MyBatis源码解析（二）：初始化SqlSessionFactory

Myth丶恋晨 2022-02-26 13:35 340阅读 0赞

一，SqlSessionFactory初始化流程图

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3UwMTE5NzYzODg_size_16_color_FFFFFF_t_70][]

二，初始化步骤

1，获取配置文件 mybatis-config.xml，并初始化为 Document

\* SqlSessionFactory.build()

public SqlSessionFactory build(InputStream inputStream, String environment, Properties properties) {
        try {
          // 初始化XMLConfigBuilder, 内部通过XPathParser解析inputStream为Document
          XMLConfigBuilder parser = new XMLConfigBuilder(inputStream, environment, properties);
          // parser.parse() : 解析Document配置文件
          // build(parser.parse()) : 构架生成DefaultSqlSessionFactory
          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.
          }
        }
      }

\* 初始化 XMLConfigBuilder 时，会关联初始化 XPathParser

public XMLConfigBuilder(InputStream inputStream, String environment, Properties props) {
        this(new XPathParser(inputStream, true, props, new XMLMapperEntityResolver()), environment, props);
      }

\* XPathParser 内部，解析 InputStream 配置文件流，生成 Document 对象，Document 对象被 XPathParser 持有，而 XPathParser 被 XMLConfigBuilder 持有

public XPathParser(InputStream inputStream, boolean validation, Properties variables, EntityResolver entityResolver) {
        commonConstructor(validation, variables, entityResolver);
        // 解析配置文件流, 生成Document文件
        this.document = createDocument(new InputSource(inputStream));
      }

2，通过 XMLConfigBuilder 解析配置文件中的每一个节点

\* MyBatis 核心配置节点定义

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3UwMTE5NzYzODg_size_16_color_FFFFFF_t_70 1][]

\* 从第一步可知，XML配置文件解析所生成的 Document 对象，已经被 XMLConfigBuilder 内部属性持有，现在进行解析

\* parser.parse()，从上图可知，MyBatis 核心配置文件，第一层标签为 <configuration>，则文件解析从该标签开始

public Configuration parse() {
        if (parsed) {
          throw new BuilderException("Each XMLConfigBuilder can only be used once.");
        }
        parsed = true;
        // 从mybatis-config.xml配置文件的根节点<configuration>开始, 解析配置文件
        parseConfiguration(parser.evalNode("/configuration"));
        return configuration;
      }

\* parser.evalNode(String) 方法内部会解析出当前节点所有子节点对象 XNode，

\* parseConfiguration(XNode)方法继续对节点所属子节点依次解析，该方法中所解析的属性基本与上图中核心配置标签一致，下面会对 <setting>标签、<environments>标签和<mappers>标签进行分析

private void parseConfiguration(XNode root) {
        // 解析mybatis-config.xml文件中各个元素节点
        try {
          //issue #117 read properties first
          propertiesElement(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 #631
          // 解析<environments>, 获取数据库连接信息
          environmentsElement(root.evalNode("environments"));
          databaseIdProviderElement(root.evalNode("databaseIdProvider"));
          typeHandlerElement(root.evalNode("typeHandlers"));
          // 解析mappers节点
          mapperElement(root.evalNode("mappers"));
        } catch (Exception e) {
          throw new BuilderException("Error parsing SQL Mapper Configuration. Cause: " + e, e);
        }
      }

3，解析Setting节点，获取配置信息

\* Setting节点解析方法

private void settingsElement(Properties props) throws Exception {
        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.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")));
        @SuppressWarnings("unchecked")
        Class<? extends TypeHandler> typeHandler = (Class<? extends TypeHandler>)resolveClass(props.getProperty("defaultEnumTypeHandler"));
        configuration.setDefaultEnumTypeHandler(typeHandler);
        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"));
        @SuppressWarnings("unchecked")
        Class<? extends Log> logImpl = (Class<? extends Log>)resolveClass(props.getProperty("logImpl"));
        configuration.setLogImpl(logImpl);
        configuration.setConfigurationFactory(resolveClass(props.getProperty("configurationFactory")));
      }

\* Setting节点解析会对 <Setting>标签中需要处理的对象进行初始化，如果没有该属性的配置信息则会初始化初值，比如后续初始化的 SimpleExecutorType 和 CacheingExecutor

\* Setting 节点所包含的属性及默认值可从官网查看 ：[http://www.mybatis.org/mybatis-3/zh/configuration.html][http_www.mybatis.org_mybatis-3_zh_configuration.html]

4，解析 Environment 节点，获取数据库配置信息

\* 节点解析方法：environmentsElement()，构建 Environment 数据后，添加到 Configuration 对象中

private void environmentsElement(XNode context) throws Exception {
        if (context != null) {
          if (environment == null) {
            // 获取默认数据库环境
            environment = context.getStringAttribute("default");
          }
          for (XNode child : context.getChildren()) {
            String id = child.getStringAttribute("id");
            // 判断当前数据库环境是否是默认数据库环境,
            if (isSpecifiedEnvironment(id)) {
              // 事务类型解析
              TransactionFactory txFactory = transactionManagerElement(child.evalNode("transactionManager"));
              // 数据库配置信息解析
              DataSourceFactory dsFactory = dataSourceElement(child.evalNode("dataSource"));
              DataSource dataSource = dsFactory.getDataSource();
              Environment.Builder environmentBuilder = new Environment.Builder(id)
                  .transactionFactory(txFactory)
                  .dataSource(dataSource);
              // 添加环境信息 + 数据库配置信息到Configuration
              configuration.setEnvironment(environmentBuilder.build());
            }
          }
        }
      }

