android異步向服務器請求數據

下面就android向服務器請求數據的問題分析如下：

1、在android4.0以後的版本，主線程（UI線程）不在支持網絡請求，原因大概是影響主線程，速度太慢，容易卡機，所以需要開啟新的線程請求數據；

thread1 = new Thread(){
			@Override
			public void run() {
				try {
					URL url = new URL(WebUrlManager.CARSEVER_GetCarsServlet);
					HttpURLConnection conn = (HttpURLConnection) url.openConnection();
					
					BufferedInputStream bis = new BufferedInputStream(conn.getInputStream());
					//緩沖讀取
					byte[] data = new byte[1024];
					int len = 0;
					String bufferString = "";
					while((len = bis.read(data)) != -1){
						bufferString+=new String(data, 0, len);
					}
					carList = new JSONArray(bufferString.trim());
					//System.out.println(carList);
					/*
					for(int i=0;i



2、新線程完成後一啟動，發現報錯，空指針nullpointerexception，要等待線程完畢後才能得到數據，下面是兩種解決方法：
1）要麼判斷線程是否還活著；
2）要麼在線程中設置一flag，結束後，更改其狀態

/*
		//等待線程thread1執行完畢
		while(true){
					if(thread1.isAlive()){
						try {
							Thread.sleep(500);
						} catch (InterruptedException e) {
							// TODO Auto-generated catch block
							e.printStackTrace();
						}
					}else{
						break;
					}
			}
		*/
		//當線程還沒結束，就睡500毫秒ms
		while(!flag){
				try {
					Thread.sleep(500);
				} catch (InterruptedException e) {
					// TODO Auto-generated catch block
					e.printStackTrace();
			}
		}
			
	}


3、處理返回的json數據

1）向服務器請求Json數據，保存在carList

URL url = new URL(WebUrlManager.CARSEVER_GetCarsServlet);
					HttpURLConnection conn = (HttpURLConnection) url.openConnection();
					
					BufferedInputStream bis = new BufferedInputStream(conn.getInputStream());
					//緩沖讀取
					byte[] data = new byte[1024];
					int len = 0;
					String bufferString = "";
					while((len = bis.read(data)) != -1){
						bufferString+=new String(data, 0, len);
					}
					carList = new JSONArray(bufferString.trim());


2)解析Json數據


JSONObject car = (JSONObject) getItem(position);
		try {
			//this.pic.setImageBitmap(carImageArray.get(position));
			this.title.setText(car.getString("title"));
			this.describe.setText(car.getString("describe"));
			this.updateTime.setText(car.getString("updateTime"));
			this.price.setText(String.format("%.1f", car.getDouble("price"))+"萬");
			this.pic.setTag(WebUrlManager.CARSERVER_CAR_IMAGE+car.getString("image"));
			new AsyncViewTask().execute(this.pic);
		} catch (JSONException e1) {
			e1.printStackTrace();
		}


4、圖片加載通常很慢，最好異步請求

1）先貼出異步請求的類源代碼

import java.io.InputStream;
import java.lang.ref.SoftReference;
import java.net.HttpURLConnection;
import java.net.URL;
import java.util.HashMap;
import android.graphics.drawable.Drawable;
import android.os.AsyncTask;
import android.util.Log;
import android.view.View;
import android.webkit.URLUtil;
import android.widget.ImageView;
 
/**
 * @author wzy qq:290581825  http://blog.csdn.net/wzygis
 */
public class AsyncViewTask extends AsyncTask {
    private View mView;
    private HashMap> imageCache;

    public AsyncViewTask() {
        imageCache = new HashMap>();
    }
 
    protected Drawable doInBackground(View... views) {
        Drawable drawable = null;
        View view = views[0];
        if (view.getTag() != null) {
            if (imageCache.containsKey(view.getTag())) {
                SoftReference cache = imageCache.get(view.getTag().toString());
                drawable = cache.get();
                if (drawable != null) {
                    return drawable;
                }
            }
            try {
                if (URLUtil.isHttpUrl(view.getTag().toString())) {// 如果為網絡地址。則連接url下載圖片
                    URL url = new URL(view.getTag().toString());
                    HttpURLConnection conn = (HttpURLConnection) url.openConnection();
                    conn.setDoInput(true);
                    conn.connect();
                    InputStream stream = conn.getInputStream();
                    drawable = Drawable.createFromStream(stream, "src");
                    stream.close();
                } else {// 如果為本地數據，直接解析
                    drawable = Drawable.createFromPath(view.getTag().toString());
                }
            } catch (Exception e) {
                Log.v("img", e.getMessage());
                return null;
            }
        }
        this.mView = view;
        return drawable;
    }
 
    protected void onPostExecute(Drawable drawable) {
        if (drawable != null) {
            ImageView view = (ImageView) this.mView;
            view.setImageDrawable(drawable);
            this.mView = null;
        }
    }
 
}



結果如下：