URLs,URIs,Proxies和Passwords 解析[12]

public PasswordAuthentication(String userName, char[] password)

每个都是通过getter 方法被访问的：

public String getUserName( )
public char[] getPassword( )

JPasswordField 类
Swing中JPasswordField 组件有个用来向用户获取密码的有用工具：

public class JPasswordField extends JTextField

这个轻量级组件和文本框的行为几乎是一样的。但是用户输入的会以“*”形式显示出来。这样的话，就可以防止其他人在后面看见用户输入的密码了。

JPasswordField 也用char 数组来存放密码，这样当你不再需要是，你就可以清空它了。方法getPassword( )  用来返回密码：

public char[] getPassword( )

不然的话，大多数时候你得使用继承超类JTextField 后得到的方法。例子7-13展示了一个来自Swing的Authenticator 的子类，它生成一个对话框向用户获取他的用户名和密码。下面的大多数代码都是用来生成GUI。JPasswordField 提取密码，JTextField 提取用户名。图7-4就是下面代码所生成的一个简单的对话框。

Example 7-13. A GUI authenticator

package com.macfaq.net;

import java.net.*;
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;

public class DialogAuthenticator extends Authenticator {

  private JDialog passwordDialog;  
  private JLabel mainLabel 
   = new JLabel("Please enter username and password: ");
  private JLabel userLabel = new JLabel("Username: ");
  private JLabel passwordLabel = new JLabel("Password: ");
  private JTextField usernameField = new JTextField(20);
  private JPasswordField passwordField = new JPasswordField(20);
  private JButton okButton = new JButton("OK");
  private JButton cancelButton = new JButton("Cancel");
  
  public DialogAuthenticator( ) {
    this("", new JFrame( ));
  }
    
  public DialogAuthenticator(String username) {
    this(username, new JFrame( ));
  }
    
  public DialogAuthenticator(JFrame parent) {
    this("", parent);
  }
    
  public DialogAuthenticator(String username, JFrame parent) {
    
    this.passwordDialog = new JDialog(parent, true);  
    Container pane = passwordDialog.getContentPane( );
    pane.setLayout(new GridLayout(4, 1));
    pane.add(mainLabel);
    JPanel p2 = new JPanel( );
    p2.add(userLabel);
    p2.add(usernameField);
    usernameField.setText(username);
    pane.add(p2);
    JPanel p3 = new JPanel( );
    p3.add(passwordLabel);
    p3.add(passwordField);
    pane.add(p3);
    JPanel p4 = new JPanel( );
    p4.add(okButton);
    p4.add(cancelButton);
    pane.add(p4);   
    passwordDialog.pack( );
    
    ActionListener al = new OKResponse( );
    okButton.addActionListener(al);
    usernameField.addActionListener(al);
    passwordField.addActionListener(al);
    cancelButton.addActionListener(new CancelResponse( ));
    
  }
  
  private void show( ) {
    
    String prompt = this.getRequestingPrompt( );
    if (prompt == null) {
      String site     = this.getRequestingSite( ).getHostName( );
      String protocol = this.getRequestingProtocol( );
      int    port     = this.getRequestingPort( );
      if (site != null & protocol != null) {
        prompt = protocol + "://" + site;