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ImageItem对象是一个项目类型的对象,他的作用是在容器中显示图片。那么如何使用ImageItem对象呢?请按照下面三个步骤进行:
1.构造一个Image对象,相关代码如下所示:
Image img=Image.createImage("/fancy/test/JavaPowered-8.png");
createImage()方法是Image类的静态方法,它的作用是根据图形文件创建一个Image对象。
J2ME程序中所用到的图片文件必须存放在apps\fancy\res文件夹下面。
2.构造ImageItem对象,相关代码如下所示:
imgItem=new ImageItem("Default Layout",img,ImageItem.LAYOUT_DEFAULT,
"Image Cannot be shown");
ImageItem类的构造函数有三个参数,第一个参数的作用是显示一个标签,第二个参数指明图片的对齐方式,第三个参数的作用是显示图片的tip。
3.利用容器类对象的append()方法将ImageItem对象添加进去。如:
props.append(imgItem);
下面我们来看一个比较完整的例子。
package fancy.test;
import javax.microedition.midlet.*;
import javax.microedition.lcdui.*;
public class ShowImageItem extends MIDlet implements CommandListener
{
private Display display;
private Form props;
private Image img;
private ImageItem imgItem;
private Command exitCommand = new Command("Exit", Command.EXIT, 1);
public ShowImageItem()
{
display = Display.getDisplay(this);
}
public void startApp()
{
props = new Form("Hello World");
//props.append("Hello World!\n");
try
{
img=Image.createImage("/fancy/test/JavaPowered-8.png");
imgItem=new ImageItem("Default Layout",
img,ImageItem.LAYOUT_DEFAULT,"Image Cannot be
shown");
props.append(imgItem);
props.append(new ImageItem("Left Layout",
img,ImageItem.LAYOUT_LEFT,"Image Cannot be
shown"));
props.append(new ImageItem("Center Layout",
img,ImageItem.LAYOUT_CENTER,"Image Cannot be
shown"));
}
catch(Exception fe)
{
//to do nothing
}
props.addCommand(exitCommand);
props.setCommandListener(this);
display.setCurrent(props);
}
public void commandAction(Command c, Displayable s)
{
if (c == exitCommand)
{
destroyApp(false);
notifyDestroyed();
}
}
public void destroyApp(boolean unconditional)
{
}
public void pauseApp()
{
display.setCurrent(null);
props = null;
}
}
ShowImageItem.java程序的运行效果如下图所示:
ChoiceGroup也是一个项目类型的对象,它代表一个选择列表,它的作用和List对象类似,不过后者是一个容器,而前者是一个项目。
我们需要特别注意ChoiceGroup类的构造函数,它有四个参数,第一个参数是标签,第二个参数是此选择列表的类型,例如多选还是单选。第三个参数是一个字符串数组,代表每个选项的标签,第四个选项是一个Image类型的数组,代表每个选项前面的小图标。下面是一个比较完整的例子。
package fancy.test;
import javax.microedition.midlet.*;
import javax.microedition.lcdui.*;
public class ShowChoiceGroup extends MIDlet implements CommandListener
{
private Display display;
private Form props;
private Image duke;
private Image[] imageArray;
private ChoiceGroup choice;
private Command exitCommand = new Command("Exit", Command.EXIT, 1);
public ShowChoiceGroup()
{
display = Display.getDisplay(this);
}
public void startApp()
{
props = new Form("Hello World");
//props.append("Hello World!\n");
try
{
Image duke= Image.createImage("/fancy/test/Icon.png");
imageArray = new Image[]{duke,duke,duke};
String[] stringArray = { "Option A", "Option B",
"Option C" };
choice=new ChoiceGroup("choice group",
ChoiceGroup.MULTIPLE,stringArray,imageArray);
props.append(choice);
}
catch(Exception fe)
{
//to do nothing.
