网络异常，图片无法展示
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我们知道 Mybatis 的入口是 SqlSessionFactoryBuilder
public SqlSessionFactory build(InputStream inputStream, String environment, Properties properties) { try { 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. } } } public SqlSessionFactory build(Configuration config) { return new DefaultSqlSessionFactory(config); } 复制代码
主要逻辑如上、主要是创建一个 SqlSessionFactory 创建该对象之前肯定需要解释全局的配置 xml 文件
XMLConfigBuilder 就是用来解释的
public XMLConfigBuilder(InputStream inputStream, String environment, Properties props) { this(new XPathParser(inputStream, true, props, new XMLMapperEntityResolver()), environment, props); } private XMLConfigBuilder(XPathParser parser, String environment, Properties props) { super(new Configuration()); ErrorContext.instance().resource("SQL Mapper Configuration"); this.configuration.setVariables(props); this.parsed = false; this.environment = environment; this.parser = parser; } 复制代码
在这里创建了 Configuration 对象
public Configuration parse() { if (parsed) { throw new BuilderException("Each XMLConfigBuilder can only be used once."); } parsed = true; parseConfiguration(parser.evalNode("/configuration")); return configuration; } private void parseConfiguration(XNode root) { try { // issue #117 read properties first propertiesElement(root.evalNode("properties")); Properties settings = settingsAsProperties(root.evalNode("settings")); loadCustomVfs(settings); loadCustomLogImpl(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 #631 environmentsElement(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); } } 复制代码
propertiesElement
解释 properties 标签
private void propertiesElement(XNode context) throws Exception { if (context != null) { Properties defaults = context.getChildrenAsProperties(); String resource = context.getStringAttribute("resource"); String url = context.getStringAttribute("url"); if (resource != null && url != null) { throw new BuilderException("The properties element cannot specify both a URL and a resource based property file reference. Please specify one or the other."); } if (resource != null) { defaults.putAll(Resources.getResourceAsProperties(resource)); } else if (url != null) { defaults.putAll(Resources.getUrlAsProperties(url)); } Properties vars = configuration.getVariables(); if (vars != null) { defaults.putAll(vars); } parser.setVariables(defaults); configuration.setVariables(defaults); } } 复制代码
放入到 Configuration 中的
protected Properties variables = new Properties(); 复制代码
settingsAsProperties
这一步主要是将属性名和值抽取出来
private Properties settingsAsProperties(XNode context) { if (context == null) { return new Properties(); } Properties props = context.getChildrenAsProperties(); // Check that all settings are known to the configuration class MetaClass metaConfig = MetaClass.forClass(Configuration.class, localReflectorFactory); for (Object key : props.keySet()) { if (!metaConfig.hasSetter(String.valueOf(key))) { throw new BuilderException("The setting " + key + " is not known. Make sure you spelled it correctly (case sensitive)."); } } return props; } 复制代码
设置值到 Configuration 中
private void loadCustomVfs(Properties props) throws ClassNotFoundException { String value = props.getProperty("vfsImpl"); if (value != null) { String[] clazzes = value.split(","); for (String clazz : clazzes) { if (!clazz.isEmpty()) { @SuppressWarnings("unchecked") Class<? extends VFS> vfsImpl = (Class<? extends VFS>)Resources.classForName(clazz); configuration.setVfsImpl(vfsImpl); } } } } 复制代码
private void loadCustomLogImpl(Properties props) { Class<? extends Log> logImpl = resolveClass(props.getProperty("logImpl")); configuration.setLogImpl(logImpl); } 复制代码
