Android网络(4):HttpClient必经之路----使用线程安全的单例模式HttpClient，及HttpClient和Application的融合

上文简单介绍了HttpClient和Tomcat服务器的交互，主角是HttpClient,然后它跟服务器交互有两种方式即get和post。所以这个HttpClient就类似于电脑上用的浏览器。当我打开多个网页的时候，并不需要开一个网页就开一个浏览器，而是一个浏览器上面开了好几个网页。对应于HttpClient，即无需连接一次就new一个HttpClient。一般，我们希望一个应用里就一个HttpClient就ok了，就像我们的手机或PC，没人会呼呼的装好几个浏览器。本文即解决此问题，代码可以直接拿过去复用。

1、自然而然想到单例。

public class MyHttpClient {
private static HttpClient mHttpClient = null;
private static final String CHARSET = HTTP.UTF_8;
//将构造函数封掉，只能通过对外接口来获取HttpClient实例
private MyHttpClient(){


}
public static HttpClient getHttpClient(){
if(mHttpClient == null){
mHttpClient = new DefaultHttpClient();
}
return mHttpClient;
}
}

上面是最简单的一种单例，确实能够满足需要。但不能满足多线程的要求，即当同时完成多个Http请求时，就出马蛋了。

2、线程安全的HttpClient

幸运的是android已经提供了可以创建线程安全的HttpClient，即通过ClientConnectionManager 来完成。下面贴出完整代码：

package org.yanzi.webutil;

import org.apache.http.HttpVersion;
import org.apache.http.client.HttpClient;
import org.apache.http.conn.ClientConnectionManager;
import org.apache.http.conn.params.ConnManagerParams;
import org.apache.http.conn.scheme.PlainSocketFactory;
import org.apache.http.conn.scheme.Scheme;
import org.apache.http.conn.scheme.SchemeRegistry;
import org.apache.http.conn.ssl.SSLSocketFactory;
import org.apache.http.impl.client.DefaultHttpClient;
import org.apache.http.impl.conn.tsccm.ThreadSafeClientConnManager;
import org.apache.http.params.BasicHttpParams;
import org.apache.http.params.HttpConnectionParams;
import org.apache.http.params.HttpParams;
import org.apache.http.params.HttpProtocolParams;
import org.apache.http.protocol.HTTP;

public class MyHttpClient {
	private static HttpClient mHttpClient = null;
	private static final String CHARSET = HTTP.UTF_8;
	//将构造函数封掉，只能通过对外接口来获取HttpClient实例
	private MyHttpClient(){

	}
	public static HttpClient getHttpClient(){
		if(mHttpClient == null){
			mHttpClient = new DefaultHttpClient();
		}
		return mHttpClient;
	}
	public static synchronized HttpClient getSaveHttpClient(){
		if(mHttpClient == null){
			HttpParams params = new BasicHttpParams();
			//设置基本参数
			HttpProtocolParams.setVersion(params, HttpVersion.HTTP_1_1);
			HttpProtocolParams.setContentCharset(params, CHARSET);
			HttpProtocolParams.setUseExpectContinue(params, true);
			//超时设置
			/*从连接池中取连接的超时时间*/
			ConnManagerParams.setTimeout(params, 1000);
			/*连接超时*/
			HttpConnectionParams.setConnectionTimeout(params, 2000);
			/*请求超时*/
			HttpConnectionParams.setSoTimeout(params, 4000);
			//设置HttpClient支持HTTp和HTTPS两种模式
			SchemeRegistry schReg = new SchemeRegistry();
			schReg.register(new Scheme("http", PlainSocketFactory.getSocketFactory(), 80));
			schReg.register(new Scheme("https", SSLSocketFactory.getSocketFactory(), 443));
			//使用线程安全的连接管理来创建HttpClient
			ClientConnectionManager conMgr = new ThreadSafeClientConnManager(params, schReg);
			mHttpClient = new DefaultHttpClient(conMgr, params);
		}
		return mHttpClient;
	}
	
}

方法getSaveHttpClient()即可获得线程安全的单例httpClient，注释很详细了啥都不说了，可以直接使用。

3、已经很完美了，还能不能再优化呢? 

