参考AsyncTask源码，依葫芦画瓢的实现一个串行执行的队列

使用AsyncTask的规则

• AsyncTask的类必须在UI线程加载（从4.1开始系统会帮我们自动完成）
• AsyncTask对象必须在UI线程创建
• execute方法必须在UI线程调用
• 不要在你的程序中去直接调用onPreExecute(), onPostExecute, doInBackground, onProgressUpdate方法
• 一个AsyncTask对象只能执行一次，即只能调用一次execute方法，否则会报运行时异常
• AsyncTask不是被设计为处理耗时操作的，耗时上限为几秒钟，如果要做长耗时操作，强烈建议你使用Executor，ThreadPoolExecutor以及FutureTask
• 在1.6之前，AsyncTask是串行执行任务的，1.6的时候AsyncTask开始采用线程池里处理并行任务，但是从3.0开始，为了避免AsyncTask所带来的并发错误，AsyncTask又采用一个线程来串行执行任务

当然我个人更建议使用Handler来实现异步。

AsyncTask也经历过一段时期的折腾，现在稳定在串行执行。无论以后如何，串行思想还是值得学习的，应用的场合也是非常多。

参考AsyncTask的源码，实现一个类似的串行执行的队列。

import java.util.ArrayDeque;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.Executor;
import java.util.concurrent.LinkedBlockingQueue;
import java.util.concurrent.ThreadFactory;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicInteger;

/**
 * Created by lichen
 */
public class StatisticTask {
    private static final String TAG = "StatisticTask";

    private static final int CORE_POOL_SIZE = 5;
    private static final int MAXIMUM_POOL_SIZE = 128;
    private static final int KEEP_ALIVE = 1;

    private static final ThreadFactory sThreadFactory = new ThreadFactory() {
        private final AtomicInteger mCount = new AtomicInteger(1);

        public Thread newThread(Runnable r) {
            return new Thread(r, "StatisticTask #" + mCount.getAndIncrement());
        }
    };

    private static final BlockingQueue<Runnable> sPoolWorkQueue =
            new LinkedBlockingQueue<Runnable>(10);

    private static final Executor THREAD_POOL_EXECUTOR
            = new ThreadPoolExecutor(CORE_POOL_SIZE, MAXIMUM_POOL_SIZE, KEEP_ALIVE,
            TimeUnit.SECONDS, sPoolWorkQueue, sThreadFactory);

    private static final Executor SERIAL_EXECUTOR = new SerialExecutor();
    private static volatile Executor sDefaultExecutor = SERIAL_EXECUTOR;

    private WriteStatisticsAble mWriteStaticticsAble;
    private BaseStatistics mBaseStatistics;
    private StatisticType mStatisticType;

    private static StatisticTask sStatisticTask;

    public static StatisticTask getSyncInstance(WriteStatisticsAble writeStaticticsAble) {
        getInstance();
        sStatisticTask.mWriteStaticticsAble = writeStaticticsAble;
        sStatisticTask.mStatisticType = StatisticType.SYNCHRONIZED;
        return sStatisticTask;
    }

    public static StatisticTask getProcessInstance(BaseStatistics baseStatistics) {
        getInstance();
        sStatisticTask.mBaseStatistics = baseStatistics;
        sStatisticTask.mStatisticType = StatisticType.PROCESS;
        return sStatisticTask;
    }

    private static void getInstance() {
        if (sStatisticTask == null) {
            synchronized (StatisticTask.class) {
                if (sStatisticTask == null) {
                    sStatisticTask = new StatisticTask();
                }
            }
        }
    }

    private static class SerialExecutor implements Executor {
        final ArrayDeque<Runnable> mTasks = new ArrayDeque<Runnable>();
        Runnable mActive;

        public synchronized void execute(final Runnable r) {
            mTasks.offer(new Runnable() {
                public void run() {
                    try {
                        r.run();
                    } finally {
                        scheduleNext();
                    }
                }
            });
            if (mActive == null) {
                scheduleNext();
            }
        }

        protected synchronized void scheduleNext() {
            if ((mActive = mTasks.poll()) != null) {
                THREAD_POOL_EXECUTOR.execute(mActive);
            }
        }
    }

    @Deprecated
    public void execute(Runnable runnable) {
        sDefaultExecutor.execute(runnable);
    }

    public void statistic(RequestParams param, String action) {
        sDefaultExecutor.execute(new StatisticRunnale(param, action));
    }

    private enum StatisticType {
        PROCESS, SYNCHRONIZED
    }

    private class StatisticRunnale implements Runnable {

        private RequestParams mParam;
        private String mAction;

        private StatisticRunnale(RequestParams param, String action) {
            mParam = param;
            mAction = action;
        }

        @Override
        public void run() {
            switch (mStatisticType) {
                case SYNCHRONIZED:
                    String data = SynchroStatistics.makeStatisticsData(mParam, mAction);
                    mWriteStaticticsAble.addStringStatistics(data);
                    break;
                case PROCESS:
                    mBaseStatistics.addProcessStatistics(mParam, mAction);
                    break;
            }
        }
    }
}

下面是源码的详细注释，来自于http://blog.csdn.net/singwhatiwanna/article/details/17596225

/* 
 * Copyright (C) 2008 The Android Open Source Project 
 * 
 * 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 android.os;  

import java.util.ArrayDeque;  
import java.util.concurrent.BlockingQueue;  
import java.util.concurrent.Callable;  
import java.util.concurrent.CancellationException;  
import java.util.concurrent.Executor;  
import java.util.concurrent.ExecutionException;  
import java.util.concurrent.FutureTask;  
import java.util.concurrent.LinkedBlockingQueue;  
import java.util.concurrent.ThreadFactory;  
import java.util.concurrent.ThreadPoolExecutor;  
import java.util.concurrent.TimeUnit;  
import java.util.concurrent.TimeoutException;  
import java.util.concurrent.atomic.AtomicBoolean;  
import java.util.concurrent.atomic.AtomicInteger;  

public abstract class AsyncTask<Params, Progress, Result> {  
    private static final String LOG_TAG = "AsyncTask";  

