DBUtils framework:
Constructor:
QueryRunner();
QueryRunner(DataSource dataSource);
Method:
batch:
batch(Connection conn, String sql, Object[][] params); -----> when you use the default constructor
batch(String sql, Object[][] params); -----> high dimensionality: the amount of statement low dimensionality: the parameter each statement needs
query:
<T> T query(String sql, ResultSetHandler<T> rsh, Object... params);
<T> T query(Connection conn, String sql, ResultSetHandler<T> rsh, Object... params);
update:
update(String sql, Object... parmas);
update(Connection conn, String sql, Object... params);
When you want to call the update method for several times, pleas use update(Connection conn, String sql, Object... parmas), and the default constructor is needed.
ResultSetHandler of DBUtils:
ArrayHandler: used when the result set has only one result in the set, the return value is Object[], the records in the list is the data of every column.
ArrayListHandler: used when the result set has many results in the set, the return value is List<Object[]> , the records are encapsulated in the List, every Object[] represents one row of data.
BeanHandler: return one JavaBean record
BeanListHandler: return a List of JavaBean record
ColumnListHandler: used when want to query one column, the return value is List<Object>, the value in the List is the column's values.
KeyedHandler: used when the result set has many records, the return value is Map<Object,Map<String,Object>>
MapHandler: used when the result set has only one record, the return value is Map<String,Object>, key is the filed name, value is the filed value.
MapListHandler: ... the return value is List<Map<String,Object>>
ScalarHandler: used when the result has only one row and one column, the return value is Object
