java mail 纯文本附件乱码的解决方案

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java mail在发送纯文本附件时，当附件内容的编码和jvm缺省的编码不一致时，出现乱码。原因时java mail处理纯文本附件，使用text_plain这个datacontenthandler来处理，而text_plain又简单的使用jvm缺省编码来读取文件内容（可以使用file.encode和mail.mime.charset系统属性来更改），两者不一致时，自然就乱码了

找到的问题的原因，也就容易解决了，一种方法就是把所有的附件类新全部设成application/octet-stream，把附件作为二进制流，还有一种就是当附件是存文本时，通过BOM（byte order mark）来探测文件的编码类型。

 

扩展FileDataSource，处理ContentType类型：

public class MyFileDataSource extends FileDataSource {
		private static final String DEFAULT_CONTENT_TYPE = "application/octet-stream";
		private final static Pattern pattern = Pattern.compile("^text/");
		
		private String contentType ;
		private int head_count=0;
		
		public MyFileDataSource(File file) {
			super(file);
			determinateType();
		}
		
		private void determinateType(){
			contentType = super.getContentType();
			Matcher m = pattern.matcher(contentType);
			if(m.find() && getFile().exists() && getFile().isFile()){
				InputStream in = null;
				try {
					in = new FileInputStream(getFile());
					if(is_utf_8(in)){
						contentType = contentType + "; charset=utf-8";
						head_count = 3;
					} else {
						contentType = DEFAULT_CONTENT_TYPE;
					}
				} catch (IOException e) {
					contentType = DEFAULT_CONTENT_TYPE;
				} finally {
					try {
						if(in!=null) {
							in.close();
						}
					} catch (IOException e1) {
					}
				}
			}
		}

		public MyFileDataSource(String s) {
			this(new File(s));
		}

		@Override
		public InputStream getInputStream() throws IOException {
			InputStream in = super.getInputStream();
			for(int i=0;i  
 
使用：
 
 
public static void main(String[] args) throws Exception {
		String host = "your host";
		String from = "mail from addr";
		String to = "to addr";

		Properties props = new Properties();
		props.put("mail.smtp.host", host);
		props.put("mail.smtp.auth", "true");
		props.put("mail.transport.protocol", "smtp");

		Session session = Session.getInstance(props, null);
		session.setDebug(true);
		System.setProperty("mail.mime.charset", "utf-8");
		MimeMessage message = new MimeMessage(session);
		message.setSentDate(new Date());
		message.setFrom(new InternetAddress(from,"test"));
		message.setRecipients(Message.RecipientType.TO, new InternetAddress[] {new InternetAddress(to)});
		
		message.setSubject("测试");
		String html="\r\n\r\n 
测试htmlmail
";
		MimeMultipart multipart = new MimeMultipart("related");
		MimeBodyPart html_body = new MimeBodyPart();
		html_body.setContent(html,"text/html; charset=utf-8");
		multipart.addBodyPart(html_body);
		MimeBodyPart file = new MimeBodyPart();
		//file.attachFile("d:\\aa.txt");
		FileDataSource fds = new MyFileDataSource("d:\\test.txt");
		file.setDataHandler(new DataHandler(fds));
				
		multipart.addBodyPart(file);
		message.setContent(multipart);
		Transport transport = session.getTransport();
		try {
			transport.connect(host, 25, "×××", "×××");
			transport.sendMessage(message, message.getAllRecipients());
		} finally {
			transport.close();
		}
	}