}
props.addCommand(exitCommand);
props.setCommandListener(this);
display.setCurrent(props);
}
public void commandAction(Command c, Displayable s)
{
if (c == exitCommand)
{
destroyApp(false);
notifyDestroyed();
}
public void destroyApp(boolean unconditional)
{
}
public void pauseApp()
{
display.setCurrent(null);
props = null;
}
}
ShowChoiceGroup.java程序的运行效果如下图所示:
Gauge对象是一个项目类型的对象,它的作用是显示一个进度条。请看下面的源代码。
Gauge类的构造函数的后面两个参数分别是进度条的最大值和初始值。
package fancy.test;
import javax.microedition.midlet.*;
import javax.microedition.lcdui.*;
public class ShowGauge extends MIDlet implements CommandListener
{
private Display display;
private Form props;
private Command exitCommand = new Command("Exit", Command.EXIT, 1);
public ShowGauge()
{
display = Display.getDisplay(this);
}
public void startApp()
{
props = new Form("Hello World");
//props.append("Hello World!\n");
Gauge gauge=new Gauge("show gauge",true,100,50);
props.append(gauge);
props.addCommand(exitCommand);
props.setCommandListener(this);
display.setCurrent(props);
}
public void commandAction(Command c, Displayable s)
{
if (c == exitCommand)
{
destroyApp(false);
notifyDestroyed();
}
}
public void destroyApp(boolean unconditional)
{
}
public void pauseApp()
{
display.setCurrent(null);
props = null;
}
}
Ticker对象是一个项目类型的对象,它的作用相当于一个滚动消息栏,在屏幕的上方显示滚动的信息。 Ticker类的构造函数仅有一个参数,那就是需要滚动显示的消息。
package fancy.test;
import javax.microedition.midlet.*;
import javax.microedition.lcdui.*;
public class ShowTicker extends MIDlet implements CommandListener
{
private Display display;
private Form props;
private Command exitCommand = new Command("Exit", Command.EXIT, 1);
public ShowTicker()
{
display = Display.getDisplay(this);
}
public void startApp()
{
props = new Form("Hello World");
props.append("Hello World!\n");
Ticker ticker=new Ticker("D??￥ò?ò1
;ìy′oóê");
props.setTicker(ticker);
props.addCommand(exitCommand);
props.setCommandListener(this);
display.setCurrent(props);
}
public void commandAction(Command c, Displayable s)
{
if (c == exitCommand)
{
destroyApp(false);
notifyDestroyed();
}
}
public void destroyApp(boolean unconditional)
{
}
public void pauseApp()
{
display.setCurrent(null);
props = null;
}
}
ShowTicker.java程序的运行效果如下图所示:
在前面的例子中,我们已经演示了如何构造J2ME程序的用户界面。现在有一个问题,那就是如何与用户界面交互呢?亦即如何获取用户通过用户界面输入的值呢?请看下面的例子。
package fancy.test;
import javax.microedition.midlet.*;
import javax.microedition.lcdui.*;
public class GetTextBoxValue extends MIDlet implements CommandListener
{
private Display display;
private TextBox txtBox;
private Command exitCommand = new Command("Exit", Command.EXIT, 1);
private Command getCommand = new Command("GETVALUE", Command.OK, 1);
public GetTextBoxValue()
{
display = Display.getDisplay(this);
}
public void startApp()
{
//or :
//String str="hello world";
//txtBox = new TextBox("Text Box",str,str.length(),0);
//the follow code is wrong:
//txtBox = new TextBox("Text Box",str,any number here,0);
txtBox = new TextBox("Text Box",null,200,0);
txtBox.addCommand(exitCommand);
txtBox.addCommand(getCommand);
txtBox.setCommandListener(this);
display.setCurrent(txtBox);
}
public void valueScreen()
{
Form props=new Form("get text box value");
props.append(txtBox.getString());
props.addCommand(exitCommand);
props.setCommandListener(this);
display.setCurrent(props);
}
public void commandAction(Command c, Displayable s)
{
if (c == exitCommand)
{
destroyApp(false);
notifyDestroyed();
}
if(c==getCommand)
{
valueScreen();
}
}
public void destroyApp(boolean unconditional)
{
}
public void pauseApp()
{
display.setCurrent(null);
txtBox = null;
}
}
在上面的例子中(GetTextBoxValue.java),当我们往文本框中输入文本,并按下退出按钮,接着选择GETVALUE命令的时候,将会调用valueScreen()方法。valueScreen()方法的源代码如下
:
public void valueScreen()
{
Form props=new Form("get text box value");
