Android与Internet(获取资源，多线程断点下载，get/post发送，发送xml)

从Internet获取数据

 

利用HttpURLConnection对象,我们可以从网络中获取网页数据.

URL url = new URL("http://www.sohu.com");

HttpURLConnection conn = (HttpURLConnection) url.openConnection();

conn.setConnectTimeout(5* 1000);//设置连接超时

conn.setRequestMethod(“GET”);//以get方式发起请求

if (conn.getResponseCode() != 200) throw new RuntimeException("请求url失败");

InputStream is = conn.getInputStream();//得到网络返回的输入流

String result = readData(is, "GBK");

conn.disconnect();

//第一个参数为输入流,第二个参数为字符集编码

public static String readData(InputStream inSream, String charsetName) throws Exception{

ByteArrayOutputStream outStream = new ByteArrayOutputStream();

byte[] buffer = new byte[1024];

int len = -1;

while( (len = inSream.read(buffer)) != -1 ){

outStream.write(buffer, 0, len);

}

byte[] data = outStream.toByteArray();

outStream.close();

inSream.close();

return new String(data, charsetName);

}

<!-- 访问internet权限 -->

<uses-permission android:name="android.permission.INTERNET"/>

利用HttpURLConnection对象,我们可以从网络中获取文件数据.

URL url = new URL("http://photocdn.sohu.com/20100125/Img269812337.jpg");

HttpURLConnection conn = (HttpURLConnection) url.openConnection();

conn.setConnectTimeout(5* 1000);

conn.setRequestMethod("GET");

if (conn.getResponseCode() != 200) throw new RuntimeException("请求url失败");

InputStream is = conn.getInputStream();

readAsFile(is, "Img269812337.jpg"); 

public static void readAsFile(InputStream inSream, File file) throws Exception{

FileOutputStream outStream = new FileOutputStream(file);

byte[] buffer = new byte[1024];

int len = -1;

while( (len = inSream.read(buffer)) != -1 ){

outStream.write(buffer, 0, len);

}

  outStream.close();

inSream.close();

}

多线程下载

 

使用多线程下载文件可以更快完成文件的下载，多线程下载文件之所以快，是因为其抢占的服务器资源多。如：假设服务器同时最多服务100个用户，在服务器中一条线程对应一个用户，100条线程在计算机中并非并发执行，而是由CPU划分时间片轮流执行，如果A应用使用了99条线程下载文件，那么相当于占用了99个用户的资源，假设一秒内CPU分配给每条线程的平均执行时间是10ms，A应用在服务器中一秒内就得到了990ms的执行时间，而其他应用在一秒内只有10ms的执行时间。就如同一个水龙头，每秒出水量相等的情况下，放990毫秒的水

肯定比放10毫秒的水要多。

多线程下载的实现过程：

1>首先得到下载文件的长度，然后设置本地文件

的长度。

HttpURLConnection.getContentLength();

RandomAccessFile file = new RandomAccessFile("QQWubiSetup.exe","rw");

file.setLength(filesize);//设置本地文件的长度

2>根据文件长度和线程数计算每条线程下载的数据长度和下载位置。如：文件的长度为6M，线程数为3，那么，每条线程下载的数据长度为2M，每条线程开始下载的位置如上图所示。

3>使用Http的Range头字段指定每条线程从文件的什么位置开始下载，如：指定从文件的2M位置开始下载文件，代码如下：

HttpURLConnection.setRequestProperty("Range", "bytes=2097152-");

4>保存文件，使用RandomAccessFile类指定每条线程从本地文件的什么位置开始写入数据。

RandomAccessFile threadfile = new RandomAccessFile("QQWubiSetup.exe ","rw");

threadfile.seek(2097152);//从文件的什么位置开始写入数据

向Internet发送请求参数

利用HttpURLConnection对象,我们可以向网络发送请求参数.

