这个程序在编译和运行都没有问题，我的“nihao.txt”这个文件的路径是在：e:\nihao.txt
但当我在文本框输入：http://127.0.0.1/nihao.txt 时，
就出现下面错误信息：
         Connection reset
        at (Unknown Source)
        at (Unknown Source)
        at (Unknown Source)
        at (Unknown Source)
        at (Unknown Source)
        at (Unknown Source)
        at (Unknown Source)
        at (Unknown So
urce)
        at DownLoad$1.actionPerformed(DownLoad.java:54)
        at javax.swing.AbstractButton.fireActionPerformed(Unknown Source)
        at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source)
        at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source)
        at javax.swing.DefaultButtonModel.setPressed(Unknown Source)
        at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(Unknown Sour
ce)
        at java.(Unknown Source)
        at javax.swing.JComponent.processMouseEvent(Unknown Source)
        at java.(Unknown Source)
        at java.awt.Container.processEvent(Unknown Source)
        at java.(Unknown Source)
        at java.awt.Container.dispatchEventImpl(Unknown Source)
        at java.(Unknown Source)
        at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source)
        at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source)
        at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source)
        at java.awt.Container.dispatchEventImpl(Unknown Source)
        at java.awt.Window.dispatchEventImpl(Unknown Source)
        at java.(Unknown Source)
        at java.awt.EventQueue.dispatchEvent(Unknown Source)
        at java.awt.EventDispatchThread.pumpOneEventForHierarchy(Unknown Source)

        at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
        at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
        at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
        at java.awt.EventDispatchThread.run(Unknown Source)
import *;
import *;
import java.awt.*;
import javax.swing.*;
import java.awt.event.*;

public class DownLoad extends JFrame
{
      final JTextField JF;
      JScrollPane JS;
      JLabel JL1;
      JTextArea JA;
      JButton JB;
      JPanel JP1;
      JPanel JP2;
      
      public DownLoad(String str)
      {
              super(str);
              //建立内容面板
              JP1=new JPanel();
              JP2=new JPanel();
              
              //建立组件
            JF=new JTextField(30);
              JL1=new JLabel("URL:");
                 JA=new JTextArea(30,20);
                 JS=new JScrollPane(JA);
              JB=new JButton("下载");
              
              //布置JP1,JP2面板
              JP1.add(JL1);
              JP1.add(JF);
              JP2.add(JB);
              
              //添加组件
              Container c=this.getContentPane();
              c.setLayout(new BorderLayout());
              c.add(JS,BorderLayout.CENTER);
              c.add(JP1,BorderLayout.NORTH);
              c.add(JP2,BorderLayout.SOUTH);
              
              //添加监听器
              JB.addActionListener(new ActionListener()
                                                       {
                                                               public void actionPerformed(ActionEvent e)
                                                               {
                                                                     try
                                                                     {
                                                                               String str=JF.getText();
                                                                               System.out.println(str);
                                                                               URL address=new URL(str);
                                                                               URLConnection conn=address.openConnection();
                                                                               InputStream in=conn.getInputStream();
                                                                               InputStreamReader ISR=new InputStreamReader(in);
                                                                               BufferedReader BR=new BufferedReader(ISR);
                                                                               FileOutputStream FS=new FileOutputStream("1.txt");
                                                                               PrintWriter FO=new PrintWriter(FS,true);
                                                                               FO.println(BR.readLine());
                                                                               BR.close();
                                                                               FO.close();
                                                                     }
                                                                     catch(Exception ee)
                                                                     {
                                                                             ee.printStackTrace();
                                                                     }
                                                               }
                                                       });
              
      }
        public static void main(String[] args)
        {
                DownLoad DL=new DownLoad("下载窗口");
                DL.setSize(500,450);
                DL.setLocation(200,150);
                DL.setVisible(true);
                DL.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        }
}

你这个好像是Java小应用程序吧，那就还应该有import Java.Applet.*而且是用html来运行的。