Java 添加到Jar以发送电子邮件后出现NoClassDef错误

我已经进行了一段时间的故障排除，可能会受到影响，所以这将是相当描述性的

目标：只需单击按钮即可发送简单的电子邮件，无需使用外部邮件应用程序

这项研究产生了一种新的方法，它被成功地编译、测试并在个人计算机上执行

因此，在花了一些时间阅读这里的答案后，我按照以下步骤添加了库

右键单击App->newmodule->Import.JAR/.AAR包

使用省略号按钮查找并添加jar

应用程序->模块设置

在模块下，应用程序->依赖项->添加->模块依赖项->选择JAR模块

除此之外，我还做了以下工作：

确保应用程序模块的build.gradle包含依赖项（在本例中，列为compile project（“：javax.mail”）

在项目根目录上，使用并运行

gradlew clean

以及

gradlew build

这已经尝试了其他一些失败的方法，但这些是最新的一系列步骤。Android Studio检测到文件，但当执行时，应用程序崩溃，出现

NoClassDefFoundError

。直觉说问题在于类路径，但在尝试了几种不同但无效的解决方案之后，是时候让更有经验的人来解决了忠告

供参考：

main活动：

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        Button testButton = (Button) findViewById(R.id.emailButton);
        testButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Emailer.send(getApplicationContext());
            }
        });
    }
}

import android.content.Context;
import android.widget.Toast;

import java.util.Properties;

import javax.mail.Message;
import javax.mail.MessagingException;
import javax.mail.PasswordAuthentication;
import javax.mail.Session;
import javax.mail.Transport;
import javax.mail.internet.InternetAddress;
import javax.mail.internet.MimeMessage;

public class Emailer {
    public static void send(Context context) {
        // Recipient's email
        String recipient = "myemail@gmail.com";

        // Sender information
        String sender = "myemail@gmail.com";
        final String username = "myUsername";
        final String password = "myPassword";

        String host = "smtp.gmail.com";

        Properties properties = new Properties();
        properties.put("mail.smtp.auth", "true");
        properties.put("mail.smtp.socketFactory.port", "465");
        properties.put("mail.smtp.socketFactory.class", "javax.net.ssl.SSLSocketFactory");
        properties.put("mail.smtp.host", host);
        properties.put("mail.smtp.port", "25");

        Session session = Session.getInstance(properties,
                new javax.mail.Authenticator() {
                    protected PasswordAuthentication getPasswordAuthentication() {
                        return new PasswordAuthentication(username, password);
                    }
                });

        try {
            // constructing the email
            Message message = new MimeMessage(session);
            message.setFrom(new InternetAddress(sender));
            message.setRecipients(Message.RecipientType.TO, InternetAddress.parse(recipient));
            message.setSubject("Email Test");
            message.setText("Testing the email capability using JavaMailAPI on Android");

            // Sending
            Transport.send(message);
            Toast.makeText(context, R.string.email_success, Toast.LENGTH_SHORT).show();
        } catch (MessagingException e) {
            throw new RuntimeException(e);
        }
    }
}

电子邮件发送者：

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        Button testButton = (Button) findViewById(R.id.emailButton);
        testButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Emailer.send(getApplicationContext());
            }
        });
    }
}

import android.content.Context;
import android.widget.Toast;

import java.util.Properties;

import javax.mail.Message;
import javax.mail.MessagingException;
import javax.mail.PasswordAuthentication;
import javax.mail.Session;
import javax.mail.Transport;
import javax.mail.internet.InternetAddress;
import javax.mail.internet.MimeMessage;

public class Emailer {
    public static void send(Context context) {
        // Recipient's email
        String recipient = "myemail@gmail.com";

        // Sender information
        String sender = "myemail@gmail.com";
        final String username = "myUsername";
        final String password = "myPassword";

        String host = "smtp.gmail.com";

        Properties properties = new Properties();
        properties.put("mail.smtp.auth", "true");
        properties.put("mail.smtp.socketFactory.port", "465");
        properties.put("mail.smtp.socketFactory.class", "javax.net.ssl.SSLSocketFactory");
        properties.put("mail.smtp.host", host);
        properties.put("mail.smtp.port", "25");

        Session session = Session.getInstance(properties,
                new javax.mail.Authenticator() {
                    protected PasswordAuthentication getPasswordAuthentication() {
                        return new PasswordAuthentication(username, password);
                    }
                });

        try {
            // constructing the email
            Message message = new MimeMessage(session);
            message.setFrom(new InternetAddress(sender));
            message.setRecipients(Message.RecipientType.TO, InternetAddress.parse(recipient));
            message.setSubject("Email Test");
            message.setText("Testing the email capability using JavaMailAPI on Android");

            // Sending
            Transport.send(message);
            Toast.makeText(context, R.string.email_success, Toast.LENGTH_SHORT).show();
        } catch (MessagingException e) {
            throw new RuntimeException(e);
        }
    }
}