多線程學(xué)習(xí)未解決的Bug

1.遇到不會(huì)解決的Bug啦

上篇博客中說想自己實(shí)現(xiàn)一下多線程下載一個(gè)文件，昨天就嘗試寫了一下，但遇到了一個(gè)不會(huì)解決的Bug，問了問別人，暫時(shí)也沒能解決。這里記錄一下，挖個(gè)坑，以后再來解決了。

2.Java中的線程池

  • newCachedThreadPool
    可緩存的線程池。沒有固定大小，如果線程池中的線程數(shù)量超過任務(wù)執(zhí)行的數(shù)量，會(huì)回收60秒不執(zhí)行的任務(wù)的空閑線程。當(dāng)任務(wù)數(shù)量增加時(shí)，線程池自己會(huì)增加線程來執(zhí)行任務(wù)。而能創(chuàng)建多少，就得看jvm能夠創(chuàng)建多少

  • newFixedThreadPool
    固定線程數(shù)量大小的線程池,并發(fā)線程數(shù)量不會(huì)超過固定大小，超出的線程會(huì)在隊(duì)列中等待。如果一個(gè)正在執(zhí)行的線程出現(xiàn)異常結(jié)束，會(huì)創(chuàng)建一個(gè)顯得線程來代替它

  • newScheduledThreadPool
    也是固定線程數(shù)量大小的線程池，可以延遲或者定時(shí)周期執(zhí)行任務(wù)

  • newSingleThreadExecutor
    單例線程池。線程池中只有一個(gè)線程工作，出現(xiàn)異常會(huì)有有個(gè)新的線程來代替。線程池會(huì)保證所有任務(wù)按照指定順序(FIFO, LIFO, 優(yōu)先級(jí))執(zhí)行。

3.Android部分代碼

思路：
將一個(gè)文件進(jìn)行分部下載，利用RandomAccessFile來進(jìn)行讀寫。一個(gè)線程負(fù)責(zé)一部分，計(jì)算好每個(gè)線程開始和結(jié)束下載位置。

public class HttpUtils {
    /**
     * 固定線程數(shù)的線程池
     */
    private static ExecutorService fixedThreadPool;
    private static String downUrl;
    private static File targetFile;
    private static ProgressCallback progressCallback;
    private static long totalLength = 0;

    public HttpUtils(String url) {
        this.downUrl = url;
        fixedThreadPool = Executors.newFixedThreadPool(5);
    }

    public static HttpUtils getInstance(String url) {
        return new HttpUtils(url);
    }

    public HttpUtils into(File file) {
        if (file != null) {
            this.targetFile = file;
        }
        return this;
    }

    public static void downLoad(ProgressCallback progressCallback) {
        if (fixedThreadPool == null) return;
        HttpUtils.progressCallback = progressCallback;
        new Thread(new Runnable() {
            @Override
            public void run() {
                down();
            }
        }).start();
    }
    private static void down() {
        URL url = null;
        URLConnection urlConnection = null;
        try {
            url = new URL(downUrl);
            urlConnection = url.openConnection();
            totalLength = urlConnection.getContentLength();
        } catch (MalformedURLException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
        //每部分的大小
        final long part = totalLength / 5;
        for (int i = 0; i < 5; i++) {
            final long startPosition = i * part;
            final URL finalUrl = url;
            final PartFileDown partFileDown = new PartFileDown();
            final int n = i;
            final long finalTotalLength = totalLength;
            fixedThreadPool.execute(new Runnable() {
                @Override
                public void run() {
                    long endLength = n == 4 ? finalTotalLength : (startPosition + part);
                    partFileDown.downData(finalUrl, targetFile, startPosition, endLength, new Callback() {
                        @Override
                        public void currentLength(long currentLength) {
                            Message message = handler.obtainMessage();
                            message.what = 101;
                            message.obj = currentLength;
                            handler.sendMessage(message);
                        }
                    });
                }
            });
        }
    }


    private static Handler handler = new Handler() {
        long current;

        @Override
        public void handleMessage(Message msg) {
            super.handleMessage(msg);
            if (msg.what == 101) {
                current += (long) msg.obj;
                progressCallback.progress(current, totalLength);
                Log.e("current", "--" + current);
            }
        }
    };
}

利用newFixedThreadPool開啟5個(gè)線程來執(zhí)行任務(wù)。

public class PartFileDown {
    public void downData(URL downLoadUrl, File targetFile, long startPosition, long endPosition, Callback callback) {
        RandomAccessFile raf = null;
        InputStream is = null;
        try {
            URLConnection urlConnection = downLoadUrl.openConnection();
            urlConnection.setAllowUserInteraction(true);
            //設(shè)置當(dāng)前線程下載的起點(diǎn)、終點(diǎn)
            urlConnection.setRequestProperty("Range", "bytes=" + startPosition + "-" + endPosition);
          //  byte[] by = new byte[1024 * 8];
            byte[] by = new byte[1024];

            is = urlConnection.getInputStream();
            raf = new RandomAccessFile(targetFile, "rw");
            int len = 0;
            raf.seek(startPosition);
            while ((len = is.read(by)) != -1) {
                raf.write(by, 0, len);
                callback.currentLength(len);
            }
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            try {
                if (is != null )
                    is.close();
            } catch (Exception e) {
                e.printStackTrace();
            } finally {
                is = null;
            }
            try {
                if (raf != null)
                    raf.close();
            } catch (Exception e) {
                e.printStackTrace();
            } finally {
                raf = null;
            }
        }
    }
}

