问题IllegalStateException: The mail session is already initialized解决

ELK以及IDEA 控制台记录如下报错日志：

c.x.c.web.controller.subscribe.BoardJobController [sendEmail:145] 发送邮件失败
java.lang.IllegalStateException: The mail session is already initialized
	at org.apache.commons.mail.Email.checkSessionAlreadyInitialized(Email.java:1940)
	at org.apache.commons.mail.Email.setSmtpPort(Email.java:529)
	at com.xy.cloudiview.common.services.impl.BoardJobServiceImpl.lambda$sendEmail$3(BoardJobServiceImpl.java:367)
	at java.util.ArrayList.forEach(ArrayList.java:1249)
	at com.xy.cloudiview.common.services.impl.BoardJobServiceImpl.sendEmail(BoardJobServiceImpl.java:296)
	at com.xy.cloudiview.web.controller.subscribe.BoardJobController.sendEmail(BoardJobController.java:141)
	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:498)
	at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:190)
	at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:138)
	at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:105)
	at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:878)
	at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:792)
	at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87)
	at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1040)
	at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:943)
	at org.springframework.web.servlet.frameworkServlet.processRequest(frameworkServlet.java:1006)
	at org.springframework.web.servlet.frameworkServlet.doPost(frameworkServlet.java:909)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:665)
	at org.springframework.web.servlet.frameworkServlet.service(frameworkServlet.java:883)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:750)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)

使用的工具包：

    org.apache.commons
    commons-email
    1.4

出错的代码片段

toList.forEach(toEmail -> {
    // 遍历每个收件人，对每个收件人发送邮件
    HtmlEmail email = new HtmlEmail();
    email.setCharset("utf-8");
    try {
        email.setHtmlMsg("");
        // 数据库查询邮箱
        EmailSftpModel mailServer = emailSftpMapper.getOneMailRand();
        email.setAuthentication(mailServer.getSmtpUsername(), mailServer.getSmtpPassword());
        email.setFrom(mailServer.getSmtpFrom());
        email.setSubject(subject);
        email.addTo(toEmail);
        if ("smtp.partner.outlook.cn".equals(mailServer.getSmtpHost())) {
            email.setStartTLSEnabled(true);
            Properties prop = new Properties();
            prop.setProperty("mail.smtp.host", mailServer.getSmtpHost());
            if (StringUtils.isNotEmpty(mailServer.getSmtpPort())) {
                prop.setProperty("mail.smtp.port", mailServer.getSmtpPort());
            }
            prop.setProperty("mail.smtp.auth", "true");
            prop.setProperty("mail.smtp.starttls.enable", "true");
            prop.setProperty("mail.smtp.ssl.protocols", "TLSv1.2");
            DefaultAuthenticator authenticator = new DefaultAuthenticator(mailServer.getSmtpUsername(), mailServer.getSmtpPassword());
            Session session = Session.getInstance(prop, authenticator);
            email.setMailSession(session);
        }
        if (!Strings.isNullOrEmpty(mailServer.getSmtpPort())) {
            email.setSmtpPort(Integer.parseInt(mailServer.getSmtpPort()));
        }
        email.setHostName(mailServer.getSmtpHost());
        email.send();
    } catch (EmailException e) {
        logger.error("发送邮件失败，收件人：" + toEmail, e);
        sendErrLog.append("发送邮件失败，收件人：").append(toEmail).append(e.getMessage()).append(";");
    }
});

报错行：
email.setSmtpPort(Integer.parseInt(mailServer.getSmtpPort()));
查看源码：

public abstract class Email {

	public void setSmtpPort(final int aPortNumber)
	{
	    checkSessionAlreadyInitialized();
	    if (aPortNumber < 1)
	    {
	        throw new IllegalArgumentException(
	            "Cannot connect to a port number that is less than 1 ( " + aPortNumber + " )");
	    }
	    this.smtpPort = Integer.toString(aPortNumber);
	}
	private void checkSessionAlreadyInitialized()
	{
	    if (this.session != null)
	    {
	        throw new IllegalStateException("The mail session is already initialized");
	    }
	}

}

解决方案，将如下代码片段

// fix IllegalStateException: The mail session is already initialized
if (!Strings.isNullOrEmpty(mailServer.getSmtpPort())) {
    email.setSmtpPort(Integer.parseInt(mailServer.getSmtpPort()));
}
email.setHostName(mailServer.getSmtpHost());

提前到：email.setMailSession(session);之前。
即放在if ("smtp.partner.outlook.cn".equals(mailServer.getSmtpHost())) {之前。