MyBatis运行原理(一) : 核心组件、SqlSessionFactory的构建过程(源码分析)

妖狐艹你老母 2023-01-15 03:54 134阅读 0赞

# MyBatis的工作原理 #

### MyBatis运行原理图 ###

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L20wXzM3OTg5OTgw_size_16_color_FFFFFF_t_70]

*  **`SqISessionFactoryBuilder (构建器)`**: 根据配置信息或Java代码来构建 **SqlSessionFactory** 对象。作用: 创建SqlSessionFactory对象。(并创建出Configuration全局配置文件对象)
 *  **`SqlSessionFactory (会话工厂)`** :好比是**DataSource(创建连接的数据源)** ,线程安全的,在应用运行期间不要重复创建多次,建议使用`单例模式`。**作用:** 创建**SqlSession**对象
 *  **`SqlSession (会话)`** :好比是**Connection** ,线程不安全的,每次使用开启新的SqlSession对象,使用完毕正常关闭,默认使用DefaultSqlSession。提供操作数据库的增删改查方法,可以调用操作方法,也可以操作`Mapper`组件。

**原理图:**  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L20wXzM3OTg5OTgw_size_16_color_FFFFFF_t_70 1]  
更具体的底层原理图:  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L20wXzM3OTg5OTgw_size_16_color_FFFFFF_t_70 2]  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L20wXzM3OTg5OTgw_size_16_color_FFFFFF_t_70 3]

涉及的对象:

*  **Configuration** : `MyBatis 全局配置对象,封装所有配置信息`。
 *  **`MappedStatement`** :映射语句对象,每一个该对象都封装了一个< insert|update|delete|select>节点的详细信息,包括标签的所有可写属性。
    
     *  **SqlSource** : SQL源(是MappedStatement的属性), `根据用户传入的参数生成SQL语句,并封装到BoundSql中`。
     *  **BoundSql** : SQL绑定, `封装SQL语句和对应的参数信息进行绑定`。
 *  **`Executor`** :执行器,是MyBatis调度的核心, **`负责SQL语句的具体操作和查询缓存的维护`**。
 *  **`StatementHandler`** :语句处理器,`封装了JDBC的DML、DQL 操作、参数设置`。
 *  **`ParameterHandler`** :参数处理器,把`用户传入参数转换为JDBC需要的参数值`。
 *  **`ResultSetHandler`** :结果集处理器,把`结果集中的数据封装到List集合`。
 *  **`TypeHandler`** :类型转换器, `Java类型和JDBC类型的相互转换`。

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L20wXzM3OTg5OTgw_size_16_color_FFFFFF_t_70 4]  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L20wXzM3OTg5OTgw_size_16_color_FFFFFF_t_70 5]

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# 二、SqlSessionFactory的初始化过程 (源码分析) #

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L20wXzM3OTg5OTgw_size_16_color_FFFFFF_t_70 6]  
1、进入到bulid方法

public SqlSessionFactory build(InputStream inputStream, String environment, Properties properties) { 
        try { 
          // 根据mybatis-config.xml包装的流, 创建了一个解析器parser;该对象是XPathParser, 
          // 基于Dom4j的XPath的方式来解析XML
          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.
          }
        }
      }

2、进入XMLConfigBuilder类的parse()方法: 用来解析mybatis-config.xml的方法

public Configuration parse() { 
        if (parsed) { 
          throw new BuilderException("Each XMLConfigBuilder can only be used once.");
        }
        parsed = true;
        // 通过parser解析器来解析mybatis-config.xml中的configuration节点,拿到该根节点
        parseConfiguration(parser.evalNode("/configuration"));
        // 返回配置对象
        return configuration;
      }

3、进入parseConfiguration方法

private void parseConfiguration(XNode root) { 
        try { 
          //issue #117 read properties first
          propertiesElement(root.evalNode("properties"));
          // 根据configuration根节点来拿到它下面的节点, 这里获取settings节点,
          // 封装到一个Properties中
          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);
        }
      }

4.1、进入到settingsElement方法中: 将保存到properties中的setting配置内容, 设置给Configuration对象

private void settingsElement(Properties props) { 
        configuration.setAutoMappingBehavior(AutoMappingBehavior.valueOf(props.getProperty("autoMappingBehavior", "PARTIAL")));
        // 省略...
        configuration.setConfigurationFactory(resolveClass(props.getProperty("configurationFactory")));
      }

4.2、进如到mapperElement方法, 解析mappers节点

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 { 
              // 因为是基于resource的方式绑定mapper.xml, 所以进入该分支
              // resourse: com/sunny/mapper/UserMapper.xml
              String resource = child.getStringAttribute("resource");
              String url = child.getStringAttribute("url"); // 没用,为null
              String mapperClass = child.getStringAttribute("class"); // 没用,为null
              if (resource != null && url == null && mapperClass == null) { 
                ErrorContext.instance().resource(resource);
                // 同加载mybatis-config.xml,来加载mapper.xml
                InputStream inputStream = Resources.getResourceAsStream(resource);
                // 创建解析器
                XMLMapperBuilder mapperParser = new XMLMapperBuilder(inputStream, configuration, resource, configuration.getSqlFragments());
                mapperParser.parse(); // 进行解析
              } 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.");
              }
            }
          }
        }
      }