props.append(txtBox.getString());
props.addCommand(exitCommand);
props.setCommandListener(this);
display.setCurrent(props);
}
valueScreen()方法的逻辑是:首先创建一个容器对象Form,然后调用TextBox对象的getString()方法,获取文本框中的输入值,追加到容器对象中,最后将此Form对象作为屏幕的当前显示对象。GetTextBoxValue.java的运行效果如下面两图所示:
Date对象是属于java.util包的,它的作用是返回当前的时间。请看下面的代码:
package fancy.test;
import javax.microedition.midlet.*;
import javax.microedition.lcdui.*;
import java.util.*;
public class GetDate extends MIDlet implements CommandListener
{
private Display display;
private Form props;
private Date date;
private Command exitCommand = new Command("Exit", Command.EXIT, 1);
public GetDate()
{
display = Display.getDisplay(this);
}
public void startApp()
{
props = new Form("Hello World");
props.append("Hello World!\n");
date=new Date();
props.append("Now Time:"+date.getTime()+"\n");
props.addCommand(exitCommand);
props.setCommandListener(this);
display.setCurrent(props);
}
public void commandAction(Command c, Displayable s)
{
if (c == exitCommand)
{
destroyApp(false);
notifyDestroyed();
}
}
public void destroyApp(boolean unconditional)
{
}
public void pauseApp()
{
display.setCurrent(null);
props = null;
}
}
GetDate.java程序的运行效果如下图所示:
TimeZone对象也是属于java.util包的。这个对象的作用是提供关于时区的信息。TimeZone类有一个静态方法----getDefault(),可以获取与当前系统相关的时区对象。getAvailableIDs()方法可以获取系统中所有可用的时区的ID号,getID()方法可以获取系统当前所设置的时
区。具体的例子如下所示:
package fancy.test;
import javax.microedition.midlet.*;
import javax.microedition.lcdui.*;
import java.util.*;
public class GetTimeZone extends MIDlet implements CommandListener
{
private Display display;
private Form props;
//private Date date;
private TimeZone zone;
private Command exitCommand = new Command("Exit", Command.EXIT, 1);
public GetTimeZone()
{
display = Display.getDisplay(this);
}
public void startApp()
{
props = new Form("Hello World");
props.append("Hello World!\n");
//date=new Date();
//props.append("Now Time:"+date.getTime()+"\n");
zone=TimeZone.getDefault();
String []zoneid=zone.getAvailableIDs();
for(int i=0;i<zoneid.length;i++)
{
props.append(zoneid[i]+"\n");
}
props.append("Current Time Zone:"+zone.getID()+"\n");
props.addCommand(exitCommand);
props.setCommandListener(this);
display.setCurrent(props);
}
public void commandAction(Command c, Displayable s)
{
if (c == exitCommand)
{
destroyApp(false);
notifyDestroyed();
}
}
public void destroyApp(boolean unconditional)
{
}
public void pauseApp()
{
display.setCurrent(null);
props = null;
}
}
Calendar对象归属于java.util包,它可以提供更为详尽的时间信息。具体的例子如下所示:
package fancy.test;
import javax.microedition.midlet.*;
import javax.microedition.lcdui.*;
import java.util.*;
public class GetCalendar extends MIDlet implements CommandListener
{
private Display display;
private Form props;
//private Date date;
//private TimeZone zone;
//private Calendar calendar;
private Command exitCommand = new Command("Exit", Command.EXIT, 1);
public GetCalendar()
{
display = Display.getDisplay(this);
}
public void startApp()
{
props = new Form("Hello World");
props.append("Hello World!\n");
Calendar rightNow = Calendar.getInstance();
props.append("YEAR:"+rightNow.get(Calendar.YEAR)+"\n");
props.append("MONTH:"+rightNow.get(Calendar.MONTH)+"\n");
props.append("DAY OF MONTH:"
+rightNow.get(Calendar.DAY_OF_MONTH)+"\n");
props.append("HOUR OF DAY:"
+rightNow.get(Calendar.HOUR_OF_DAY)+"\n");
props.append("MINUTE:"
+rightNow.get(Calendar.MINUTE)+"\n");
props.append("SECOND:"
+rightNow.get(Calendar.SECOND)+"\n");
props.append("MILLISECOND:"
+rightNow.get(Calendar.MILLISECOND)+"\n");
//date=new Date();
//props.append("Now Time:"+date.getTime()+"\n");
//zone=TimeZone.getDefault();
//String []zoneid=zone.getAvailableIDs();
//for(int i=0;i<zoneid.length;i++)
//{
// props.append(zoneid[i]+"\n");
//}
