mybatis学习(二)
纠错   19 Mar 2017

前言

本文主要讲述mybatis执行简单的查询语句的过程,有兴趣可以自己debug一下。(以mapper接口方式映射sql语句,Mybatis的最佳实践)

正文

  1. Reader reader = Resources.getResourceAsReader(“conf.xml”); 读取配置文件信息
  2. 建立SqlSessionFactory,其中build方法主要解析配置文件,即XMLConfigBuilder解析mybatis的conf.xml
  3. SqlSession sqlSession = sqlSessionFactory.openSession(); 建议一个SqlSession(DefaultSqlSession),传入配置信息及executor,autoCommit
  4. 通过MapperProxyFactory获取mapper,使用了java动态代理,注意此处是用对应mapping.xml的namespace + id去对应接口中的方法
  5. 调用接口中的方法

mapper实现原理 MapperProxy类中invoke方法源码

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);
  }

此处对mapper接口中的方法做了本地缓存,然后执行MapperMethod中的execute方法。

MapperMethod中的execute方法源码

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;
  }

总结下整个sql的执行过程:

picture

最后说明下若不是通过Mapper接口调用,而是直接调用DefaultSqlSession的方法，那么，流程图从SqlSession的地方开始即可，后续都是一样的。



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