采用HttpURLConnection
HttpURLConnection从继承URLConnection，它也可以被用来发送到指定的网站GET求
POST求。
办法：
int getResponseCode ():
获取server的响应代码
String getResponseMessage ():
获取server的响应消息
String getResponseMethod ():
获取发送请求的方法
void setRequestMethod ():
设置发送请求的方法
多线程下载
步骤：
1.创建URL对象
2.获取指定URL对象所指向资源的大小 由getContentLength()实现
3.在本地磁盘上创建一个与网络资源同样大小的空文件
4.计算每条线程应该下载网络资源的那个部分（从哪个字节開始，到哪个字节结束）
5.依次创建、启动多条线程来下载网络资源的指定部分。
下载工具类：
public class DownUtil
{
// 定义下载资源的路径
private String path;
// 指定所下载的文件的保存位置
private String targetFile;
// 定义须要使用多少线程下载资源
private int threadNum;
// 定义下载的线程对象
private DownThread[] threads;
// 定义下载的文件的总大小
private int fileSize; public DownUtil(String path, String targetFile, int threadNum)
{
this.path = path;
this.threadNum = threadNum;
// 初始化threads数组
threads = new DownThread[threadNum];
this.targetFile = targetFile;
} public void download() throws Exception
{
URL url = new URL(path);
HttpURLConnection conn = (HttpURLConnection) url.openConnection();
conn.setConnectTimeout(5 * 1000);
conn.setRequestMethod("GET");
conn.setRequestProperty(
"Accept",
"image/gif, image/jpeg, image/pjpeg, image/pjpeg, "
+ "application/x-shockwave-flash, application/xaml+xml, "
+ "application/vnd.ms-xpsdocument, application/x-ms-xbap, "
+ "application/x-ms-application, application/vnd.ms-excel, "
+ "application/vnd.ms-powerpoint, application/msword, */*");
conn.setRequestProperty("Accept-Language", "zh-CN");
conn.setRequestProperty("Charset", "UTF-8");
conn.setRequestProperty("Connection", "Keep-Alive");
// 得到文件大小
fileSize = conn.getContentLength();
conn.disconnect();
int currentPartSize = fileSize / threadNum + 1;
RandomAccessFile file = new RandomAccessFile(targetFile, "rw");
// 设置本地文件的大小
file.setLength(fileSize);
file.close();
for (int i = 0; i < threadNum; i++)
{
// 计算每条线程的下载的開始位置
int startPos = i * currentPartSize;
// 每一个线程使用一个RandomAccessFile进行下载
RandomAccessFile currentPart = new RandomAccessFile(targetFile,
"rw");
// 定位该线程的下载位置
currentPart.seek(startPos);
// 创建下载线程
threads[i] = new DownThread(startPos, currentPartSize,
currentPart);
// 启动下载线程
threads[i].start();
}
} // 获取下载的完毕百分比
public double getCompleteRate()
{
// 统计多条线程已经下载的总大小
int sumSize = 0;
for (int i = 0; i < threadNum; i++)
{
sumSize += threads[i].length;
}
// 返回已经完毕的百分比
return sumSize * 1.0 / fileSize;
} private class DownThread extends Thread
{
// 当前线程的下载位置
private int startPos;
// 定义当前线程负责下载的文件大小
private int currentPartSize;
// 当前线程须要下载的文件块
private RandomAccessFile currentPart;
// 定义已经该线程已下载的字节数
public int length; public DownThread(int startPos, int currentPartSize,
RandomAccessFile currentPart)
{
this.startPos = startPos;
this.currentPartSize = currentPartSize;
this.currentPart = currentPart;
} @Override
public void run()
{
try
{
URL url = new URL(path);
HttpURLConnection conn = (HttpURLConnection)url
.openConnection();
conn.setConnectTimeout(5 * 1000);
conn.setRequestMethod("GET");
conn.setRequestProperty(
"Accept",
"image/gif, image/jpeg, image/pjpeg, image/pjpeg, "
+ "application/x-shockwave-flash, application/xaml+xml, "
+ "application/vnd.ms-xpsdocument, application/x-ms-xbap, "
+ "application/x-ms-application, application/vnd.ms-excel, "
+ "application/vnd.ms-powerpoint, application/msword, */*");
conn.setRequestProperty("Accept-Language", "zh-CN");
conn.setRequestProperty("Charset", "UTF-8");
InputStream inStream = conn.getInputStream();
// 跳过startPos个字节，表明该线程仅仅下载自己负责哪部分文件。
inStream.skip(this.startPos);
byte[] buffer = new byte[1024];
int hasRead = 0;
// 读取网络数据，并写入本地文件
while (length < currentPartSize
&& (hasRead = inStream.read(buffer)) > 0)
{
currentPart.write(buffer, 0, hasRead);
// 累计该线程下载的总大小
length += hasRead;
}
currentPart.close();
inStream.close();
}
catch (Exception e)
{
e.printStackTrace();
}
}
}
}
Activity：
public class MainActivity extends Activity {
EditText url;
EditText target;
Button downButton;
ProgressBar bar;
DownUtil downUtil;
private int mDownStatus;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
url = (EditText) findViewById(R.id.url);
target = (EditText) findViewById(R.id.target);
downButton = (Button) findViewById(R.id.down);
bar = (ProgressBar) findViewById(R.id.bar);
final Handler handler = new Handler() {
@Override
public void handleMessage(Message msg) {
if (msg.what == 0x123) {
bar.setProgress(mDownStatus);
}
}
};
downButton.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
downUtil = new DownUtil(url.getText().toString(), target
.getText().toString(), 6);
new Thread() {
public void run() {
try {
downUtil.download();
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
final Timer timer = new Timer();
timer.schedule(new TimerTask() {
@Override
public void run() {
// 获取下载任务的完毕比率
double completeRate = downUtil
.getCompleteRate();
mDownStatus = (int) (completeRate * 100);
// 发送消息通知界面更新进度条
handler.sendEmptyMessage(0x123);
// 下载全然后取消任务调度
if (mDownStatus >= 100) {
timer.cancel();
}
}
}, 0, 100);
};
}.start();
}
});
}
}
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