前言

上一篇文章中简单的介绍了Mybatis的执行流程.
执行的第一步就是构建一个SqlSessionFactory, 那到底我们是如何获取到SqlSessionFactory的呢?
接下来让我们一起学习一下吧!

1.SqlSessionFactory源码详解

SqlSessionFactory是一个接口,引用代码的文档解释: 它的作用就是从Connection或者DataSource中创建一个SqlSession
它有两个实现DefaultSqlSessionFactory和SqlSessionManager

public interface SqlSessionFactory {/**获取一个默认配置的SqlSession* @return              默认配置的SqlSession*/SqlSession openSession();/**获取一个指定事务提交方式的SqlSession* @param autoCommit    事务提交方式, true,false 自动或手动* @return              指定事务提交方式的SqlSession*/SqlSession openSession(boolean autoCommit);/**获取一个给定数据库连接的SqlSession* @param connection    数据库连接* @return              指定数据库连接的SqlSession*/SqlSession openSession(Connection connection);/**获取一个给定事务隔离级别的SqlSession* @param level         事务隔离级别* @return              给定事务隔离级别的SqlSession*/SqlSession openSession(TransactionIsolationLevel level);/**获取一个给定执行器类型的SqlSession* @param execType      DefaultSqlSession中维护的一个执行器的类型* @return              给定执行器类型的SqlSession*/SqlSession openSession(ExecutorType execType);/**获取一个给定执行器类型和事务提交方式的SqlSession* @param execType      DefaultSqlSession中维护的一个执行器的类型* @param autoCommit    事务提交方式, true,false 自动或手动* @return              给定执行器类型和事务提交方式的SqlSession*/SqlSession openSession(ExecutorType execType, boolean autoCommit);/**获取一个给定执行器类型和事务隔离级别的SqlSession* @param execType      DefaultSqlSession中维护的一个执行器的类型* @param level         事务隔离级别* @return              给定执行器类型和事务隔离级别的SqlSession*/SqlSession openSession(ExecutorType execType, TransactionIsolationLevel level);/**获取一个给定执行器类型和数据库连接的SqlSession* @param execType      DefaultSqlSession中维护的一个执行器的类型* @param connection    数据库连接* @return              给定执行器类型和数据库连接的SqlSession*/SqlSession openSession(ExecutorType execType, Connection connection);/**获取核心配置文件对象* @return              核心配置文件对象*/Configuration getConfiguration();}

1.1 DefaultSqlSessionFactory源码详解

DefaultSqlSessionFactory是SqlSessionFactory的默认实现,接口的openSession(xxx …)的实现都是通过内部的两个函数实现
openSessionFromDataSource() 和 openSessionFromConnection()
这也和接口的文档上描述的一致

openSessionFromDataSource()和openSessionFromConnection() 的实现对比
他们的主体实现基本一致,区别是在于事务的构造上
openSessionFromDataSource 是通过数据源和参数指定的事务隔离级别,参数指定的是否自动提交来构建事务
openSessionFromConnection 是通过连接中的属性来构建事务
它们最终返回的都是DefaultSqlSession

/**从数据源中获取SqlSession* @param execType      执行器的类型* @param level         事务隔离级别* @param autoCommit    事务提交方式, true,false 自动或手动* @return              DefaultSqlSession*/private SqlSession openSessionFromDataSource(ExecutorType execType, TransactionIsolationLevel level, boolean autoCommit) {Transaction tx = null;try {//读取环境参数final Environment environment = configuration.getEnvironment();//获取事务工厂final TransactionFactory transactionFactory = getTransactionFactoryFromEnvironment(environment);//使用事务工厂创建事务tx = transactionFactory.newTransaction(environment.getDataSource(), level, autoCommit);//创建一个sql执行器final Executor executor = configuration.newExecutor(tx, execType);//构建一个DefaultSqlSessionreturn new DefaultSqlSession(configuration, executor, autoCommit);} catch (Exception e) {//如果失败,关闭事务closeTransaction(tx); // may have fetched a connection so lets call close()throw ExceptionFactory.wrapException("Error opening session.  Cause: " + e, e);} finally {ErrorContext.instance().reset();}}/**从连接中获取SqlSession* @param execType      执行器的类型* @param connection    数据库连接* @return              DefaultSqlSession*/private SqlSession openSessionFromConnection(ExecutorType execType, Connection connection) {try {boolean autoCommit;try {//从连接中获取事务提交类型autoCommit = connection.getAutoCommit();} catch (SQLException e) {// Failover to true, as most poor drivers// or databases won't support transactions//默认为true, 有的数据库或驱动不支持事务autoCommit = true;}//读取环境参数final Environment environment = configuration.getEnvironment();//获取事务工厂final TransactionFactory transactionFactory = getTransactionFactoryFromEnvironment(environment);//使用事务工厂创建事务final Transaction tx = transactionFactory.newTransaction(connection);//创建一个sql执行器final Executor executor = configuration.newExecutor(tx, execType);//构建一个DefaultSqlSessionreturn new DefaultSqlSession(configuration, executor, autoCommit);} catch (Exception e) {throw ExceptionFactory.wrapException("Error opening session.  Cause: " + e, e);} finally {ErrorContext.instance().reset();}}

