用J2ME实现简单电子邮件发送功能

在GCF中并没有提供给我们能够发送电子邮件的API，J2ME的可选包也没有提供相关的功能。那么我们能用J2ME实现发送电子邮件功能嘛？答案是肯定的。本文将主要讲述如何在J2ME中实现发送电子邮件的功能。
这里一个非常重要的思想就是代理。我们知道GCF提供给我们进行联网的能力了，比如通过Http联网。在MIDP2.0中甚至提供了socket联网的API。那么我们可以通过他们连接服务器端的程序比如servlet，然后servlet可以通过JavaMail提供的接口发送邮件。那么我们需要做的只是通过Http协议或者其他协议把邮件的标题、内容、收件人等发送给servlet。就是这个简单的思想却是非常灵活非常有用。

首先我们构造一个Message类来代表发送的消息。它包括主题、收件人和内容三个字段。

package com.j2medev.mail;

public class Message
{

private String to;

private String subject;

private String content;

public Message()
{

}

public Message(String to, String subject, String content)
{
this.to = to;
this.subject = subject;
this.content = content;
}

public String getContent()
{
return content;
}

public void setContent(String content)
{
this.content = content;
}
public String getSubject()
{
return subject;
}

public void setSubject(String subject)
{
this.subject = subject;
}

public String getTo()
{
return to;
}
public void setTo(String to)
{
this.to = to;
}

public String toString()
{
return to+subject+content;
}
}

在用户界面的设计上，我们需要两个界面。一个让用户输入收件人和主题，另一个用于收集用户输入的内容。由于TextBox要独占一个屏幕的，因此我们不能把他们放在一起。

/*
* Created on 2004-12-8
*
* TODO To change the template for this generated file go to
* Window - Preferences - Java - Code Style - Code Templates
*/
package com.j2medev.mail;

import javax.microedition.lcdui.Form;
import javax.microedition.lcdui.Item;
import javax.microedition.lcdui.*;
import javax.microedition.midlet.MIDlet;

/**
* @author P2800
*
* TODO To change the template for this generated type comment go to Window -
* Preferences - Java - Code Style - Code Templates
*/
public class MainForm extends Form implements CommandListener
{

private MailClient midlet;

private TextField toField;

private TextField subField;

private boolean first = true;

public static final Command nextCommand = new Command("NEXT", Command.OK, 1);

public MainForm(MailClient midlet, String arg0)
{
super(arg0);
this.midlet = midlet;
if(first)
{
first = false;
init();
}

}

public void init()
{
toField = new TextField("To:", null, 25, TextField.ANY);
subField = new TextField("Subject:", null, 30, TextField.ANY);
this.append(toField);
this.append(subField);
this.addCommand(nextCommand);
this.setCommandListener(this);

}

public void commandAction(Command cmd,Displayable disp)
{
if(cmd == nextCommand)
{
String to = toField.getString();
String subject = subField.getString();
if(to == "" && subject == "")
{
midlet.displayAlert("Null to or sub",AlertType.WARNING,this);
}
else
{
midlet.getMessage().setTo(to);
midlet.getMessage().setSubject(subject);
midlet.getDisplay().setCurrent(midlet.getContentForm());
}
}
}

}

package com.j2medev.mail;

import javax.microedition.lcdui.Command;
import javax.microedition.lcdui.CommandListener;
import javax.microedition.lcdui.Displayable;
import javax.microedition.lcdui.TextBox;
import javax.microedition.midlet.MIDlet;

public class ContentForm extends TextBox implements CommandListener
{
private MailClient midlet;

private boolean first = true;

public static final Command sendCommand = new Command("SEND", Command.ITEM,
1);

public ContentForm(String arg0, String arg1, int arg2, int arg3,
MailClient midlet)
{
super(arg0, arg1, arg2, arg3);
this.midlet = midlet;
if (first)
{
first = false;
init();
}

}

public void init()
{
this.addCommand(sendCommand);
this.setCommandListener(this);
}

public void commandAction(Command cmd, Displayable disp)
{
if (cmd == sendCommand)
{
String content = this.getString();
midlet.getMessage().setContent(content);
System.out.println(midlet.getMessage());
try
{
synchronized (midlet)
{
midlet.notify();
}

} catch (Exception e)
{
}

}
}
}

最后我们完成MIDlet，在其中包括联网的程序代码，由于本站已经提供了很多关于J2ME联网的介绍，因此这里不再进行更多的解释。

package com.j2medev.mail;

import java.io.DataOutputStream;
import java.io.IOException;

import javax.microedition.midlet.MIDlet;
import javax.microedition.midlet.MIDletStateChangeException;
import javax.microedition.lcdui.*;
import javax.microedition.io.*;

public class MailClient extends MIDlet
{
private MainForm mainForm;

private ContentForm contentForm;

private Display display;

private Message message;

public Message getMessage()
{
return message;
}

public void setMessage(Message message)
{
this.message = message;
}

public void displayAlert(String text, AlertType type, Displayable disp)
{
Alert alert = new Alert("Application Error");
alert.setString(text);
alert.setType(type);
alert.setTimeout(2000);
display.setCurrent(alert, disp);

