Http网络连接处理

周sir | 2015年8月5日 | 网络通讯 | 0 条评论 | 1699

这里我们将学习Android程序如何进行网络连接，获取网络返回数据，如果对HTTP网络协议还不了解的可以参考深入理解HTTP协议，在进行网络连接操作前需要先在程序的manifest文件中添加下面的permissions:

[java]
<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
[/java]

同时要检查当前网络环境是否可用

[java]
ConnectivityManager connMgr = (ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE);
NetworkInfo networkInfo = connMgr.getActiveNetworkInfo();
if (isGpsConnection() || isWiFiConnection()) {
//网络连接可用
} else {
//网络连接不可用!
}
[/java]

[java] /**
* 检查网络连接是否可用
*/
public boolean isGpsConnection(){
ConnectivityManager connMgr = (ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE);
NetworkInfo networkInfo = connMgr.getActiveNetworkInfo();
if (networkInfo != null && networkInfo.isConnected()) {
//网络连接可用
return true;
} else {
//网络连接不可用!
return false;
}
}

public boolean isWiFiConnection(Context inContext) {
Context context = inContext.getApplicationContext();
ConnectivityManager connectivity = (ConnectivityManager) context.getSystemService(Context.CONNECTIVITY_SERVICE);

if (connectivity != null) {
NetworkInfo[] info = connectivity.getAllNetworkInfo();
if (info != null) {
for (int i = 0; i < info.length; i++) {
if (info[i].getTypeName().equals("WIFI") && info[i].isConnected()) {
return true;
}
}
}
}
return false;
}
[/java]

网络操作会遇到不可预期的延迟。显然为了避免一个不好的用户体验，总是在UI Thread之外去执行网络操作。AsyncTask 类提供了一种简单的方式来处理这个问题
doInBackground()) 执行 downloadUrl()方法。Web URL作为参数，方法downloadUrl() 获取并处理网页返回的数据，执行完毕后，传递结果到onPostExecute()。参数类型为String.
onPostExecute()) 获取到返回数据并显示到UI上。

[java]private class DownloadWebpageText extends AsyncTask<String, Void, String> {
@Override
protected String doInBackground(String… urls) {

// 参数从execute()方法传入, params[0]表示url.
//获取url资源数据并返回
}

// onPostExecute方法中处理AsyncTask返回的结果
@Override
protected void onPostExecute(String result) {

}

}
[/java]

我们来看下完整的实例代码
布局文件activity_httpconnection_layout.xml

[java]<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" >

</LinearLayout>[/java]

原代码 HttpExampleActivity.java

[java]
public class HttpExampleActivity extends Activity {
private static final String DEBUG_TAG = "HttpExample";
private EditText mUrlText;
private TextView mShowMessageTxt;

@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_httpconnection_layout);
mUrlText = (EditText) findViewById(R.id.http_url_edit);
mShowMessageTxt = (TextView) findViewById(R.id.http_content_txt);
}

/**
* 用户点击此按钮时执行异步任务，在执行前需检查网络是否可用.
*
*/
public void onConnectionClickHandler(View view) {
String stringUrl = mUrlText.getText().toString();// 获取请求的URL从EditText控件中.
ConnectivityManager connMgr = (ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE);
NetworkInfo networkInfo = connMgr.getActiveNetworkInfo();
if (networkInfo != null && networkInfo.isConnected()) {
new DownloadWebpageText().execute(stringUrl);
} else {
mShowMessageTxt.setText("网络连接不可用!");
}
}

private class DownloadWebpageText extends AsyncTask<String, Void, String> {
@Override
protected String doInBackground(String… urls) {

// 参数从execute()方法传入, params[0]表示url.
try {
return downloadUrl(urls[0]);
} catch (IOException e) {
return "Unable to retrieve web page. URL may be invalid.";
}
}

// onPostExecute方法中处理AsyncTask返回的结果
@Override
protected void onPostExecute(String result) {
mShowMessageTxt.setText(result);
}

}

/**
* 根据给定的url地址，建立一个HttpUrlConnection连接它将以流的形式返回页面内容，将流转换成字符串返回
* @param myurl
* @return
* @throws IOException
*/
private String downloadUrl(String myurl) throws IOException {
InputStream is = null;

try {
URL url = new URL(myurl);
HttpURLConnection conn = (HttpURLConnection) url.openConnection();
conn.setReadTimeout(10000); /*读数据超时*/
conn.setConnectTimeout(15000);/*连接超时*/
conn.setRequestMethod("GET"); /*请求方式*/
conn.setDoInput(true);/* 设置允许输入流*/

conn.connect();
int response = conn.getResponseCode();
Log.d(DEBUG_TAG, "The response is: " + response);
is = conn.getInputStream();

String contentAsString = readIt(is);
return contentAsString;

//关闭InputStream
} finally {
if (is != null) {
is.close();
}
}
}

/**
* 将InputStream转换成String返回
* @param stream
* @return
* @throws IOException
* @throws UnsupportedEncodingException
*/
public String readIt(InputStream stream) throws IOException,UnsupportedEncodingException {
Reader reader = new InputStreamReader(stream, "UTF-8");
// 创建包装流
BufferedReader br = new BufferedReader(reader);
// 定义String类型用于储存单行数据
String line = null;
// 创建StringBuffer对象用于存储所有数据
StringBuffer sb = new StringBuffer();
while ((line = br.readLine()) != null) {
sb.append(line);
}

return sb.toString();

}

}[/java]

请注意，getResponseCode() 会返回连接状态码( status code). 这是一种获知额外网络连接信息的有效方式。status code 是 200 则意味着连接成功.

Convert the InputStream to a String(把InputStream的数据转换为String)
InputStream 是一种可读的byte数据源。如果你获得了一个 InputStream, 通常会进行decode或者转换为制定的数据类型。例如，如果你是在下载一张image数据，你可能需要像下面一下进行decode：

[java]
InputStream is = null;
…
Bitmap bitmap = BitmapFactory.decodeStream(is);
ImageView imageView = (ImageView) findViewById(R.id.image_view);
imageView.setImageBitmap(bitmap);[/java]

大多数连接网络的Android app会使用HttpURLConnection作为客户端来发送与接受数据。除此之外还可用Apache HttpClient。

[java]HttpClient httpClient = new DefaultHttpClient();
HttpGet httpGet = new HttpGet(httpUrl);
HttpResponse response = httpClient.execute(httpGet);

int statusCode = response.getStatusLine().getStatusCode();
Logs.v("statusCode >>> :" + statusCode);

if (statusCode == HttpURLConnection.HTTP_OK) {
InputStream ins = response.getEntity().getContent();

BufferedReader br = new BufferedReader(new InputStreamReader(ins,"utf-8"));

StringBuilder sb = new StringBuilder();
String line = null;
while ((line = br.readLine()) != null) {
sb.append(line);
}

}[/java]