Question

我尝试使用 CachedRowSet 编写一个方法来执行SQl查询。示例代码如下（用户和密码在前面定义），

public CachedRowSet getContentsOfCoffeesTable( Connection connection ) throws SQLException {

    CachedRowSet crs = null;

    try {

        crs = new CachedRowSetImpl();

        crs.setType(ResultSet.TYPE_SCROLL_INSENSITIVE);
        crs.setConcurrency(ResultSet.CONCUR_UPDATABLE);
        crs.setUsername(user);
        crs.setPassword(password);


        crs.setCommand("select COF_NAME, SUP_ID, PRICE, SALES, TOTAL from COFFEES");
        crs.execute();


    } catch (SQLException e) {

        e.printStackTrace();
    }
    return crs;
}

当我尝试使用示例代码读取数据时，我什么都没得到。

CachedRowSet myValues =  getContentsOfCoffeesTable( myConn );
while( myValues != null && myValues.next() ){

     // get the values of 2nd column of the table 
     System.out.println( myValues.getString(2) );
}

已填充COFFEES表。我该如何改进代码？感谢。

Answer 1

我找到了如何使用CachedRowSet进行SQL查询的解决方案，并将方法更改为如下，

public CachedRowSet getContentsOfCoffeesTable(Connection mycConn)
    throws SQLException {

CachedRowSet crs = null;
ResultSet resultSet = null;
Statement stmt = null;
String sql = "select COF_NAME, SUP_ID, PRICE, SALES, TOTAL from COFFEES";

try {

    stmt = myConn.createStatement();
    resultSet = stmt.executeQuery(sql);

    crs = new CachedRowSetImpl();
    crs.populate(resultSet);

}

catch (Exception e) {

    e.printStackTrace();
}

return crs;
 }

然后，可以打印下面的值，

// I get the Connection myConn here 
//  then pass the connection info to the method and get myValues 
// prit myValues for column index of 2 

CachedRowSet myValues =  getContentsOfCoffeesTable( myConn );
while( myValues != null && myValues.next() ){

     // get the values of 2nd column of the table 
     System.out.println( myValues.getString(2) );
}

Answer 2

我找到了另一种方法。在最初的帖子 url 中没有提供如下信息，

cr.setUrl(url);

url 的值，

url = "jdbc:mysql://localhost:3306/myDemo"

方法如下，

private CachedRowSet getContentsOfCoffeesTable(Connection con)
        throws SQLException {

    CachedRowSet cr = null;

    try {

        cr = new CachedRowSetImpl();
        cr.setType(ResultSet.TYPE_SCROLL_INSENSITIVE);
        cr.setConcurrency(ResultSet.CONCUR_UPDATABLE);
        cr.setUsername(username);
        cr.setPassword(password);
        cr.setUrl(url);

        cr.setCommand("select COF_NAME, SUP_ID, PRICE, SALES, TOTAL from COFFEES");
        cr.execute();

    }

    catch (Exception ex) {

        ex.printStackTrace();
    }

    return cr;
}

如何使用CachedRowSet进行SQL查询？

2 个答案: