Java电子邮件处理开发指南

### Java 电子邮件处理开发指南 #### 1. 引言 在当今数字化的时代，电子邮件已经成为人们日常沟通和业务交流的重要工具。对于 Java 开发者来说，如何在 Java 程序中实现电子邮件的读取和发送功能是一个常见的需求。本文将详细介绍如何使用 JavaMail API 来实现这些功能，包括读取邮件、构建邮件阅读器和邮件客户端等。 #### 2. 读取邮件的问题与解决方案 在 Java 中读取邮件时，我们可能会遇到一些问题，例如如何连接到邮件服务器、如何获取邮件列表以及如何显示邮件内容等。为了解决这些问题，我们可以使用 JavaMail API 中的 Store 类。 ##### 2.1 使用 JavaMail Store 读取邮件的步骤 以下是使用 Store 读取邮件的基本步骤： 1. **获取 Session 对象**：使用 `Session.getDefaultInstance()` 方法获取一个 Session 对象，并可以传递 `System.getProperties()` 作为 Properties 参数。 ```java Session session = Session.getDefaultInstance(System.getProperties(), null); session.setDebug(false); ``` 2. **从 Session 对象获取 Store**：根据指定的协议从 Session 对象中获取一个 Store 对象。 ```java Store store = session.getStore(protocol); store.connect(host, user, password); ``` 3. **获取根 Folder**：根据根文件夹的名称获取相应的 Folder 对象。 ```java Folder rf; if (root.length() != 0) { System.out.println("Getting folder " + root + "."); rf = store.getFolder(root); } else { System.out.println("Getting default folder."); rf = store.getDefaultFolder(); } rf.open(Folder.READ_WRITE); ``` 4. **列出子文件夹（如果有）**：如果根文件夹可以包含子文件夹，则列出这些子文件夹。 ```java if (rf.getType() == Folder.HOLDS_FOLDERS) { Folder[] f = rf.list(); for (int i = 0; i < f.length; i++) listFolder(f[i], "", recursive); } else listFolder(rf, "", false); ``` 5. **获取邮件消息**：对于每个可以包含邮件消息的文件夹，调用 `getMessages()` 方法获取邮件消息数组。 ```java Message[] msgs = folder.getMessages(); ``` 6. **处理邮件消息**：通常，我们会显示邮件的头部信息，并让用户选择要查看的邮件。 ```java for (int i = 0; i < msgs.length; i++) { Message m = msgs[i]; Address from = m.getFrom()[0]; String fromAddress; if (from instanceof InternetAddress) fromAddress = ((InternetAddress)from).getAddress(); else fromAddress = from.toString(); StringBuffer sb = new StringBuffer(); fromFmt.format(fromAddress, sb, null); sb.append(" "); subjFmt.format(m.getSubject(), sb, null); System.out.println(sb.toString()); } ``` ##### 2.2 示例代码：MailLister.java 以下是一个完整的示例代码，用于列出指定邮箱中的所有邮件： ```java import com.darwinsys.util.*; import java.util.Properties; import javax.mail.*; import javax.mail.internet.*; /** * List all available folders. */ public class MailLister { static StringAlign fromFmt = new StringAlign(20, StringAlign.JUST_LEFT); static StringAlign subjFmt = new StringAlign(40, StringAlign.JUST_LEFT); public static void main(String[] argv) throws Exception { String fileName = MailConstants.PROPS_FILE_NAME; String protocol = null; String host = null; String user = null; String password = null; String root = null; // If argc == 1, assume it's a Properties file. if (argv.length == 1) { fileName = argv[0]; FileProperties fp = new FileProperties(fileName); fp.load(); protocol = fp.getProperty(MailConstants.RECV_PROTO); host = fp.getProperty(MailConstants.RECV_HOST); user = fp.getProperty(MailConstants.RECV_USER); password = fp.getProperty(MailConstants.RECV_PASS); root = fp.getProperty(MailConstants.RECV_ROOT); } // If not, assume listing all args in long form. else if (argv.length == 5) { protocol = argv[0]; host = argv[1]; user = argv[2]; password = argv[3]; root = argv[4]; } // Otherwise give up. else { System.err.println( "Usage: MailLister protocol host user pw root"); System.exit(0); } boolean recursive = false; // Start with a Session object, as usual Session session = Session.getDefaultInstance( System.getProperties(), null); session.setDebug(false); // Get a Store object for the given protocol Store store = session.getStore(protocol); store.connect(host, user, password); // Get Folder object for root, and list it // If root name = "", getDefaultFolder( ), else getFolder(root) Folder rf; if (root.length() != 0) { System.out.println("Getting folder " + root + "."); rf = store.getFolder(root); } else { System.out.println("Getting default folder."); rf = store.getDefaultFolder(); } rf.open(Folder.READ_WRITE); if (rf.getType() == Folder.HOLDS_FOLDERS) { Folder[] f = rf.list(); for (int i = 0; i < f.length; i++) listFolder(f[i], "", recursive); } else listFolder(rf, "", false); } static void listFolder(Folder folder, String tab, boolean recurse) throws Exception { folder.open(Folder.READ_WRITE); System.out.println(tab + "Name: " + folder.getName() + '(' + folder.getFullName() + ')'); if (!folder.isSubscribed()) System.out.println(tab + "Not Subscribed"); if ((folder.getType() & Folder.HOLDS_MESSAGES) != 0) { if (folder.hasNewMessages()) System.out.println(tab + "Has New Messages"); else System.out.println(tab + "No New Messages"); Message[] msgs = folder.getMessages(); for (int i = 0; i < msgs.length; i++) { Message m = msgs[i]; Address from = m.getFrom()[0]; String fromAddress; if (from instanceof InternetAddress) fromAddress = ((InternetAddress)from).getAddress(); else fromAddress = from.toString(); StringBuffer sb = new StringBuffer(); fromFmt.format(fromAddress, sb, null); sb.append(" "); subjFmt.format(m.getSubject(), sb, null); System.out.println(sb.toString()); } } if ((folder.getType() & Folder.HOLDS_FOLDERS) != 0) { System.out.println(tab + "Is Directory"); if (recurse) { Folder[] f = folder.list(); for (int i = 0; i < f.length; i++) listFolder(f[i], tab + "", recurse); } } } } ``` #### 3. 构建邮件阅读器 为了更方便地查看邮件，我们可以构建一个邮件阅读器。以下是一个使用 Swing GUI 组件和 JavaMail API 构建的邮件阅读器示例： ##### 3.1 MailReaderBean.java ```java import java.awt.*; import java.awt.event.*; import javax.swing.*; import javax.swing.tree.*; import javax.swing.event.*; import javax.mail.*; import javax.mail.internet.*; /** * Display a mailbox or mailboxes. * This is the generic version in javasrc/email, split off from * JabaDex because of the latter's domain-specific "implements module" stuff. */ public class MailReaderBean extends JSplitPane { private JTextArea bodyText; /* Construct a mail reader bean with all defaults. */ public MailReaderBean() throws Exception { this("smtp", "mailhost", "user", "nopasswd", "/"); } /* Construct a mail reader bean with all values. */ public MailReaderBean( String protocol, String host, String user, String password, String rootName) throws Exception { super(VERTICAL_SPLIT); boolean recursive = false; // Start with a Mail Session object Session session = Session.getDefaultInstance( System.getProperties(), null); session.setDebug(false); // Get a Store object for the given protocol Store store = session.getStore(protocol); store.connect(host, user, password); // Get Folder object for root, and list it // If root name = "", getDefaultFolder( ), else getFolder(root) FolderNode top; if (rootName.length() != 0) { // System.out.println("Getting folder " + rootName + "."); top = new FolderNode(store.getFolder(rootName)); } else { // System.out.println("Getting default folder."); top = new FolderNode(store.getDefaultFolder()); } if (top == null || !top.f.exists()) { System.out.println("Invalid folder " + rootName); return; } if (top.f.getType() == Folder.HOLDS_FOLDERS) { Folder[] f = top.f.list(); for (int i = 0; i < f.length; i++) listFolder(top, new FolderNode(f[i]), recursive); } else listFolder(top, top, false); // Now that (all) the foldernodes and treenodes are in, // construct a JTree object from the top of the list down, // make the JTree scrollable (put in JScrollPane), // and add it as the MailComposeBean's Northern child. JTree tree = new JTree(top); JScrollPane treeScroller = new JScrollPane(tree); treeScroller.setBackground(tree.getBackground()); this.setTopComponent(treeScroller); // The Southern (Bottom) child is a textarea to display the msg. bodyText = new JTextArea(15, 80); this.setBottomComponent(new JScrollPane(bodyText)); // Add a notification listener for the tree; this will // display the cli ```