用J2ME的通用联网框架开发联网的应用程序

7/31/2004来源:移动短信技术人气:30459

  尽管目前的无线网络不够理想,手机联网还是给我们开发人员不小的震撼的。毕竟这真的是件神奇的事情,不是吗?本文将讲述如何应用J2ME平台中的通用联网框架开发联网的应用程序。

  首先,必须说明一点:MIDP中规定,任何移动信息设备都必须提供通过http协议的支持,而像其他的通信方式例如socket是设备相关的。有些手机会支持,有些则不支持。这里只大概的说明一下http协议相关的内容,如果不了解这个方面的知识请参考http协议。在javax.microedition.io里面是大量的接口,只有一个connector类,当然在midp2.0里面添加了对push技术的支持,这个留做以后讲。connector类提供的最重要的方法是open()方法,它的返回值为Connection,你可以对他进行转换得到你需要的类型,比如我们以http协议访问服务器。

void postViaHttpConnection(String url) throws IOException {
 HttpConnection c = null;
 InputStream is = null;
 OutputStream os = null;
 int rc;

 try {
  c = (HttpConnection)Connector.open(url);

  // Set the request method and headers
  c.setRequestMethod(HttpConnection.POST);
  c.setRequestPRoperty("If-Modified-Since","29 Oct 1999 19:43:31 GMT");
  c.setRequestProperty("User-Agent","Profile/MIDP-2.0 Configuration/CLDC-1.0");
  c.setRequestProperty("Content-Language", "en-US");

  // Getting the output stream may flush the headers
  os = c.openOutputStream();
  os.write("LIST games\n".getBytes());
  os.flush(); // Optional, getResponseCode will flush

  // Getting the response code will open the connection,
  // send the request, and read the HTTP response headers.
  // The headers are stored until requested.
  rc = c.getResponseCode();
  if (rc != HttpConnection.HTTP_OK) {
   throw new IOException("HTTP response code: " + rc);
  }

  is = c.openInputStream();

  // Get the ContentType
  String type = c.getType();
  processType(type);

  // Get the length and process the data
  int len = (int)c.getLength();
  if (len > 0) {
   int actual = 0;
   int bytesread = 0 ;
   byte[] data = new byte[len];
   while ((bytesread != len) && (actual != -1)) {
    actual = is.read(data, bytesread, len - bytesread);
    bytesread += actual;
   }
   process(data);
   } else {
    int ch;
    while ((ch = is.read()) != -1) {
     process((byte)ch);
    }
   }
  } catch (ClassCastException e) {
   throw new IllegalArgumentException("Not an HTTP URL");
  } finally {
   if (is != null)
    is.close();
   if (os != null)
    os.close();
   if (c != null)
    c.close();
  }
}

  上面的代码是我取自API doc(建议多读一下api doc)。
  下面根据自己的经验说明一下联网中比较重要的问题:

  我们应该明白这是如何工作的,手机发送请求通过无线网络传输到运营商的WAP网关,WAP网关将请求转发到web服务器,服务器可以用cgi,asp,servlet/jsp等构建。服务器处理后会把响应转发到WAP网关,WAP网关再把它发送到手机上。WAP网关对我们开发人员来说是透明的我们不用管它。

  如果在你的联网程序上看不到Thread,Runnable这样的字眼,那么你的程序是不能运行的。因为考虑到网络的因素,为了避免操作堵塞。你必须把联网动作放到另外一个线程去运行,而不能在主线程运行。最好当联网的时候提供给用户一个等待的界面比如作一个动画界面。我下面提供的例子中没有用,因为我想把这个单独出来以后谈。

  通常联网的应用程序的界面是比较多的,最好我们使用MVC的模式来实现界面的导航。

  考虑好你想如何传递你数据,这一点是非常重要的。你可以用GET方法也可以使用POST方法,推荐后者。因为get方法只能是通过URL编码的传输。而POST更加灵活,配合DataInputStream、DataOutputStream来使用更是方便。必须清楚我们如何接受数据是跟数据如何发送过来相关的,例如在client端writeUTF(message);writeInt(4);writeBoolean(true),那么接受就应该readUTF();readInt();readBoolean();如果发送过来数据长度是可用的,那么我们可以建立一个适当的数组来接受,如果不可用我们就要一个适当容量的数组来接受。

  下面我提供一个实例来说明以上的问题,在应用程序中我们输入任意字符,通过连接server得到响应并显示出来。server我用servlet写的非常简单,只是在受到的内容后面加上“haha”,程序我安装到自己的手机上运行没有任何问题,就是GPRS网络不够快。Server是tomcat5实现的,关于如何部署servlet的问题超出了本文的讨论范围。我只提供代码,推荐用Eclipse+Lomboz开发j2ee程序。

/*
* Created on 2004-7-5
*
* TODO To change the template for this generated file go to Window -
* Preferences - Java - Code Generation - Code and Comments
*/
package com.north;
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
/**
* @author P2800
*
* TODO To change the template for this generated type comment go to Window -
* Preferences - Java - Code Generation - Code and Comments
*/
public class MyServlet extends HttpServlet {
 protected void doGet(HttpServletRequest request,
 HttpServletResponse response) throws ServletException, IOException {
  DataInputStream dis = new DataInputStream(request.getInputStream());
  String result = dis.readUTF();
  DataOutputStream dos = new DataOutputStream(response.getOutputStream());
  dos.writeUTF(result+"haha");
  dos.close();
  dis.close();
  //TODO Method stub generated by Lomboz
 }
 protected void doPost(HttpServletRequest request,
  HttpServletResponse response) throws ServletException, IOException {
   doGet(request,response);
   //TODO Method stub generated by Lomboz
  }
}

  联网的时候一定按照如下的流程做

  1、建立连接,设置传输方式推荐POST,设置方法头

  2、打开输出流,传输数据给服务器

  3、判断相应的状态码,进入不同流程控制,注意错误处理。如果OK则开始接受数据

  4、关闭连接和流

  下面是客户端的代码,对错误处理没有考虑太多。一共是5个class

import javax.microedition.midlet.MIDlet;
import javax.microedition.midlet.MIDletStateChangeException;
/*
* Created on 2004-7-4
*
* TODO To change the template for this generated file go to
* Window - Preferences - Java - Code Style - Code Templates
*/

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

private UIController uicontroller;
/* (non-Javadoc)
* @see javax.microedition.midlet.MIDlet#startApp()
*/
protected void startApp() throws MIDletStateChangeException
{
 // TODO Auto-generated method stub
 uicontroller = new UIController(this);
 uicontroller.init();
}

/* (non-Javadoc)
* @see javax.microedition.midlet.MIDlet#pauseApp()
*/
protected void pauseApp()
{
 // TODO Auto-generated method stub
}

/* (non-Javadoc)
* @see javax.microedition.midlet.MIDlet#destroyApp(boolean)
*/
protected void destroyApp(boolean arg0) throws MIDletStateChangeException
{
 // TODO Auto-generated method stub
}

}

import java.io.IOException;
import javax.microedition.lcdui.Display;
import javax.microedition.lcdui.Displayable;

/*
* Created on 2004-7-4
*
* TODO To change the template for this generated file go to
* Window - Preferences - Java - Code Style - Code Templates
*/

/**
* @author P2800
*
* TODO To change the template for this generated type comment go to Window -
* Preferences - Java - Code Style - Code Templates
*/
public class UIController
{
 private HttpCommMIDlet midlet;
 private InputCanvas inputUI;
 private DisplayCanvas displayUI;
 private Display display;
 private HttpCommHandler httpHandler;

/**
*
*/
public UIController(HttpCommMIDlet midlet)
{
 this.midlet = midlet;
 // TODO Auto-generated constructor stub
}

public static class EventID
{
 public static final int CONNECT_TO_SERVER = 0;
 public static final int DISPLAY_BACK_TO_INPUT = 1;
}

public void init()
{
 display = Display.getDisplay(midlet);
 httpHandler = new HttpCommHandler(
  "http://222.28.218.222:8088/http/myservlet");
 inputUI = new InputCanvas(this);
 displayUI = new DisplayCanvas(this);
 display.setCurrent(inputUI);
}

public void setCurrent(Displayable disp)
{
 display.setCurrent(disp);
}

public void handleEvent(int EventID, Object[] obj)
{
 new EventHandler(EventID, obj).start();
}

private class EventHandler extends Thread
{
 private int eventID;
 private Object[] obj;
 private Displayable backUI;

 public EventHandler(int eventID, Object[] obj)
 {
  this.eventID = eventID;
  this.obj = obj;
 }

public void run()
{
 synchronized (this)
 {
  run(eventID, obj);
 }
}

private void run(int eventID, Object[] obj)
{
 switch (eventID)
 {
  case EventID.CONNECT_TO_SERVER:
  {
   try
   {
    String result = httpHandler.sendMessage((String) obj[0]);
    displayUI.init(result);
    setCurrent(displayUI);
    break;
   } catch (IOException e)
   {
   }
  }
  case EventID.DISPLAY_BACK_TO_INPUT:
  {
   setCurrent(inputUI);
   break;
  }
  default:
   break;
  }
 }
};

}

import javax.microedition.lcdui.Command;
import javax.microedition.lcdui.CommandListener;
import javax.microedition.lcdui.Displayable;
import javax.microedition.lcdui.Form;
import javax.microedition.lcdui.StringItem;
import javax.microedition.lcdui.TextField;

/*
* Created on 2004-7-4
*
* TODO To change the template for this generated file go to
* Window - Preferences - Java - Code Style - Code Templates
*/

