如何在 Java 中使用不同的列方法来计数列数、获取列名、获取列类型

问题说明

如何使用不同的列方法来计数列数、获取列名、获取列类型等？

解决方案

以下示例使用 getColumnCount、getColumnName、getColumnTypeName、getColumnDisplaySize 方法来获取列数、列名或表中列的类型。

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://: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

上述代码示例将生成以下结果。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