Mybatis Session工作过程

测试代码

sqlSessionFactory.openSession(false).getMapper(StudentMapper.class).findStudentById(id)

核心方法：org.apache.ibatis.session.Configuration#getMapper

public 
    
      T getMapper(Class
     
       type, SqlSession sqlSession) {    //从Mybatis初始化过程中绑定的名称空间和接口类，获取接口工厂    final MapperProxyFactory
      
        mapperProxyFactory = (MapperProxyFactory
       
        ) knownMappers.get(type);    if (mapperProxyFactory == null) {      throw new BindingException("Type " + type + " is not known to the MapperRegistry.");    }    try {        //生成接口代理类      return mapperProxyFactory.newInstance(sqlSession);    } catch (Exception e) {      throw new BindingException("Error getting mapper instance. Cause: " + e, e);    }  }
       
      
     
    

动态代理工厂

public class MapperProxyFactory
    
      {  private final Class
     
       mapperInterface;  private final Map
      
        methodCache = new ConcurrentHashMap
       
        ();  public MapperProxyFactory(Class
        
          mapperInterface) {    this.mapperInterface = mapperInterface;  }  public Class
         
           getMapperInterface() { return mapperInterface; } public Map
          
            getMethodCache() { return methodCache; } @SuppressWarnings("unchecked") protected T newInstance(MapperProxy
           
             mapperProxy) { //JDK动态代理 return (T) Proxy.newProxyInstance(mapperInterface.getClassLoader(), new Class[] { mapperInterface }, mapperProxy); } public T newInstance(SqlSession sqlSession) { final MapperProxy
            
              mapperProxy = new MapperProxy
             
              (sqlSession, mapperInterface, methodCache); return newInstance(mapperProxy); }}
             
            
           
          
         
        
       
      
     
    

动态代理对象：MapperProxy

[@Override](https://my.oschina.net/u/1162528)  public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {    try {      if (Object.class.equals(method.getDeclaringClass())) {        return method.invoke(this, args);      } else if (isDefaultMethod(method)) {        return invokeDefaultMethod(proxy, method, args);      }    } catch (Throwable t) {      throw ExceptionUtil.unwrapThrowable(t);    }    final MapperMethod mapperMethod = cachedMapperMethod(method);    return mapperMethod.execute(sqlSession, args);  }

sql操作

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);        }        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;  }

org.apache.ibatis.binding.MapperMethod#executeForMany

private 
    
      Object executeForMany(SqlSession sqlSession, Object[] args) {    List
     
       result;    Object param = method.convertArgsToSqlCommandParam(args);    if (method.hasRowBounds()) {      RowBounds rowBounds = method.extractRowBounds(args);      result = sqlSession.
      
       selectList(command.getName(), param, rowBounds);    } else {      result = sqlSession.
       
        selectList(command.getName(), param);    }    // issue #510 Collections & arrays support    if (!method.getReturnType().isAssignableFrom(result.getClass())) {      if (method.getReturnType().isArray()) {        return convertToArray(result);      } else {        return convertToDeclaredCollection(sqlSession.getConfiguration(), result);      }    }    return result;  }//具体的操作通过Executor操作，本质底层也是JDBC操作，只是通过configuration配置按照业务进行数据转换[@Override](https://my.oschina.net/u/1162528)  public 
        
          List
         
           selectList(String statement, Object parameter, RowBounds rowBounds) { try { MappedStatement ms = configuration.getMappedStatement(statement); return executor.query(ms, wrapCollection(parameter), rowBounds, Executor.NO_RESULT_HANDLER); } catch (Exception e) { throw ExceptionFactory.wrapException("Error querying database. Cause: " + e, e); } finally { ErrorContext.instance().reset(); } }