URLConnection，单线程下载，多线程下载
在UI主线程中是不允许进行耗时操作的，像连接服务器，下载等操作都是耗时操作，不可以在UI主线程中进行，必须在子线程中进行。
URLConnection
URLConnection获得服务器的反应。代码如下：
try {
URL url = new URL("http://192.168.0.43:8080/www/MyserverTest");
URLConnection connection = url.openConnection();
InputStream is = connection.getInputStream();
BufferedReader reader = new BufferedReader(new InputStreamReader(is));
String line= reader.readLine();
reader.read();
StringBuffer s= new StringBuffer();
while (line!=null){
Log.d("",line);
s.append(line);
line=reader.readLine();
}
Message message =handler.obtainMessage();
message.what=URL_NET;
message.obj=s.toString().trim();
handler.sendMessage(message);
reader.close();
is.close();
} catch (MalformedURLException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}注意连接服务器是需要声明权限的：
<uses-permission android:name="android.permission.INTERNET"/>单线程下载
下载就是获得服务器的资源。
这里我们用AsyncTask机制下载和更新进度条。代码如下：
class MyAsyncTask extends AsyncTask<String,Integer,String> {
@Override
protected String doInBackground(String... params) {
try {
URL url = new URL("http://192.168.0.43:8080/www/music/sj.mp3");
URLConnection connection = url.openConnection();
int length=connection.getContentLength();//获得内容的长度
InputStream in = connection.getInputStream();
File file = new File(Environment.getExternalStorageDirectory(),"/sj.mp3");
if(!file.exists()){
file.createNewFile();
}
FileOutputStream os = new FileOutputStream(file);
byte[]array = new byte[1024];
int sum = 0;
int index = in.read(array);//返回读取的字节数
while (index!=-1){
sum+=index;
os.write(array,0,index);//把数组的值写入对应的文件中
publishProgress(sum,length);//传给onProgressUpdate（）的参数，使其更新进度条
index=in.read(array);
}
os.flush();
os.close();
in.close();
} catch (MalformedURLException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
return null;
}
@Override
protected void onPostExecute(String s) {
super.onPostExecute(s);
progressBar.setVisibility(View.INVISIBLE);
}
@Override
protected void onProgressUpdate(Integer... values) {
super.onProgressUpdate(values);
progressBar.setProgress((int)(values[0]*100.0/values[1]));
}
}在启动按钮的点击事件中：
MyAsyncTask myAsyncTask =new MyAsyncTask();
myAsyncTask.execute("dd");//dd是随便写的。是传给doInBackground（）的参数注意:
Handler机制与AsyncTask都不是在onCreat（）机制中进行的。
多线程下载
多线程下载就不可以用AsyncTask机制了。必须用Handler机制。启动多线程，为每一个线程的下载设定开始和结束点。代码如下：
在Activity中按钮的点击事件中：
new Thread(new Runnable() {
@Override
public void run() {
try {
String path="http://192.168.0.43:8080/www/music/sj.mp3";
URL url = new URL(path);
URLConnection connection = url.openConnection();
length=connection.getContentLength();
File file = new File(Environment.getExternalStorageDirectory(),"/sj.mp3");
if(!file.exists()){
file.createNewFile();
}
array =new Item_Thread[5];
for(int i =0;i<5;i++){
if(i==4){
thread=new Item_Thread(length/5*i,length,path,file.getAbsolutePath());
array[4]=thread;
}else {
thread= new Item_Thread(length/5*i,length/5*(i+1),path,file.getAbsolutePath());
array[i]=thread;
}
thread.start();
}
boolean isfinish=false;
while (!isfinish){
for(Item_Thread thread : array){
sum+=thread.getSum();
}
Message message = handler.obtainMessage();
message.what=PRO;
message.arg1=sum;
handler.sendMessage(message);
if(length<=sum+10){
isfinish=true;
thread.sleep(1000);
}
}
} catch (MalformedURLException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}).start();
break;Handler机制的代码：
Handler handler = new Handler(){
@Override
public void handleMessage(Message msg) {
super.handleMessage(msg);
switch (msg.what){
case PRO:
progressBar.setProgress(msg.arg1);
if(length<=msg.arg1+10){
progressBar.setVisibility(View.INVISIBLE);
}
break;
}
}
};在子线程中：
public class Item_Thread extends Thread {
private long start;
private long end;
private String urlpath;
private String filePath;
private int sum;
public int getSum() {
return sum;
}
public Item_Thread(long start,long end, String urlpath,String filePath) {
this.end = end;//下载的结束点
this.filePath = filePath;//下载到的文件路径
this.start = start;//下载的开始点
this.urlpath = urlpath;//下载文件的路径
}
@Override
public void run() {
try {
URL url = new URL(urlpath);
URLConnection connection = url.openConnection();
connection.setRequestProperty("Range","bytes="+start+"-"+end);//设置下载的开始点与结束点
InputStream in = connection.getInputStream();
File file = new File(filePath);
if(!file.exists()){
file.createNewFile();
}
RandomAccessFile randomAccessFile = new RandomAccessFile(file,"rw");
randomAccessFile.seek(start);//设置下载到文件的开始点。
byte[]array = new byte[1024];
sum = 0;
int index = in.read(array);//返回读取的字节数
while (index!=-1){
sum+=index;
randomAccessFile.write(array,0,index);//把数组的值写入对应的文件中
index=in.read(array);
}
randomAccessFile.close();
in.close();
} catch (MalformedURLException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
}这样就结束了。