android异步请求服务器数据示例

1、在android4.0以后的版本，主线程（ui线程）不在支持网络请求，原因大概是影响主线程，速度太慢，容易卡机，所以需要开启新的线程请求数据；

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());
    //缓冲读取
    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、新线程完成后一启动，发现报错，空指针 nullpointerexception，要等待线程完毕后才能得到数据，下面是两种解决方法：

1）要么判断线程是否还活着；

2）要么在线程中设置一flag，结束后，更改其状态

/*
    //等待线程thread1执行完毕
    while(true){
    if(thread1.isalive()){
try {
  thread.sleep(500);
} catch (interruptedexception e) {
  // todo auto-generated catch block
  e.printstacktrace();
}
    }else{
break;
    }
}
    */
    //当线程还没结束，就睡500毫秒ms
    while(!flag){
  try {
    thread.sleep(500);
  } catch (interruptedexception e) {
    // todo auto-generated catch block
    e.printstacktrace();
}}}

3、处理返回的json数据
1）向服务器请求json数据，保存在carlist

url url = new url(weburlmanager.carsever_getcarsservlet);
httpurlconnection conn = (httpurlconnection) url.openconnection();

bufferedinputstream bis = new bufferedinputstream(conn.getinputstream());
//缓冲读取
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数据

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"))+"万");
this.pic.settag(weburlmanager.carserver_car_image+car.getstring("image"));
new asyncviewtask().execute(this.pic);
} catch (jsonexception e1) {
e1.printstacktrace();
}

4、图片加载通常很慢，最好异步请求
异步请求类源代码

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())) {// 如果为网络地址。则连接url下载图片
  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 {// 如果为本地数据，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;
}}}