Android版多线程下载器核心代码分享

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