JavaMail API - 获取电子邮件
在上一章中，我们学习了如何检查电子邮件。现在让我们看看如何获取每封电子邮件并阅读其内容。让我们编写一个 Java 类 FetchingEmail，它将读取以下类型的电子邮件:
简单电子邮件
带附件的电子邮件
带内嵌图像的电子邮件
代码中遵循的基本步骤如下:
获取 Session 对象。
创建 POP3 存储对象并连接到存储。
创建 Folder 对象并打开邮箱中的相应文件夹。
检索消息。
分别关闭文件夹和存储对象。
创建 Java 类
创建一个 java 类文件FetchingEmail，其内容如下:
package com.tutorialspoint;
import java.io.BufferedOutputStream;
import java.io.BufferedReader;
import java.io.DataOutputStream;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.Date;
import java.util.Properties;
import javax.mail.Address;
import javax.mail.Folder;
import javax.mail.Message;
import javax.mail.MessagingException;
import javax.mail.Multipart;
import javax.mail.NoSuchProviderException;
import javax.mail.Part;
import javax.mail.Session;
import javax.mail.Store;
public class FetchingEmail {
public static void fetch(String pop3Host, String storeType, String user,
String password) {
try {
// 创建属性字段
Properties properties = new Properties();
properties.put("mail.store.protocol", "pop3");
properties.put("mail.pop3.host", pop3Host);
properties.put("mail.pop3.port", "995");
properties.put("mail.pop3.starttls.enable", "true");
Session emailSession = Session.getDefaultInstance(properties);
// emailSession.setDebug(true);
// 创建 POP3 存储对象并连接 pop 服务器
Store store = emailSession.getStore("pop3s");
store.connect(pop3Host, user, password);
// 创建文件夹对象并打开它
Folder emailFolder = store.getFolder("INBOX");
emailFolder.open(Folder.READ_ONLY);
BufferedReader reader = new BufferedReader(new InputStreamReader(
System.in));
// 从文件夹中检索数组中的消息并打印
Message[] messages = emailFolder.getMessages();
System.out.println("messages.length---" + messages.length);
for (int i = 0; i < messages.length; i++) {
Message message = messages[i];
System.out.println("---------------------------------");
writePart(message);
String line = reader.readLine();
if ("YES".equals(line)) {
message.writeTo(System.out);
} else if ("QUIT".equals(line)) {
break;
}
}
// 关闭存储和文件夹对象
emailFolder.close(false);
store.close();
} catch (NoSuchProviderException e) {
e.printStackTrace();
} catch (MessagingException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} catch (Exception e) {
e.printStackTrace();
}
}
public static void main(String[] args) {
String host = "pop.gmail.com";// 相应改变
String mailStoreType = "pop3";
String username =
"abc@gmail.com";// 相应改变
String password = "*****";// 相应改变
//Call method fetch
fetch(host, mailStoreType, username, password);
}
/*
* This method checks for content-type
* based on which, it processes and
* fetches the content of the message
*/
public static void writePart(Part p) throws Exception {
if (p instanceof Message)
//调用方法写信封
writeEnvelope((Message) p);
System.out.println("----------------------------");
System.out.println("CONTENT-TYPE: " + p.getContentType());
//检查内容是否是纯文本
if (p.isMimeType("text/plain")) {
System.out.println("This is plain text");
System.out.println("---------------------------");
System.out.println((String) p.getContent());
}
//检查内容是否有附件
else if (p.isMimeType("multipart/*")) {
System.out.println("This is a Multipart");
System.out.println("---------------------------");
Multipart mp = (Multipart) p.getContent();
int count = mp.getCount();
for (int i = 0; i < count; i++)
writePart(mp.getBodyPart(i));
}
//检查内容是否是嵌套消息
else if (p.isMimeType("message/rfc822")) {
System.out.println("This is a Nested Message");
System.out.println("---------------------------");
writePart((Part) p.getContent());
}
//检查内容是否为内联图像
else if (p.isMimeType("image/jpeg")) {
System.out.println("--------> image/jpeg");
Object o = p.getContent();
InputStream x = (InputStream) o;
// 构造所需的字节数组
System.out.println("x.length = " + x.available());
while ((i = (int) ((InputStream) x).available()) > 0) {
int result = (int) (((InputStream) x).read(bArray));
if (result == -1)
int i = 0;
byte[] bArray = new byte[x.available()];
break;
}
FileOutputStream f2 = new FileOutputStream("/tmp/image.jpg");
f2.write(bArray);
}
else if (p.getContentType().contains("image/")) {
System.out.println("content type" + p.getContentType());
