J2ME 文件下载实例 jar包为例
package com.wanchong;
/**
* 作者：万冲
* QQ：569845790
* Mail:wanchong998@qq.com
*/
import javax.microedition.lcdui.Display;
import javax.microedition.midlet.MIDlet;
import javax.microedition.midlet.MIDletStateChangeException;

public class DMIDlet extends MIDlet{

protected void destroyApp(boolean arg0) throws MIDletStateChangeException {
// TODO Auto-generated method stub

}

protected void pauseApp() {
// TODO Auto-generated method stub

}

protected void startApp() throws MIDletStateChangeException {
// TODO Auto-generated method stub
Display.getDisplay(this).setCurrent(new DCanvas());
}

}



package com.wanchong;
/**
* 作者：万冲
* QQ：569845790
* Mail:wanchong998@qq.com
*/
import java.io.ByteArrayOutputStream;
import java.io.InputStream;
import java.io.OutputStream;
import java.util.Enumeration;
import java.util.Vector;

import javax.microedition.io.Connector;
import javax.microedition.io.HttpConnection;
import javax.microedition.io.file.FileConnection;
import javax.microedition.io.file.FileSystemRegistry;
import javax.microedition.lcdui.Canvas;
import javax.microedition.lcdui.Graphics;
import javax.microedition.lcdui.Image;

public class DCanvas extends Canvas implements Runnable{



Image image;

public DCanvas()
{
setFullScreenMode(true);
repaint();
//启动下载线程
new Thread(this).start();
}
String downFilecon=null;

protected void paint(Graphics g) {
// TODO Auto-generated method stub
g.setColor(0x0);
g.fillRect(0, 0, getWidth(), getHeight());
g.setColor(0xff0000);
g.drawString("正在下载中....", 0, 0, 0);
if(downFilecon!=null){
g.setColor(0xff0000);
g.drawString(downFilecon, 50, 50, 0);
}
}


public void run() {
// TODO Auto-generated method stub
try {
connect();
} catch (Exception e) {
e.printStackTrace();
}

}

String url = "http://www.xxx.com/wandown/wan_down_test.jar";
public void connect() throws Exception
{
HttpConnection http = null;
InputStream is = null;
OutputStream os = null;
byte[] data = null;
try
{
http = getHttpConnection(url);

int code = http.getResponseCode();
// 返回200 表示连接成功
if (code == HttpConnection.HTTP_OK)
{
is = http.openInputStream();
ByteArrayOutputStream baos = new ByteArrayOutputStream();
int ch = -1;
while ((ch = is.read()) != -1) {
baos.write(ch);
//System.out.println(ch);
}
data = baos.toByteArray();

}
else
{
System.out.println("网络连接错误");
}
//下载图片数据完成后创建图片
if(data != null)
{



// image = Image.createImage(data, 0, data.length);
//repaint();//重绘


int t = this.saveFile("file://localhosst/root1/wanchong.jar",data, true);
downFilecon = "下载完成！";

}

}
finally
{
if(os != null)
{
os.close();
os = null;
}

if(is != null)
{
is.close();
is = null;
}
if(http != null)
{
http.close();
http = null;
}
}
}


/**
* 取得一个URL的连接
* @param url
* @return
* @throws Exception
*/
private HttpConnection getHttpConnection(String url) throws Exception
{
HttpConnection http = (HttpConnection) Connector.open(url);
http.setRequestProperty("Content-Type", "application/octet-stream");//get
http.setRequestMethod(HttpConnection.GET);

return http;
}
/**
* 保存文件　
* @param path　　　 文件路径
* @param fileData　文件数据
* @param overrite　是否要强制覆盖
* @return 1:成功写入文件　-1:文件已经存在没有重写　0:写入文件时出错
*
*/
public int saveFile(String path, byte[] fileData, boolean overrite) {
try {

FileConnection fc = (FileConnection) (Connector.open(path));

if (fc.exists()) {
if (overrite) {
fc.delete(); //如果文件已经存在，先删除
fc.create();
fc.setWritable(true);
OutputStream os = fc.openOutputStream();
os.write(fileData,0,fileData.length);
os.close();
return 1;
} else
return -1;
} else {
fc.create();
fc.setWritable(true);
OutputStream os = fc.openOutputStream();
os.write(fileData,0,fileData.length);
os.close();
return 1;
}
} catch (Exception e) {
System.out.println("saveFileErr:" + e.getMessage());
e.printStackTrace();
return 0;
}
}
/**
* 获取路径
* @return
*/
    public String[] DeviceGetRoots() {
        Enumeration enumRoot = FileSystemRegistry.listRoots();// 返回根目录组成的序列
        Vector list = new Vector();
        while (enumRoot.hasMoreElements()) {
            list.addElement(enumRoot.nextElement());
        }

        String[] ret = null;
        if (list.size() > 0) {
            ret = new String[list.size()];
            for (int i = 0; i < list.size(); i++) {
                ret[i] = (String) list.elementAt(i);
            }
        }
        return ret;
    }

}