在无线J2ME设备上实现超文本传输协议【转】
} finally {
if ( hc != null ) hc.close();
if ( dis != null ) dis.close();
if ( dos != null ) dis.close();
}//结束 try/finally
这就是所有的程序代码!并请参见本文后附带的程序代码。
随着可以使用国际互联网络和支持网络的无线设备日益的增多普及，Java和J2ME的重要性也在不断的变大。因为HTTP协议是当前仅有的，被所有的遵从MIDP规范的设备支持的网络协议，它也是用于开发无线网络应用程序的最好的候选者。
在本文中，我们探究了无线网络编程的基本结构和几个核心问题，我们看了如何调用两个最常用的HTTP请求方法：GET和POST。J2ME仍然在它的发展初期，并且无线设备也即将得到大面积的普及。所以，所有有志投身于无线网络编程中的开发者们将得到大展拳脚的好机会。
附录：
/*
* HttpMidlet.java
*/
import javax.microedition.midlet.*;
import javax.microedition.lcdui.*;
import javax.microedition.io.*;
import java.io.*;
public class HttpMidlet extends MIDlet implements CommandListener {
//使用默认的URL。用户可以从图形用户接口改变这个值
private static String defaultURL = "http://localhost:8080/test/servlet/EchoServlet";
// 主MIDP 显示
private Display myDisplay = null;
// 输入URL的图形用户接口组件
private Form requestScreen;
private TextField requestField;
// 用于提交请求的图形用户接口组件
private List list;
private String[] menuItems;
// 用于显示服务器响应的图形用户接口组件
private Form resultScreen;
private StringItem resultField;
//用于requestScreen的"send"按钮
Command sendCommand;
// 用于requestScreen的"exit"按钮
Command exitCommand;
// 用于requestScreen的"back"按钮
Command backCommand;
public HttpMidlet(){
// 初始化图形用户接口组件
myDisplay = Display.getDisplay( this );
sendCommand = new Command( "SEND", Command.OK, 1 );
exitCommand = new Command( "EXIT", Command.OK, 1 );
backCommand = new Command( "BACK", Command.OK, 1 );
//显示请求的URL
requestScreen = new Form( "Type in a URL:" );
requestField = new TextField( null, defaultURL, 100, TextField.URL );
requestScreen.append( requestField );
requestScreen.addCommand( sendCommand );
requestScreen.addCommand( exitCommand );
requestScreen.setCommandListener( this );
// 选择想要的HTTP请求方法
menuItems = new String[] {"GET Request", "POST Request"};
list = new List( "Select an HTTP method:", List.IMPLICIT, menuItems, null );
list.setCommandListener( this );
// 先是从服务器上收到的信息
resultScreen = new Form( "Server Response:" );
resultScreen.addCommand( backCommand );
resultScreen.setCommandListener( this );
}//结束HttpMidlet()
public void startApp() {
myDisplay.setCurrent( requestScreen );
}//结束 startApp()
public void commandAction( Command com, Displayable disp ) {
// 当用户点击"send"按钮
if ( com == sendCommand ) {
myDisplay.setCurrent( list );
} else if ( com == backCommand ) {
requestField.setString( defaultURL );
myDisplay.setCurrent( requestScreen );
} else if ( com == exitCommand ) {
destroyApp( true );
notifyDestroyed();
}//结束 if ( com == sendCommand )
if ( disp == list && com == List.SELECT_COMMAND ) {
String result;
if ( list.getSelectedIndex() == 0 ) // 发送一个 GET 请求到服务器
result = sendHttpGet( requestField.getString() );
else // 发送一个 POST 请求到服务器
result = sendHttpPost( requestField.getString() );
resultField = new StringItem( null, result );
resultScreen.append( resultField );
myDisplay.setCurrent( resultScreen );
}//结束if ( dis == list && com == List.SELECT_COMMAND )
}//结束 commandAction( Command, Displayable )
private String sendHttpGet( String url )
{
HttpConnection hcon = null;
DataInputStream dis = null;
StringBuffer responseMessage = new StringBuffer();
try {
//使用READ权限的标准的 HttpConnection
hcon = ( HttpConnection )Connector.open( url );
//从HttpConnection取得一个 DataInputStream
dis = new DataInputStream( hcon.openInputStream() );
// 从服务器上取回响应
int ch;
while ( ( ch = dis.read() ) != -1 ) {
responseMessage.append( (char) ch );
}//结束while ( ( ch = dis.read() ) != -1 )
}
catch( Exception e )
{
e.printStackTrace();
responseMessage.append( "ERROR" );
} finally {
try {
if ( hcon != null ) hcon.close();
if ( dis != null ) dis.close();
} catch ( IOException ioe ) {
ioe.printStackTrace();
}//结束try/catch
}//结束try/catch/finally
return responseMessage.toString();
}//结束sendHttpGet( String )
private String sendHttpPost( String url )
{
HttpConnection hcon = null;
DataInputStream dis = null;
DataOutputStream dos = null;
StringBuffer responseMessage = new StringBuffer();
// 请求体
String requeststring = "This is a POST.";
try {
// 使用读写权限的 HttpConnection
hcon = ( HttpConnection )Connector.open( url, Connector.READ_WRITE );
//设置请求方法为POST
hcon.setRequestMethod( HttpConnection.POST );
// 取得发送请求字符串的DataOutputStream
dos = hcon.openDataOutputStream();
byte[] request_body = requeststring.getBytes();
// 发送请求字符串到服务器
for( int i = 0; i < request_body.length; i++ ) {
dos.writeByte( request_body[i] );
}//结束 for( int i = 0; i < request_body.length; i++ )
// 取得做为接收服务器响应的DataInputStream
dis = new DataInputStream( hcon.openInputStream() );
// 从服务器上取回响应
int ch;
while( ( ch = dis.read() ) != -1 ) {
responseMessage.append( (char)ch );
}//结束while( ( ch = dis.read() ) != -1 ) {
}
catch( Exception e )
{
e.printStackTrace();
responseMessage.append( "ERROR" );
}
finally {
// 释放输入输出流和HTTP连接
try {
if( hcon != null ) hcon.close();
if( dis != null ) dis.close();
if( dos != null ) dos.close();
} catch ( IOException ioe ) {
ioe.printStackTrace();
}//结束try/catch
}//结束try/catch/finally
return responseMessage.toString();
}//结束sendHttpPost( String )
public void pauseApp() {
}//结束pauseApp()
public void destroyApp( boolean unconditional ) {
myDisplay = null;
requestScreen = null;
requestField = null;
resultScreen = null;
resultField = null;
}//结束 destroyApp( boolean )
}//结束HttpMidlet
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