1.2 SqlSessionManager源码详解

SqlSessionManager实现了SqlSessionFactory和SqlSession两个接口,本章我们主要学习下SqlSessionFactory相关的接口.
后续再进行SqlSession的学习

SqlSessionManager内部维护了一个SqlSessionFactory和一个SqlSession对象还有一个ThreadLocal变量,他提供的newInstance()方法都是创建一个DefaultSqlSessionFactory,然后调用私有的构造方法进行构造.所以他的openSession()相关方法的实现都是通过DefaultSqlSessionFactory去实现的

从上述的学习我们可以发现DefaultSqlSessionFactory目前都是通过SqlSessionFactoryBuilder的build()方法构建的,接下来我们就来学习SqlSessionFactoryBuilder

2. SqlSessionFactoryBuilder源码详解

打开SqlSessionFactory源码, 我们可以看见提供了build()方法的9种重载方式

具体可以分为以下三类

1. 以Reader为基础

 前四个方法都是以Reader为基础的, 真正逻辑的实现在第四个方法,前三个方法通过传递默认参数null进行内部调用

public SqlSessionFactory build(Reader reader, String environment, Properties properties) {try {XMLConfigBuilder parser = new XMLConfigBuilder(reader, environment, properties);return build(parser.parse());} catch (Exception e) {throw ExceptionFactory.wrapException("Error building SqlSession.", e);} finally {ErrorContext.instance().reset();try {reader.close();} catch (IOException e) {// Intentionally ignore. Prefer previous error.}}
}

2. 以InputStream为基础

 第五到第八个方法都是以InputStream为基础的, 真正逻辑的实现在第八个方法,前三个方法通过传递默认参数null进行内部调用

 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.}}}

3. 以Configuration为基础

public SqlSessionFactory build(Configuration config) {return new DefaultSqlSessionFactory(config);
}

其实第一种和第二种的实现方式都是类似,通过构建XMLConfigBuilder,然后调用parse()方法获得一个Configuration对象.
最终调用第三种方式获取SqlSessionFactory

自己YY

第二种方式也可以改造成如下方式, 通过InputStreamReader来包装InputStream的方式获得一个Reader,然后调用以Reader为基础的方法进行操作

public SqlSessionFactory build(InputStream inputStream, String environment, Properties properties) {return build(new InputStreamReader(inputStream), environment, properties);}

3. XMLConfigBuilder源码详解

我们对XMLConfigBuilder进行简单的分解

1. 六个公共的构造方法提供调用
2. 一个私有的构造方法,是仅供内部调用, 六个公共的构造方法最终都是通过私有方法去实现初始化
3. 一个公共的parse()方法,调用了内部的N个私有方法
4. 一堆私有的方法, 在parse()中被调用
   

1.私有的构造方法解析

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;
}

在这个构造方法中主要做了两件事

1. 调用父类的构造方法,并创建一个Configuration对象传入
2. 将参数设置到属性中

2.parse()方法解析

public Configuration parse() {if (parsed) {throw new BuilderException("Each XMLConfigBuilder can only be used once.");}parsed = true;parseConfiguration(parser.evalNode("/configuration"));return configuration;
}

在parse()方法中完成的逻辑

1. 判断是否解析过,没解析则进行解析,并返回Configuration对象
2. 如果已经被解析过,则抛出异常,一个XMLConfigBuilder只能解析一次

