我在使用mime4j解析电子邮件时遇到了一个问题。这封电子邮件有一个附件，我使用MimeStreamParser来解析它。解析器根本不调用startMultipart方法。相反，它只调用一次body方法，并且BodyDescriptor是"text/plain"。
我不知道这个问题的根源，是电子邮件格式还是我的程序？
这是我的测试程序：
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStream;
import org.apache.james.mime4j.*;
import org.apache.james.mime4j.dom.BinaryBody;
import org.apache.james.mime4j.dom.Body;
import org.apache.james.mime4j.dom.Entity;
import org.apache.james.mime4j.dom.Header;
import org.apache.james.mime4j.dom.Message;
import org.apache.james.mime4j.dom.MessageBuilder;
import org.apache.james.mime4j.dom.Multipart;
import org.apache.james.mime4j.dom.TextBody;
import org.apache.james.mime4j.dom.address.Mailbox;
import org.apache.james.mime4j.dom.address.MailboxList;
import org.apache.james.mime4j.dom.field.AddressListField;
import org.apache.james.mime4j.dom.field.ContentTypeField;
import org.apache.james.mime4j.dom.field.DateTimeField;
import org.apache.james.mime4j.dom.field.UnstructuredField;
import org.apache.james.mime4j.field.address.AddressFormatter;
import org.apache.james.mime4j.message.BodyPart;
import org.apache.james.mime4j.message.MessageImpl;
import org.apache.james.mime4j.message.DefaultMessageBuilder;
import org.apache.james.mime4j.message.SimpleContentHandler;
import org.apache.james.mime4j.parser.ContentHandler;
import org.apache.james.mime4j.parser.MimeStreamParser;
import org.apache.james.mime4j.stream.BodyDescriptor;
import org.apache.james.mime4j.stream.Field;
import org.apache.james.mime4j.stream.MimeConfig;
public class TestClass extends SimpleContentHandler{
public static void main(String[] args) throws MimeException, IOException {
ContentHandler handler = new TestClass();
MimeConfig config = new MimeConfig();
MimeStreamParser parser = new MimeStreamParser(config);
parser.setContentHandler(handler);
InputStream instream = new FileInputStream("mail/testuser1");
try {
parser.parse(instream);
} finally {
instream.close();
}
}
@Override
public void headers(Header arg0) {
// TODO Auto-generated method stub
System.out.println("headers args: "+arg0);
}
@Override
public void body(BodyDescriptor bd, InputStream is) {
// TODO Auto-generated method stub
System.out.println("body descriptor: "+bd);
}
public void startMessage(){
System.out.println("startMessage");
}
public void endMessage(){
System.out.println("endMessage");
}
public void startBodyPart(){
System.out.println("startBodyPart");
}
public void endBodyPart() {
System.out.println("endBodyPart");
}
public void preamble(InputStream is){
System.out.println("preamble");
}
public void epilogue(InputStream is) {
System.out.println("epilogue");
}
public void startMultipart(BodyDescriptor bd){
System.out.println("startMultipart");
}
public void endMultipart() {
System.out.println("endMultipart");
}
public void raw(InputStream is) {
System.out.println("raw");
}
}
这是我的电子邮件文件的一部分：
From MAILER_DAEMON Wed Aug 21 19:24:53 2013
Date: Wed, 21 Aug 2013 19:24:53 +0800
From: Mail System Internal Data <MAILER-DAEMON@mail.abc.com>
Subject: DON'T DELETE THIS MESSAGE -- FOLDER INTERNAL DATA
Message-ID: <1377084293@mail.abc.com>
X-IMAP: 1377072167 0000000003
Status: RO
This text is part of the internal format of your mail folder, and is not
a real message. It is created automatically by the mail system software.
If deleted, important folder data will be lost, and it will be re-created
with the data reset to initial values.