File f = new File("image" + new Date().getTime() + ".jpg");
DataOutputStream output = new DataOutputStream(
new BufferedOutputStream(new FileOutputStream(f)));
com.sun.mail.util.BASE64DecoderStream test =
(com.sun.mail.util.BASE64DecoderStream) p
.getContent();
byte[] buffer = new byte[1024];
int bytesRead;
while ((bytesRead = test.read(buffer)) != -1) {
output.write(buffer, 0, bytesRead);
}
}
else {
Object o = p.getContent();
if (o instanceof String) {
System.out.println("This is a string");
System.out.println("---------------------------");
System.out.println((String) o);
}
else if (o instanceof InputStream) {
System.out.println("This is just an input stream");
System.out.println("---------------------------");
InputStream is = (InputStream) o;
is = (InputStream) o;
int c;
while ((c = is.read()) != -1)
System.out.write(c);
}
else {
System.out.println("This is an unknown type");
System.out.println("---------------------------");
System.out.println(o.toString());
}
}
}
/*
* This method would print FROM,TO and SUBJECT of the message
*/
public static void writeEnvelope(Message m) throws Exception {
System.out.println("This is the message envelope");
System.out.println("---------------------------");
Address[] a;
// FROM
if ((a = m.getFrom()) != null) {
for (int j = 0; j < a.length; j++)
System.out.println("FROM: " + a[j].toString());
}
// TO
if ((a = m.getRecipients(Message.RecipientType.TO)) != null) {
for (int j = 0; j < a.length; j++)
System.out.println("TO: " + a[j].toString());
}
// SUBJECT
if (m.getSubject() != null)
System.out.println("SUBJECT: " + m.getSubject());
}
}
您可以通过取消注释语句 emailSession.setDebug(true); 来启用调试
编译并运行
现在我们的类已准备就绪，让我们编译上述类。我已将类 FetchingEmail.java 保存到目录:/home/manisha/JavaMailAPIExercise。我们需要类路径中的 jar javax.mail.jar 和 activation.jar。从命令提示符执行以下命令来编译类(两个 jar 都放在 /home/manisha/ 目录中):
javac -cp /home/manisha/activation.jar:/home/manisha/javax.mail.jar: FetchingEmail.java
现在类已编译完毕，执行以下命令运行:
java -cp /home/manisha/activation.jar:/home/manisha/javax.mail.jar: FetchingEmail
验证输出
您应该在命令控制台上看到以下消息:
messages.length---3 --------------------------------- This is the message envelope --------------------------- FROM: XYZ <xyz@gmail.com> TO: ABC <abc@gmail.com> SUBJECT: Simple Message ---------------------------- CONTENT-TYPE: multipart/alternative; boundary=047d7b343d6ad3e4ea04e8ec6579 This is a Multipart --------------------------- ---------------------------- CONTENT-TYPE: text/plain; charset=ISO-8859-1 This is plain text --------------------------- Hi am a simple message string.... -- Regards xyz This is the message envelope --------------------------- FROM: XYZ <xyz@gmail.com> TO: ABC <abc@gmail.com> SUBJECT: Attachement ---------------------------- CONTENT-TYPE: multipart/mixed; boundary=047d7b343d6a99180904e8ec6751 This is a Multipart --------------------------- ---------------------------- CONTENT-TYPE: text/plain; charset=ISO-8859-1 This is plain text --------------------------- Hi I've an attachment.Please check -- Regards XYZ ---------------------------- CONTENT-TYPE: application/octet-stream; name=sample_attachement This is just an input stream --------------------------- Submit your Tutorials, White Papers and Articles into our Tutorials Directory. This is a tutorials database where we are keeping all the tutorials shared by the internet community for the benefit of others. This is the message envelope --------------------------- FROM: XYZ <xyz@gmail.com> TO: ABC <abc@gmail.com> SUBJECT: Inline Image ---------------------------- CONTENT-TYPE: multipart/related; boundary=f46d04182582be803504e8ece94b This is a Multipart --------------------------- ---------------------------- CONTENT-TYPE: text/plain; charset=ISO-8859-1 This is plain text --------------------------- Hi I've an inline image [image: Inline image 3] -- Regards XYZ ---------------------------- CONTENT-TYPE: image/png; name="javamail-mini-logo.png" content typeimage/png; name="javamail-mini-logo.png"
在这里您可以看到我们的邮箱中有三封电子邮件。第一封是一封简单的邮件，内容是"嗨，我是一个简单的消息字符串……"。第二封邮件有一个附件。附件的内容也打印出来，如上所示。第三封邮件有一个内嵌图像。
