如何使用Gmail API和Java发送电子邮件

Question

我在Openshift上部署了Web服务。目前，我正在开发一种使用我的Gmail帐户在特定时间发送自动电子邮件的方法。

因此，我已经记录了自己两到三天，得出的结论是我有两个选择：

1）使用JavaMail库。2）使用Gmail API。

对于第一个选项，我使用了以下类：

public class EmailSenderService {  
private final Properties properties = new Properties();  

private String password = "*******";  

private Session session;  

private void init() {  

    //ssl
    properties.put("mail.smtp.host", "smtp.gmail.com");
    properties.put("mail.smtp.socketFactory.port", "465");
    properties.put("mail.smtp.socketFactory.class",
            "javax.net.ssl.SSLSocketFactory");
    properties.put("mail.smtp.auth", "true");
    properties.put("mail.smtp.port", "465");

    session = Session.getDefaultInstance(properties,
        new javax.mail.Authenticator() {
            protected PasswordAuthentication getPasswordAuthentication() {
                return new PasswordAuthentication("eu***@gmail.com",password);
            }
        });
}  

public void sendEmail(){  

    init();  

    //ssl
    try {
        Message message = new MimeMessage(session);
        message.setFrom(new InternetAddress("eu***@gmail.com"));
        message.setRecipients(Message.RecipientType.TO,
                InternetAddress.parse("c***6@gmail.com"));
        message.setSubject("Testing Subject");
        message.setText("Dear Mail Crawler," +
                "\n\n No spam to my email, please!");
        Transport t = session.getTransport("smtp");
        t.connect("smtp.gmail.com", "eu***@gmail.com", password);
        t.sendMessage(message, message.getAllRecipients());

        System.out.println("Done");

    } catch (MessagingException e) {
        e.printStackTrace();
    }   
}  
} 

并使用以下命令呼叫他们：

EmailSenderService ess = new EmailSenderService();
        ess.sendEmail();

2）我正在使用的第二个选项如下：

public class EmailSenderGmailApi {

/*
 * Atributos
 */
// Check https://developers.google.com/gmail/api/auth/scopes for all available scopes
private static final String SCOPE = "https://www.googleapis.com/auth/gmail.compose";
private static final String APP_NAME = "eu***l";
// Email address of the user, or "me" can be used to represent the currently authorized user.
private static final String USER = "eu***@gmail.com";
// Path to the client_secret.json file downloaded from the Developer Console
private static final String CLIENT_SECRET_PATH = "../app-root/data/eu***.json";

private static GoogleClientSecrets clientSecrets;


/*
 * Metodos
 */

public static Gmail init() throws IOException{

    System.out.println("***Working Directory = " + System.getProperty("user.dir"));


    HttpTransport httpTransport = new NetHttpTransport();
    JsonFactory jsonFactory = new JacksonFactory();

    clientSecrets = GoogleClientSecrets.load(jsonFactory,  new FileReader(CLIENT_SECRET_PATH));

    // Allow user to authorize via url.
    GoogleAuthorizationCodeFlow flow = new GoogleAuthorizationCodeFlow.Builder(
        httpTransport, jsonFactory, clientSecrets, Arrays.asList(SCOPE))
        .setAccessType("online")
        .setApprovalPrompt("auto").build();

    String code = "***";

    // Generate Credential using retrieved code.
    GoogleTokenResponse response = flow.newTokenRequest(code)
        .setRedirectUri(GoogleOAuthConstants.OOB_REDIRECT_URI).execute();
    GoogleCredential credential = new GoogleCredential()
        .setFromTokenResponse(response);

    // Create a new authorized Gmail API client
    return new Gmail.Builder(httpTransport, jsonFactory, credential)
        .setApplicationName(APP_NAME).build();


}

/**
   * Create a MimeMessage using the parameters provided.
   *
   * @param to Email address of the receiver.
   * @param from Email address of the sender, the mailbox account.
   * @param subject Subject of the email.
   * @param bodyText Body text of the email.
   * @return MimeMessage to be used to send email.
   * @throws MessagingException
   */
  public static MimeMessage createEmail(String to, String from, String subject,
      String bodyText) throws MessagingException {

