首先给大家分享多线程下载核心类：
package com.example.urltest; 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.net.URLDecoder; public class DownUtil {
private String urlPath;
private String defaultTargetPath;
private int threadNum;
private DownThread[] threads;
private int fileSize = -100;
private String fileName = "未知文件";
private boolean isGetFileInformation = false; public DownUtil(String urlPath, int threadNum) {
this.urlPath = urlPath;
this.defaultTargetPath = "/mnt/sdcard/";
this.threadNum = threadNum;
this.threads = new DownThread[threadNum];
} private HttpURLConnection connection() throws IOException { URL url = new URL(urlPath);
HttpURLConnection connection = (HttpURLConnection) url.openConnection();
connection.setConnectTimeout(5 * 1000);
connection.setRequestMethod("GET");
connection.setRequestProperty(
"Accept",
"image/gif, image/jpeg, image/pjpeg, image/pjpeg, "
+ "application/x-shockwave-flash, application/xaml+xml, "
+ "application/vnd.ms-xpsdocument, application/x-ms-xbap, "
+ "application/x-ms-application, application/vnd.ms-excel, "
+ "application/vnd.ms-powerpoint, application/msword, */*");
connection.setRequestProperty("Accept-Language", "zh-CN");
connection.setRequestProperty("Charset", "UTF-8");
connection.setRequestProperty("Connection", "Keep-Alive"); return connection;
} public void getFileInformation() throws IOException { HttpURLConnection connection = connection(); connection.setInstanceFollowRedirects(false); int status = connection.getResponseCode();
if (status != -1) { if (status / 100 == 3) {// 当响应码是302时，说明可以获得重定向的资源地址
// 得到文件名(此方法不能正确的获取所有url的资源文件名)
String name = connection.getHeaderField("Location");
name = URLDecoder.decode(name.substring(name.lastIndexOf('/')), "UTF-8");
this.fileName = name;
} // 得到文件大小
this.fileSize = connection.getContentLength();
if (fileSize <= 0) {
isGetFileInformation = false;
} else {
isGetFileInformation = true;
}
connection.disconnect(); } else { connection.disconnect();
isGetFileInformation = false; } } public boolean download(String targetPath, String fileName) throws IOException { if (isGetFileInformation == false) {
getFileInformation();
} if (isGetFileInformation) { String absFilePath = targetPath + fileName; int currentPartSize = (fileSize / threadNum) + 1;// 每一部分需要下载的大小，注意此处加1是为了避免不能整除带来的误差
RandomAccessFile file = new RandomAccessFile(absFilePath, "rw");
file.setLength(fileSize);
file.close();
for (int i = 0; i < threadNum; i++) {
int startPos = i * currentPartSize;
RandomAccessFile currentPart = new RandomAccessFile(absFilePath, "rw");// 打开目标文件
currentPart.seek(startPos);
threads[i] = new DownThread(startPos, currentPartSize, currentPart);
threads[i].start(); } return true;
} else {
return false; }
} public boolean download() throws IOException {
if (isGetFileInformation) { return download(this.defaultTargetPath, this.getFileName()); } else {
getFileInformation();
return download(this.defaultTargetPath, this.getFileName()); } } public double getCompleteRate() { int sumSize = 0;
for (int i = 0; i < threadNum; i++) { sumSize += threads[i].length;
} return sumSize * 1.0 / fileSize; } public String getDefaultTargetPath() {
return defaultTargetPath;
} public int getFileSize() {
return fileSize;
} public String getFileName() {
return fileName;
} public void setFileName(String fileName) {
this.fileName = fileName;
} public boolean isGetFileInformation() {
return isGetFileInformation;
} private class DownThread extends Thread {
private int startPos;
private int currentPartSize;
private RandomAccessFile currentPart;
int length; // 该线程已经下载的字节数 public DownThread(int startPos, int currentPartSize, RandomAccessFile currentPart) { this.startPos = startPos;
this.currentPartSize = currentPartSize;
this.currentPart = currentPart;
} @Override
public void run() { try { HttpURLConnection connection = connection();
int endPos = startPos + currentPartSize;
connection.setRequestProperty("Range", "bytes=" + startPos + "-" + endPos);// 使用http来设置一个文件的下载范围（startPos-endPos）
InputStream inStream = connection.getInputStream();
// inStream.skip(startPos); // skip函数有时候不起作用
byte[] buffer = new byte[1024];
int hasRead = 0;
while (length < currentPartSize && (hasRead = inStream.read(buffer)) > 0) { currentPart.write(buffer, 0, hasRead);
length = length + hasRead; } inStream.close();
currentPart.close();
connection.disconnect(); } catch (MalformedURLException e2) {
e2.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} } } }
下面是界面的逻辑代码：
package com.example.urltest; import android.app.Activity;
import android.app.AlertDialog;
import android.app.ProgressDialog;
import android.content.DialogInterface;
import android.os.Bundle;
import android.os.Message;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ProgressBar;
import android.widget.TextView;
import android.widget.Toast; import java.io.IOException;
import java.util.Timer;