3.parseConfiguration(XNode root)方法解析

private void parseConfiguration(XNode root) {try {// issue #117 read properties first//解析properties然后放入Configuration中propertiesElement(root.evalNode("properties"));//解析settingsProperties settings = settingsAsProperties(root.evalNode("settings"));//VFS含义是虚拟文件系统；主要是通过程序能够方便读取本地文件系统、FTP文件系统等系统中的文件资源loadCustomVfs(settings);//自定义log实现loadCustomLogImpl(settings);//处理别名typeAliasesElement(root.evalNode("typeAliases"));//处理插件pluginElement(root.evalNode("plugins"));//处理自定义对象工厂objectFactoryElement(root.evalNode("objectFactory"));//处理自定义对象包装工厂objectWrapperFactoryElement(root.evalNode("objectWrapperFactory"));//处理反射工厂reflectorFactoryElement(root.evalNode("reflectorFactory"));//解析自定义setting,并设置到ConfigurationsettingsElement(settings);// read it after objectFactory and objectWrapperFactory issue #631//解析环境配置environmentsElement(root.evalNode("environments"));//解析数据库提供厂商databaseIdProviderElement(root.evalNode("databaseIdProvider"));//解析类型处理器typeHandlerElement(root.evalNode("typeHandlers"));//解析自定义mappermapperElement(root.evalNode("mappers"));} catch (Exception e) {throw new BuilderException("Error parsing SQL Mapper Configuration. Cause: " + e, e);}
}

4. 解析Properties

private void propertiesElement(XNode context) throws Exception {if (context != null) {//读取所有子节点构建一个Properties, 遍历读取name和value属性,然后进行赋值Properties defaults = context.getChildrenAsProperties();//读取resourceString resource = context.getStringAttribute("resource");//读取urlString url = context.getStringAttribute("url");//url和resource不能共存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) {//从resource中解析Properties,并放入默认的Propertiesdefaults.putAll(Resources.getResourceAsProperties(resource));} else if (url != null) {//从url中解析Properties,并放入默认的Propertiesdefaults.putAll(Resources.getUrlAsProperties(url));}Properties vars = configuration.getVariables();if (vars != null) {defaults.putAll(vars);}//合并configuration中已存在的配置和默认配置,并设置到configuration中parser.setVariables(defaults);configuration.setVariables(defaults);}}

5. 解析Setting

private Properties settingsAsProperties(XNode context) {//为空,返回一个默认全空的Propertiesif (context == null) {return new Properties();}//读取所有子节点作为PropertiesProperties props = context.getChildrenAsProperties();//检查所有的配置能被Configuration识别// Check that all settings are known to the configuration classMetaClass 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;
}

6. 根据Setting设置虚拟文件系统VFS

private void loadCustomVfs(Properties props) throws ClassNotFoundException {//获取虚拟文件的自定义实现类String value = props.getProperty("vfsImpl");if (value != null) {String[] clazzes = value.split(",");for (String clazz : clazzes) {if (!clazz.isEmpty()) {@SuppressWarnings("unchecked")//反射创建虚拟文件的自定义实现类,并设置到configurationClass<? extends VFS> vfsImpl = (Class<? extends VFS>)Resources.classForName(clazz);configuration.setVfsImpl(vfsImpl);}}}
}

7.根据Setting设置LogImpl

private void loadCustomLogImpl(Properties props) {//解析LogImplClass<? extends Log> logImpl = resolveClass(props.getProperty("logImpl"));//设置LogImplconfiguration.setLogImpl(logImpl);
}

其中resolveClass(props.getProperty(“logImpl”))的底层是调用了TypeAliasRegistry的resolveAlias(String string) 实现

public <T> Class<T> resolveAlias(String string) {try {if (string == null) {return null;}// issue #748String key = string.toLowerCase(Locale.ENGLISH);Class<T> value;//typeAliases是一个维护了常用的java类的一个Map, 是在TypeAliasRegistry的构造函数中进行的初始化赋值//使用常用类是不用每次通过反射创建Class对象if (typeAliases.containsKey(key)) {value = (Class<T>) typeAliases.get(key);} else {value = (Class<T>) Resources.classForName(string);}return value;} catch (ClassNotFoundException e) {throw new TypeException("Could not resolve type alias '" + string + "'.  Cause: " + e, e);}
}

8. 解析别名

private void typeAliasesElement(XNode parent) {if (parent != null) {for (XNode child : parent.getChildren()) {if ("package".equals(child.getName())) {String typeAliasPackage = child.getStringAttribute("name");//通过包名解析类configuration.getTypeAliasRegistry().registerAliases(typeAliasPackage);} else {//注册单个别名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);}}}}
}