}

public ContentForm getContentForm()
{
return contentForm;
}

public Display getDisplay()
{
return display;
}

public MainForm getMainForm()
{
return mainForm;
}

public void initMIDlet()
{
MailThread t = new MailThread(this);
t.start();
message = new Message();
display = Display.getDisplay(this);
mainForm = new MainForm(this, "Simple Mail Client");
contentForm = new ContentForm("Content", null, 150, TextField.ANY, this);
display.setCurrent(mainForm);
}

protected void startApp() throws MIDletStateChangeException
{

initMIDlet();

}

protected void pauseApp()
{

}

protected void destroyApp(boolean arg0) throws MIDletStateChangeException
{

}

}

class MailThread extends Thread
{
private MailClient midlet;

public MailThread(MailClient midlet)
{
this.midlet = midlet;
}

public void run()
{
synchronized(midlet)
{
try
{
midlet.wait();
}
catch(Exception e)
{
e.printStackTrace();
}

}
System.out.println("connecting to server.....");
HttpConnection httpConn = null;
DataOutputStream dos = null;

try
{
httpConn = (HttpConnection)Connector.open("http://localhost:8088/mail/maildo");
httpConn.setRequestMethod("POST");
dos = new DataOutputStream(httpConn.openOutputStream());
dos.writeUTF(midlet.getMessage().getTo());
dos.writeUTF(midlet.getMessage().getSubject());
dos.writeUTF(midlet.getMessage().getContent());
dos.close();
httpConn.close();
System.out.println("end of sending mail");
}
catch(IOException e)
{}
}}

在服务器端，我们要完成自己的servlet。他的任务比较简单就是接受客户端的数据然后通过JavaMail发送到指定的收件人那里。如果您对JavaMail还不熟悉请参考如下文章。这里直接给出servlet代码。
使用JavaMail实现收发电子邮件功能
使用Servlet发送电子邮件

package com.j2medev.servletmail;

import java.io.DataInputStream;
import java.io.IOException;
import java.util.Properties;

import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.mail.*;
import javax.mail.internet.InternetAddress;
import javax.mail.internet.MimeMessage;
import java.util.*;
import java.net.*;

public class MailServlet extends HttpServlet
{
private static String host;

private static String from;

public void init(ServletConfig config) throws ServletException
{
super.init(config);
host = config.getInitParameter("host");
from = config.getInitParameter("from");
System.out.println(host + from);
}

protected void doGet(HttpServletRequest request,
HttpServletResponse response) throws ServletException, IOException
{

doPost(request, response);
}

protected void doPost(HttpServletRequest request,
HttpServletResponse response) throws ServletException, IOException
{

DataInputStream dis = new DataInputStream(request.getInputStream());
String send = dis.readUTF();
String subject = dis.readUTF();
String content = dis.readUTF();
try
{
Properties props = System.getProperties();
// Setup mail server
props.put("mail.smtp.host", host);
// Get session
Session session = Session.getDefaultInstance(props, null);
// Define message
MimeMessage message = new MimeMessage(session);
// Set the from address
message.setFrom(new InternetAddress(from));
// Set the to address
message.addRecipient(Message.RecipientType.TO, new InternetAddress(
send));
// Set the subject
message.setSubject(subject);
// Set the content
message.setText(content);
// Send message
Transport.send(message);
} catch (Exception e)
{
e.printStackTrace();
}
}
}

web.xml
<?xml version="1.0" ?>
<!DOCTYPE web-app PUBLIC "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN" "http://java.sun.com/dtd/web-app_2_3.dtd">

<web-app>
<servlet>
<servlet-name>ServletMail</servlet-name>
<servlet-class>com.j2medev.servletmail.MailServlet</servlet-class>
<init-param>
<param-name>host</param-name>
<param-value>smtp.263.net</param-value>
</init-param>
<init-param>
<param-name>from</param-name>
<param-value>[e-mail]</param-value>
</init-param>
</servlet>

<servlet-mapping>
<servlet-name>ServletMail</servlet-name>
<url-pattern>/maildo</url-pattern>
</servlet-mapping>
<welcome-file-list>
<welcome-file>index.jsp</welcome-file>
</welcome-file-list>

<error-page>
<error-code>404</error-code>
<location>/error.jsp</location>
</error-page>

</web-app>

总结：本文更多要介绍的其实还是这个代理的思想，利用所学的知识灵活应用。不要局限于J2ME提供给你的API。文章中实现的客户端服务器都比较简单，也不够友好，如果感兴趣可以稍微修饰一下，对提高能力还是有帮助的。在MIDP中只是提供了RMS作为持久存储用，因此实现接受存储邮件不是很方便。如果手机支持FileConnection的话可以编写一个接受邮件的客户端。