private void settingsElement(Properties props) { configuration.setAutoMappingBehavior(AutoMappingBehavior.valueOf(props.getProperty("autoMappingBehavior", "PARTIAL"))); configuration.setAutoMappingUnknownColumnBehavior(AutoMappingUnknownColumnBehavior.valueOf(props.getProperty("autoMappingUnknownColumnBehavior", "NONE"))); configuration.setCacheEnabled(booleanValueOf(props.getProperty("cacheEnabled"), true)); configuration.setProxyFactory((ProxyFactory) createInstance(props.getProperty("proxyFactory"))); configuration.setLazyLoadingEnabled(booleanValueOf(props.getProperty("lazyLoadingEnabled"), false)); configuration.setAggressiveLazyLoading(booleanValueOf(props.getProperty("aggressiveLazyLoading"), false)); configuration.setMultipleResultSetsEnabled(booleanValueOf(props.getProperty("multipleResultSetsEnabled"), true)); configuration.setUseColumnLabel(booleanValueOf(props.getProperty("useColumnLabel"), true)); configuration.setUseGeneratedKeys(booleanValueOf(props.getProperty("useGeneratedKeys"), false)); configuration.setDefaultExecutorType(ExecutorType.valueOf(props.getProperty("defaultExecutorType", "SIMPLE"))); configuration.setDefaultStatementTimeout(integerValueOf(props.getProperty("defaultStatementTimeout"), null)); configuration.setDefaultFetchSize(integerValueOf(props.getProperty("defaultFetchSize"), null)); configuration.setDefaultResultSetType(resolveResultSetType(props.getProperty("defaultResultSetType"))); configuration.setMapUnderscoreToCamelCase(booleanValueOf(props.getProperty("mapUnderscoreToCamelCase"), false)); configuration.setSafeRowBoundsEnabled(booleanValueOf(props.getProperty("safeRowBoundsEnabled"), false)); configuration.setLocalCacheScope(LocalCacheScope.valueOf(props.getProperty("localCacheScope", "SESSION"))); configuration.setJdbcTypeForNull(JdbcType.valueOf(props.getProperty("jdbcTypeForNull", "OTHER"))); configuration.setLazyLoadTriggerMethods(stringSetValueOf(props.getProperty("lazyLoadTriggerMethods"), "equals,clone,hashCode,toString")); configuration.setSafeResultHandlerEnabled(booleanValueOf(props.getProperty("safeResultHandlerEnabled"), true)); configuration.setDefaultScriptingLanguage(resolveClass(props.getProperty("defaultScriptingLanguage"))); configuration.setDefaultEnumTypeHandler(resolveClass(props.getProperty("defaultEnumTypeHandler"))); configuration.setCallSettersOnNulls(booleanValueOf(props.getProperty("callSettersOnNulls"), false)); configuration.setUseActualParamName(booleanValueOf(props.getProperty("useActualParamName"), true)); configuration.setReturnInstanceForEmptyRow(booleanValueOf(props.getProperty("returnInstanceForEmptyRow"), false)); configuration.setLogPrefix(props.getProperty("logPrefix")); configuration.setConfigurationFactory(resolveClass(props.getProperty("configurationFactory"))); configuration.setShrinkWhitespacesInSql(booleanValueOf(props.getProperty("shrinkWhitespacesInSql"), false)); configuration.setDefaultSqlProviderType(resolveClass(props.getProperty("defaultSqlProviderType"))); } 复制代码
将解析得到的配置信息记录到 Configuration 这个全局配置对象的同名属性中
网络异常，图片无法展示
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typeAliasesElement&typeHandlerElement
类型别名
private void typeAliasesElement(XNode parent) { if (parent != null) { for (XNode child : parent.getChildren()) { if ("package".equals(child.getName())) { String typeAliasPackage = child.getStringAttribute("name"); configuration.getTypeAliasRegistry().registerAliases(typeAliasPackage); } else { String alias = child.getStringAttribute("alias"); String type = child.getStringAttribute("type"); try { Class<?> clazz = Resources.classForName(type); if (alias == null) { typeAliasRegistry.registerAlias(clazz); } else { typeAliasRegistry.registerAlias(alias, clazz); } } catch (ClassNotFoundException e) { throw new BuilderException("Error registering typeAlias for '" + alias + "'. Cause: " + e, e); } } } } } 复制代码
将配置文件中的别名注册到 Configuration 中
