android异步向服务器请求数据
2014-08-14 09:58
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下面就android向服务器请求数据的问题分析如下:
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;
<span style="font-family:System;font-size:12px;">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<carList.length();i++){
System.out.println("加载图片");
JSONObject json = (JSONObject) carList.get(i);
String imageName = json.getString("image");
bm = BitmapFactory.decodeStream(new URL(WebUrlManager.CARSERVER_CAR_IMAGE+imageName).openStream());
carImageArray.add(bm);
}
*/
} catch (MalformedURLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (JSONException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
flag = true;
}
};
thread1.start();</span>
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
<span style="font-family:System;font-size:12px;">/*
//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();
}
}
}</span>
3、处理返回的json数据
1)向服务器请求Json数据,保存在carList
<span style="font-family:System;font-size:12px;">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());</span>
2)解析Json数据
<span style="font-family:System;font-size:12px;">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();
}</span>
4、图片加载通常很慢,最好异步请求
1)先贴出异步请求的类源代码
<span style="font-family:System;font-size:12px;">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<View, Void, Drawable> {
private View mView;
private HashMap<String, SoftReference<Drawable>> imageCache;
public AsyncViewTask() {
imageCache = new HashMap<String, SoftReference<Drawable>>();
}
protected Drawable doInBackground(View... views) {
Drawable drawable = null;
View view = views[0];
if (view.getTag() != null) {
if (imageCache.containsKey(view.getTag())) {
SoftReference<Drawable> 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;
}
}
}</span>
结果如下:
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;
<span style="font-family:System;font-size:12px;">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<carList.length();i++){
System.out.println("加载图片");
JSONObject json = (JSONObject) carList.get(i);
String imageName = json.getString("image");
bm = BitmapFactory.decodeStream(new URL(WebUrlManager.CARSERVER_CAR_IMAGE+imageName).openStream());
carImageArray.add(bm);
}
*/
} catch (MalformedURLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (JSONException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
flag = true;
}
};
thread1.start();</span>
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
<span style="font-family:System;font-size:12px;">/*
//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();
}
}
}</span>
3、处理返回的json数据
1)向服务器请求Json数据,保存在carList
<span style="font-family:System;font-size:12px;">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());</span>
2)解析Json数据
<span style="font-family:System;font-size:12px;">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();
}</span>
4、图片加载通常很慢,最好异步请求
1)先贴出异步请求的类源代码
<span style="font-family:System;font-size:12px;">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<View, Void, Drawable> {
private View mView;
private HashMap<String, SoftReference<Drawable>> imageCache;
public AsyncViewTask() {
imageCache = new HashMap<String, SoftReference<Drawable>>();
}
protected Drawable doInBackground(View... views) {
Drawable drawable = null;
View view = views[0];
if (view.getTag() != null) {
if (imageCache.containsKey(view.getTag())) {
SoftReference<Drawable> 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;
}
}
}</span>
结果如下:
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