//props.append("Current Time Zone:"+zone.getID()+"\n");
props.addCommand(exitCommand);
props.setCommandListener(this);
display.setCurrent(props);
}
public void commandAction(Command c, Displayable s)
{
if (c == exitCommand)
{
destroyApp(false);
notifyDestroyed();
}
}
public void destroyApp(boolean unconditional)
{
}
public void pauseApp()
{
display.setCurrent(null);
props = null;
}
}
GetCalendar.java程序的运行效果如下图所示:
在J2ME程序中,可以利用HttpConnection接口建立HTTP连接,访问远程服务器上的资源。具体的代码如下所示:
package fancy.test;
import javax.microedition.midlet.*;
import javax.microedition.lcdui.*;
import javax.microedition.io.*;
public class GetHttpConnection extends MIDlet implements CommandListener
{
private Display display;
private Form props;
private Command exitCommand = new Command("Exit", Command.EXIT, 1);
public GetHttpConnection()
{
display = Display.getDisplay(this);
}
public void startApp()
{
props = new Form("Get Http Connection");
//props.append("Hello World!\n");
try
{
HttpConnection conn=(HttpConnection) Connector.open
("http://rainbow:8080/index.html");
//conn.setRequestProperty("user","fancy");
props.append("Date:"+conn.getDate()+"\n");
props.append("Expiration:"+
conn.getExpiration()+"\n");
props.append(conn.getHost()+"\n");
props.append("Last Modified:"+
conn.getLastModified()+"\n");
props.append("Port:"+conn.getPort()+"\n");
props.append("Protocol:"+
conn.getProtocol()+"\n");
props.append("Request Method:"+
conn.getRequestMethod()+"\n");
props.append("Response Code:"+
conn.getResponseCode()+"\n");
props.append("Encoding:"+
conn.getEncoding()+"\n");
props.append("Length:"+conn.getLength()+"\n");
props.append("Type:"+conn.getType()+"\n");
props.append("URL:"+conn.getURL()+"\n");
props.append("Response Message:"+
conn.getResponseMessage()+"\n");
}
catch(Exception fe)
{
props.append("Error:"+fe.getMessage());
}
props.addCommand(exitCommand);
props.setCommandListener(this);
display.setCurrent(props);
}
public void commandAction(Command c, Displayable s)
{
if (c == exitCommand)
{
destroyApp(false);
notifyDestroyed();
}
}
public void destroyApp(boolean unconditional)
{
}
public void pauseApp()
{
display.setCurrent(null);
props = null;
}
}
Connector类提供了open()方法,可以和各种各样的远程资源建立连接。open()方法的参数就是远程资源的URL地址。open()方法的返回值是一个Connection接口。为了建立HTTP连接,我们应该将它强制转换为HttpConnection接口的形式。一旦获取HttpConnection接
口的实例对象,就可以调用HttpConnection接口的各种方法,得到关于HTTP连接的各种信息。
我的想法是建立一个Web服务器,使用Tomcat 4.0,支持JSP技术。再配置一个Mail服务器,使用的软件是Imail 7.0.4。首先编写一个可以发送电子邮件的JSP程序(post.jsp),
具体代码
如下所示:
<%@ page import="java.net.*" %>
<%@ page import="java.io.*" %>
<%@ page import="javax.activation.*" %>
<%@ page import="java.util.*" %>
<%@ page import="javax.mail.*" %>
<%@ page import="javax.mail.internet.*" %>
<%!
public class SmtpAuthenticator extends javax.mail.Authenticator
{
public javax.mail.PasswordAuthentication
getPasswordAuthentication()
{
return new javax.mail.PasswordAuthentication("fancy",
"fancy");
}
}
%>
<%
String username="fancyrainbow";
String password="fancy";
String from="fancy@rainbow";
String to="fancy@rainbow";
String cc="fancy@rainbow";
String subject="J2ME Mail Test";
//String content="J2ME Mail Test";
String content=request.getParameter("content");
Properties props = System.getProperties();
props.put("mail.smtp.auth","true");
props.put("mail.smtp.host","rainbow"); //263
SmtpAuthenticator sa=new SmtpAuthenticator();
Session sess = Session.getInstance(props, sa);
sess.setDebug(true);
Message msg = new MimeMessage(sess);
msg.setFrom(new InternetAddress(from));
msg.setRecipients(Message.RecipientType.TO,InternetAddress.parse(to,
false));
msg.addRecipients(Message.RecipientType.CC,InternetAddress.parse(cc,
false));
msg.setSubject(subject);
msg.setSentDate(new Date());
msg.setText(content);
Transport.send(msg);
%>
Send Message OK!