String requestUrl = "http://localhost:8080/itcast/contanctmanage.do";

Map<String, String> requestParams = new HashMap<String, String>();

requestParams.put("age", "12");

requestParams.put("name", "中国");

 StringBuilder params = new StringBuilder();

for(Map.Entry<String, String> entry : requestParams.entrySet()){

params.append(entry.getKey());

params.append("=");

params.append(URLEncoder.encode(entry.getValue(), "UTF-8"));

params.append("&");

}

if (params.length() > 0) params.deleteCharAt(params.length() - 1);

byte[] data = params.toString().getBytes();

URL realUrl = new URL(requestUrl);

HttpURLConnection conn = (HttpURLConnection) realUrl.openConnection();

conn.setDoOutput(true);//发送POST请求必须设置允许输出

conn.setUseCaches(false);//不使用Cache

conn.setRequestMethod("POST");        

conn.setRequestProperty("Connection", "Keep-Alive");//维持长连接

conn.setRequestProperty("Charset", "UTF-8");

conn.setRequestProperty("Content-Length", String.valueOf(data.length));

conn.setRequestProperty("Content-Type","application/x-www-form-urlencoded");

DataOutputStream outStream = new DataOutputStream(conn.getOutputStream());

outStream.write(data);

outStream.flush();

if( conn.getResponseCode() == 200 ){

        String result = readAsString(conn.getInputStream(), "UTF-8");

        outStream.close();

        System.out.println(result);

}

向Internet发送xml数据

利用HttpURLConnection对象,我们可以向网络发送请求参数.

String requestUrl = "http://localhost:8080/itcast/contanctmanage.do";

Map<String, String> requestParams = new HashMap<String, String>();

requestParams.put("age", "12");

requestParams.put("name", "中国");

 StringBuilder params = new StringBuilder();

for(Map.Entry<String, String> entry : requestParams.entrySet()){

params.append(entry.getKey());

params.append("=");

params.append(URLEncoder.encode(entry.getValue(), "UTF-8"));

params.append("&");

}

if (params.length() > 0) params.deleteCharAt(params.length() - 1);

byte[] data = params.toString().getBytes();

URL realUrl = new URL(requestUrl);

HttpURLConnection conn = (HttpURLConnection) realUrl.openConnection();

conn.setDoOutput(true);//发送POST请求必须设置允许输出

conn.setUseCaches(false);//不使用Cache

conn.setRequestMethod("POST");        

conn.setRequestProperty("Connection", "Keep-Alive");//维持长连接

conn.setRequestProperty("Charset", "UTF-8");

conn.setRequestProperty("Content-Length", String.valueOf(data.length));

conn.setRequestProperty("Content-Type","application/x-www-form-urlencoded");

DataOutputStream outStream = new DataOutputStream(conn.getOutputStream());

outStream.write(data);

outStream.flush();

if( conn.getResponseCode() == 200 ){

        String result = readAsString(conn.getInputStream(), "UTF-8");

        outStream.close();

        System.out.println(result);

}

向Internet发送xml数据

利用HttpURLConnection对象,我们可以向网络发送xml数据.

StringBuilder xml =  new StringBuilder();

xml.append("<?xml version=\"1.0\" encoding=\"utf-8\" ?>");

xml.append("<M1 V=10000>");

xml.append("<U I=1 D=\"N73\">中国</U>");

xml.append("</M1>");

byte[] xmlbyte = xml.toString().getBytes("UTF-8");

URL url = new URL("http://localhost:8080/itcast/contanctmanage.do?method=readxml");

HttpURLConnection conn = (HttpURLConnection) url.openConnection();

conn.setConnectTimeout(5* 1000);

conn.setDoOutput(true);//允许输出

conn.setUseCaches(false);//不使用Cache

conn.setRequestMethod("POST");        

conn.setRequestProperty("Connection", "Keep-Alive");//维持长连接

conn.setRequestProperty("Charset", "UTF-8");

conn.setRequestProperty("Content-Length", String.valueOf(xmlbyte.length));

conn.setRequestProperty("Content-Type", "text/xml; charset=UTF-8");

DataOutputStream outStream = new DataOutputStream(conn.getOutputStream());

outStream.write(xmlbyte);//发送xml数据

outStream.flush();

if (conn.getResponseCode() != 200) throw new RuntimeException("请求url失败");

InputStream is = conn.getInputStream();//获取返回数据

String result = readAsString(is, "UTF-8");

outStream.close();

评论

1 楼 yiersanxuexi 2013-04-01  

LZ，请教下，你这样的频繁操作数据库，下载速度应该很受限制吧？