SQL执行器-executor

将操作数据库的操作从 sqlSession 中解耦，放到 Executor 中。

包括事务操作也放到 Executor 中。

public interface Executor {

    ResultHandler NO_RESULT_HANDLER = null;

    <E> List<E> query(MappedStatement ms, Object parameter, ResultHandler resultHandler, BoundSql boundSql);

    Transaction getTransaction();

    void commit(boolean required) throws SQLException;

    void rollback(boolean required) throws SQLException;

    void close(boolean forceRollback) throws SQLException;

}

反射赋值

/**
     * 采用反射进行结果集赋值
     * 反射调用setXX方法赋值
     * @param resultSet
     * @param clazz
     * @return
     * @param <T>
     */
    private <T> List<T> resultSet2Obj(ResultSet resultSet, Class<?> clazz) {
        List<T> list = new ArrayList<>();
        try {
            ResultSetMetaData metaData = resultSet.getMetaData();
            int columnCount = metaData.getColumnCount();
            // 每次遍历行值
            while (resultSet.next()) {
                T obj = (T) clazz.newInstance();
                for (int i = 1; i <= columnCount; i++) {
                    Object value = resultSet.getObject(i);
                    String columnName = metaData.getColumnName(i);
                    //获取set方法
                    String setMethod = "set" + columnName.substring(0, 1).toUpperCase() + columnName.substring(1);
                    Method method;
                    if (value instanceof Timestamp) {
                        method = clazz.getMethod(setMethod, Date.class);
                    } else {
                        method = clazz.getMethod(setMethod, value.getClass());
                    }
                    //反射执行set方法
                    method.invoke(obj, value);
                }
                list.add(obj);
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
        return list;
    }