private void typeHandlerElement(XNode parent) { if (parent != null) { for (XNode child : parent.getChildren()) { if ("package".equals(child.getName())) { String typeHandlerPackage = child.getStringAttribute("name"); typeHandlerRegistry.register(typeHandlerPackage); } else { String javaTypeName = child.getStringAttribute("javaType"); String jdbcTypeName = child.getStringAttribute("jdbcType"); String handlerTypeName = child.getStringAttribute("handler"); Class<?> javaTypeClass = resolveClass(javaTypeName); JdbcType jdbcType = resolveJdbcType(jdbcTypeName); Class<?> typeHandlerClass = resolveClass(handlerTypeName); if (javaTypeClass != null) { if (jdbcType == null) { typeHandlerRegistry.register(javaTypeClass, typeHandlerClass); } else { typeHandlerRegistry.register(javaTypeClass, jdbcType, typeHandlerClass); } } else { typeHandlerRegistry.register(typeHandlerClass); } } } } } 复制代码
同样的、类型转换器也被注册到 Configuration 中
pluginElement
private void pluginElement(XNode parent) throws Exception { if (parent != null) { for (XNode child : parent.getChildren()) { String interceptor = child.getStringAttribute("interceptor"); Properties properties = child.getChildrenAsProperties(); Interceptor interceptorInstance = (Interceptor) resolveClass(interceptor).getDeclaredConstructor().newInstance(); interceptorInstance.setProperties(properties); configuration.addInterceptor(interceptorInstance); } } } 复制代码
注册 Mybatis 的插件到 Configuration 中
environmentsElement
private void environmentsElement(XNode context) throws Exception { if (context != null) { if (environment == null) { environment = context.getStringAttribute("default"); } for (XNode child : context.getChildren()) { String id = child.getStringAttribute("id"); if (isSpecifiedEnvironment(id)) { TransactionFactory txFactory = transactionManagerElement(child.evalNode("transactionManager")); DataSourceFactory dsFactory = dataSourceElement(child.evalNode("dataSource")); DataSource dataSource = dsFactory.getDataSource(); Environment.Builder environmentBuilder = new Environment.Builder(id) .transactionFactory(txFactory) .dataSource(dataSource); configuration.setEnvironment(environmentBuilder.build()); } } } } 复制代码
我们可以使用 environment 标签为不同的环境添加不同的配置、例如测试、开发、生产。每一个 environment 标签只对应一种特定的环境配置。
databaseIdProviderElement
private void databaseIdProviderElement(XNode context) throws Exception { DatabaseIdProvider databaseIdProvider = null; if (context != null) { String type = context.getStringAttribute("type"); // awful patch to keep backward compatibility if ("VENDOR".equals(type)) { type = "DB_VENDOR"; } Properties properties = context.getChildrenAsProperties(); databaseIdProvider = (DatabaseIdProvider) resolveClass(type).getDeclaredConstructor().newInstance(); databaseIdProvider.setProperties(properties); } Environment environment = configuration.getEnvironment(); if (environment != null && databaseIdProvider != null) { String databaseId = databaseIdProvider.getDatabaseId(environment.getDataSource()); configuration.setDatabaseId(databaseId); } } 复制代码
Mybatis 中 编写的都是原生的 SQL 语句、而很多数据库产品都会有一些 SQL 方言、这些方言与标准 SQL 不兼容。
我们可以通过 标签定义需要支持的全部数据库的 DatabaseId，在后续编写 Mapper 映射配置文件的时候，就可以为同一个业务场景定义不同的 SQL 语句（带有不同的 DataSourceId），来支持不同的数据库，这里就是靠 DatabaseId 来确定哪个 SQL 语句支持哪个数据库的。
普遍情况下、我们的 Sql 是没有声明这个属性的、那么没有声明 databaseId 的将作为一个默认执行 SQL
private String getDatabaseName(DataSource dataSource) throws SQLException { String productName = getDatabaseProductName(dataSource); if (this.properties != null) { for (Map.Entry<Object, Object> property : properties.entrySet()) { if (productName.contains((String) property.getKey())) { return (String) property.getValue(); } } // no match, return null return null; } return productName; } 复制代码
<databaseIdProvider type="DB_VENDOR"> <property name="SQL Server" value="sqlserver"/> <property name="DB2" value="db2"/> <property name="Oracle" value="oracle" /> </databaseIdProvider> 复制代码
如果没有配置 value 则使用数据库返回的产品名称作为 databaseId
mapperElement
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."); } } } } } 复制代码
会初始化 XMLMapperBuilder 对象来加载各个 Mapper.xml 映射文件。同时，还会扫描 Mapper 映射文件相应的 Mapper 接口，处理其中的注解并将 Mapper 接口注册到 MapperRegistry 中。
