Find why QueryRunner runner can be null

Why is QueryRunner runner null in my code?

I am a beginner in java programming. I am trying to develop a program but when I ran my program which is posted below and it came back with this error

Exception in thread "main" java.lang.NullPointerException
    at Dao.GoodsImp.getByName(GoodsImp.java:94)
    at Dao.GoodsImp.main(GoodsImp.java:119)

public class GoodsImp implements GoodsDao{
    private static Connection conn;
    private static QueryRunner runner;
    @BeforeClass
    public static void bc() throws SQLException {
        conn = myDBUtils.getConnection();
        runner = new QueryRunner();
    }
    @AfterClass
    public static void ac() throws SQLException {
        if (conn != null && !conn.isClosed())
            conn.close();
    }


    @Override
    public List<User> getByName(String name) throws SQLException {
        /*String sql = "select * from goods where name like ?";
        List<Goods> list = runner.query(conn, sql, new BeanListHandler<>(Goods.class), name);
        for (Goods goods : list) {
            System.out.println(goods);
        }
        return list;*/
        String sql = "select * from user where name like ?";
        List<User> list = runner.query(conn, sql, new BeanListHandler<>(User.class), name);
        return list;
    }


    public static void main(String[] args) throws SQLException {
        GoodsImp gd = new GoodsImp();
        List<User> list = new ArrayList<>();
        list = gd.getByName("zhangsan");
        for (User user : list) {
            System.out.println(user);
        }
    }
}

Answer

You’re mixing test systems (that’s what @BeforeClass and @AfterClass are about) and actual apps.

Essentially: @BeforeClass and @AfterClass are just ‘markers’. They do nothing at all on their own; other software interacts with them. Specifically, junit. Which you aren’t running here, so they do nothing.

Move the initialization code to your main method. (for example, invoke bc() there).

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Answer