我将post.jsp程序保存在Tomcat 4.0的ROOT目录下面,然后使用Web浏览器测试此程序成功。然后再将上一个J2ME程序(GetHttpConnection.java)改一改,让它与Tomcat 4.0
服务器建立连接,请求post.jsp程序。相关代码如下所示:
package fancy.test;
import javax.microedition.midlet.*;
import javax.microedition.lcdui.*;
import javax.microedition.io.*;
import java.io.*;
public class SendMail extends MIDlet implements CommandListener
{
private Display display;
private Form props;
private Command exitCommand = new Command("Exit", Command.EXIT, 1);
public SendMail()
{
display = Display.getDisplay(this);
}
public void startApp()
{
props = new Form("Get Http Connection");
//props.append("Hello World!\n");
try
{
HttpConnection
conn=(HttpConnection)Connector.open("http://rainbow:8080/post.
jsp?content=Hello World");
//conn.setRequestProperty("user","fancy");
props.append("Date:"+conn.getDate()+"\n");
props.append("Expiration:"+conn.getExpiration()+"\n");
props.append(conn.getHost()+"\n");
props.append("Last Modified:"+conn.getLastModified()+"\n
props.append("Port:"+conn.getPort()+"\n");
props.append("Protocol:"+conn.getProtocol()+"\n");
props.append("Request Method:"+conn.getRequestMethod()+"
props.append("Response Code:"+conn.getResponseCode()+"\n
props.append("Encoding:"+conn.getEncoding()+"\n");
props.append("Length:"+conn.getLength()+"\n");
props.append("Type:"+conn.getType()+"\n");
props.append("URL:"+conn.getURL()+"\n");
props.append("Response
Message:"+conn.getResponseMessage()+"\n");
//InputStream is=conn.openInputStream();
//DataInputStream dis=new DataInputStream(is);
//props.append("System Info:"+dis.readUTF()+"\n");
props.append("Send Mail OK!"+"\n");
}
catch(Exception fe)
{
props.append("Error:"+fe.getMessage());
}
props.addCommand(exitCommand);
props.setCommandListener(this);
display.setCurrent(props);
}
public void commandAction(Command c, Displayable s)
{
if (c == exitCommand)
{
destroyApp(false);
notifyDestroyed();
}
}
public void destroyApp(boolean unconditional)
{
}
public void pauseApp()
{
display.setCurrent(null);
props = null;
}
}
启动Tomcat 4.0、Imail 7.0.4、J2MEWTK。在J2MEWTK中运行SendMail.java程序
,
事后检查邮箱,发现已经成功的收到了邮件。
有两点需要说明一下:
首先,按照上面的模式,我们可以编写出功能更为强大的程序来,例如使用
J2ME+JDBC+JSP访问远程的数据库系统,访问EJB组件等等。
其次，如果要读取post.jsp程序的输出信息，你可以从HttpConnection接口中获取一个输入流对象，逐个读取输入流中的数据即可。具体的代码我就不举了，你可以参考J2ME
的DOC。
终于写完啦!
自从大一接触Java以来,四年了,每天不Java一下就手痒,每天不Java一下就觉得有些失落,Java已经成为我的生活的一个部分。Java给予我很多的乐趣，我想我应该为Java作些什么。四天前，当我开始接触J2ME,当我使用J2MEWTK成功运行HelloWorld程序的时候,这个念头再次浮现在我的脑海里。我应该为Java做些自己力所能及的事情,所以才会有这篇不算太长的文章
《J2ME学习札记》。不管别人的看法怎么样,我总算是了了自己的一番心事。我之所以写这篇文章，还有另一个目的,那就是将我从Java中得到乐趣与你分享,希望你也能够将你从Java中获取的乐趣写出来,与大家分享。
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