8.1 通过包名注册别名

public void registerAliases(String packageName, Class<?> superType) {ResolverUtil<Class<?>> resolverUtil = new ResolverUtil<>();resolverUtil.find(new ResolverUtil.IsA(superType), packageName);Set<Class<? extends Class<?>>> typeSet = resolverUtil.getClasses();for (Class<?> type : typeSet) {// Ignore inner classes and interfaces (including package-info.java)// Skip also inner classes. See issue #6if (!type.isAnonymousClass() && !type.isInterface() && !type.isMemberClass()) {registerAlias(type);}}
}

ResolverUtil的find()方法

public ResolverUtil<T> find(Test test, String packageName) {//包名解析为路径名String path = getPackagePath(packageName);try {//通过文件系统获取所有的路径List<String> children = VFS.getInstance().list(path);for (String child : children) {if (child.endsWith(".class")) {//找到所有.class文件,然后进行匹配,匹配成功加入到内部维护的Set<Class<? extends T>> matchesaddIfMatching(test, child);}}} catch (IOException ioe) {log.error("Could not read package: " + packageName, ioe);}return this;
}

8.2 单个别名的注册

if (alias == null) {typeAliasRegistry.registerAlias(clazz);
} else {typeAliasRegistry.registerAlias(alias, clazz);
}

如果别名未给定
获取有没有Alias.class注解,如果有注解,则用注解的值作为别名,否则取类型名字作为别名

public void registerAlias(Class<?> type) {String alias = type.getSimpleName();Alias aliasAnnotation = type.getAnnotation(Alias.class);if (aliasAnnotation != null) {alias = aliasAnnotation.value();}registerAlias(alias, type);
}

给定别名的情况
如果别名已经被注册并且重新注册的值和之前不同,抛出异常

public void registerAlias(String alias, Class<?> value) {if (alias == null) {throw new TypeException("The parameter alias cannot be null");}// issue #748String key = alias.toLowerCase(Locale.ENGLISH);if (typeAliases.containsKey(key) && typeAliases.get(key) != null && !typeAliases.get(key).equals(value)) {throw new TypeException("The alias '" + alias + "' is already mapped to the value '" + typeAliases.get(key).getName() + "'.");}typeAliases.put(key, value);
}

9. 解析自定义拦截器

private void pluginElement(XNode parent) throws Exception {if (parent != null) {for (XNode child : parent.getChildren()) {//解析所有的interceptorString interceptor = child.getStringAttribute("interceptor");//即系interceptor下的属性值Properties properties = child.getChildrenAsProperties();//反射获取Interceptor的实例Interceptor interceptorInstance = (Interceptor) resolveClass(interceptor).getDeclaredConstructor().newInstance();//设置属性interceptorInstance.setProperties(properties);//添加interceptorconfiguration.addInterceptor(interceptorInstance);}}
}

10. 解析对象工厂

private void objectFactoryElement(XNode context) throws Exception {if (context != null) {//解析typeString type = context.getStringAttribute("type");//解析对象工厂的属性Properties properties = context.getChildrenAsProperties();//根据type解析对象工厂类ObjectFactory factory = (ObjectFactory) resolveClass(type).getDeclaredConstructor().newInstance();//设置属性factory.setProperties(properties);//设置对象工厂configuration.setObjectFactory(factory);}
}

11.解析对象包装工厂

private void objectWrapperFactoryElement(XNode context) throws Exception {if (context != null) {//解析typeString type = context.getStringAttribute("type");//根据type解析对象包装工厂类ObjectWrapperFactory factory = (ObjectWrapperFactory) resolveClass(type).getDeclaredConstructor().newInstance();//设置对象包装工厂configuration.setObjectWrapperFactory(factory);}
}

12. 解析反射工厂

private void reflectorFactoryElement(XNode context) throws Exception {if (context != null) {//解析typeString type = context.getStringAttribute("type");//根据type解析反射工厂类ReflectorFactory factory = (ReflectorFactory) resolveClass(type).getDeclaredConstructor().newInstance();//设置对象反射工厂类configuration.setReflectorFactory(factory);}}