代碼有Bug就不再解釋了。: )

4.bug說明

遇到的Bug就是，除了采用newSingleThreadExecutor這個(gè)線程池外，其他3個(gè)線程池，都會(huì)遇到一個(gè)同樣的Bug。文件在下載過程中，進(jìn)度會(huì)在4/5左右中斷，每次中斷位置還基本不同。放置1,2分鐘后，又會(huì)繼續(xù)下載，直到完成。

推測(cè)是因?yàn)榫€程在下載過程中出現(xiàn)了異常然后結(jié)束，線程池創(chuàng)建新的線程來代替掛掉的線程需要時(shí)間。

5.OkHttp下載

OkHttp下載文件倒是很方便。直接上代碼：

public class MainModel implements MainContract.MainBiz {
    private Platform platform;
    private Call call = null;

    public MainModel() {
        platform = Platform.get();
    }

    @Override
    public void onStart(String url, String fileName, onStartDownListener onStartDownListener) {
        downLoad(url, fileName, onStartDownListener);
    }

    @Override
    public void onStop(String fileName, onStartDownListener onStartDownListener) {
        if (call != null) {
            if (!call.isCanceled()) {
                call.cancel();
            }
            File f = FileUtils.getTargetFile(fileName);
            if (f != null && f.exists()) {
                f.delete();
                sendLoadProgressCallback(onStartDownListener,0,100);
                sendInfoCallback(onStartDownListener,"停止下載");
            }


        } else {
            sendLoadProgressCallback(onStartDownListener,0,100);
            sendInfoCallback(onStartDownListener,"call出現(xiàn)錯(cuò)誤");
        }

    }

    private void downLoad(String url, final String fileName, final onStartDownListener onStartDownListener) {
        final OkHttpClient okHttpClient = new OkHttpClient();

        Request request = new Request.Builder().url(url).build();
        call = okHttpClient.newCall(request);
        call.enqueue(new Callback() {
            @Override
            public void onFailure(Call call, IOException e) {
                sendInfoCallback(onStartDownListener, e.getMessage());
            }

            @Override
            public void onResponse(Call call, Response response) throws IOException {
                sendInfoCallback(onStartDownListener, "已經(jīng)開始下載");
                InputStream is = response.body().byteStream();
                long total = response.body().contentLength();
                int current = 0;
                byte[] by = new byte[1024 * 8];
                FileOutputStream fos = new FileOutputStream(FileUtils.getTargetFile(fileName));
                int len;
                while ((len = is.read(by)) != -1) {
                    fos.write(by, 0, len);
                    current += len;
                    sendLoadProgressCallback(onStartDownListener, current, total);
                }
                is.close();
                fos.close();
                sendInfoCallback(onStartDownListener, "下載完成");
            }
        });
    }

    private void sendLoadProgressCallback(final onStartDownListener onStartDownListener, final int current, final long total) {
        if (onStartDownListener == null) return;
        platform.execute(new Runnable() {
            @Override
            public void run() {
                onStartDownListener.onLoading(current, (int) total);
            }
        });
    }

    private void sendInfoCallback(final onStartDownListener onStartDownListener, final String message) {
        if (onStartDownListener == null) return;
        platform.execute(new Runnable() {
            @Override
            public void run() {
                onStartDownListener.onFailed(message);
            }
        });
    }
}

Platform是在張鴻洋大神封裝的OkHttpUtils庫(kù)中看的一個(gè)工具類，方便拿到Handler。直接回調(diào)就可以。

/*
 * Copyright (C) 2013 Square, Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package utils;

import android.os.Build;
import android.os.Handler;
import android.os.Looper;

import java.util.concurrent.Executor;
import java.util.concurrent.Executors;

public class Platform
{
    private static final Platform PLATFORM = findPlatform();

    public static Platform get()
    {
        L.e(PLATFORM.getClass().toString());
        return PLATFORM;
    }

    private static Platform findPlatform()
    {
        try
        {
            Class.forName("android.os.Build");
            if (Build.VERSION.SDK_INT != 0)
            {
                return new Android();
            }
        } catch (ClassNotFoundException ignored)
        {
        }
        return new Platform();
    }

    public Executor defaultCallbackExecutor()
    {
        return Executors.newCachedThreadPool();
    }

    public void execute(Runnable runnable)
    {
        defaultCallbackExecutor().execute(runnable);
        
    }


    static class Android extends Platform
    {
        @Override
        public Executor defaultCallbackExecutor()
        {
            return new MainThreadExecutor();
        }

        static class MainThreadExecutor implements Executor
        {
            private final Handler handler = new Handler(Looper.getMainLooper());

            @Override
            public void execute(Runnable r)
            {
                handler.post(r);
            }
        }
    }
}

6.最后

多線程的學(xué)習(xí)暫時(shí)先告以段落。Android中，下載大文件，感覺還是OkHttp方便。OkHttp配合Handler也可以比較方便地進(jìn)行更新進(jìn)度

最后編輯于 ：
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