📅 最后修改于: 2020-11-14 10:04:43 🧑 作者: Mango
到目前为止，我们在前几章中主要使用INBOX文件夹。这是大多数邮件所在的默认文件夹。一些系统可能将其称为INBOX，而另一些系统可能将其称为其他名称。但是，您始终可以使用名称INBOX从JavaMail API访问它。
JavaMail API将文件夹表示为抽象Folder类的实例：
public abstract class Folder extends Object
此类声明用于从服务器请求命名文件夹，从文件夹中删除消息，在文件夹中搜索特定消息，列出文件夹中的消息等的方法。
我们不能直接创建文件夹，因为Folder类中的唯一构造函数是受保护的。我们可以从以下位置获取文件夹：
一个会议
一家商店
或另一个文件夹
以上所有类均具有相似的具有相似签名的getFolder()方法：
public abstract Folder getFolder(String name) throws MessagingException
一些有助于获取Folder对象的方法是：
| Method | Description |
|---|---|
| boolean exists() | Checks if the folder really exists. Use this method before getting the Folder object. |
| abstract void open(int mode) | When you get a Folder, its closed. Use this method to open it. mode can be Folder.READ_ONLY or Folder.READ_WRITE. |
| abstract boolean isOpen() | This method returns true if the folder is open, false if it’s closed |
| abstract void close(boolean expunge) | Closes the folder. If the expunge argument is true, any deleted messages in the folder are deleted from the actual file on the server. Otherwise, they’re simply marked as deleted, but the messages can still be undeleted. |
以下是Folder类中的一些方法，这些方法返回有关文件夹的基本信息：
| Method | Description |
|---|---|
| abstract String getName() | Returns the name of the folder, such as “TutorialsPoint Mail” |
| abstract String getFullName() | Returns the complete hierarchical name from the root such as “books/Manisha/TutorialsPoint Mail”. |
| URLName getURLName() | Return a URLName representing this folder. |
| abstract Folder getParent() | Returns the name of the folder that contains this folder i.e the parent folder. E.g “Manisha” from the previous “TutorialsPoint Mail” example. |
| abstract int getType() | Returns an int indicating whether the folder can contain messages and/or other folders. |
| int getMode() | It returns one of the two named constants Folder.READ_ONLY or Folder.READ_WRITE or -1 when the mode is unknown. |
| Store getStore() | Returns the Store object from which this folder was retrieved. |
| abstract char getSeparator() | Return the delimiter character that separates this Folder’s pathname from the names of immediate subfolders. |
以下是一些有助于管理文件夹的方法：
| Method | Description |
|---|---|
| abstract boolean create(int type) | This creates a new folder in this folder’s Store. Where type would be:Folder.HOLDS_MESSAGES or Folder.HOLDS_FOLDERS. Returns true if folder is successfully created else returns false. |
| abstract boolean delete(boolean recurse) | This deletes the folder only if the folder is closed. Otherwise, it throws an IllegalStateException. If recurse is true, then subfolders are deleted. |
| abstract boolean renameTo(Folder f) | This changes the name of this folder. A folder must be closed to be renamed. Otherwise, an IllegalStateException is thrown. |
以下是一些有助于管理“文件夹”中的邮件的方法：
| Method | Description |
|---|---|
| abstract void appendMessages(Message[] messages) | As the name implies, the messages in the array are placed at the end of this folder. |
| void copyMessages(Message[] messages, Folder destination) | This copies messages from this folder into a specified folder given as an argument. |
| abstract Message[] expunge() | To delete a message from a folder, set its Flags.Flag.DELETED flag to true. To physically remove deleted messages from a folder, you have to call this method. |
有四种方法可以列出文件夹包含的文件夹：
| Method | Description |
|---|---|
| Folder[] list() | This returns an array listing the folders that this folder contains. |
| Folder[] listSubscribed() | This returns an array listing all the subscribed folders that this folder contains. |
| abstract Folder[] list(String pattern) | This is similar to the list() method except that it allows you to specify a pattern. The pattern is a string giving the name of the folders that match. |
| Folder[] listSubscribed(String pattern) | This is similar to the listSubscribed() method except that it allows you to specify a pattern. The pattern is a string giving the name of the folders that match. |
| Method | Description |
|---|---|
| abstract int getMessageCount() | This method can be invoked on an open or closed folder. However, in the case of a closed folder, this method may (or may not) return -1 to indicate that the exact number of messages isn’t easily available. |
| abstract boolean hasNewMessages() | This returns true if new messages have been added to the folder since it was last opened. |
| int getNewMessageCount() | It returns the new message count by checking messages in the folder whose RECENT flag is set. |
| int getUnreadMessageCount() | This can be invoked on either an open or a closed folder. However, in the case of a closed folder, it may return -1 to indicate that the real answer would be too expensive to obtain. |
Folder类提供了四种从打开的文件夹中检索邮件的方法：
| Method | Description |
|---|---|
| abstract Message getMessage(int messageNumber) | This returns the nth message in the folder. The first message in the folder is number 1. |
| Message[] getMessages() | This returns an array of Message objects representing all the messages in this folder. |
| Message[] getMessages(int start, int end) | This returns an array of Message objects from the folder, beginning with start and finishing with end, inclusive. |
| Message[] getMessages(int[] messageNumbers) | This returns an array containing only those messages specifically identified by number in the messageNumbers array. |
| void fetch(Message[] messages, FetchProfile fp) | Prefetch the items specified in the FetchProfile for the given Messages. The FetchProfile argument specifies which headers in the messages to prefetch. |
如果服务器支持搜索(许多IMAP服务器支持而大多数POP服务器则不支持)，则很容易在文件夹中搜索满足特定条件的邮件。条件在SearchTerm对象中编码。以下是两种搜索方法：
| Method | Description |
|---|---|
| Message[] search(SearchTerm term) | Search this Folder for messages matching the specified search criterion. Returns an array containing the matching messages. Returns an empty array if no matches were found. |
| Message[] search(SearchTerm term, Message[] messages) | Search the given array of messages for those that match the specified search criterion. Returns an array containing the matching messages. Returns an empty array if no matches were found. The the specified Message objects must belong to this folder. |
当您需要更改文件夹中整个邮件集的标志时，标志修改很有用。以下是Folder类中提供的方法：
| Method | Description |
|---|---|
| void setFlags(Message[] messages, Flags flag, boolean value) | Sets the specified flags on the messages specified in the array. |
| void setFlags(int start, int end, Flags flag, boolean value) | Sets the specified flags on the messages numbered from start through end, both start and end inclusive. |
| void setFlags(int[] messageNumbers, Flags flag, boolean value) | Sets the specified flags on the messages whose message numbers are in the array. |
| abstract Flags getPermanentFlags() | Returns the flags that this folder supports for all messages. |