13. 设置Configuration的各个属性

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")));}

14.设置Environment

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)) {//事务工厂TransactionFactory txFactory = transactionManagerElement(child.evalNode("transactionManager"));//数据源工厂DataSourceFactory dsFactory = dataSourceElement(child.evalNode("dataSource"));//构建数据源DataSource dataSource = dsFactory.getDataSource();//构建EnvironmentEnvironment.Builder environmentBuilder = new Environment.Builder(id).transactionFactory(txFactory).dataSource(dataSource);//设置Environmentconfiguration.setEnvironment(environmentBuilder.build());}}}}

15. 解析数据库厂商

private void databaseIdProviderElement(XNode context) throws Exception {DatabaseIdProvider databaseIdProvider = null;if (context != null) {String type = context.getStringAttribute("type");// awful patch to keep backward compatibilityif ("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);}
}

16. 解析TypeHandler

private void typeHandlerElement(XNode parent) {if (parent != null) {for (XNode child : parent.getChildren()) {if ("package".equals(child.getName())) {//指定包名方式配置String typeHandlerPackage = child.getStringAttribute("name");//指定包下进行扫描,找到所有为TypeHandler.class的class,然后进行注册//会排除接口,匿名内部类,还有抽象类typeHandlerRegistry.register(typeHandlerPackage);} else {//指定单个的处理器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);}}}}
}

17.解析所有的Mapper配置

private void mapperElement(XNode parent) throws Exception {if (parent != null) {for (XNode child : parent.getChildren()) {if ("package".equals(child.getName())) {//通过包名配置String mapperPackage = child.getStringAttribute("name");configuration.addMappers(mapperPackage);} else {String resource = child.getStringAttribute("resource");String url = child.getStringAttribute("url");String mapperClass = child.getStringAttribute("class");//优先从resource进行解析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) {//其次从url解析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) {//最后从class解析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.");}}}}
}

17.1 package 配置 和 class配置

package配置通过扫描包名,找到所有的.class文件,然后调用MapperRegistry的addMapper方法
class配置通过反射获取Mapper类,然后调用MapperRegistry的addMapper方法

public <T> void addMapper(Class<T> type) {//只对指定包下的接口进行处理if (type.isInterface()) {//如果重复解析,会抛出异常if (hasMapper(type)) {throw new BindingException("Type " + type + " is already known to the MapperRegistry.");}boolean loadCompleted = false;try {//为每个Interface生成一个代理工厂MapperProxyFactory,后续接口的方法执行时获通过代理工厂生成的代理进行执行//后续章节我们再详细的对MapperProxyFactory进行解析knownMappers.put(type, new MapperProxyFactory<>(type));// It's important that the type is added before the parser is run// otherwise the binding may automatically be attempted by the// mapper parser. If the type is already known, it won't try.MapperAnnotationBuilder parser = new MapperAnnotationBuilder(config, type);//解析类中的方法和注解等parser.parse();loadCompleted = true;} finally {if (!loadCompleted) {//如果加载未完成,map中移除该对象knownMappers.remove(type);}}}
}

17.2 resource 配置和url 配置

都是通过构造XMLMapperBuilder,调用parse()方法进行解析

public void parse() {if (!configuration.isResourceLoaded(resource)) {//解析mapper文件的各个节点configurationElement(parser.evalNode("/mapper"));//加载资源configuration.addLoadedResource(resource);//绑定命名空间和Mapper,最终调用MapperRegistry的addMapper方法bindMapperForNamespace();}//解析resultMapparsePendingResultMaps();//解析缓存parsePendingCacheRefs();//解析语句parsePendingStatements();
}

总结

通过上述的代码学习,可以发现,大量的工作都是在一开始的xml解析.通过xml解析之后,获取Configuration对象,然后构造SqlSessionFactory.文中并没有对XMLMapperBuilder和MapperAnnotationBuilder中的sql语句解析等进行详细的学习感兴趣的读者可以留言,也可以专门写一遍解析的文章,大家一起学习!

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文章链接

Mybatis源码学习（一）初探执行流程
Mybatis源码学习（二）配置文件解析到SqlSessionFactory构建
Mybatis源码学习（三）SqlSession详解
Mybatis源码学习（四）自定义Mapper方法执行流程
Mybatis源码学习（五）Executor和StatementHandler详解
Mybatis源码学习（六）结果集自动封装机制
Mybatis源码学习（七）mybatis缓存详解
Mybatis源码学习（八）Mybatis设计模式总结