logseq-1/pages/Mybatis源码.md

• Mybatis初始化过程
  • 通过InputStream来获取配置文件
  • ClassLoaderWarpper中的getResourceAsStream可以根据配置的resoutce来获取到配置文件的输入六
  • 使用ClassLoader是因为类加载器可具有读取外部资源的能力
  • 
  • 读取到配置文件后传入SqlSessionFactoryBuilder，内部使用XMLConfigBuilder的parse方法读取配置并set到一个configuration变量中返回一个Configuration对象
  • 
  • 使用build方法创建一个DefaultSqlSessionFactory并返回
  • 在其中会创建一个SqlSession，其中会创建事务工厂之类的
  • 
  • 将mapper类传入session，通过session.getMapper方法在mapperRegistry获取到一个该mapper类的代理类MapperProxy
  • 执行时会执行该代理类的invoke方法
  • 
  • 触发mapperMethod的execute方法

  • 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;
    }
    

  • 会根据不同的语句类型执行不同的execute方法，查询list会执行executeForMany方法

  • private <E> Object executeForMany(SqlSession sqlSession, Object[] args) {
      List<E> 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;
    }
    

  • selectList获取MappedStatement，再执行executor.query方法

  • @Override
    public <E> List<E> query(MappedStatement ms, Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler) throws SQLException {
      BoundSql boundSql = ms.getBoundSql(parameterObject);
      CacheKey key = createCacheKey(ms, parameterObject, rowBounds, boundSql);
      return query(ms, parameterObject, rowBounds, resultHandler, key, boundSql);
    }
    

  • BoundSql为去掉if，where标签的sql语句，Cachekey为缓存key
  • 查询时先从缓存获取，获取不到或list为null就执行delegate.query方法查询
  • 检查executor是否被关闭，是否清理缓存
  • 通过queryFromDatabase，先在缓存中放一个占位符，接着使用doQuery方法查询，然后把缓存中的占位符换成真正的结果

  • private <E> List<E> queryFromDatabase(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, CacheKey key, BoundSql boundSql) throws SQLException {
      List<E> list;
      localCache.putObject(key, *EXECUTION_PLACEHOLDER*);
      try {
        list = doQuery(ms, parameter, rowBounds, resultHandler, boundSql);
      } finally {
        localCache.removeObject(key);
      }
      localCache.putObject(key, list);
      if (ms.getStatementType() == StatementType.*CALLABLE*) {
        localOutputParameterCache.putObject(key, parameter);
      }
      return list;
    }
    

  • 执行doQuery方法，为BatchExecutor类的方法

  • public <E> List<E> doQuery(MappedStatement ms, Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql)
        throws SQLException {
      Statement stmt = null;
      try {
        flushStatements();
        Configuration configuration = ms.getConfiguration();
        StatementHandler handler = configuration.newStatementHandler(wrapper, ms, parameterObject, rowBounds, resultHandler, boundSql);
        Connection connection = getConnection(ms.getStatementLog());
        stmt = handler.prepare(connection, transaction.getTimeout());
        handler.parameterize(stmt);
        return handler.query(stmt, resultHandler);
      } finally {
        closeStatement(stmt);
      }
    }
    

  • 通过Statement执行静态语句获取结果
  • 执行的是PrepareStatementHandler.query方法，获取结果后交给ResultSetHandler处理，通过resultMap将值赋值给对象