java 实现一个单线程的资源下载器

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package cn.lruihao.base;

import java.awt.FlowLayout;
import java.awt.Font;
import java.awt.HeadlessException;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.io.FileOutputStream;
import java.io.InputStream;
import java.net.URL;
import java.net.URLConnection;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.JTextField;

public class SingleThreadDown extends JFrame implements ActionListener {
  private final JPanel panel=new JPanel();
  private final JLabel label1=new JLabel("网络资源的单线程下载：");
  private final JLabel label2=new JLabel("网络资源的网址：");
  JButton StartButton = new JButton("单击开始下载");
  JButton resetButton = new JButton("清空");
  JButton exitButton = new JButton("退出");
  JTextField urlField  = new JTextField(20);

  public SingleThreadDown() {
    panel.setLayout(new FlowLayout()); //布局管理器
    label1.setFont(new Font("雅黑",Font.BOLD,15));
    panel.add(label1);
    panel.add(label2);
    panel.add(urlField);
    panel.add(StartButton);
    panel.add(resetButton);
    panel.add(exitButton);
    setContentPane(panel);
    setSize(400,200);
    setLocation(400,400);
    setVisible(true); //面板可视化，也可以在 main 中通过 JFrame 子类对象调用方法设置
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); //默认关闭事件
    StartButton.addActionListener(this);//添加点击事件，传入 ActionListener 对象，由于子类继承了 ActionListener 接口，所以 this
    resetButton.addActionListener(this);
    exitButton.addActionListener(this);
  }

  public void download(String address) throws Exception {
    URL url = new URL(address);
    URLConnection urlcon = url.openConnection();
    urlcon.connect();
    InputStream in=urlcon.getInputStream();//获取的字节流对象
    String filePath = url.getFile();
    int pos=filePath.lastIndexOf("/"); //"/"分割的最后一个串的下标
    String fileName = filePath.substring(pos+1);
    FileOutputStream out = new FileOutputStream("C:\\Users\\李瑞豪、\Desktop\\"+fileName);
    byte[] b = new byte[1024];
    int len=0;
    while((len=in.read(b,0,1024))!=-1) {
      out.write(b,0,len);
    }
    out.close();
    in.close();
    JOptionPane.showMessageDialog(this, "下载完毕");
  }

  @Override
  public void actionPerformed(ActionEvent e) {
    if(e.getSource()==StartButton) {
      if("".equals(urlField.getText())){
        JOptionPane.showMessageDialog(this, "请输入资源地址");
      }
      String url = urlField.getText();
      try {
        download(url);
      } catch (Exception e1) {
        JOptionPane.showMessageDialog(this, "资源地址有误，请检查~");
        e1.printStackTrace();
      }
    }else if(e.getSource()==resetButton) {
      urlField.setText("");
    }else {
      System.exit(0);
    }

  }

  public static void main(String[] args) {
    new SingleThreadDown();

  }

}