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不从恶人的计谋#xff0c;不站罪人的道路#xff0c;不坐亵慢人的座位#xff0c;惟喜爱耶和华的律法#xff0c;昼夜思想#xff0c;这人便为有福#xff01;他要像一棵树栽在溪水旁#xff0c;按时候结果子#xff0c;叶子也不枯干。凡他所做的尽…给自己的每日一句
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本文内容整理自《孙哥说Mybatis系列课程》
Cache是在什么时候、什么地点被创建的
不管是我们使用Mybatis写测试程序还是在真实企业级项目中使用MybatisMybatis框架被启动加载的前几行代码一定是如下 InputStream inputStream Resources.getResourceAsStream(mybatis-config.xml);SqlSessionFactory sqlSessionFactory new SqlSessionFactoryBuilder().build(inputStream);SqlSession sqlSession sqlSessionFactory.openSession();然后我们的二级缓存Cache对象就是在这个期间也就是Mybatis被启动和初始化的时候完成的那么我们就详细展开吧。
首先我要告诉大家的是这个过程一定是在SqlSessionFactory工厂被创建的时候完成的那就是上述的第二行代码并且这里应用的是构建者设计模式这个精华必须隐藏在build()方法中我们查看一下 public SqlSessionFactory build(InputStream inputStream) {return build(inputStream, null, null);}//重载的build方法真正的精华是在这里public SqlSessionFactory build(InputStream inputStream, String environment, Properties properties) {try {//将Mybatis和核心配置文件读取成inputStream之后我们有将他转换成Mybatis中重要的//XMLConfigBuilder对象XMLConfigBuilder parser new XMLConfigBuilder(inputStream, environment, properties);return build(parser.parse());} catch (Exception e) {throw ExceptionFactory.wrapException(Error building SqlSession., e);} finally {ErrorContext.instance().reset();try {inputStream.close();} catch (IOException e) {// Intentionally ignore. Prefer previous error.}}}return build(parser.parse());这里边硬货就多了build方法就是为了创建 public SqlSessionFactory build(Configuration config) {return new DefaultSqlSessionFactory(config);}所以里边的parser.parse()的返回值一定是生成的Configuration对象原材料就是Mybatis核心配置文件读取到的InputStream有因为InputStream当中记录了Mapper.xml的路径所以这些Mapper文件必定也是在这里边解析的。 public Configuration parse() {if (parsed) {throw new BuilderException(Each XMLConfigBuilder can only be used once.);}parsed true;parseConfiguration(parser.evalNode(/configuration));return configuration;}parser.evalNode(“/configuration”)兄弟们这玩意用脚趾头都知道这读的是mybatis-config.xml里边的Configuration标签这样就把mybatis-config.xml整个文件作为一个Node对象被放到了parseConfiguration方法当中这个方法的目的从方法上就能看出来为了构建Configuration对象 private void parseConfiguration(XNode root) {try {//issue #117 read properties firstpropertiesElement(root.evalNode(properties));Properties settings settingsAsProperties(root.evalNode(settings));loadCustomVfs(settings);typeAliasesElement(root.evalNode(typeAliases));pluginElement(root.evalNode(plugins));objectFactoryElement(root.evalNode(objectFactory));objectWrapperFactoryElement(root.evalNode(objectWrapperFactory));reflectorFactoryElement(root.evalNode(reflectorFactory));settingsElement(settings);// read it after objectFactory and objectWrapperFactory issue #631environmentsElement(root.evalNode(environments));databaseIdProviderElement(root.evalNode(databaseIdProvider));typeHandlerElement(root.evalNode(typeHandlers));mapperElement(root.evalNode(mappers));} catch (Exception e) {throw new BuilderException(Error parsing SQL Mapper Configuration. Cause: e, e);}}兄弟们眼熟了吧这不就是mybatis-config.xml里边的一个一个的标签么一个一个的排队解析看最后一行这玩意里边存储的不就是Mapper标签么所以Mapper.xml必定就是在这里边解析的再加上我们知道Cache标签是写在Mapper.xml里边的所以Cache对象必是在里边创建的。 private void mapperElement(XNode parent) throws Exception {if (parent ! null) {for (XNode child : parent.getChildren()) {if (package.equals(child.getName())) {String mapperPackage child.getStringAttribute(name);configuration.addMappers(mapperPackage);} else {String resource child.getStringAttribute(resource);String url child.getStringAttribute(url);String mapperClass child.getStringAttribute(class);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());mapperParser.parse();} else if (resource null url ! null mapperClass null) {ErrorContext.instance().resource(url);InputStream inputStream Resources.getUrlAsStream(url);XMLMapperBuilder mapperParser new XMLMapperBuilder(inputStream, configuration, url, configuration.getSqlFragments());mapperParser.parse();} else if (resource null url null mapperClass ! null) {Class? mapperInterface Resources.classForName(mapperClass);configuration.addMapper(mapperInterface);} else {throw new BuilderException(A mapper element may only specify a url, resource or class, but not more than one.);}}}}}
兄弟们XMLMapperBuilder mapperParser new XMLMapperBuilder(inputStream, configuration, resource, configuration.getSqlFragments());这玩意不就是在读Mapper.xml文件么mapperParser.parse();又去parse去了我们进去看看 public void parse() {if (!configuration.isResourceLoaded(resource)) {configurationElement(parser.evalNode(/mapper));configuration.addLoadedResource(resource);bindMapperForNamespace();}parsePendingResultMaps();parsePendingCacheRefs();parsePendingStatements();}configurationElement兄弟们看到名字还不明白么这是在解析Mapper.xml当中的元素解析到Configurantion对象当中呀Cache标签也是其中的一个元素呀 private void configurationElement(XNode context) {try {String namespace context.getStringAttribute(namespace);if (namespace null || namespace.equals()) {throw new BuilderException(Mappers 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. The XML location is resource . Cause: e, e);}} 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);}}兄弟们到这里基本上知道在哪里创建的吧至于怎么创建咱们后期出文章玩~
