Mybatis的SqlSession理解

Posted 2020-12-31 暖暖

Mybaits加载执行该xml配置

class SqlSessionFactoryBean implements FactoryBean<SqlSessionFactory>, InitializingBean

 spring 在初始化 sqlsessionbean的时候通过createBean调用了在SqlSessionFactoryBean中实现了接口InitializingBean的afterPropertiesSet()方法在该方法中调用了buildSqlSessionFactory()开始创建SqlSessionFactory

buildSqlSessionFactory()方法完成以下功能

一：

a)    创建configuration

b)    typeAliasesPackage

c)    typeAliases TYPE_ALIASES将类型存放到此map里面同b

d)    plugins configuration添加插件

e)    typeHandlersPackage

f)    typeHandlers

g)    xmlConfigBuilder.parse()将所有的配置从xml中读取并放入到对应的变量里面

h)    mapperLocations

二：xmlMapperBuilder.parse()——> configurationElement

a)    parameterMapElement(context.evalNodes("/mapper/parameterMap"));将mapper.xml中的prameterMap节点的数据添加到configuration.parameterMaps中

b)    resultMapElements(context.evalNodes("/mapper/resultMap"));将mapper.xml中的resultMap节点的数据添加到configuration.incompleteResultMaps中

c)    sqlElement(context.evalNodes("/mapper/sql"));

d)    buildStatementFromContext(select|insert|update|delete);buildStatementFromContext：从mapper 中获取sql语句，执行类型（增删改查），parseStatementNode中addMappedStatement创建每个mapper对应的方法创建MappedStatement并添加到 configuration.mappedStatements.put(com.qb.mysql.dao.TRoleDao.getUserRoleByRid, MappedStatement)

最后返回了一个 DefaultSqlSessionFactory(config)

在调用SqlSessionTemplate进行dao层操作时，其会将工作委托给sqlSessionProxy属性进行，而sqlSessionProxy在进行相关method调用时，用到了JDK动态代理机制，首先SqlSessionUtils.getSqlSession获取sqlSession    

 private class SqlSessionInterceptor implements InvocationHandler {
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
//返回一个DefaultSqlsession
      SqlSession sqlSession = getSqlSession(
          SqlSessionTemplate.this.sqlSessionFactory,
          SqlSessionTemplate.this.executorType,
          SqlSessionTemplate.this.exceptionTranslator);
      try {
     //调用该类的MapperProxy的invoke方法
        Object result = method.invoke(sqlSession, args);
        if (!isSqlSessionTransactional(sqlSession, SqlSessionTemplate.this.sqlSessionFactory)) {
          // force commit even on non-dirty sessions because some databases require
          // a commit/rollback before calling close()
          sqlSession.commit(true);
        }
        return result;
      } catch (Throwable t) {
        Throwable unwrapped = unwrapThrowable(t);
        if (SqlSessionTemplate.this.exceptionTranslator != null && unwrapped instanceof PersistenceException) {
          // release the connection to avoid a deadlock if the translator is no loaded. See issue #22
          closeSqlSession(sqlSession, SqlSessionTemplate.this.sqlSessionFactory);
          sqlSession = null;
          Throwable translated = SqlSessionTemplate.this.exceptionTranslator.translateExceptionIfPossible((PersistenceException) unwrapped);
          if (translated != null) {
            unwrapped = translated;
          }
        }
        throw unwrapped;
      } finally {
        if (sqlSession != null) {
          closeSqlSession(sqlSession, SqlSessionTemplate.this.sqlSessionFactory);
        }
      }
    }
  }

在getSqlSession方法中创建事务，创建Executor，默认创建SimpleExecutor；InterceptorChain添加拦截器 InterceptorChain.pluginAll()

SqlSessionTemplate ->SqlSessionInterceptor->SqlSessionUtils. getSqlSession()->(defaultsqlsessionfactory)sessionFactory.openSession()->openSessionFromDataSource()

MapperProxy的invoke方法的方法

 public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
    if (Object.class.equals(method.getDeclaringClass())) {
      return method.invoke(this, args);
    }
    final MapperMethod mapperMethod = cachedMapperMethod(method);
//执行execute
    return mapperMethod.execute(sqlSession, args);
  }
//根据sql类型选择对应的方法
public Object execute(SqlSession sqlSession, Object[] args) {
    Object result;
    if (SqlCommandType.INSERT == command.getType()) {
      Object param = method.convertArgsToSqlCommandParam(args);
      result = rowCountResult(sqlSession.insert(command.getName(), param));
    } else if (SqlCommandType.UPDATE == command.getType()) {
      Object param = method.convertArgsToSqlCommandParam(args);
      result = rowCountResult(sqlSession.update(command.getName(), param));
    } else if (SqlCommandType.DELETE == command.getType()) {
      Object param = method.convertArgsToSqlCommandParam(args);
      result = rowCountResult(sqlSession.delete(command.getName(), param));
    } else if (SqlCommandType.SELECT == command.getType()) {
      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 {
        Object param = method.convertArgsToSqlCommandParam(args);
        result = sqlSession.selectOne(command.getName(), param);
      }
    } else {
      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;
  }

SqlSessionTemplate 执行了创建sqlsession，openSqlsession，执行sql,closeSqlsession