Question

您好我的SQL查询使用Prepared Statement有问题。我得到的错误如下：

com.ibm.db2.jcc.am.ro:DB2 SQL错误：SQLCODE = -206，SQLSTATE = 42703，SQLERRMC = NAME，DRIVER = 3.58.82

显然，使用我的变量name存在问题，其中包括用户输入的JTsextField的内容，或者内容未保存在所述变量中。以下是我的SQL查询的以下重要类。我正在使用MVC模型和DAO模式。

我的控制器类（仅显示重要部分）：

public class Controller implements Observer, ActionListener{

Connection dbConnection = null;
public static PreparedStatement preparedStatement = null;

@Override
public void actionPerformed(ActionEvent e) {
    switch (e.getActionCommand()) {
    case View.SEARCH:
        try {

            String name = View.searchname.getText();
            String plz = View.searchplz.getText();
            String result = "SELECT BBSTBBNR, BBSTNABEG, BBSTPLZ FROM BP.TBBBST WHERE BBSTNABEG = name AND BBSTPLZ = plz";

            dbConnection = ConnectionManager.getConnection();
            preparedStatement = dbConnection.prepareStatement(result);


            model.search();
        } catch (SQLException e1) {
            System.out.println("An SQL-Error occured: ");
            e1.printStackTrace();
        } catch (IOException e1) {
            System.out.println("An error occured: ");
            e1.printStackTrace();
        }
        break;

    default:
        System.out.println("Search error: " + e.getActionCommand());
        break;
    }

}

我的BtrDao课程：

public interface BtrDao {

Collection<BTRBean> getBTR() throws SQLException, IOException;
}

我的DaoImpl课程：

public class BtrDaoImpl extends AbstractDao implements BtrDao {

public Collection<BTRBean> getBTR() throws SQLException,
        IOException {
    final Collection<BTRBean> result = new ArrayList<BTRBean>();

    ResultSet resultset = null;
    try {
        //This is where the Nullpointerexception happens!
        resultset = Controller.preparedStatement.executeQuery();

        // while loop for finding all results
        while (resultset.next()) {
            BTRBean btr = new BTRBean();
            int btrid = resultset.getInt(1);
            String btrplz = resultset.getString(2);
            String btrname = resultset.getString(3);
            result.add(btr);
            System.out.println(btrid + " " + btrplz + " " + btrname);
        }

    } catch (SQLException e) {
        e.printStackTrace();
        System.out.println("There was an SQL processing error: (getBTR)");
        e.printStackTrace();
    } catch (NullPointerException npe) {
        System.out.println("NullPointerException");
        npe.printStackTrace();
    } finally {

        closeConnection(resultset);

    }

    return result;
}

}

我的AbstractDao课程：

public class AbstractDao {

    public static Connection getConnection() throws SQLException {
        return ConnectionManager.getInstance().getConnection();
    }

    public ResultSet getResultset(final String statement) throws SQLException {
        final Statement stmnt = getConnection().createStatement();
        return stmnt.executeQuery(statement);
    }

    public void closeConnection(final ResultSet resultset) throws SQLException {
        if(resultset != null)
        resultset.close();
        getConnection().close();
    }
}

我的ConnectionManager类：

public class ConnectionManager {

    public Connection getConnection() throws SQLException {

        try {
        Properties props = new Properties();
        FileInputStream in = new FileInputStream(".//required.\\dbprop.\\DBConn.properties");
        props.load(in);
        in.close();
        String drivers = props.getProperty("jdbc.drivers");
        if (drivers !=null) 
            System.setProperty("jdbc.drivers", drivers);

        String url = props.getProperty("jdbc.url");
        if (url !=null)
            System.setProperty("jdbc.url", url);

        String username = props.getProperty("jdbc.username");
        if (username !=null)
            System.setProperty("jdbc.username", username);
        String password = props.getProperty("jdbc.password");
        if (password !=null)
            System.setProperty("jdbc.password", password);

        return DriverManager.getConnection(url, username, password);
        } catch (IOException e) {
            throw new SQLException(e.getMessage(), e.getCause());
        }

    }


    //Close connection
    public void closeConnection(Connection con) throws SQLException {
        if (con != null)
            con.close();
    }

    // Making sure that there's only one instance of the class
    private static ConnectionManager singleton_Instance;

    // default constructor
    private ConnectionManager() {
    }

    // returns the single instance of the class
    public static ConnectionManager getInstance() {
        if (singleton_Instance == null) {
            singleton_Instance = new ConnectionManager();
        }
        return singleton_Instance;
    }

}

Answer 1

占位符必须以UserSurvey Item = new UserSurvey(); Item.Survey = s; Item.ApplicationUser = userinfo; Item.Active = true; Item.StartDate = Convert.ToDateTime(dateFrom); Item.EndDate = Convert.ToDateTime(dateTo); db.UserSurvey.Add(Item); db.SaveChanges();开头，因此您的查询必须如下所示：

您必须在准备语句后设置参数。

Answer 2

您需要在查询中指明要使用哪些参数，并且需要显式设置值。 JDBC API本身仅支持位置参数，因此您需要将代码更改为：

String name = View.searchname.getText();
String plz = View.searchplz.getText();

// Use ? for parameters
String result = "SELECT BBSTBBNR, BBSTNABEG, BBSTPLZ FROM BP.TBBBST " + 
        " WHERE BBSTNABEG = ? AND BBSTPLZ = ?";

preparedStatement = dbConnection.prepareStatement(result);

// Set values for parameters
preparedStatement.setString(1, name);
preparedStatement.setString(2, plz);

正如评论中的mustaccio所示，IBM DB2 JDBC驱动程序支持命名参数，请参阅Using named parameter markers with PreparedStatement objects。您的示例将如下所示：

String name = View.searchname.getText();
String plz = View.searchplz.getText();

// Use :<name> for parameters
String result = "SELECT BBSTBBNR, BBSTNABEG, BBSTPLZ FROM BP.TBBBST " + 
        " WHERE BBSTNABEG = :name AND BBSTPLZ = :plz";

DB2PreparedStatement preparedStatement = (DB2PreparedStatement) dbConnection.prepareStatement(result);

// Set values for parameters
preparedStatement.setJccStringAtName("name", name);
preparedStatement.setJccStringAtName("plz", plz);

可能并非总是可以转换为DB2PreparedStatement（例如，在使用第三方连接池时）。您可能需要使用unwrap代替（但这并非总是可行）。

将PreparedStatement用于SQL查询（DB2）SQLCODE = -206 SQLSTATE = 42703

2 个答案: