在上篇文章中分析了mybatis解析<mappers>標籤,《mybatis原始碼配置檔案解析之五:解析mappers標籤 》重點分析瞭如何解析<mappers>標籤中的<package>子標籤的過程。mybatis解析<mappers>標籤主要完成了兩個操作,第一個是把對應的介面類,封裝成MapperProxyFactory放入kownMappers中;另一個是把要執行的方法封裝成MapperStatement。
一、概述
在上篇文章中分析了<mappers>標籤,重點分析了<package>子標籤,除了可以配置<package>子標籤外,在<mappers>標籤中還可以配置<mapper>子標籤,該子標籤可以配置的熟悉有resource、url、class三個屬性,解析resource和url的過程大致相同,看解析resource屬性的過程。
下面看部分程式碼,
if (resource != null && url == null && mapperClass == null) { ErrorContext.instance().resource(resource); InputStream inputStream = Resources.getResourceAsStream(resource); XMLMapperBuilder mapperParser = new XMLMapperBuilder(inputStream, configuration, resource, configuration.getSqlFragments()); /** * 處理mapper檔案和對應的介面 */ mapperParser.parse(); }
可以看到呼叫了XMLMapperBuilder的parse方法,
public void parse() { if (!configuration.isResourceLoaded(resource)) { //1、解析mapper檔案中的<mapper>標籤及其子標籤,並設定CurrentNamespace的值,供下面第2步使用 configurationElement(parser.evalNode("/mapper")); configuration.addLoadedResource(resource); //2、繫結Mapper介面,並解析對應的XML對映檔案 bindMapperForNamespace(); } parsePendingResultMaps(); parsePendingCacheRefs(); parsePendingStatements(); }
從上面的程式碼中可以看出首先解析resource資源說代表的XML對映檔案,然後解析XML;對映檔案中的namespace配置的介面。
二、詳述
通過上面的分析知道,解析resource配置的XML對映檔案,分為兩步,第一步就是解析XML對映檔案的內容;第二步是解析XML對映檔案中配置的namespace屬性,也就是對於的Mapper介面。
1、解析XML對映檔案
看如何解析XML對映檔案內容,也就是下面的這行程式碼,
configurationElement(parser.evalNode("/mapper"));
看具體的實現,
/** * 解析XML對映檔案的內容 * @param context */ private void configurationElement(XNode context) { try { //獲得namespace屬性 String namespace = context.getStringAttribute("namespace"); if (namespace == null || namespace.equals("")) { throw new BuilderException("Mapper's namespace cannot be empty"); } //設定到currentNamespace中 builderAssistant.setCurrentNamespace(namespace); //解析<cache-ref>標籤 cacheRefElement(context.evalNode("cache-ref"));
//二級快取標籤 cacheElement(context.evalNode("cache")); parameterMapElement(context.evalNodes("/mapper/parameterMap")); resultMapElements(context.evalNodes("/mapper/resultMap")); sqlElement(context.evalNodes("/mapper/sql")); //解析select、insert、update、delete子標籤 buildStatementFromContext(context.evalNodes("select|insert|update|delete")); } catch (Exception e) { throw new BuilderException("Error parsing Mapper XML. The XML location is '" + resource + "'. Cause: " + e, e); } }
上面方法解析XML對映檔案的內容,其中有個和二級快取相關的配置,即<cache>標籤。那麼xml對映檔案可以配置哪些標籤那,看下面,
在XML對映檔案中可以配置上面的這些標籤,也就是上面方法中解析的內容。重點看解析select、update、delete、select。也就是下面這行程式碼
//解析select、insert、update、delete子標籤 buildStatementFromContext(context.evalNodes("select|insert|update|delete"));
其方法定義如下,
private void buildStatementFromContext(List<XNode> list) { if (configuration.getDatabaseId() != null) { buildStatementFromContext(list, configuration.getDatabaseId()); } buildStatementFromContext(list, null); }
這裡會校驗databaseId,如果自定義配置了,則使用自定義的,否則使用預設的,看方法buildStatementFromContext方法
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) { configuration.addIncompleteStatement(statementParser); } } }
呼叫XMLStatementBuilder的parseStatementNode方法