/**
* @author P2800
*
* TODO To change the template for this generated type comment go to Window -
* Preferences - Java - Code Style - Code Templates
*/
public class InputCanvas extends Form implements CommandListener
{
 private UIController uicontroller;
 private TextField inputField;
 private StringItem result;
 public static final Command okCommand = new Command("OK", Command.OK, 1);

 public InputCanvas(UIController uicontroller)
 {
  super("Http Comunication");
  this.uicontroller = uicontroller;
  inputField = new TextField("Input:", null, 20, TextField.ANY);
  this.append(inputField);
  this.addCommand(okCommand);
  this.setCommandListener(this);
 }

/*
* (non-Javadoc)
*
* @see javax.microedition.lcdui.CommandListener#commandAction(javax.microedition.lcdui.Command,
* javax.microedition.lcdui.Displayable)
*/
public void commandAction(Command arg0, Displayable arg1)
{
 // TODO Auto-generated method stub
 if (arg0 == okCommand)
 {
  String input = inputField.getString();
  uicontroller.handleEvent(UIController.EventID.CONNECT_TO_SERVER,
  new Object[] { input });
 }
}

}

import java.io.*;
import javax.microedition.io.Connector;
import javax.microedition.io.HttpConnection;

/*
* Created on 2004-7-4
*
* TODO To change the template for this generated file go to
* Window - Preferences - Java - Code Style - Code Templates
*/

/**
* @author P2800
*
* TODO To change the template for this generated type comment go to Window -
* Preferences - Java - Code Style - Code Templates
*/
public class HttpCommHandler
{
 private String URL;
 public HttpCommHandler(String URL)
 {
  this.URL = URL;
 }

 public String sendMessage(String message) throws IOException
 {
  HttpConnection httpConn;
  DataInputStream input;
  DataOutputStream output;
  String result;
  try
  {
   httpConn = open();
   output = this.openDataOutputStream(httpConn);
   output.writeUTF(message);
   output.close();
   input = this.openDataInputStream(httpConn);
   result = input.readUTF();
   closeConnection(httpConn,input,output);
   return result;
  }
 finally
 {
  }
}

public HttpConnection open() throws IOException
{
 try
 {
  HttpConnection connection = (HttpConnection) Connector.open(URL);
  connection.setRequestProperty("User-Agent", System
.getProperty("microedition.profiles"));
  connection.setRequestProperty("Content-Type",
"application/octet-stream");
  connection.setRequestMethod(HttpConnection.POST);
  return connection;
 } catch (IOException ioe)
 {
  throw ioe;
 }
}

private DataInputStream openDataInputStream(HttpConnection conn)
throws IOException
{
 int code = conn.getResponseCode();
 if (code == HttpConnection.HTTP_OK)
 {
  return conn.openDataInputStream();
 } else
 {
  throw new IOException();
 }
}

private DataOutputStream openDataOutputStream(HttpConnection conn)
throws IOException
{
 return conn.openDataOutputStream();
}

private void closeConnection(HttpConnection conn, DataInputStream dis,
DataOutputStream dos)
{
 if(conn!= null)
 {
  try
  {
   conn.close();
  }
  catch(IOException e)
  {}
 }
 if(dis!=null)
 {
  try
  {
   dis.close();
  }
  catch(IOException e)
  {}
 }
 if(dos!=null)
 {
  try
  {
   dos.close();
  }
  catch(IOException e)
  {}
 }
}

}

 import javax.microedition.lcdui.Command;
 import javax.microedition.lcdui.CommandListener;
 import javax.microedition.lcdui.Displayable;
 import javax.microedition.lcdui.Form;
 import javax.microedition.lcdui.StringItem;

 /*
  * Created on 2004-7-6
  *
  * TODO To change the template for this generated file go to
  * Window - Preferences - Java - Code Style - Code Templates
 */

 /**
  * @author P2800
  *
  * TODO To change the template for this generated type comment go to Window -
  * Preferences - Java - Code Style - Code Templates
 */
 public class DisplayCanvas extends Form implements CommandListener
 {
  private UIController uicontroller;
  private StringItem result;
  private int index = 0;
  private boolean first = true;
  public static Command backCommand = new Command("Back", Command.BACK, 2);

  public DisplayCanvas(UIController uicontroller)
  {
   super("Result");
   this.uicontroller = uicontroller;
   result = new StringItem("you have input:", null);
   this.addCommand(backCommand);
   this.setCommandListener(this);
  }

 public void init(String message)
 {
  if (first)
  {
   result.setText(message);
   index = this.append(result);
   first = false;
  }
  else
  {
   this.delete(index);
   result.setText(message);
   this.append(result);
  }
 }

 /*
  * (non-Javadoc)
  *
  * @see   javax.microedition.lcdui.CommandListener#commandAction(javax.microedition.lcdui.Command,
  * javax.microedition.lcdui.Displayable)
 */
 public void commandAction(Command arg0, Displayable arg1)
 {
  // TODO Auto-generated method stub
  uicontroller.handleEvent(UIController.EventID.DISPLAY_BACK_TO_INPUT,null);
 }
}