面试篇--android下网络通讯机制（三种网络通讯方式）

HttpClient

HttpClient是Apache对java中的HttpURLClient接口的封装，主要引用org.apache.http.**。Google在2.3版本之前推荐使用HttpClient，因为这个封装包安全性高，bug较少。

使用方法：

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.List;
import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.HttpStatus;
import org.apache.http.NameValuePair;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.HttpClient;
import org.apache.http.client.entity.UrlEncodedFormEntity;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.impl.client.DefaultHttpClient;
import org.apache.http.message.BasicNameValuePair;

public class HttpClientUtils {
private static HttpClient httpClient;
private static HttpClientUtils instance = null;

public static synchronized HttpClientUtils getInstance() {
if (instance == null) {
instance = new HttpClientUtils();
}
return instance;
}

private HttpClientUtils() {
// 学习volley请求队列，HttpClient使用单例模式
if (httpClient == null) {
httpClient = new DefaultHttpClient();
}
}
/**
* 以get方式发送请求，访问接口
* @param uri链接地址
* @return 响应数据
*/
private static String doHttpGet(String uri) {
BufferedReader reader = null;
StringBuffer sb = null;
String result = "";
HttpGet request = new HttpGet(uri);
try {
// 发送请求，得到响应
HttpResponse response = httpClient.execute(request);
// 请求成功，statuscode返回200
if (response.getStatusLine().getStatusCode() == HttpStatus.SC_OK) {
reader = new BufferedReader(new InputStreamReader(response.getEntity().getContent()));
sb = new StringBuffer();
String line = "";
while ((line = reader.readLine()) != null) {
sb.append(line);
}
}
} catch (ClientProtocolException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} finally {
try {
if (null != reader) {
reader.close();
reader = null;
}
} catch (IOException e) {
e.printStackTrace();
}
}
if (null != sb) {
result = sb.toString();
}
return result;
}

/**
* 以post方式发送请求，访问接口
* @param uri链接地址
* @return 响应数据
*/
private static String doHttpPost(String uri) {
BufferedReader reader = null;
StringBuffer sb = null;
String result = "";
HttpPost request = new HttpPost(uri);

// 保存要传递的参数
List<NameValuePair> params = new ArrayList<NameValuePair>();
// 添加参数
params.add(new BasicNameValuePair("parameter", "以Post方式发送请求"));

try {
// 设置字符集
HttpEntity entity = new UrlEncodedFormEntity(params, "utf-8");
// 请求对象
request.setEntity(entity);
// 发送请求
HttpResponse response = httpClient.execute(request);
// 请求成功
if (response.getStatusLine().getStatusCode() == HttpStatus.SC_OK) {
System.out.println("post success");
reader = new BufferedReader(new InputStreamReader(response.getEntity().getContent()));
sb = new StringBuffer();
String line = "";
while ((line = reader.readLine()) != null) {
sb.append(line);
}
}
} catch (ClientProtocolException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} finally {
try {
// 关闭流
if (null != reader) {
reader.close();
reader = null;
}
} catch (IOException e) {
e.printStackTrace();
}
}
if (null != sb) {
result = sb.toString();
}
return result;
}

}

HttpURLConnection

HttpURLConnection在java.NET下，继承自URLConnection类，相对于HttpClient具有扩展性高、灵活性高，更轻量级的优点，所以Google在2.3版本之后推荐大家使用HttpURLConnection来操作网络请求。

使用方法：

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.ObjectOutputStream;
import java.io.OutputStream;
import java.net.HttpURLConnection;
import java.net.URL;
import java.net.URLEncoder;

public class HttpURLConnectUtils {

private static HttpURLConnectUtils instance = null;

public static synchronized HttpURLConnectUtils getInstance() {
if (instance == null) {
instance = new HttpURLConnectUtils();
}
return instance;
}

private HttpURLConnectUtils() {
}

// post
public String dohttppost(String mUrl) throws IOException {

URL url = new URL(mUrl);
HttpURLConnection httpURLConnection = (HttpURLConnection) url.openConnection();//初始化创建HttpURLConnection实例
httpURLConnection.setConnectTimeout(5000);//推荐设置网络延时
httpURLConnection.setDoOutput(true);
httpURLConnection.setDoInput(true);
httpURLConnection.setUseCaches(false);
httpURLConnection.setRequestProperty("Content-type", "application/x-java-serialized-object");
httpURLConnection.setRequestMethod("POST");
//设置参数
OutputStream outputStream = httpURLConnection.getOutputStream();
ObjectOutputStream objectOutputStream = new ObjectOutputStream(outputStream);
String params = new String();//这里简单设置参数
params = "name=" + URLEncoder.encode("高冉", "GBK");
objectOutputStream.writeBytes(params);
objectOutputStream.flush();
objectOutputStream.close();
//接收返回值
//String msg = httpURLConnection.getResponseMessage();// 接收简单string
InputStreamReader inputStreamReader = new InputStreamReader(httpURLConnection.getInputStream());
BufferedReader bufferedReader = new BufferedReader(inputStreamReader);
StringBuilder builder = new StringBuilder();
for (String s = bufferedReader.readLine(); s != null; s = bufferedReader.readLine()) {
builder.append(s);
}
return builder.toString();
}

// get
public String dohttpget(String mUrl) throws IOException {
URL url = new URL(mUrl);
HttpURLConnection httpURLConnection = (HttpURLConnection) url.openConnection();
httpURLConnection.setConnectTimeout(5000);//推荐设置网络延时
httpURLConnection.setRequestMethod("GET");
httpURLConnection.connect();

// String msg = httpURLConnection.getResponseMessage();

InputStreamReader inputStreamReader = new InputStreamReader(httpURLConnection.getInputStream());
BufferedReader bufferedReader = new BufferedReader(inputStreamReader);
StringBuilder builder = new StringBuilder();
for (String s = bufferedReader.readLine(); s != null; s = bufferedReader.readLine()) {
builder.append(s);
}

return builder.toString();
}
}

还需要注意一些细节：

1、post与get区别在于post将参数置于请求数据中，get则跟在url链接后面。

2、大文件下载操作要置于sd卡中，不要放在手机内存中操作，而且需要边读边写，不要使用Buffered做缓存。

三、我们看一个简单的socket编程，实现服务器回发客户端信息。

下面用个例子来说明：

A、客户端：

新建Android项目工程：SocketForAndroid（这个随意起名字了吧，我是以这个建立的！）

下面是main_activity.xml的代码：

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MainActivity.java的代码入下：

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最后别忘记添加访问网络权限：

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

B、服务端：

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C、启动服务器，控制台会打印出“start...”字符串！

D、运行Android项目文件，如下图：



在输入框里输入如下字符串，点发送按钮：



服务器收到客户端发来的消息并打印到控制台：