How can I determine if the column name exist in th

问题:

As the ResultSet contains the data returned from the dynamic SQL, if there are any method to determine if the ResultSet contains a particular column name ? For example , if I run rs.getString("Column_ABC"); but Column_ABC does not really exist, it will throw out the exception . How can I test if the ResultSet can get a data from a column named "Column_ABC" ?

回答1:

Use the ResultSetMetaData class.

public static boolean hasColumn(ResultSet rs, String columnName) throws SQLException {
    ResultSetMetaData rsmd = rs.getMetaData();
    int columns = rsmd.getColumnCount();
    for (int x = 1; x <= columns; x++) {
        if (columnName.equals(rsmd.getColumnName(x))) {
            return true;
        }
    }
    return false;
}

The thing I don't understand is why this function would ever be needed. The query or stored procedure being executed should have known results. The columns of the query should be known. Needing a function like this may be a sign that there is a design problem somewhere.

回答2:

Not sure if this is more or less efficient than Erick's answer but it's easier.

String str;

try {
    str = rs.getString(columnName);
} catch (java.sql.SQLException e) {
    str = null;
}

回答3:

/**
 * returns default value if column is not present in resultset
 * 
 * @param rs
 * @param columnLabel
 * @param defaultValue
 * @return
 */
@SuppressWarnings("unchecked")
private static <T> T getValueFromResultSet(final ResultSet rs,
        String columnLabel, T defaultValue) {
    try {
        return (T) rs.getObject(columnLabel);
    } catch (SQLException e) {
        return defaultValue;
    }
}

In java version >=7 you have a option of passing Class type in ResultSet#getObject method

回答4:

if not rs.getString("Column_ABC")= nothing then ' your code here