ndroid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：

<span style="font-family:Comic Sans MS;font-size:18px;">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;
    }

}
</span>

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:

<span style="font-family:Comic Sans MS;font-size:18px;">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;
    }

}
</span>

然后再AndroidManifest.xml理添加：

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

<span style="font-family:Comic Sans MS;font-size:18px;">    <application
        android:name="org.yanzi.application.MyApplication"
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >
        <activity
            android:name="org.yanzi.testtomecat.MainActivity"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application></span>

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。