\* 数据库连接配置信息解析 dataSourceElement()

private DataSourceFactory dataSourceElement(XNode context) throws Exception {
        if (context != null) {
          // 获取数据库连接类型
          String type = context.getStringAttribute("type");
          // 获取数据库连接基础配置信息
          Properties props = context.getChildrenAsProperties();
          DataSourceFactory factory = (DataSourceFactory) resolveClass(type).newInstance();
          factory.setProperties(props);
          return factory;
        }
        throw new BuilderException("Environment declaration requires a DataSourceFactory.");
      }

\* 数据库连接信息 Properties 获取，

public Properties getChildrenAsProperties() {
        Properties properties = new Properties();
        for (XNode child : getChildren()) {
          String name = child.getStringAttribute("name");
          String value = child.getStringAttribute("value");
          if (name != null && value != null) {
            properties.setProperty(name, value);
          }
        }
        return properties;
      }

5，解析 Mapper 节点

\* Mapper映射文件节点定义，   [http://www.mybatis.org/mybatis-3/zh/sqlmap-xml.html][http_www.mybatis.org_mybatis-3_zh_sqlmap-xml.html]

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\* 节点解析方法：mapperElement()，并以常用配置参数 Resource 为例进行后续解析

private void mapperElement(XNode parent) throws Exception {
        if (parent != null) {
          for (XNode child : parent.getChildren()) {
            // 解析<package name="org.mybatis.builder"/>形式
            if ("package".equals(child.getName())) {
              String mapperPackage = child.getStringAttribute("name");
              configuration.addMappers(mapperPackage);
            } else {
              // 解析<mapper resource="org/mybatis/builder/AuthorMapper.xml"/>形式
              String resource = child.getStringAttribute("resource");
              // 解析<mapper url="file:///var/mappers/AuthorMapper.xml"/>形式
              String url = child.getStringAttribute("url");
              // 解析<mapper class="org.mybatis.builder.AuthorMapper"/>形式
              String mapperClass = child.getStringAttribute("class");
              if (resource != null && url == null && mapperClass == null) {
                ErrorContext.instance().resource(resource);
                InputStream inputStream = Resources.getResourceAsStream(resource);
                // 内部通过XPathParser生成当前resource指向的xml文件的document
                XMLMapperBuilder mapperParser = new XMLMapperBuilder(inputStream, configuration, resource, configuration.getSqlFragments());
                // 解析当前mapper.xml文件
                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.");
              }
            }
          }
        }
      }

\* 构建 XMLMapperBuilder，并在内部通过 XPathParser 生成mapper.xml映射文件的Document

public XMLMapperBuilder(InputStream inputStream, Configuration configuration, String resource, Map<String, XNode> sqlFragments) {
        this(new XPathParser(inputStream, true, configuration.getVariables(), new XMLMapperEntityResolver()),
            configuration, resource, sqlFragments);
      }

\* 通过 XMLMapperBuilder 对象解析Document

public void parse() {
        // 判断当前mapper.xml是否已经被解析
        // 没有被解析, 直接解析
        if (!configuration.isResourceLoaded(resource)) {
          // 配置解析mapper大标签内每一个组件
          // mapper大标签标识一个mapper.xml文件
          // 此处解析完成后, 直接添加到Configuration中
          configurationElement(parser.evalNode("/mapper"));
          // 添加当前已经被解析的mapper.xml文件到集合中, 进行是否已经被解析判断
          configuration.addLoadedResource(resource);
          bindMapperForNamespace();
        }
        // 解析其余未被解析的元素
        // 通过部分操作, 可在不重启的情况下触发Mapper二次解析(个人理解)
        parsePendingResultMaps();
        parsePendingCacheRefs();
        parsePendingStatements();
      }

6，加载 Mapper 节点到 Configuration 和 MapperRegistery 中

\* Mapper 标签解析完成后，添加当前 Mapper 到Configuration

private void bindMapperForNamespace() {
        // 获取当前Mapper的名称空间
        String namespace = builderAssistant.getCurrentNamespace();
        if (namespace != null) {
          Class<?> boundType = null;
          try {
            boundType = Resources.classForName(namespace);
          } catch (ClassNotFoundException e) {
            //ignore, bound type is not required
          }
          if (boundType != null) {
            if (!configuration.hasMapper(boundType)) {
              // 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
              // 添加当前名称空间和Mapper对象到configuration
              configuration.addLoadedResource("namespace:" + namespace);
              configuration.addMapper(boundType);
            }
          }
        }
      }

\* Configuration 类委托 MapperRegistry 进行Mapper实例添加

public <T> void addMapper(Class<T> type) {
        mapperRegistry.addMapper(type);
      }

\* MapperRegistry 最终添加 Mapper 实例到 Map 集合中，后续通过SqlSession.getMapper()会从该集合中获取 Mapper实例

public <T> void addMapper(Class<T> type) {
        if (type.isInterface()) {
          if (hasMapper(type)) {
            throw new BindingException("Type " + type + " is already known to the MapperRegistry.");
          }
          boolean loadCompleted = false;
          try {
            knownMappers.put(type, new MapperProxyFactory<T>(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);
            parser.parse();
            loadCompleted = true;
          } finally {
            if (!loadCompleted) {
              knownMappers.remove(type);
            }
          }
        }
      }

7，MyBatis 核心配置文件所关联需要解析的数据解析完成后，直接初始化 DefaultSqlSessionFactory，从方法可以看出，DefaultSqlSessionFactory默认持有 Configuration 引用

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

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[http_www.mybatis.org_mybatis-3_zh_configuration.html]: http://www.mybatis.org/mybatis-3/zh/configuration.html
[http_www.mybatis.org_mybatis-3_zh_sqlmap-xml.html]: http://www.mybatis.org/mybatis-3/zh/sqlmap-xml.html
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