downloadmidlet.java

J2ME 无线通信技术应用开发源代码

//程序名DownloadMIDlet.java，项目DownloadMIDlet
//一个通过HTTP方式从网络下载图象的综合例子，并利用存储系统对图象进行管理
import javax.microedition.midlet.*;
import javax.microedition.lcdui.*;
import javax.microedition.rms.*;

public class DownloadMIDlet extends MIDlet implements CommandListener{
  Display display = null;

  static final String rsName = "MyPicture";
  static final Command downCmd = new Command("下载", Command.SCREEN, 1);
  static final Command viewCmd = new Command("查看", Command.SCREEN, 1);
  static final Command deleteCmd = new Command("删除", Command.SCREEN, 1);
  static final Command deleteAllCmd = new Command("删除全部", Command.SCREEN, 1);
  static final Command exitCmd = new Command("退出", Command.SCREEN, 1);
  static final Command returnCmd = new Command("返回", Command.SCREEN, 1);
  TextField uriField = new TextField("图象地址:", "", 100, TextField.URL);
  TextField nameField = new TextField("保存名称:", "", 15, TextField.ANY);
  String uri;
  String[] picNames;
  String picName;
  Image listIcon;
  Image[] listIcons;
  RecordStore rs;

  List viewList;
  Form downloadForm;

  public DownloadMIDlet() {
  	try {
  		listIcon = Image.createImage("/listIcon.png");
  	} catch (Exception e) {
  	}
    display = Display.getDisplay(this);
  }

	public void startApp() {
		getPicNames();
		viewList = new List("浏览下载的图片",List.IMPLICIT,picNames,listIcons);
		viewList.addCommand(downCmd);
		viewList.addCommand(viewCmd);
		viewList.addCommand(deleteCmd);
		viewList.addCommand(deleteAllCmd);
		viewList.addCommand(exitCmd);
    viewList.setCommandListener(this);
    
    downloadForm = new Form("下载图片");
    downloadForm.append(uriField);
    downloadForm.append(nameField);
    downloadForm.addCommand(downCmd);
    downloadForm.addCommand(returnCmd);
    downloadForm.setCommandListener(this);

    display.setCurrent(viewList);
	}
  
	public void pauseApp() {
	}

	public void destroyApp( boolean unconditional ) {
	}
	
	public void getPicNames() {
		try {
			rs= RecordStore.openRecordStore(rsName, true);
			int numOfPic = rs.getNumRecords()/2;
			picNames = new String[numOfPic];
			listIcons = new Image[numOfPic];
			for (int i = 0;i<numOfPic;i++) {
				picNames[i] = new String(rs.getRecord(2*i+1));
				listIcons[i] = listIcon;
			}
		} catch (Exception e) {
		}
	}

	public void viewImage(int n) {
    try {
    	//rs中的数据结构为：图象名1->图象1->图象名2->图象2->...
			byte[] imageBytes = rs.getRecord(2*(n+1));
			Image image = Image.createImage(imageBytes,0,imageBytes.length);
			Alert alert = new Alert(picNames[n],null, image, AlertType.INFO);
			alert.setTimeout(Alert.FOREVER);
			display.setCurrent(alert,viewList);
    } catch( Exception e ){
			Alert alert = new Alert(picNames[n],"读取图象时发生错误，请重新下载！",null, AlertType.INFO);
			alert.setTimeout(Alert.FOREVER);
			display.setCurrent(alert,viewList);
    }
	}
	
	public void deletePic(int n) {
		Alert alert = new Alert("发生错误","此功能还未完成，请读者实现！",null, AlertType.ERROR);
		alert.setTimeout(Alert.FOREVER);
		display.setCurrent(alert,viewList);
	}

	public void deleteAll() {
		while (true) {
			try {
   			rs.closeRecordStore();
    	} catch(RecordStoreNotOpenException e ){
    		break;
    	} catch(RecordStoreException e ){
    	}
    }

    try {
    	RecordStore.deleteRecordStore(rsName);
			rs= RecordStore.openRecordStore(rsName, true);
      picNames = null;
      int nums = viewList.size();
			while(nums-->0) {
				viewList.delete(nums);
			}
    } catch( Exception e ){
    }
	}

	public void startDownload() {
 		uri = uriField.getString();
   	picName = nameField.getString();
   	if (uri == null | picName == null | uri.equals("") | picName.equals("")) {
			Alert alert = new Alert("发生错误","URL或保存图象名不能为空！",null, AlertType.ERROR);
			alert.setTimeout(Alert.FOREVER);
			display.setCurrent(alert,downloadForm);
   	} else {
   		Thread downloadThread = new DownloadThread(this,uri,picName);
   		downloadThread.start();
   	}
	}

  public void commandAction(Command c, Displayable d) {
    if(c == exitCmd) {
   		destroyApp(true);
   		notifyDestroyed();
    } else if (c == returnCmd){
    	display.setCurrent(viewList);
    } else if (c == deleteAllCmd) {
     	deleteAll();
    } else if (c == deleteCmd) {
     	deletePic(viewList.getSelectedIndex());
    } else if (c == downCmd) {
    	if (d == viewList) {
    		display.setCurrent(downloadForm);
     	} else {
     		startDownload();
      }
    } else if (c == List.SELECT_COMMAND | c == viewCmd) {
     	viewImage(viewList.getSelectedIndex());
    }
  }
}