jsp - 通过 javamail 发送电子邮件时出现 NullPointer 异常

Question

我有一个使用 javamail 发送电子邮件的 servlet 代码。一切看起来都很好，但是在调用我的 send() 方法时抛出了 NullPointerException。下面是我的代码。

小服务程序:

package com.lsp.web;

import com.lsp.service.Mailer;
import javax.ejb.EJB;
import javax.mail.MessagingException;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

@WebServlet(name = "contact", urlPatterns = {"/contact"})
public class ContactServlet extends SpringInjectedServlet {
@EJB
private Mailer emailBean;

@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    req.getRequestDispatcher("contact.jsp").forward(req, resp);
}

@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    String customerEmail = req.getParameter("email");
    String subject = req.getParameter("subject");
    String body = req.getParameter("message");

    String error = null;
    String succMess = null;

    try {
        javax.mail.internet.InternetAddress ia = new javax.mail.internet.InternetAddress(customerEmail);
        ia.validate();
        emailBean.send(customerEmail, subject, body); //HERE I CALL MAILER.SEND() METHOD WHERE NULLPOINTEREXCEPTION CAME FROM
        req.setAttribute("succMessage", succMess);
        req.getRequestDispatcher("sent.jsp").forward(req, resp);

    } catch (javax.mail.internet.AddressException ae) {
        error = "您指出的邮箱地址不存在";
        req.setAttribute("errorMessage", error);
        req.getRequestDispatcher("contact.jsp").forward(req, resp);
    }
    catch (MessagingException mex) {
        error = "发送失败";
        req.setAttribute("errorMessage", error);
        req.getRequestDispatcher("contact.jsp").forward(req, resp);
    }
}
}

然后我调用 Mailer 类来发送邮件:

package com.lsp.service;

import javax.mail.Message;
import javax.mail.MessagingException;
import javax.mail.Session;
import javax.mail.Transport;
import javax.mail.internet.InternetAddress;
import javax.mail.internet.MimeMessage;
import java.util.Properties;

public class Mailer {
public void send(String from, String subject, String body) {
    String to = "jshao745@gmail.com";
    String host = "localhost";

    Properties properties = System.getProperties();
    properties.setProperty("mail.smtp.host", host);

    Session session = Session.getDefaultInstance(properties);

    try{
        // Create a default MimeMessage object.
        MimeMessage message = new MimeMessage(session);

        // Set From: header field of the header.
        message.setFrom(new InternetAddress(from));

        // Set To: header field of the header.
        message.addRecipient(Message.RecipientType.TO, new InternetAddress(to));

        // Set Subject: header field
        message.setSubject(subject);

        // Send the actual HTML message, as big as you like
        message.setSubject(body);

        // Send message
        Transport.send(message);
        System.out.println("Sent message successfully....");
    }catch (MessagingException mex) {
        mex.printStackTrace();
    }
}
}

我的 JSP 提交表单:

<form action="contact" method="post">
<p>Your email address: <input name="email"></p>
<p>Mail subject: <input name="subject"></p>
<p>Mail message: <textarea name="message"></textarea></p>
<p><input type="submit"><span class="message"></span></p>
</form>

当我键入所有信息并单击提交按钮时，我在 ContactServlet 调用 send() 方法的一行中得到了 NullPointerException在 Mailer 类中(我用所有大写词发表评论)。

我找不到我做错了什么。

如果有人能帮助我，我将不胜感激。

Answer 1

我建议不要使用

message.setBody(body);

首先将主体包裹在 DataHandler 中:

DataHandler messageDataHandler = new DataHandler(body, "text/plain; charset=\"UTF-8\"");
message.setDataHandler(messageDataHandler);