From testuser2@abc.com Sat Aug 24 10:53:42 2013
Return-Path: <testuser2@abc.com>
X-Original-To: testuser1@abc.com
Delivered-To: testuser1@abc.com
Received: from shupc (unknown [192.168.75.130])
by mail.abc.com (Postfix) with SMTP id C0F5B1EFBC3
for <testuser1@abc.com>; Sat, 24 Aug 2013 10:53:42 +0800 (CST)
Message-ID: <7F1C30C9CB284CA594D01CBE210257D3@shupc>
From: "john" <testuser2@abc.com>
To: "smith" <testuser1@abc.com>
Subject: aaa
Date: Sat, 24 Aug 2013 10:53:42 +0800
MIME-Version: 1.0
Content-Type: multipart/mixed;
boundary="----=_NextPart_000_000B_01CEA0B8.32903020"
X-Priority: 3
X-MSMail-Priority: Normal
X-Mailer: Microsoft Outlook Express 6.00.2900.5512
X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.5512
X-UID: 3
Status: O
Content-Length: 386430
This is a multi-part message in MIME format.
------=_NextPart_000_000B_01CEA0B8.32903020
Content-Type: multipart/alternative;
boundary="----=_NextPart_001_000C_01CEA0B8.32903020"
------=_NextPart_001_000C_01CEA0B8.32903020
Content-Type: text/plain;
charset="gb2312"
Content-Transfer-Encoding: base64
dGVzdCBhYSBiYiBjYw==
------=_NextPart_001_000C_01CEA0B8.32903020
Content-Type: text/html;
charset="gb2312"
Content-Transfer-Encoding: base64
PCFET0NUWVBFIEhUTUwgUFVCTElDICItLy9XM0MvL0RURCBIVE1MIDQuMCBUcmFuc2l0aW9uYWwv
L0VOIj4NCjxIVE1MPjxIRUFEPg0KPE1FVEEgaHR0cC1lcXVpdj1Db250ZW50LVR5cGUgY29udGVu
dD0idGV4dC9odG1sOyBjaGFyc2V0PWdiMjMxMiI+DQo8TUVUQSBjb250ZW50PSJNU0hUTUwgNi4w
MC4yOTAwLjU1MTIiIG5hbWU9R0VORVJBVE9SPg0KPFNUWUxFPjwvU1RZTEU+DQo8L0hFQUQ+DQo8
Qk9EWSBiZ0NvbG9yPSNmZmZmZmY+DQo8RElWPjxGT05UIHNpemU9Mj50ZXN0IGFhIGJiIGNjPC9G
T05UPjwvRElWPjwvQk9EWT48L0hUTUw+DQo=
------=_NextPart_001_000C_01CEA0B8.32903020--
------=_NextPart_000_000B_01CEA0B8.32903020
Content-Type: application/octet-stream;
name="10112716229607.doc"
Content-Transfer-Encoding: base64
Content-Disposition: attachment;
filename="10112716229607.doc"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问题在于示例电子邮件不是多部分的。它以内联文本的形式包含一封由多部分组成的电子邮件。
删除第一个标题（"FROM MAILER"），然后确保Content-Type后面的所有行都按照规范（RFC822或更高版本）的要求缩进至少一个空白字符（如字符集和边界），或者删除换行符。参见示例：
更改自：
Content-Type: multipart/mixed;
boundary="----=_NextPart_000_000B_01CEA0B8.32903020"
至任一：
Content-Type: multipart/mixed;
boundary="----=_NextPart_000_000B_01CEA0B8.32903020"
或：
Content-Type: multipart/mixed; boundary="----=_NextPart_000_000B_01CEA0B8.32903020"
或者，尝试其他消息。
使用以下基于mime4j的库：电子邮件mime解析器
提供的示例代码负责电子邮件解析，生成的"电子邮件"对象为解决您的问题提供了方便的方法：
ContentHandler contentHandler = new CustomContentHandler();
MimeConfig mime4jParserConfig = new MimeConfig();
BodyDescriptorBuilder bodyDescriptorBuilder = new DefaultBodyDescriptorBuilder();
MimeStreamParser mime4jParser = new MimeStreamParser(mime4jParserConfig,DecodeMonitor.SILENT,bodyDescriptorBuilder);
mime4jParser.setContentDecoding(true);
mime4jParser.setContentHandler(contentHandler);
InputStream mailIn = 'Provide email mime stream here';
mime4jParser.parse(mailIn);
Email email = ((CustomContentHandler) contentHandler).getEmail();