache

private void cacheElement(XNode context) throws Exception {if (context != null) {String type = context.getStringAttribute("type", "PERPETUAL");Class<? extends Cache> typeClass = typeAliasRegistry.resolveAlias(type);String eviction = context.getStringAttribute("eviction", "LRU");Class<? extends Cache> evictionClass = typeAliasRegistry.resolveAlias(eviction);Long flushInterval = context.getLongAttribute("flushInterval");Integer size = context.getIntAttribute("size");boolean readWrite = !context.getBooleanAttribute("readOnly", false);boolean blocking = context.getBooleanAttribute("blocking", false);Properties props = context.getChildrenAsProperties();builderAssistant.useNewCache(typeClass, evictionClass, flushInterval, size, readWrite, blocking, props);}}public Cache useNewCache(Class<? extends Cache> typeClass,Class<? extends Cache> evictionClass,Long flushInterval,Integer size,boolean readWrite,boolean blocking,Properties props) {Cache cache = new CacheBuilder(currentNamespace).implementation(valueOrDefault(typeClass, PerpetualCache.class)).addDecorator(valueOrDefault(evictionClass, LruCache.class)).clearInterval(flushInterval).size(size).readWrite(readWrite).blocking(blocking).properties(props).build();configuration.addCache(cache);currentCache = cache;return cache;}

3、解析resultMap节点

resultMap会解析成ResultMap结构，对于没有嵌套结构的子项，会解析成ResultMapping结构。在解析时会解析三类，一类是constructor,一类是 discriminator、另外一类是id,result,association,collection,case。如果结点类型为association,collection,case并且属性中没有select，不会生成嵌套resultMap。如果指定了extend，在 resultMap解析时会先获取父类的resultMapping,然后删除子类中重写的父类的resultMapping。在resultMap没有指定id时，通过getValueBasedIdentifier来生成，生成规则为从根结点到当前结点路径来，结点名_[(id,value,property）属性名]拼接而成。如果属性名中有点，则用_替换。最后将 resultMap添加到 configuration中,添加到resultMaps时，会添加namespace+id和id两个对应的。StrictMap是继承HashMap,重写了put和get

discriminator结点属性及子结点

类型

名称

属性

column

javaType

jdbcType

typeHandler

子结点

case，其支持的属性有value, resultMap

private ResultMap resultMapElement(XNode resultMapNode, List<ResultMapping> additionalResultMappings) throws Exception {ErrorContext.instance().activity("processing " + resultMapNode.getValueBasedIdentifier());String id = resultMapNode.getStringAttribute("id",resultMapNode.getValueBasedIdentifier());String type = resultMapNode.getStringAttribute("type",resultMapNode.getStringAttribute("ofType",resultMapNode.getStringAttribute("resultType",resultMapNode.getStringAttribute("javaType"))));String extend = resultMapNode.getStringAttribute("extends");Boolean autoMapping = resultMapNode.getBooleanAttribute("autoMapping");Class<?> typeClass = resolveClass(type);Discriminator discriminator = null;List<ResultMapping> resultMappings = new ArrayList<ResultMapping>();resultMappings.addAll(additionalResultMappings);List<XNode> resultChildren = resultMapNode.getChildren();for (XNode resultChild : resultChildren) {if ("constructor".equals(resultChild.getName())) {processConstructorElement(resultChild, typeClass, resultMappings);} else if ("discriminator".equals(resultChild.getName())) {discriminator = processDiscriminatorElement(resultChild, typeClass, resultMappings);} else {List<ResultFlag> flags = new ArrayList<ResultFlag>();if ("id".equals(resultChild.getName())) {flags.add(ResultFlag.ID);}resultMappings.add(buildResultMappingFromContext(resultChild, typeClass, flags));}}ResultMapResolver resultMapResolver = new ResultMapResolver(builderAssistant, id, typeClass, extend, discriminator, resultMappings, autoMapping);try {return resultMapResolver.resolve();} catch (IncompleteElementException  e) {configuration.addIncompleteResultMap(resultMapResolver);throw e;}}private ResultMapping buildResultMappingFromContext(XNode context, Class<?> resultType, List<ResultFlag> flags) throws Exception {String property;if (flags.contains(ResultFlag.CONSTRUCTOR)) {property = context.getStringAttribute("name");} else {property = context.getStringAttribute("property");}String column = context.getStringAttribute("column");String javaType = context.getStringAttribute("javaType");String jdbcType = context.getStringAttribute("jdbcType");String nestedSelect = context.getStringAttribute("select");String nestedResultMap = context.getStringAttribute("resultMap",processNestedResultMappings(context, Collections.<ResultMapping> emptyList()));String notNullColumn = context.getStringAttribute("notNullColumn");String columnPrefix = context.getStringAttribute("columnPrefix");String typeHandler = context.getStringAttribute("typeHandler");String resultSet = context.getStringAttribute("resultSet");String foreignColumn = context.getStringAttribute("foreignColumn");boolean lazy = "lazy".equals(context.getStringAttribute("fetchType", configuration.isLazyLoadingEnabled() ? "lazy" : "eager"));Class<?> javaTypeClass = resolveClass(javaType);@SuppressWarnings("unchecked")Class<? extends TypeHandler<?>> typeHandlerClass = (Class<? extends TypeHandler<?>>) resolveClass(typeHandler);JdbcType jdbcTypeEnum = resolveJdbcType(jdbcType);return builderAssistant.buildResultMapping(resultType, property, column, javaTypeClass, jdbcTypeEnum, nestedSelect, nestedResultMap, notNullColumn, columnPrefix, typeHandlerClass, flags, resultSet, foreignColumn, lazy);}private String processNestedResultMappings(XNode context, List<ResultMapping> resultMappings) throws Exception {if ("association".equals(context.getName())|| "collection".equals(context.getName())|| "case".equals(context.getName())) {if (context.getStringAttribute("select") == null) {ResultMap resultMap = resultMapElement(context, resultMappings);return resultMap.getId();}}return null;}public V put(String key, V value) {if (containsKey(key)) {throw new IllegalArgumentException(name + " already contains value for " + key);}if (key.contains(".")) {final String shortKey = getShortName(key);if (super.get(shortKey) == null) {super.put(shortKey, value);} else {super.put(shortKey, (V) new Ambiguity(shortKey));}}return super.put(key, value);}public V get(Object key) {V value = super.get(key);if (value == null) {throw new IllegalArgumentException(name + " does not contain value for " + key);}if (value instanceof Ambiguity) {throw new IllegalArgumentException(((Ambiguity) value).getSubject() + " is ambiguous in " + name+ " (try using the full name including the namespace, or rename one of the entries)");}return value;}

4、解析sql节点

解析sql片段，将其添加到sqlFragments中

private void sqlElement(List<XNode> list, String requiredDatabaseId) throws Exception {for (XNode context : list) {String databaseId = context.getStringAttribute("databaseId");String id = context.getStringAttribute("id");id = builderAssistant.applyCurrentNamespace(id, false);if (databaseIdMatchesCurrent(id, databaseId, requiredDatabaseId)) {sqlFragments.put(id, context);}}}

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