javamail 修改草稿箱中邮件的内容?报错

public boolean updateDraftMail(MailInfo mailInfo, Integer mailType , String mailNum) throws Exception {
        
        //已读写的方式打开草稿箱
        Store store = mailInfo.getReceiveProperties();    
        //qq邮箱的设置
        String typeName = "";
        switch (mailType) {
        case 1:
            typeName = "INBOX";
            break;
        case 2:
            typeName = "Sent Messages";
            break;
        case 3:
            typeName = "Drafts";
            break;
        default:
            break;
        }
        //暂时只支持qq邮箱
        Folder folder =  store.getFolder(typeName);
        folder.open(Folder.READ_WRITE);
        //读取已有的邮件
        MimeMessage message = null;
        try {
            message = (MimeMessage) folder.getMessage(Integer.parseInt(mailNum));
        } catch (ArrayIndexOutOfBoundsException ex) {
            message = (MimeMessage) folder.getMessage(Integer.parseInt(mailNum) - 1);
        }
        //更新邮件信息
        updateMessageMsg(message, mailInfo);
        
        if(null!=folder)
            folder.close(true);
        if(null!=store)
            store.close();
        
        return true;
    }

public void updateMessageMsg(MimeMessage mailMessage, MailInfo mailInfo) throws GeneralSecurityException, MessagingException {
        //设置可修改
        mailMessage.saveChanges();
        try {
            //设置自定义发件人昵称  
            String nick="";  
            try {  
                if(!StringUtil.isEmpty(mailInfo.getNick())){
                    nick=javax.mail.internet.MimeUtility.encodeText(mailInfo.getNick());
                }
            } catch (UnsupportedEncodingException e) {  
                e.printStackTrace();  
            }
            // 设置邮件消息的发送者
            mailMessage.setFrom(new InternetAddress(nick+" <"+mailInfo.getUsername()+">"));
            // 创建邮件的接收者地址 to：发送；cc：抄送
            Address[][] maillToArr = getMailToAddress(mailInfo);

            // 设置邮件消息的接收者，发送，抄送
            if (maillToArr != null && maillToArr[0] != null && maillToArr[0].length > 0) {
                mailMessage.setRecipients(Message.RecipientType.TO, maillToArr[0]);
            }
            if (maillToArr != null && maillToArr[1] != null && maillToArr[1].length > 0) {
                mailMessage.setRecipients(Message.RecipientType.CC, maillToArr[1]);
            }

            // 设置邮件消息的主题
            mailMessage.setSubject(mailInfo.getSubject());
            // 设置邮件消息发送的时间
            mailMessage.setSentDate(Calendar.getInstance().getTime());

            // MimeMultipart类是一个容器类，包含MimeBodyPart类型的对象
            Multipart multiPart = new MimeMultipart();
            // 创建一个包含HTML内容的MimeBodyPart
            BodyPart bodyPart = new MimeBodyPart();
            // 设置html邮件消息内容
            bodyPart.setContent(mailInfo.getContent(), "text/html; charset=utf-8");
            multiPart.addBodyPart(bodyPart);

            //添加附件
            int i = 0; 
            if(null!=mailInfo.getAttachFilePaths()&&mailInfo.getAttachFilePaths().length != 0){
                for(String attachFile : mailInfo.getAttachFilePaths()){
                    bodyPart=new MimeBodyPart();  
                    FileDataSource fds=new FileDataSource(attachFile); //得到数据源  
                    bodyPart.setDataHandler(new DataHandler(fds)); //得到附件本身并放入BodyPart  
                    bodyPart.setFileName(MimeUtility.encodeText(mailInfo.getAttachFileNames()[i]));  //得到文件名并编码（防止中文文件名乱码）同样放入BodyPart  
                    multiPart.addBodyPart(bodyPart);  
                    i++;
                }
            }

            // 设置邮件消息的主要内容
            mailMessage.setContent(multiPart);
            
        } catch (Exception e) {
            e.printStackTrace();
        }
        
    }

报错信息：

    javax.mail.IllegalWriteException: IMAPMessage is read-only
    at com.sun.mail.imap.IMAPMessage.setHeader(IMAPMessage.java:813)
    at javax.mail.internet.MimeMessage.updateHeaders(MimeMessage.java:2181)
    at javax.mail.internet.MimeMessage.saveChanges(MimeMessage.java:2142)
    at util.javaEmail.MailSender.updateMessageMsg(MailSender.java:138)
    at util.javaEmail.MailSender.updateDraftMail(MailSender.java:323)
    at controller.mail.mailController.updateDraftBox(mailController.java:325)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:497)
    at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:221)
    at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:136)
    at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:110)
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:832)
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:743)
    at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:85)
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:961)
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:895)
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:967)
    at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:869)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:650)
    at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:843)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:731)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:303)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
    at org.springframework.orm.hibernate4.support.OpenSessionInViewFilter.doFilterInternal(OpenSessionInViewFilter.java:152)
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
    at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:121)
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
    at org.apache.shiro.web.servlet.ProxiedFilterChain.doFilter(ProxiedFilterChain.java:61)
    at org.apache.shiro.web.servlet.AdviceFilter.executeChain(AdviceFilter.java:108)
    at org.apache.shiro.web.servlet.AdviceFilter.doFilterInternal(AdviceFilter.java:137)
    at org.apache.shiro.web.servlet.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:125)
    at org.apache.shiro.web.servlet.ProxiedFilterChain.doFilter(ProxiedFilterChain.java:66)
    at org.apache.shiro.web.servlet.AbstractShiroFilter.executeChain(AbstractShiroFilter.java:449)
    at org.apache.shiro.web.servlet.AbstractShiroFilter$1.call(AbstractShiroFilter.java:365)
    at org.apache.shiro.subject.support.SubjectCallable.doCall(SubjectCallable.java:90)
    at org.apache.shiro.subject.support.SubjectCallable.call(SubjectCallable.java:83)
    at org.apache.shiro.subject.support.DelegatingSubject.execute(DelegatingSubject.java:383)
    at org.apache.shiro.web.servlet.AbstractShiroFilter.doFilterInternal(AbstractShiroFilter.java:362)
    at org.apache.shiro.web.servlet.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:125)
    at org.springframework.web.filter.DelegatingFilterProxy.invokeDelegate(DelegatingFilterProxy.java:346)
    at org.springframework.web.filter.DelegatingFilterProxy.doFilter(DelegatingFilterProxy.java:262)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:218)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:110)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:506)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:169)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103)
    at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:962)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:116)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:452)
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1087)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:637)
    at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:318)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    at java.lang.Thread.run(Thread.java:745)