作者：mingjava  文章来源：http://www.j2medev.com/Article/ShowArticle.asp?ArticleID=141

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>eric.zhan@263.net</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。