如何在java中使用不同的列方法？（How to use different column methods in java?）

问题描述 (Problem Description)

如何使用不同的列方法来计算列数，获取列名，获取列类型等？

解决方案 (Solution)

以下示例使用getColumnCount，getColumnName，getColumnTypeName，getColumnDisplaySize方法来获取列的列数，列的名称或表中列的类型。

import java.sql.*;
public class jdbcConn {
   public static void main(String[] args) throws Exception {
      Class.forName("org.apache.derby.jdbc.ClientDriver");
      Connection con = DriverManager.getConnection(
         "jdbc:derby://localhost:1527/testDb","name","pass");
      Statement stmt = con.createStatement();
      String query = "select * from emp order by name";
      ResultSet rs = stmt.executeQuery(query);
      ResultSetMetaData rsmd = rs.getMetaData();
      System.out.println("no of columns in the table = "+ rsmd.getColumnCount());
      System.out.println("Name of the first column "+ rsmd.getColumnName(1));
      System.out.println("Type of the second column "+ rsmd.getColumnTypeName(2));
      System.out.println("No of characters in 3rd column "+ rsmd.getColumnDisplaySize(2));
   }
}

结果 (Result)

上面的代码示例将产生以下结果。 结果可能会有所不同。

no of columns in the table= 3
Name of the first columnID
Type of the second columnVARCHAR
No of characters in 3rd column20