java - java中如何处理表列中的空值？

Question

我在从数据库表获取值时一次又一次地遇到空指针异常......为什么它给我空指针异常？

这是我的代码:

private HashSet getPlayerList() {
        HashSet hs = new HashSet();
        String soccername = "";
        try {
            conn = ConnectionProvider.getConnection();
            rs = null;
            pstmt = null;
            String sql = "Select * from Players where deleted = false";

            if (conn != null) {
                pstmt = conn.prepareStatement(sql);
                rs = pstmt.executeQuery();

                while (rs.next()) {
                    soccername = rs.getString("soccername").trim();// this line giving exception
                    if (soccername == null || soccername.isEmpty()) {
                        soccername = rs.getString("name").trim();
                    }
                    hs.add(soccername);
                }
            }
        } catch (NamingException ex) {
            System.out.println(ex);
        } catch (SQLException ex) {
            System.out.println(ex);
        } finally {
            try {
                pstmt.close();
                rs.close();
                conn.close();
            } catch (SQLException ex) {
                System.out.println(ex);
            }
        }
        return hs;
   }

Answer 1

这是错误的:

soccername = rs.getString("soccername").trim();// this line giving exception
if (soccername == null || soccername.isEmpty()) {

如果rs.getString("soccername")返回null，它一定会导致NPE，因为它后面跟着函数trim()。

更好的是:

soccername = rs.getString("soccername");
if (soccername == null || soccername.trim().isEmpty()) {