向EML文件追加附件的Java實現

• 說明
  以前在網上也找了一下該需求的實現，可是後面測試發現幾乎所有都只可以對沒有附件的eml文件進行追加，若是已近帶了附件的eml文件在執行時源文件會被破壞掉。全部在此寫下能夠附件追加代碼。

• 代碼

import org.apache.commons.mail.util.MimeMessageUtils;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import utils.ParseEmailUtil;

import javax.activation.DataHandler;
import javax.activation.DataSource;
import javax.activation.FileDataSource;
import javax.mail.*;
import javax.mail.internet.*;
import java.io.*;
import java.util.List;

/**
 * Created by jacob on 2016/11/28.
 */
public class AddAttachemnt2Eml {
    private static final Logger logger  =  LoggerFactory.getLogger(AddAttachemnt2Eml.class );
    public static void add(String emlPath, String writeto, List<File> attachments) {

        Properties props = new Properties();
        Session session = Session.getDefaulInstance(props, null);
        InputStream inMsg;
        inMsg = new FileInputStream(emlPath);
        Message message = new MimeMessage(session, inMsg);
        OutputStream os = null;
        try {
            os = new FileOutputStream(writeto+File.separator+new File(emlPath).getName());
//            ParseEmailUtil.getContentHtml(emlPath);
//            Message message = ParseEmailUtil.getMessage();
            for(File filename : attachments){
                message = attachment(message,filename);
            }
            new File(emlPath).delete();
            message.saveChanges();
            message.writeTo(os);
        }catch (Exception e){
            logger.error(String.format("failed to add attachment to eml file %s",emlPath ),e);
        }finally {
            try {
                os.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }

    }
    private static Message attachment (Message message,File filename) {
        try{

        Multipart mp = (Multipart) message.getContent();
        MimeBodyPart attachment = new MimeBodyPart();
        DataSource source = new FileDataSource(filename);
        attachment.setDataHandler(new DataHandler(source));
        attachment.setFileName(filename.getName());
        if (mp.getContentType().equalsIgnoreCase("multipart/alternative")) {    //原始文件已近有附件的狀況直接追加便可
            mp.addBodyPart(attachment);
            message.setContent(mp);
        } else {    //原始文件不帶附件須要將以前的正文與新加附件並列
            Multipart allPart = new MimeMultipart();
            MimeBodyPart contentPart = new MimeBodyPart();
            contentPart.setContent(mp);
            allPart.addBodyPart(contentPart);
            allPart.addBodyPart(attachment);
            message.setContent(allPart);
        }
        source.getInputStream().close();
        }catch (javax.mail.MessagingException e){
            logger.error(String.format("add attachment %s fail",filename.getAbsolutePath() ),e);
        }catch (IOException e2){
            logger.error(String.format("add attachment %s fail", filename),e2);
        }
        return message;
    }
}

注：manve依賴：

<dependency>
            <groupId>org.apache.commons</groupId>
            <artifactId>commons-email</artifactId>
            <version>1.4</version>
        </dependency>