      System.out.println("***Empezando a enviar email...");

    Properties props = new Properties();
    Session session = Session.getDefaultInstance(props, null);

    MimeMessage email = new MimeMessage(session);
    InternetAddress tAddress = new InternetAddress(to);
    InternetAddress fAddress = new InternetAddress(from);

    email.setFrom(new InternetAddress(from));
    email.addRecipient(javax.mail.Message.RecipientType.TO,
                       new InternetAddress(to));
    email.setSubject(subject);
    email.setText(bodyText);
    return email;
  }

  /**
   * Create a Message from an email
   *
   * @param email Email to be set to raw of message
   * @return Message containing base64 encoded email.
   * @throws IOException
   * @throws MessagingException
   */
  public static Message createMessageWithEmail(MimeMessage email)
      throws MessagingException, IOException {
    ByteArrayOutputStream bytes = new ByteArrayOutputStream();
    email.writeTo(bytes);
    String encodedEmail = Base64.encodeBase64URLSafeString(bytes.toByteArray());
    Message message = new Message();
    message.setRaw(encodedEmail);
    return message;
  }

  /**
   * Send an email from the user's mailbox to its recipient.
   *
   * @param service Authorized Gmail API instance.
   * @param userId User's email address. The special value "me"
   * can be used to indicate the authenticated user.
   * @param email Email to be sent.
   * @throws MessagingException
   * @throws IOException
   */
  public static void sendMessage(Gmail service, String userId, MimeMessage email)
      throws MessagingException, IOException {
    Message message = createMessageWithEmail(email);
    message = service.users().messages().send(userId, message).execute();

    System.out.println("Message id: " + message.getId());
    System.out.println(message.toPrettyString());
  }

}

第一个选项，当调用它时，Openshift COnsole中显示的消息如下：

javax.mail.AuthenticationFailedException
    at javax.mail.Service.connect(Service.java:306)
    at javax.mail.Service.connect(Service.java:156)
    at main.java.model.EmailSenderService.sendEmail(EmailSenderService.java:86)
    at main.java.model.AccessManager.renewPassStepOne(AccessManager.java:234)
    at main.java.webService.UsuarioService.renewPassStepOne(UsuarioService.java:192)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:606)
    at com.sun.jersey.spi.container.JavaMethodInvokerFactory$1.invoke(JavaMethodInvokerFactory.java:60)
    at com.sun.jersey.server.impl.model.method.dispatch.AbstractResourceMethodDispatchProvider$TypeOutInvoker._dispatch(AbstractResourceMethodDispatchProvider.java:185)
    at com.sun.jersey.server.impl.model.method.dispatch.ResourceJavaMethodDispatcher.dispatch(ResourceJavaMethodDispatcher.java:75)
    at com.sun.jersey.server.impl.uri.rules.HttpMethodRule.accept(HttpMethodRule.java:302)
    ...

我一直在尝试自己修复它，查看google，stackoverflow ...但是，每次引入的更改，都会得到相同的消息。

在选项2中，我不知道如何使用它。我正在尝试这样的事情：

MimeMessage msg = EmailSenderGmailApi.createEmail("ca***@gmail.com", "eu***@gmail.com", "test", "holaaaaa");

        EmailSenderGmailApi.sendMessage(
                EmailSenderGmailApi.init(), 
                "cap***@gmail.com", 
                msg);

无论如何，老实说，我已经研究了很多Java Mail，希望有人可以帮助我解决我可能遇到的任何错误。

关于Gmail Api，根据官方文档，我还无法弄清楚如何发送电子邮件。互联网上也没有太多的文档。

有人可以帮我吗？

Answer 1

Gmail API公共文档提供了有关发送电子邮件的指南，甚至提供了Java示例代码：

https://developers.google.com/gmail/api/guides/sending

上面的代码似乎相去不远。首先，我要通过做一些简单的事情（例如labels.list（））来确保Oauth2正常工作，如果可行，那么请继续进行更复杂的事情，例如发送电子邮件。（构建，转换为字符串，使用base64url编码然后再发送，这是您的正确想法。）尝试使用Gmail API发送消息时，您遇到的确切问题是什么？收到一些错误输出或代码中缺少某些内容？