Http通信模仿迅雷多线程下载
用到的知识点：
1.Http 协议字段"Range", "bytes="+start+"-"+end
2.RandomAccessFile设置写入的位置
3.开启线程发送网络请求以及线程池操作
首先，在服务器端放一张图片，如下在WebRoot下放置了一张lufei.jpg图片
跟访问网页一样通过url直接访问：http://pc-20141102midc:8080/DownLoadFile/lufei.jpg
然后在Android端写多线程下载的代码：
为了防止遗忘现在配置文件中声明权限：
<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
<uses-permission android:name="android.permission.MOUNT_UNMOUNT_FILESYSTEMS" />
布局文件：
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
tools:context="com.example.download_file.MainActivity" >
<Button
android:id="@+id/start_download_bt"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="下载"
android:textColor="@android:color/background_dark" />
<TextView
android:id="@+id/my_tv"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="@string/hello_world" />
</LinearLayout>
下载类：
DownLoad.java
package com.example.download_file;
import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.io.RandomAccessFile;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.concurrent.Executor;
import java.util.concurrent.Executors;
import android.os.Environment;
import android.os.Handler;
import android.os.Message;
/**
* 多线程下载例子
* @author weichongchong
*
*/
public class DownLoad {
private Handler mHandler;
public DownLoad(Handler handle){
this.mHandler= handle;
}
//通过线程池下载，创建线程池对象
private Executor threadPool = Executors.newFixedThreadPool(3);//创建三个线程池
static class DownLoadRunnable implements Runnable{
private String url;
private String fileName;
private long start;
private long end;
private Handler handler;
public DownLoadRunnable(String url ,String fileName,long start,long end,Handler handler ){
this.url=url;
this.fileName = fileName;
this.start = start;
this.end = end;
this.handler= handler;
}
@Override
public void run() {
// TODO Auto-generated method stub
try {
URL httpUrl = new URL(url);
HttpURLConnection conn = (HttpURLConnection) httpUrl.openConnection();
conn.setReadTimeout(5000);
conn.setRequestProperty("Range", "bytes="+start+"-"+end);//指定长度
conn.setRequestMethod("GET");
//创建随机读取流进行读取
RandomAccessFile access = new RandomAccessFile(new File(fileName), "rwd");//第二个参数代表可读，可写，可执行
access.seek(start);
InputStream in = conn.getInputStream();
byte[] b = new byte[1024*4];
int len=0;
while((len = in.read())!=-1){
access.write(b,0,len);
}
if(access!=null){
access.close();
}
if(in!=null){
in.close();
}
//下载完成通知更新UI
Message message = new Message();
message.what=1;
handler.sendMessage(message);
// int count = conn.getContentLength();//拿到下载对象的长度
// int block = count/3;//平均到每个线程池
} catch (MalformedURLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
public void downLoadFile(String url){
try {
URL httpUrl = new URL(url);
HttpURLConnection conn = (HttpURLConnection) httpUrl.openConnection();
conn.setReadTimeout(5000);
conn.setRequestMethod("GET");
int count = conn.getContentLength();//拿到下载对象的长度
int block = count/3;//平均到每个线程池
String fileName = getFileName(url);
// File parent = Environment.getExternalStorageDirectory();
// File fileDownLoad = new File(parent,fileName);
File fileDownLoad = new File(Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_PICTURES),fileName);
/**
* 11/3 3
* 第一个线程0-2
* 第二个3-5
* 第三个6-10
*/
for(int i=0;i<3;i++){
long start = i*block;
long end = (i+1)*block-1;
if(i==2){
end=count;
}
DownLoadRunnable runnable = new DownLoadRunnable(url,fileDownLoad.getAbsolutePath(),start,end,mHandler);
threadPool.execute(runnable);//通过线程池提交任务
}
} catch (MalformedURLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
/**
*
* @return
* 得到url后缀名，即文件名
*/
public String getFileName(String url){
return url.substring(url.lastIndexOf("/")+1);
}
}
MainActivity中代码使用下载类进行下载
package com.example.download_file;
import android.app.Activity;
import android.os.Bundle;
import android.os.Handler;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.TextView;
import android.widget.Toast;
public class MainActivity extends Activity {
private Button start_download_bt;
private TextView mytv;
private int count = 0;
private Handler mHandler = new Handler(){
public void handleMessage(android.os.Message msg) {
int result = msg.what;
count+=result;//如果三个线程都下载完成，都返回一个1，相加为3
if(count==3){
mytv.setText("下载完成");
start_download_bt.setText("下载完成");
}
};
};
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
start_download_bt = (Button) findViewById(R.id.start_download_bt);
mytv = (TextView) findViewById(R.id.my_tv);
start_download_bt.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
start_download_bt.setText("正在下载");
Toast.makeText(MainActivity.this, "正在下载", 0).show();
new Thread(){
@Override
public void run() {
// TODO Auto-generated method stub
DownLoad mDownLoad = new DownLoad(mHandler);
mDownLoad.downLoadFile("http://192.168.1.105:8080/DownLoadFile/lufei.jpg");
}
}.start();
}
});
}
}