可以使用Application来进一步优化创建HttpClient的时机及其他配置。Application的相关知识参见:链接 

新建包名org.yanzi.application，在里面新建MyApplication.java，完整代码如下:

package org.yanzi.application;

import org.apache.http.HttpVersion;
import org.apache.http.client.HttpClient;
import org.apache.http.conn.ClientConnectionManager;
import org.apache.http.conn.params.ConnManagerParams;
import org.apache.http.conn.scheme.PlainSocketFactory;
import org.apache.http.conn.scheme.Scheme;
import org.apache.http.conn.scheme.SchemeRegistry;
import org.apache.http.conn.ssl.SSLSocketFactory;
import org.apache.http.impl.client.DefaultHttpClient;
import org.apache.http.impl.conn.tsccm.ThreadSafeClientConnManager;
import org.apache.http.params.BasicHttpParams;
import org.apache.http.params.HttpConnectionParams;
import org.apache.http.params.HttpParams;
import org.apache.http.params.HttpProtocolParams;
import org.apache.http.protocol.HTTP;

import android.app.Application;

public class MyApplication extends Application {
	private HttpClient mHttpClient = null;
	private static final String CHARSET = HTTP.UTF_8;
	@Override
	public void onCreate() {
		// TODO Auto-generated method stub
		super.onCreate();
		mHttpClient = this.createHttpClient();
	}

	@Override
	public void onTerminate() {
		// TODO Auto-generated method stub
		super.onTerminate();
		this.shutdownHttpClient();
	}

	@Override
	public void onLowMemory() {
		// TODO Auto-generated method stub
		super.onLowMemory();
		this.shutdownHttpClient();
	}
	
	/**创建HttpClient实例
	 * @return
	 */
	private HttpClient createHttpClient(){
		HttpParams params = new BasicHttpParams();
		//设置基本参数
		HttpProtocolParams.setVersion(params, HttpVersion.HTTP_1_1);
		HttpProtocolParams.setContentCharset(params, CHARSET);
		HttpProtocolParams.setUseExpectContinue(params, true);
		//超时设置
		/*从连接池中取连接的超时时间*/
		ConnManagerParams.setTimeout(params, 1000);
		/*连接超时*/
		HttpConnectionParams.setConnectionTimeout(params, 2000);
		/*请求超时*/
		HttpConnectionParams.setSoTimeout(params, 4000);
		//设置HttpClient支持HTTp和HTTPS两种模式
		SchemeRegistry schReg = new SchemeRegistry();
		schReg.register(new Scheme("http", PlainSocketFactory.getSocketFactory(), 80));
		schReg.register(new Scheme("https", SSLSocketFactory.getSocketFactory(), 443));
		//使用线程安全的连接管理来创建HttpClient
		ClientConnectionManager conMgr = new ThreadSafeClientConnManager(params, schReg);
		HttpClient client = new DefaultHttpClient(conMgr, params);
		return client;
	}
	private void shutdownHttpClient(){
		if(mHttpClient != null && mHttpClient.getConnectionManager() != null){
			mHttpClient.getConnectionManager().shutdown();
		}
	}
	public HttpClient getHttpClient(){
		return mHttpClient;
	}

}

然后再AndroidManifest.xml理添加：

android:name="org.yanzi.application.MyApplication"

然后再Activity里，通过mMyApplication = (MyApplication)getApplication();

mMyApplication.getHttpClient()得到HttpClient就可以使用了。

可以看到在Application的onCreate里就实例化了HttpClient，且在低内存和关闭时关闭连接管理器，释放资源，比2中的写到一个普通文件里更优。