/** * 解析select、update、delete、insert標籤 */ public void parseStatementNode() { String id = context.getStringAttribute("id"); String databaseId = context.getStringAttribute("databaseId"); if (!databaseIdMatchesCurrent(id, databaseId, this.requiredDatabaseId)) { return; } Integer fetchSize = context.getIntAttribute("fetchSize"); Integer timeout = context.getIntAttribute("timeout"); String parameterMap = context.getStringAttribute("parameterMap"); String parameterType = context.getStringAttribute("parameterType"); Class<?> parameterTypeClass = resolveClass(parameterType); String resultMap = context.getStringAttribute("resultMap"); String resultType = context.getStringAttribute("resultType"); String lang = context.getStringAttribute("lang"); LanguageDriver langDriver = getLanguageDriver(lang); Class<?> resultTypeClass = resolveClass(resultType); String resultSetType = context.getStringAttribute("resultSetType"); StatementType statementType = StatementType.valueOf(context.getStringAttribute("statementType", StatementType.PREPARED.toString())); ResultSetType resultSetTypeEnum = resolveResultSetType(resultSetType); String nodeName = context.getNode().getNodeName(); SqlCommandType sqlCommandType = SqlCommandType.valueOf(nodeName.toUpperCase(Locale.ENGLISH)); boolean isSelect = sqlCommandType == SqlCommandType.SELECT; boolean flushCache = context.getBooleanAttribute("flushCache", !isSelect); //查詢語句預設開啟一級快取,這裡預設是true boolean useCache = context.getBooleanAttribute("useCache", isSelect); boolean resultOrdered = context.getBooleanAttribute("resultOrdered", false); // Include Fragments before parsing XMLIncludeTransformer includeParser = new XMLIncludeTransformer(configuration, builderAssistant); includeParser.applyIncludes(context.getNode()); // Parse selectKey after includes and remove them. processSelectKeyNodes(id, parameterTypeClass, langDriver); // Parse the SQL (pre: <selectKey> and <include> were parsed and removed) //生成SqlSource,這裡分兩種,DynamicSqlSource和RawSqlSource SqlSource sqlSource = langDriver.createSqlSource(configuration, context, parameterTypeClass); String resultSets = context.getStringAttribute("resultSets"); String keyProperty = context.getStringAttribute("keyProperty"); String keyColumn = context.getStringAttribute("keyColumn"); KeyGenerator keyGenerator; //例,id="selectUser" //這裡的keyStatementId=selectUser!selectKey String keyStatementId = id + SelectKeyGenerator.SELECT_KEY_SUFFIX; //keyStatementId=cn.com.dao.userMapper.selectUser!selectKey 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; } builderAssistant.addMappedStatement(id, sqlSource, statementType, sqlCommandType, fetchSize, timeout, parameterMap, parameterTypeClass, resultMap, resultTypeClass, resultSetTypeEnum, flushCache, useCache, resultOrdered, keyGenerator, keyProperty, keyColumn, databaseId, langDriver, resultSets); }
上面的程式碼主要是解析標籤中的各種屬性,那麼標籤中可以配置哪些屬性那,下面看select標籤的屬性,詳情可參見https://www.w3cschool.cn/mybatis/f4uw1ilx.html
上面是select標籤中可以配置的屬性列表。
上面的程式碼重點看以下重點
二級快取
下面看和快取相關的
boolean isSelect = sqlCommandType == SqlCommandType.SELECT; boolean flushCache = context.getBooleanAttribute("flushCache", !isSelect); //查詢語句預設開啟一級快取,這裡預設是true boolean useCache = context.getBooleanAttribute("useCache", isSelect);
這裡僅針對select查詢語句使用快取,這裡的預設不會重新整理快取flushCache為false,預設開啟快取useCache為ture,這裡的快取指的是一級快取,經常說的mybatis一級快取,一級快取是sqlSession級別的。
看完了一級快取,下面看SqlSource的內容
SqlSource
下面是SqlSource相關的,
//生成SqlSource,這裡分兩種,DynamicSqlSource和RawSqlSource SqlSource sqlSource = langDriver.createSqlSource(configuration, context, parameterTypeClass);
上面是生成SqlSource的過程,
@Override public SqlSource createSqlSource(Configuration configuration, XNode script, Class<?> parameterType) { XMLScriptBuilder builder = new XMLScriptBuilder(configuration, script, parameterType); return builder.parseScriptNode(); }