import java.util.TimerTask; public class MultiThreadDown extends Activity {
EditText url, target;
Button downButton;
ProgressBar bar;
ProgressDialog progressDialog;
View downView;
DownUtil downUtil;
private int mDownStatus;
private int threadNum = 6; // 默认的线程数
android.os.Handler handler = new android.os.Handler() { @Override
public void handleMessage(Message msg) {
if (msg.what == 0x123) {
bar.setProgress(mDownStatus);
if (mDownStatus >= 100) {
Toast.makeText(MultiThreadDown.this, "下载完成", Toast.LENGTH_SHORT).show();
}
// Log.i("csx", "" + mDownStatus); }
} }; @Override
protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState);
setContentView(R.layout.layout_down);
url = (EditText) findViewById(R.id.url); downButton = (Button) findViewById(R.id.down);
bar = (ProgressBar) findViewById(R.id.bar);
progressDialog = new ProgressDialog(this);
progressDialog.setTitle("尝试连接");
progressDialog.setMessage("正在连接...");
downButton.setOnClickListener(new DownButtonOnClickListener()); } private class DownButtonOnClickListener implements OnClickListener { EditText targetFilePath, fileName;
TextView fileSize;
Thread connectionThread; public Thread instanceOfConnectionThread() {
return new Thread() { @Override
public void run() {
try {
downUtil.getFileInformation(); } catch (IOException e1) {
e1.printStackTrace();
} } };
} @Override
public void onClick(View v) { String urlPath = url.getText().toString();
if (urlPath == null || urlPath.equals("")) {
return;
}
progressDialog.show();
downUtil = new DownUtil(urlPath, threadNum);
connectionThread = instanceOfConnectionThread();
connectionThread.start(); int connectionNum = 3;
while (!downUtil.isGetFileInformation() && connectionNum > 0) {// 循环请求连接,如果3次之后还没有连接成功，就退出
if (!connectionThread.isAlive()) {
connectionThread = null;
connectionThread = instanceOfConnectionThread();
connectionThread.start();
connectionNum--;
} } progressDialog.cancel();
if (!downUtil.isGetFileInformation()) {
Toast.makeText(MultiThreadDown.this, "请求失败！", Toast.LENGTH_SHORT).show();
return;
}
downView = getLayoutInflater().inflate(R.layout.layout_download_view, null);
targetFilePath = (EditText) downView.findViewById(R.id.editText_target_path);
fileName = (EditText) downView.findViewById(R.id.editText_file_name);
fileSize = (TextView) downView.findViewById(R.id.textView_file_size);
targetFilePath.setText(downUtil.getDefaultTargetPath());
fileName.setText(downUtil.getFileName());
fileSize.append("" + ((double) downUtil.getFileSize()) / 1024 + "k"); new AlertDialog.Builder(MultiThreadDown.this).setView(downView)
.setPositiveButton("确定", new DialogInterface.OnClickListener() { @Override
public void onClick(DialogInterface dialog, int which) {
if (!downUtil.isGetFileInformation()) {
dialog.dismiss();
return;
}
final String path = targetFilePath.getText().toString();
final String name = fileName.getText().toString(); new Thread() { @Override
public void run() {
try {
downUtil.download(path, name);
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} final Timer timer = new Timer();
TimerTask task = new TimerTask() { @Override
public void run() { mDownStatus = (int) (downUtil.getCompleteRate() * 100);
handler.sendEmptyMessage(0x123);
if (mDownStatus >= 100) {
timer.cancel();
} }
};
timer.schedule(task, 0, 100); } }.start(); }
}).setNegativeButton("取消", null)
.setTitle(downUtil.isGetFileInformation() ? "链接可用" : "链接不可用").show(); }
} }
下面是主页面布局：layout_down.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" > <ScrollView
android:id="@+id/scrollView1"
android:layout_width="match_parent"
android:layout_height="wrap_content" > <LinearLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" > <TextView
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="要下载的资源的URL：" /> <EditText
android:id="@+id/url"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="在在这里输入URL" /> <Button
android:id="@+id/down"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="下载" />
<!-- 定义一个水平进度条,用于显示下载进度 --> <ProgressBar
android:id="@+id/bar"
style="?android:attr/progressBarStyleHorizontal"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:max="100" />
</LinearLayout>
</ScrollView> </LinearLayout>
下面是下载选项dialog布局：layout_download_view.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" > <TextView
android:id="@+id/textView1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="下载路径：" /> <EditText
android:id="@+id/editText_target_path"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:ems="10" > <requestFocus />
</EditText> <TextView
android:id="@+id/textView2"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="文件名：" /> <EditText
android:id="@+id/editText_file_name"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:maxLines="1"
android:ems="10" /> <TextView
android:id="@+id/textView_file_size"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="文件大小：" /> </LinearLayout>
效果图如下：输入URL，点击下载弹出对话框，输入路径和文件名 点击确定开始下载
