android異步請求服務器數據示例

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；

復制代碼 代碼如下:
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

復制代碼 代碼如下:
/*
    //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

復制代碼 代碼如下:
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

復制代碼 代碼如下:
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
異步請求類源代碼
復制代碼 代碼如下:
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;

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;
}}}