看parseScriptNode方法
public SqlSource parseScriptNode() { MixedSqlNode rootSqlNode = parseDynamicTags(context); SqlSource sqlSource = null; if (isDynamic) { //含義${}符合的為DynamicSqlSource sqlSource = new DynamicSqlSource(configuration, rootSqlNode); } else { //不含有${}的為rawSqlSource sqlSource = new RawSqlSource(configuration, rootSqlNode, parameterType); } return sqlSource; }
從上面的程式碼可以看到在對映檔案中根據引數佔位符的識別符號(${}、#{})分為DynamicSqlSource和RawSqlSource。具體如何判斷,後面詳細分析。
addMappedStatement
最後看builderAssistant.addMappedStatement方法,
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"); } //cn.com.dao.UserMapper.selectUser id = applyCurrentNamespace(id, false); boolean isSelect = sqlCommandType == SqlCommandType.SELECT; 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) .resultMaps(getStatementResultMaps(resultMap, resultType, id)) .resultSetType(resultSetType) .flushCacheRequired(valueOrDefault(flushCache, !isSelect)) .useCache(valueOrDefault(useCache, isSelect)) .cache(currentCache); ParameterMap statementParameterMap = getStatementParameterMap(parameterMap, parameterType, id); if (statementParameterMap != null) { statementBuilder.parameterMap(statementParameterMap); } MappedStatement statement = statementBuilder.build(); /*向mappedStatements欄位中加入MappedStatement,這裡會加入兩個key * cn.com.dao.UserMapper.selectUser statement * selectUser statement * 每次都會插入上面的兩種key,兩種key對應的value都是同一個statement * */ configuration.addMappedStatement(statement); return statement; }
該方法主要完成的功能是生成MappedStatement,且放入configuration中。
2、解析namespace屬性
上面分析瞭解析XML對映檔案的內容的過程,最後的結果是把XML對映檔案中的select、update、insert、delete標籤的內容解析為MappedStatement。下面看解析XML對映檔案中的namespace屬性,
//2、繫結Mapper介面,並解析對應的XML對映檔案 bindMapperForNamespace();
上面我給的註釋是繫結介面並解析對應的XML對映檔案,這個方法沒有引數,怎麼繫結具體的介面並解析對應的對映檔案那,
private void bindMapperForNamespace() { String namespace = builderAssistant.getCurrentNamespace(); if (namespace != null) { Class<?> boundType = null; try { //載入類,這裡載入的是mapper檔案中配置的namespace配置的介面 boundType = Resources.classForName(namespace); } catch (ClassNotFoundException e) { //ignore, bound type is not required } if (boundType != null) { if (!configuration.hasMapper(boundType)) {//判斷該介面是否被載入過,在mapperRegistry中的knowsMapper中判斷 // Spring may not know the real resource name so we set a flag // to prevent loading again this resource from the mapper interface // look at MapperAnnotationBuilder#loadXmlResource //把該Mapper介面作為已載入的資源存放到loadedResources中,loadedResources存放的是已載入的mapper檔案的路徑 configuration.addLoadedResource("namespace:" + namespace); //把該介面放到mapperRegistry中的knowsMapper中,並解析該介面,根據loadedResources判定是否需要解析該Mapper介面 configuration.addMapper(boundType); } } } }
獲得builderAssistant.getCurrentNamespace(),在解析XML對映檔案時,第一步便是設定該屬性,這裡用到的便是上一步中設定的那個XML對映檔案中的namespace屬性值。獲得該介面的名稱,判斷是否生成過MapperProxyFactory,即放入過knownMappers中,看configuration.hasMapper方法,
public boolean hasMapper(Class<?> type) { return mapperRegistry.hasMapper(type); }
public <T> boolean hasMapper(Class<T> type) { return knownMappers.containsKey(type); }
如果在knownMappers中,則不進行解析,如果不在才進行下面的邏輯處理,呼叫configuration.addLoadedResource方法,放入loadedResources中,標識在第一步已經解析過對應的XML對映檔案;呼叫configuration.addMapper方法,解析該介面,這個過程和在<mapper>標籤中配置class屬性的過程是一樣的,後面詳細分析。
三、總結
本文分析了mappers標籤中mapper子標籤中resource和url屬性的解析過程,首先解析對應的XML對映檔案,解析的結果為MappedStatement物件,然後解析其namespace對應的介面,解析的結果為MapperProxyFactory物件。
有不當之處,歡迎指正,感謝!