J2ME：使用后台线程按制HTTP连接

首先，在没有使用后台线程控制HTTP连接时，常常会造成手机系统死机的假象。

方法一：

主程序中直接使用后台线程：

可以设计一个网络连接按钮connectCommand,当用户按下该按钮的时候，才开始进入网络连接状态。

但是J2ME不能够在commandAction()方法中直接进行网络连接，因此需要创建一个后台网络连接的线程。

如下：

 1:  public void commandAction(Command c, Displayable d) {

 2:          if (c == connectCommand) {//按下连接按钮，则启动一个后台线程

 3:              Thread t = new Thread(){

 4:                  public void run(){

 5:                      //进行网络连接

 6:                      

 7:                  }

 8:              };

 9:              t.start();

10:          }

11:          if (c == exitCommand) {

12:              try {

13:                  destroyApp(false);

14:                  notifyDestroyed();

15:              } catch (MIDletStateChangeException e) {

16:                  e.printStackTrace();

17:              }

18:          }

19:      }

方法二：

主程序中调用后台线程子类

单独创建一个类来实现网络连接，这个类可以继承Thread 也可以继承Runnable，然后这个类处理各种网络连接以后来实现它的功能。使用的基本方法：

 1:      public void commandAction(Command c, Displayable d) {

 2:          if (c == okCommand) {

 3:              Logger f = new Logger (this,getString());

 4:              Thread t =new Thread(f);

 5:              t.start();//启动线程

 6:              display.setCurrent(f);

 7:          }

 8:      }

 9:  

10:  class Logger extends Form implements Runnable,CommandListener{

11:      Logger (Displayable next,String url){

12:      }

13:  }

下面是完整的程序：

  1:  import javax.microedition.io.Connector;

  2:  import javax.microedition.io.HttpConnection;

  3:  import javax.microedition.lcdui.Alert;

  4:  import javax.microedition.lcdui.Command;

  5:  import javax.microedition.lcdui.CommandListener;

  6:  import javax.microedition.lcdui.Display;

  7:  import javax.microedition.lcdui.Displayable;

  8:  import javax.microedition.lcdui.Form;

  9:  import javax.microedition.lcdui.StringItem;

 10:  import javax.microedition.lcdui.TextBox;

 11:  import javax.microedition.midlet.MIDlet;

 12:  import javax.microedition.midlet.MIDletStateChangeException;

 13:  

 14:  public class HttpLogger extends MIDlet {

 15:      private Command exitCommand = new Command("Exit", Command.EXIT, 1);

 16:      private Command okCommand = new Command("OK", Command.OK, 1);

 17:      private Command cancelCommand = new Command("Cancel", Command.CANCEL, 1);

 18:      private Display display;

 19:      private URLEntry mainForm;

 20:  

 21:      public HttpLogger() {

 22:      }

 23:  

 24:      protected void destroyApp(boolean arg0) throws MIDletStateChangeException {

 25:          exitMIDlet();

 26:      }

 27:  

 28:      protected void pauseApp() {

 29:          // TODO Auto-generated method stub

 30:  

 31:      }

 32:  

 33:      protected void startApp() throws MIDletStateChangeException {

 34:          if (display == null) {

 35:              display = Display.getDisplay(this);

 36:              mainForm = new URLEntry();

 37:              // 显示主屏幕

 38:              display.setCurrent(mainForm);

 39:          }

 40:      }

 41:  

 42:      // 退出程序

 43:      private void exitMIDlet() {

 44:          notifyDestroyed();

 45:      }

 46:  

 47:      // 显示错误信息

 48:      void displayError(Throwable e, Displayable next) {

 49:          Alert a = new Alert("错误");

 50:          a.setString(e.toString());

 51:          a.setTimeout(Alert.FOREVER);

 52:          display.setCurrent(a, next);

 53:      }

 54:  

 55:      // 输入URL,内部类

 56:      class URLEntry extends TextBox implements CommandListener {

 57:  

 58:          public URLEntry() {

 59:              super("Enter URL", "http://127.0.0.1:8080/HelloWorld.html", 100, 0);

 60:              addCommand(exitCommand);

 61:              addCommand(okCommand);

 62:              setCommandListener(this);

 63:          }

 64:  

 65:          public void commandAction(Command c, Displayable d) {

 66:              if (c == exitCommand) {

 67:                  exitMIDlet();

 68:              } else if (c == okCommand) {

 69:                  // 创建后台的网络连接

 70:                  Logger f = new Logger(this, getString());

 71:                  Thread t = new Thread(f);

 72:                  t.start();

 73:                  display.setCurrent(f);

 74:              }

 75:          }

 76:      }

 77:  

 78:      // 连接网络的新线程，内部类

 79:      class Logger extends Form implements Runnable, CommandListener {

 80:  

 81:          private String url;

 82:          private Displayable next;

 83:          private StringItem text = new StringItem(null, "");

 84:          private HttpConnection conn;

 85:  

 86:          public Logger(Displayable next, String url) {

 87:              super("HTTP 信息");

 88:              // 获得地址信息

 89:              this.url = url;

 90:              this.next = next;

 91:  

 92:              addCommand(cancelCommand);

 93:              setCommandListener(this);

 94:              // 屏幕上使用StringItem来显示信息

 95:              append(text);

 96:          }

 97:  

 98:          public void run() {

 99:              // 创建一个连接不要放在构造函数中

100:              try {

101:                  conn = (HttpConnection) Connector.open(url);

102:              } catch (Exception e) {

103:                  e.printStackTrace();

104:              }

105:              // 屏幕上显示服务器上的信息

106:              update("连接到" + conn.getURL());

107:              try {

108:                  int rc = conn.getResponseCode();

109:                  update("Response code" + rc);

110:                  update("Response message:" + conn.getResponseMessage());

111:                  String key;

112:                  for (int i = 0; (key = conn.getHeaderFieldKey(i)) != null; ++i) {

113:                      // 获得网页Head信息

114:                      update(key + ":" + conn.getHeaderField(i));

115:                  }

116:              } catch (Exception e) {

117:                  update("获得的异常：" + e.toString());

118:              }

119:              // 取消cancelCommand按钮

120:              removeCommand(cancelCommand);

121:              addCommand(okCommand);

122:          }

123:  

124:          // 使用String item 显示获得的信息

125:          private void update(String line) {

126:              if (display.getCurrent() != this) {

127:                  return;

128:              }

129:              String old = text.getText();

130:              StringBuffer buf = new StringBuffer();

131:  

132:              buf.append(old);

133:              if (old.length() > 0) {

134:                  buf.append('\n');

135:              }

136:              buf.append(line);

137:              text.setText(buf.toString());

138:          }

139:  

140:          public void commandAction(Command arg0, Displayable arg1) {

141:              display.setCurrent(next);

142:              try {

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2010-04-21 17:07
      
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