使用mysql数据库的连接，使用只进结果集，在后面调用beforeFirst()方法，让指针回到第一条数据之前。设想应该是报错，结果没有报错。
package test.use;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
public class JDBC1 {
public static void main(String[] args) throws ClassNotFoundException, SQLException {
test1();
}
private static final String DRIVER = "com.mysql.jdbc.Driver";
private static final String URL = "jdbc:mysql://localhost:3306/test";
private static final String USERNAME = "root";
private static final String PASSWORD = "123456";
// private static final String DRIVER = "com.microsoft.sqlserver.jdbc.SQLServerDriver";
// private static final String URL = "jdbc:sqlserver://localhost:1433;databaseName=test1;";
// private static final String USERNAME = "sa";
// private static final String PASSWORD = "123456";
private static void test1() throws ClassNotFoundException, SQLException {
Class.forName(DRIVER);
Connection connection = DriverManager.getConnection(URL, USERNAME, PASSWORD);
Statement statement = connection.createStatement(ResultSet.TYPE_FORWARD_ONLY, ResultSet.CONCUR_READ_ONLY);
ResultSet resultSet = statement.executeQuery("select * from userr");
while (resultSet.next()) {
System.out.println(resultSet.getString(1));
System.out.println(resultSet.getString(2));
System.out.println(resultSet.getString(1));
}
resultSet.beforeFirst();
resultSet.close();
statement.close();
connection.close();
}
}
同一段代码，使用sqlserver数据库，结果报错了。
package test.use;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
public class JDBC1 {
public static void main(String[] args) throws ClassNotFoundException, SQLException {
test1();
}
// private static final String DRIVER = "com.mysql.jdbc.Driver";
// private static final String URL = "jdbc:mysql://localhost:3306/test";
// private static final String USERNAME = "root";
// private static final String PASSWORD = "123456";
private static final String DRIVER = "com.microsoft.sqlserver.jdbc.SQLServerDriver";
private static final String URL = "jdbc:sqlserver://localhost:1433;databaseName=test1;";
private static final String USERNAME = "sa";
private static final String PASSWORD = "123456";
private static void test1() throws ClassNotFoundException, SQLException {
Class.forName(DRIVER);
Connection connection = DriverManager.getConnection(URL, USERNAME, PASSWORD);
Statement statement = connection.createStatement(ResultSet.TYPE_FORWARD_ONLY, ResultSet.CONCUR_READ_ONLY);
ResultSet resultSet = statement.executeQuery("select * from account");
while (resultSet.next()) {
System.out.println(resultSet.getString(1));
System.out.println(resultSet.getString(2));
System.out.println(resultSet.getString(1));
}
resultSet.beforeFirst();
resultSet.close();
statement.close();
connection.close();
}
}
会抛出异常
...
// 正常数据
...
Exception in thread "main" com.microsoft.sqlserver.jdbc.SQLServerException: 只进结果集不支持请求的操作。
at com.microsoft.sqlserver.jdbc.SQLServerException.makeFromDriverError(SQLServerException.java:170)
at com.microsoft.sqlserver.jdbc.SQLServerResultSet.throwNotScrollable(SQLServerResultSet.java:376)
at com.microsoft.sqlserver.jdbc.SQLServerResultSet.verifyResultSetIsScrollable(SQLServerResultSet.java:399)
at com.microsoft.sqlserver.jdbc.SQLServerResultSet.beforeFirst(SQLServerResultSet.java:1239)
at test.use.JDBC1.test1(JDBC1.java:75)
at test.use.JDBC1.main(JDBC1.java:15)
稍微看了下mysql-connector的源码，它没有完全按照java.sql.ResultSet中对于接口的规定来实现：当只进结果集调用prevous(),beforeFirst()等方法时应该抛出异常。
/**
* Moves the cursor to the front of
* this <code>ResultSet</code> object, just before the
* first row. This method has no effect if the result set contains no rows.
*
* @exception SQLException if a database access error
* occurs; this method is called on a closed result set or the
* result set type is <code>TYPE_FORWARD_ONLY</code>
* @exception SQLFeatureNotSupportedException if the JDBC driver does not support
* this method
* @since 1.2
*/
void beforeFirst() throws SQLException;
生命不息，学习不止