精通android2_精通Android3笔记
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精通Android3笔记--第十一章
2011-11-30 09:12:28标签：
1、Android附带了Apache的HttpClient用于HTTP交互。
2、HttpClient Get程序
public class HttpGetDemo extends Activity {
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
BufferedReader in = null;
try {
HttpClient client = new DefaultHttpClient();
HttpGet request = new HttpGet("");
HttpResponse response = client.execute(request);
in = new BufferedReader(new InputStreamReader(response
.getEntity().getContent()));
StringBuffer sb = new StringBuffer("");
String line = "";
String NL = System.getProperty("line.separator");
while ((line = in.readLine()) != null) {
sb.append(line + NL);
}
in.close();
String page = sb.toString();
System.out.println(page);
} catch (Exception e) {
e.printStackTrace();
} finally {
if (in != null) {
try {
in.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
}
HttpClient不附加到activity上，并且应该作为一个独立的类来使用它。
2、用Get方法传递参数，URL的长度应该控制在2048个字符以内
HttpGet request = new HttpGet("?one=valueGoesHere");
client.execute(request);
3、Post方法
HttpClient client = new DefaultHttpClient();
HttpPost request = new HttpPost("");
List<NameValuePair> postParameters = new ArrayList<NameValuePair>();
postParameters.add(new BasicNameValuePair("first","param value one"));
postParameters.add(new BasicNameValuePair("issuenum", "10317"));
postParameters.add(new BasicNameValuePair("username", "dave"));
UrlEncodedFormEntity formEntity = new UrlEncodedFormEntity(postParameters);
request.setEntity(formEntity);
HttpResponse response = client.execute(request);
4、多部分POST，Android本身不支持，可以下载以下jar包
以下网站也有相应的项目
Commons IO:
Mime4j:
HttpMime: (inside of HttpClient)
多部分POST代码：
public void executeMultipartPost() throws Exception {
try {
InputStream is = this.getAssets().open("data.xml");
HttpClient httpClient = new DefaultHttpClient();
HttpPost postRequest = new HttpPost(
"");
byte[] data = IOUtils.toByteArray(is);
InputStreamBody isb = new InputStreamBody(
new ByteArrayInputStream(data), "uploadedFile");
StringBody sb1 = new StringBody("some text goes here");
StringBody sb2 = new StringBody("some text goes here too");
MultipartEntity multipartContent = new MultipartEntity();
multipartContent.addPart("uploadedFile", isb);
multipartContent.addPart("one", sb1);
multipartContent.addPart("two", sb2);
postRequest.setEntity(multipartContent);
HttpResponse response = httpClient.execute(postRequest);
response.getEntity().getContent().close();
} catch (Throwable e) {
// handle exception here
}
}
5、Android本身不支持SOAP，可从以下网站寻找相关资源：
6、Android支持JSON
7、HTTP中可能发生的异常：网络连接异常，协议异常如身份验证错误，无效的cookie等。例如，如果必须在HTTP请求中提供登录凭证但未成功，则可能看到协议异常。对于HTTP调用，超时包含两个方面：连接超时和套接字超时，其中套接字超时为HttpClient可以连接到服务器，，但是在规定时间内未接收到响应。
8、HttpClient简单的重试代码：
public class TestHttpGet {
public String executeHttpGetWithRetry() throws Exception {
int retry = 3;
int count = 0;
while (count < retry) {
count += 1;
try {
String response = executeHttpGet();
/**
* if we get here, that means we were successful and we can
* stop.
*/
return response;
} catch (Exception e) {
/**
* if we have exhausted our retry limit
*/
if (count < retry) {
/**
* we have retries remaining, so log the message and go
* again.
*/
System.out.println(e.getMessage());
} else {
System.out.println("all retries failed");
throw e;
}
}
}
return null;
}
public String executeHttpGet() throws Exception {
BufferedReader in = null;
try {
HttpClient client = new DefaultHttpClient();
HttpGet request = new HttpGet("");
HttpResponse response = client.execute(request);
in = new BufferedReader(new InputStreamReader(response
.getEntity().getContent()));
StringBuffer sb = new StringBuffer("");
String line = "";
String NL = System.getProperty("line.separator");
while ((line = in.readLine()) != null) {
sb.append(line + NL);
}
in.close();
String result = sb.toString();
return result;
} finally {
if (in != null) {
try {
in.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
9、在实际应用中，应该为整个应用程序创建一个HttpClient，并将其用于所有HTTP通信。此时就要考虑同时发出多个请求的多线程问题，Android中已经有了相关方法，即使用ThreadSafeClientConnManager创建DefaultHttpClient：
public class CustomHttpClient {
private static HttpClient customHttpClient;
/** A private Constructor prevents instantiation */
private CustomHttpClient() {
}
public static synchronized HttpClient getHttpClient() {
if (customHttpClient == null) {
HttpParams params = new BasicHttpParams();
HttpProtocolParams.setVersion(params, HttpVersion.HTTP_1_1);
HttpProtocolParams.setContentCharset(params,
HTTP.DEFAULT_CONTENT_CHARSET);
HttpProtocolParams.setUseExpectContinue(params, true);
HttpProtocolParams.setUserAgent(params,
"Mozilla/5.0 (Linux; U; Android 2.2.1; en-us; Nexus One Build/FRG83) AppleWebKit/533.1
(KHTML, like Gecko) Version/4.0 Mobile Safari/533.1"
);
ConnManagerParams.setTimeout(params, 1000);
HttpConnectionParams.setConnectionTimeout(params, 5000);
HttpConnectionParams.setSoTimeout(params, 10000);
SchemeRegistry schReg = new SchemeRegistry();
schReg.register(new Scheme("http",
PlainSocketFactory.getSocketFactory(), 80));
schReg.register(new Scheme("https",
SSLSocketFactory.getSocketFactory(), 443));
ClientConnectionManager conMgr = new
ThreadSafeClientConnManager(params,schReg);
customHttpClient = new DefaultHttpClient(conMgr, params);
}
return customHttpClient;
}
public Object clone() throws CloneNotSupportedException {
throw new CloneNotSupportedException();
}
}
10、AsyncTask：如果主线程没有在5秒内处理完某个事件，将触发ANR（应用程序未响应）条件，影响用户体验。如果用户只是希望简单计算，无需更新用户界面，则可以使用简单的Thread对象来从主线程转移一些处理工作，但是此技术不适用于对用户界面施行更新，因为Android用户界面工具包不是线程安全的，所以它应该始终只从主线程更新。如果希望从后台线程以任何方式更新用户界面，应该认真考虑使用AsyncTask。AsyncTask负责创建一个后台线程来完成工作，提供将在主线程上运行的回调函数来实现对用户界面元素的访问。回调可在后台线程运行之前、期间、之后触发。
11、
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本文关键词：精通Android3，由笔耕文化传播整理发布。
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