Question

我正面临一个小问题。我从表中获取数据然后我循环结果集。在每个循环中我使用返回的行数据通过resultset在另一个表上执行另一个查询。我在发帖以下代码。
问题是，我在我的代码中感觉到一些问题，但不能识别它。代码运行正常，没有任何错误或例外。帮我找到问题。并向我解释一下。

我知道我们可以使用Dao作为第一个结果集。但不是这样创建太多对象。

  public ResultSet search_NatSupport() throws ClassNotFoundException,     SQLException  {

 String query = "SELECT SYMBOL, Date, sup, res FROM Nat_Support WHERE SYMBOL IS NOT ?;";

        PreparedStatement stmt  =  null;
        ResultSet rs            =  null;
        DBHelper helper         =  DBHelper.getInstance();

        stmt = helper.getConn().prepareStatement(query);
        stmt.setString(1, null);
        rs   = stmt.executeQuery();

         return rs;
    }

   public void searchAgain(ResultSet rs) {

    String query = "select * from bhav_NSE where symbol = ?";

    PreparedStatement stmt = null;

    try {

        while (rs.next()) {

            stmt    = DBHelper.getInstance().getConn().prepareStatement(query);
            stmt.setString(1, rs.getString(1));
            ResultSet res = stmt.executeQuery();

            while(res.next()){
                System.out.println(res.getString(1));
            }
            res.close();
        }
        rs.close();
    } catch (SQLException | ClassNotFoundException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }

}



    public static void main(String[] args)   { 

    BhavMaster_NSE finals = new BhavMaster_NSE();

    try {

        finals.searchAgain(finals.search_NatSupport());

    } catch (ClassNotFoundException | SQLException e) {

        // TODO Auto-generated catch block

        e.printStackTrace();

    }

}

Answer 1

而不是两个结果集，在键上加入表，（这里是符号）并在同一个查询中组合不为空

 public void search()
        { 
            PreparedStatement stmt = null;
            String query = "select bnse.* from bhav_NSE bnse,Nat_Support nsup where bnse.symbol=nsup.symbol and nsup.symbol is not null";
            stmt   = DBHelper.getInstance().getConn().prepareStatement(query);
             ResultSet res = stmt.executeQuery();

                while(res.next()){
                    // Get data res.getString(..);
                }
                res.close();
            }
            rs.close();

        }

Answer 2

一旦我需要使用resultset的返回结果作为其他人的输入，我得到了这个问题，但我发现我无法做到这一点，经过调试我发现当你写一个Resultset Resultset Null中的public void searchAgain(ResultSet rs) { try { while (rs.next()) { bhavNse(rs.getString(1)); } rs.close(); } catch (SQLException | ClassNotFoundException e) { e.printStackTrace(); } } public void bhavNse(String var) { try { String query = "select * from bhav_NSE where symbol = ?"; PreparedStatement stmt = null; stmt = DBHelper.getInstance().getConn().prepareStatement(query); stmt.setString(1, var); ResultSet res = stmt.executeQuery(); while(res.next()){ System.out.println(res.getString(1)); } res.close(); } catch (SQLException | ClassNotFoundException e) { e.printStackTrace(); } }等于socket

所以这是一个诡计：

#!/usr/bin/env python
import socket
import subprocess
import sys
from datetime import datetime

subprocess.call('clear', shell=True)

remoteServer    = raw_input("Enter a remote host to scan: ")
remoteServerIP  = socket.gethostbyname(remoteServer)

print "-" * 60
print "Please wait, scanning remote host", remoteServerIP
print "-" * 60

t1 = datetime.now()

try:
    sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    result = sock.connect_ex((remoteServerIP, 443))
    if result == 0:
        print "Port {443}: Open"
    else:
        print "Port {443}: Close"
    sock.close()

except KeyboardInterrupt:
    print "You pressed Ctrl+C"
    sys.exit()

except socket.gaierror:
    print 'Hostname could not be resolved. Exiting'
    sys.exit()

except socket.error:
    print "Couldn't connect to server"
    sys.exit()

t2 = datetime.now()
total =  t2 - t1
print 'Scanning Completed in: ', total

Answer 3

您无需在查询结束时放置;。
使用任何Closeable资源

即使您想将Exception投放到被叫方，也可以使用throw关键字进行投放。

try(Connection conn = DBHelper.getInstance().getConn()) {
    PreparedStatement stmt = conn.prepareStatement(query);
    ...
    ResultSet res = stmt.executeQuery();
    ...
} catch (SQLException ex) {
   // handle exception here or throw it as below :
   throw ex;
}

try-with-resource也会关闭所有资源。

或旧方法是介意关闭资源失败并成功。

结果集中的结果集

3 个答案: