我的代码有问题。它（应该是）一个电子邮件客户端，可以选择读取消息并发送它们 - 问题是，不下载消息而无法发送消息 - 我认为问题在于连接。
该计划包括以下课程
EmailClient：电子邮件客户端应用程序的主要类ConnectDialog：此类显示用于输入电子邮件服务器连接设置的对话框。MessagesTableModel：此类管理电子邮件表的数据。MessageDialog：此类显示用于创建消息的对话框。这是主要类，最有趣的是名为sendMessage()和connect()的方法：
import java.awt.*;
import java.awt.event.*;
import java.net.*;
import java.util.*;
import javax.mail.*;
import javax.mail.internet.*;
import javax.swing.*;
import javax.swing.event.*;
// The E-mail Client.
public class EmailClient extends JFrame {
// Message table's data model.
private MessagesTableModel tableModel;
// Table listing messages.
private JTable table;
// This the text area for displaying messages.
private JTextArea messageTextArea;
/* This is the split panel that holds the messages
table and the message view panel. */
private JSplitPane splitPane;
// These are the buttons for managing the selected message.
private JButton replyButton, forwardButton, deleteButton;
// Currently selected message in table.
private Message selectedMessage;
// Flag for whether or not a message is being deleted.
private boolean deleting;
// This is the JavaMail session.
private Session session;
// Constructor for E-mail Client.
public EmailClient() {
// Set application title.
setTitle("E-mail Client");
// Set window size.
setSize(640, 480);
// Handle window closing events.
addWindowListener(new WindowAdapter() {
public void windowClosing(WindowEvent e) {
actionExit();
}
});
// Setup file menu.
JMenuBar menuBar = new JMenuBar();
JMenu fileMenu = new JMenu("File");
fileMenu.setMnemonic(KeyEvent.VK_F);
JMenuItem fileExitMenuItem = new JMenuItem("Exit",
KeyEvent.VK_X);
fileExitMenuItem.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
actionExit();
}
});
fileMenu.add(fileExitMenuItem);
menuBar.add(fileMenu);
setJMenuBar(menuBar);
// Setup buttons panel.
JPanel buttonPanel = new JPanel();
JButton newButton = new JButton("New Message");
newButton.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
actionNew();
}
});
buttonPanel.add(newButton);
// Setup messages table.
tableModel = new MessagesTableModel();
table = new JTable(tableModel);
table.getSelectionModel().addListSelectionListener(new
ListSelectionListener() {
public void valueChanged(ListSelectionEvent e) {
tableSelectionChanged();
}
});
// Allow only one row at a time to be selected.
table.setSelectionMode(ListSelectionModel.SINGLE_SELECTION);
// Setup E-mails panel.
JPanel emailsPanel = new JPanel();
emailsPanel.setBorder(
BorderFactory.createTitledBorder("E-mails"));
messageTextArea = new JTextArea();
messageTextArea.setEditable(false);
splitPane = new JSplitPane(JSplitPane.VERTICAL_SPLIT,
new JScrollPane(table), new JScrollPane(messageTextArea));
emailsPanel.setLayout(new BorderLayout());
emailsPanel.add(splitPane, BorderLayout.CENTER);
// Setup buttons panel 2.
JPanel buttonPanel2 = new JPanel();
replyButton = new JButton("Reply");
replyButton.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
actionReply();
}
});
replyButton.setEnabled(false);
buttonPanel2.add(replyButton);
forwardButton = new JButton("Forward");
forwardButton.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
actionForward();
}
});
forwardButton.setEnabled(false);
buttonPanel2.add(forwardButton);
deleteButton = new JButton("Delete");
deleteButton.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
actionDelete();
}
});
deleteButton.setEnabled(false);
buttonPanel2.add(deleteButton);
// Add panels to display.
getContentPane().setLayout(new BorderLayout());
getContentPane().add(buttonPanel, BorderLayout.NORTH);
getContentPane().add(emailsPanel, BorderLayout.CENTER);
getContentPane().add(buttonPanel2, BorderLayout.SOUTH);
}
// Exit this program.
private void actionExit() {
System.exit(0);
}
// Create a new message.
private void actionNew() {
sendMessage(MessageDialog.NEW, null);
}
// Called when table row selection changes.
private void tableSelectionChanged() {
/* If not in the middle of deleting a message, set
the selected message and display it. */
if (!deleting) {
selectedMessage =
tableModel.getMessage(table.getSelectedRow());
showSelectedMessage();
updateButtons();
}
}
// Reply to a message.
private void actionReply() {
sendMessage(MessageDialog.REPLY, selectedMessage);
}
// Forward a message.
private void actionForward() {
sendMessage(MessageDialog.FORWARD, selectedMessage);
}
// Delete the selected message.
private void actionDelete() {
deleting = true;
try {
// Delete message from server.
selectedMessage.setFlag(Flags.Flag.DELETED, true);
Folder folder = selectedMessage.getFolder();
folder.close(true);
folder.open(Folder.READ_WRITE);
} catch (Exception e) {
showError("Unable to delete message.", false);
}
// Delete message from table.
tableModel.deleteMessage(table.getSelectedRow());
// Update GUI.
messageTextArea.setText("");
deleting = false;
selectedMessage = null;
updateButtons();
}
// Send the specified message.
private void sendMessage(int type, Message message) {
// Display message dialog to get message values.
MessageDialog dialog;
try {
dialog = new MessageDialog(this, type, message);
if (!dialog.display()) {
// Return if dialog was cancelled.
return;
}
} catch (Exception e) {
showError("Unable to send message.", false);
return;
}
try {
// Create a new message with values from dialog.
Message newMessage = new MimeMessage(session);
newMessage.setFrom(new InternetAddress(dialog.getFrom()));
newMessage.setRecipient(Message.RecipientType.TO,
new InternetAddress(dialog.getTo()));
newMessage.setSubject(dialog.getSubject());
newMessage.setSentDate(new Date());
newMessage.setText(dialog.getContent());
// Send new message.
Transport.send(newMessage);
} catch (Exception e) {
showError("Unable to send message.", false);
}
}
// Show the selected message in the content panel.
private void showSelectedMessage() {
// Show hour glass cursor while message is loaded.
setCursor(Cursor.getPredefinedCursor(Cursor.WAIT_CURSOR));
try {
messageTextArea.setText(
getMessageContent(selectedMessage));
messageTextArea.setCaretPosition(0);
} catch (Exception e) {
showError("Unabled to load message.", false);
} finally {
// Return to default cursor.
setCursor(Cursor.getDefaultCursor());
}
}
/* Update each button's state based off of whether or not
there is a message currently selected in the table. */
private void updateButtons() {
if (selectedMessage != null) {
replyButton.setEnabled(true);
forwardButton.setEnabled(true);
deleteButton.setEnabled(true);
} else {
replyButton.setEnabled(false);
forwardButton.setEnabled(false);
deleteButton.setEnabled(false);
}
}
// Show the application window on the screen.
public void show() {
super.show();
// Update the split panel to be divided 50/50.
splitPane.setDividerLocation(.5);
}
// Connect to e-mail server.
public void connect() {
// Display connect dialog.
ConnectDialog dialog = new ConnectDialog(this);
dialog.show();
// Build connection URL from connect dialog settings.
StringBuffer connectionUrl = new StringBuffer();
connectionUrl.append(dialog.getType() + "://");
connectionUrl.append(dialog.getUsername() + ":");
connectionUrl.append(dialog.getPassword() + "@");
connectionUrl.append(dialog.getServer() + "/");
/* Display dialog stating that messages are
currently being downloaded from server. */
final DownloadingDialog downloadingDialog =
new DownloadingDialog(this);
SwingUtilities.invokeLater(new Runnable() {
public void run() {
downloadingDialog.show();
}
});
// Establish JavaMail session and connect to server.
Store store = null;
try {
// Initialize JavaMail session with SMTP server.
Properties props = new Properties();
props.put("mail.smtp.host", dialog.getSmtpServer());
session = Session.getDefaultInstance(props, null);
// Connect to e-mail server.
URLName urln = new URLName(connectionUrl.toString());
store = session.getStore(urln);
store.connect();
} catch (Exception e) {
// Close the downloading dialog.
downloadingDialog.dispose();
// Show error dialog.
showError("Unable to connect.", true);
}
// Download message headers from server.
try {
// Open main "INBOX" folder.
Folder folder = store.getFolder("INBOX");
folder.open(Folder.READ_WRITE);
// Get folder's list of messages.
Message[] messages = folder.getMessages();
// Retrieve message headers for each message in folder.
FetchProfile profile = new FetchProfile();
profile.add(FetchProfile.Item.ENVELOPE);
folder.fetch(messages, profile);
// Put messages in table.
tableModel.setMessages(messages);
} catch (Exception e) {
// Close the downloading dialog.
downloadingDialog.dispose();
// Show error dialog.
showError("Unable to download messages.", true);
}
// Close the downloading dialog.
downloadingDialog.dispose();
}
// Show error dialog and exit afterwards if necessary.
private void showError(String message, boolean exit) {
JOptionPane.showMessageDialog(this, message, "Error",
JOptionPane.ERROR_MESSAGE);
if (exit)
System.exit(0);
}
// Get a message's content.
public static String getMessageContent(Message message)
throws Exception {
Object content = message.getContent();
if (content instanceof Multipart) {
StringBuffer messageContent = new StringBuffer();
Multipart multipart = (Multipart) content;
for (int i = 0; i < multipart.getCount(); i++) {
Part part = (Part) multipart.getBodyPart(i);
if (part.isMimeType("text/plain")) {
messageContent.append(part.getContent().toString());
}
}
return messageContent.toString();
} else {
return content.toString();
}
}
// Run the E-mail Client.
public static void main(String[] args) {
EmailClient client = new EmailClient();
client.show();
// Display connect dialog.
client.connect();
}
}
将printStackTrace（）添加到异常会显示以下消息：
javax.mail.NoSuchProviderException: No provider for NORMAL
at javax.mail.Session.getProvider(Session.java:464)
at javax.mail.Session.getStore(Session.java:539)
at EmailClient.connect(EmailClient.java:296)
at EmailClient.main(EmailClient.java:365)
我很感激能得到的所有帮助！