MyBatis 流程

时间:2021-6-4 作者:qvyue

整体处理流程

源码版本3.5.6
从基本的查询代码引入

  private static SqlSessionFactory sqlSessionFactory;

  @BeforeAll
  static void setUp() throws Exception {
    // create an SqlSessionFactory
    try (Reader reader = Resources.getResourceAsReader("org/apache/ibatis/submitted/keygen/MapperConfig.xml")) {
      sqlSessionFactory = new SqlSessionFactoryBuilder().build(reader);
    }
    // populate in-memory database
    BaseDataTest.runScript(sqlSessionFactory.getConfiguration().getEnvironment().getDataSource(),
        "org/apache/ibatis/submitted/keygen/CreateDB.sql");
  }

  @Test
  void shouldAssignKeyToBean() {
    try (SqlSession sqlSession = sqlSessionFactory.openSession()) {
      try {
        CountryMapper mapper = sqlSession.getMapper(CountryMapper.class);
        Country country = new Country("China", "CN");
        mapper.insertBean(country);
        assertNotNull(country.getId());
      } finally {
        sqlSession.rollback();
      }
    }
  }

代码分四步
1、创建SqlSessionFactory
2、openSession
3、getMapper
4、执行Mapper对应方法

一、创建SqlSessionFactory

SqlSessionFactoryBuilder#build -> XMLConfigBuilder#parse(
解析XML封装Configuration配置信息)

  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"));//解析mapper对象信息
    } catch (Exception e) {
      throw new BuilderException("Error parsing SQL Mapper Configuration. Cause: " + e, e);
    }
  }
  • XMLConfigBuilder#parse
    执行XMLConfigBuilder#parseConfiguration,解析配置的Mapper信息,如果配置的是source或url类型则通过
    XMLMapperBuilder#parse -> XMLMapperBuilder#configurationElement(解析入参sql返回等信息) ->XMLMapperBuilder#buildStatementFromContext -> 创建XMLStatementBuilder -> XMLStatementBuilder#parseStatementNode -> MappedStatement.Builder -> configuration.addMappedStatement(statement) -> configuration.addMapper(boundType) 创建Mapper对应mapperProxyFactory

此阶段配置了Executor类型以及主要是定义了mapper的MappedStatement,封装成Configuration对象

二、openSession

  private SqlSession openSessionFromDataSource(ExecutorType execType, TransactionIsolationLevel level, boolean autoCommit) {
    Transaction tx = null;
    try {
      final Environment environment = configuration.getEnvironment();
      final TransactionFactory transactionFactory = getTransactionFactoryFromEnvironment(environment);
      tx = transactionFactory.newTransaction(environment.getDataSource(), level, autoCommit);
      final Executor executor = configuration.newExecutor(tx, execType);
      return new DefaultSqlSession(configuration, executor, autoCommit);
    } catch (Exception e) {
      closeTransaction(tx); // may have fetched a connection so lets call close()
      throw ExceptionFactory.wrapException("Error opening session.  Cause: " + e, e);
    } finally {
      ErrorContext.instance().reset();
    }
  }

此阶段主要创建Transaction、Exceutor、SqlSession

三、getMapper

  public  T getMapper(Class type, SqlSession sqlSession) {
    final MapperProxyFactory mapperProxyFactory = (MapperProxyFactory) knownMappers.get(type);
    if (mapperProxyFactory == null) {
      throw new BindingException("Type " + type + " is not known to the MapperRegistry.");
    }
    try {
      // 创建代理类
      return mapperProxyFactory.newInstance(sqlSession);
    } catch (Exception e) {
      throw new BindingException("Error getting mapper instance. Cause: " + e, e);
    }
  }

获取Mapper的mapperProxyFactory并创建MapperProxy代理实例。

四、执行Mapper方法

MapperMethod#exceute


  public Object execute(SqlSession sqlSession, Object[] args) {
    Object result;
    switch (command.getType()) {
      case INSERT: {
        Object param = method.convertArgsToSqlCommandParam(args);
        result = rowCountResult(sqlSession.insert(command.getName(), param));
        break;
      }
      case UPDATE: {
        Object param = method.convertArgsToSqlCommandParam(args);
        result = rowCountResult(sqlSession.update(command.getName(), param));
        break;
      }
      case DELETE: {
        Object param = method.convertArgsToSqlCommandParam(args);
        result = rowCountResult(sqlSession.delete(command.getName(), param));
        break;
      }
      case SELECT:
        if (method.returnsVoid() && method.hasResultHandler()) {
          executeWithResultHandler(sqlSession, args);
          result = null;
        } else if (method.returnsMany()) {
          result = executeForMany(sqlSession, args);
        } else if (method.returnsMap()) {
          result = executeForMap(sqlSession, args);
        } else if (method.returnsCursor()) {
          result = executeForCursor(sqlSession, args);
        } else {
          Object param = method.convertArgsToSqlCommandParam(args);
          result = sqlSession.selectOne(command.getName(), param);
          if (method.returnsOptional()
              && (result == null || !method.getReturnType().equals(result.getClass()))) {
            result = Optional.ofNullable(result);
          }
        }
        break;
      case FLUSH:
        result = sqlSession.flushStatements();
        break;
      default:
        throw new BindingException("Unknown execution method for: " + command.getName());
    }
    if (result == null && method.getReturnType().isPrimitive() && !method.returnsVoid()) {
      throw new BindingException("Mapper method '" + command.getName()
          + " attempted to return null from a method with a primitive return type (" + method.getReturnType() + ").");
    }
    return result;
  }

这个过程从MapperProxy#invoke方法开始跟踪。
MapperProxy#invoke -> MapperMethodInvoker#invoke ->
MapperMethod#exceute -> SqlSession执行select/insert/update等方法 -> Exceutor执行select/insert/update等方法

总结

MyBatis执行过程主要环节与核心概念。在初始阶段负责解析配置生成
Configuration、MappedStatement,执行阶段创建Exceutor、MapperProxy,通过动态代理方式执行。以上是XML方式的MyBatis执行过程,Annotation注解方式的处理,其实就是判断if/else的判断处理初始阶段的处理区别。

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