5、进入到mapperPaser.parse方法: 用来解析mapper.xml的方法, 将解析mapper.xml的标签都保存到全局配置文件中

public void parse() { 
        if (!configuration.isResourceLoaded(resource)) { 
          // 解析并拿到mapper标签
          configurationElement(parser.evalNode("/mapper"));
          // 将解析mapper.xml的标签都保存到全局配置文件中
          configuration.addLoadedResource(resource);
          bindMapperForNamespace();
        }
    
        parsePendingResultMaps();
        parsePendingCacheRefs();
        parsePendingStatements();
      }

6、进入XMLMapperBuilder类的configurationElement方法

private void configurationElement(XNode context) { 
        try { 
          String namespace = context.getStringAttribute("namespace");
          if (namespace == null || namespace.equals("")) { 
            throw new BuilderException("Mapper's namespace cannot be empty");
          }
          // 通过mapper根节点来拿到其他子节点
          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"));
          // 以crud为例来分析
          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);
        }
      }

7、进入buildStatementFromContext方法

private void buildStatementFromContext(List<XNode> list) { 
    	// configuration用来保存所有的mybatis的配置信息
        if (configuration.getDatabaseId() != null) { 
          buildStatementFromContext(list, configuration.getDatabaseId());
        }
        // 进入该方法
        buildStatementFromContext(list, null);
      }
      
    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);
        }
      }
    }

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L20wXzM3OTg5OTgw_size_16_color_FFFFFF_t_70 7]  
8、XMLStatementBuilder的parseStatementNode方法: 用来解析select | insert | update | delete标签的方法

// 拿到select | insert | update | delete标签能写的所有属性
    public void parseStatementNode() { 
        String id = context.getStringAttribute("id");
        String databaseId = context.getStringAttribute("databaseId");
    
        if (!databaseIdMatchesCurrent(id, databaseId, this.requiredDatabaseId)) { 
          return;
        }
    	// 省略.....
        }
        String keyProperty = context.getStringAttribute("keyProperty");
        String keyColumn = context.getStringAttribute("keyColumn");
        String resultSets = context.getStringAttribute("resultSets");
    
    	// 将获取到的所有crud的标签属性通过下面方法构造出来
    	// public MappedStatement addMappedStatement(){} 该方法返回一个 MappedStatement
    	// 也就说明每个增删改查标签的所有信息, 都封装成了MappedStatement对象
        builderAssistant.addMappedStatement(id, sqlSource, statementType, sqlCommandType,
            fetchSize, timeout, parameterMap, parameterTypeClass, resultMap, resultTypeClass,
            resultSetTypeEnum, flushCache, useCache, resultOrdered,
            keyGenerator, keyProperty, keyColumn, databaseId, langDriver, resultSets);
      }

9、进入到addMappedStatement方法, 根据select | insert | update | delete标签构建出MappedStatement对象

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");
        }
    
        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);
        }
    	
    	// 根据select | insert | update | delete标签构建出MappedStatement对象
        MappedStatement statement = statementBuilder.build();
        // 将statement对象扔保存到configuration对象中
        configuration.addMappedStatement(statement);
        return statement;
      }

每一个MappedStatement保存的信息如下图  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L20wXzM3OTg5OTgw_size_16_color_FFFFFF_t_70 8]  
10、回到XMLConfigBuilder类的parse()方法, 返回configuration, 此时该对象就保存了mybatis-config.xml和mapper.xml以及crud标签的详细信息, 如下图:  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L20wXzM3OTg5OTgw_size_16_color_FFFFFF_t_70 9]  
configuration中的mappedStatements来保存了crud标签信息  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L20wXzM3OTg5OTgw_size_16_color_FFFFFF_t_70 10]  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L20wXzM3OTg5OTgw_size_16_color_FFFFFF_t_70 11]  
11、最终返回了一个DefaultSqlSession对象, 该对象包含了全局配置信息Configuration  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L20wXzM3OTg5OTgw_size_16_color_FFFFFF_t_70 12]  
12、最终new SqlSessionFactoryBuilder().build(in)返回了SqlSessionFactory --> DefaultSqlSessionFactory对象  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L20wXzM3OTg5OTgw_size_16_color_FFFFFF_t_70 6]  
**上面1-12步时序图**

*  总结: new SqlSessionFactoryBuilder().build(in)流程: **`把配置文件的信息解析并保存在Configuration对象中, 返回包含了Configurationd对DefaultSqlSessionFactory对象`**  
    ![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L20wXzM3OTg5OTgw_size_16_color_FFFFFF_t_70 13]

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