    //获取当前的cpu核心数  
    private static final int CPU_COUNT = Runtime.getRuntime().availableProcessors();  
    //线程池核心容量  
    private static final int CORE_POOL_SIZE = CPU_COUNT + 1;  
    //线程池最大容量  
    private static final int MAXIMUM_POOL_SIZE = CPU_COUNT * 2 + 1;  
    //过剩的空闲线程的存活时间  
    private static final int KEEP_ALIVE = 1;  
    //ThreadFactory 线程工厂，通过工厂方法newThread来获取新线程  
    private static final ThreadFactory sThreadFactory = new ThreadFactory() {  
        //原子整数，可以在超高并发下正常工作  
        private final AtomicInteger mCount = new AtomicInteger(1);  

        public Thread newThread(Runnable r) {  
            return new Thread(r, "AsyncTask #" + mCount.getAndIncrement());  
        }  
    };  
    //静态阻塞式队列，用来存放待执行的任务，初始容量：128个  
    private static final BlockingQueue<Runnable> sPoolWorkQueue =  
            new LinkedBlockingQueue<Runnable>(128);  

    /** 
     * 静态并发线程池，可以用来并行执行任务，尽管从3.0开始，AsyncTask默认是串行执行任务 
     * 但是我们仍然能构造出并行的AsyncTask 
     */  
    public static final Executor THREAD_POOL_EXECUTOR  
            = new ThreadPoolExecutor(CORE_POOL_SIZE, MAXIMUM_POOL_SIZE, KEEP_ALIVE,  
                    TimeUnit.SECONDS, sPoolWorkQueue, sThreadFactory);  

    /** 
     * 静态串行任务执行器，其内部实现了串行控制， 
     * 循环的取出一个个任务交给上述的并发线程池去执行 
     */  
    public static final Executor SERIAL_EXECUTOR = new SerialExecutor();  
    //消息类型：发送结果  
    private static final int MESSAGE_POST_RESULT = 0x1;  
    //消息类型：更新进度  
    private static final int MESSAGE_POST_PROGRESS = 0x2;  
    /**静态Handler，用来发送上述两种通知，采用UI线程的Looper来处理消息 
     * 这就是为什么AsyncTask必须在UI线程调用，因为子线程 
     * 默认没有Looper无法创建下面的Handler，程序会直接Crash 
     */  
    private static final InternalHandler sHandler = new InternalHandler();  
    //默认任务执行器，被赋值为串行任务执行器，就是它，AsyncTask变成串行的了  
    private static volatile Executor sDefaultExecutor = SERIAL_EXECUTOR;  
    //如下两个变量我们先不要深究，不影响我们对整体逻辑的理解  
    private final WorkerRunnable<Params, Result> mWorker;  
    private final FutureTask<Result> mFuture;  
    //任务的状态 默认为挂起，即等待执行，其类型标识为易变的（volatile）  
    private volatile Status mStatus = Status.PENDING;  
    //原子布尔型，支持高并发访问，标识任务是否被取消  
    private final AtomicBoolean mCancelled = new AtomicBoolean();  
    //原子布尔型，支持高并发访问，标识任务是否被执行过  
    private final AtomicBoolean mTaskInvoked = new AtomicBoolean();  

    /*串行执行器的实现，我们要好好看看，它是怎么把并行转为串行的 
     *目前我们需要知道，asyncTask.execute(Params ...)实际上会调用 
     *SerialExecutor的execute方法，这一点后面再说明。也就是说：当你的asyncTask执行的时候， 
     *首先你的task会被加入到任务队列，然后排队，一个个执行 
     */  
    private static class SerialExecutor implements Executor {  
        //线性双向队列，用来存储所有的AsyncTask任务  
        final ArrayDeque<Runnable> mTasks = new ArrayDeque<Runnable>();  
        //当前正在执行的AsyncTask任务  
        Runnable mActive;  

        public synchronized void execute(final Runnable r) {  
            //将新的AsyncTask任务加入到双向队列中  
            mTasks.offer(new Runnable() {  
                public void run() {  
                    try {  
                        //执行AsyncTask任务  
                        r.run();  
                    } finally {  
                        //当前AsyncTask任务执行完毕后，进行下一轮执行，如果还有未执行任务的话  
                        //这一点很明显体现了AsyncTask是串行执行任务的，总是一个任务执行完毕才会执行下一个任务  
                        scheduleNext();  
                    }  
                }  
            });  
            //如果当前没有任务在执行，直接进入执行逻辑  
            if (mActive == null) {  
                scheduleNext();  
            }  
        }  

        protected synchronized void scheduleNext() {  
            //从任务队列中取出队列头部的任务，如果有就交给并发线程池去执行  
            if ((mActive = mTasks.poll()) != null) {  
                THREAD_POOL_EXECUTOR.execute(mActive);  
            }  
        }  
    }  

    /** 
     * 任务的三种状态 
     */  
    public enum Status {  
        /** 
         * 任务等待执行 
         */  
        PENDING,  
        /** 
         * 任务正在执行 
         */  
        RUNNING,  
        /** 
         * 任务已经执行结束 
         */  
        FINISHED,  
    }  

    /** 隐藏API：在UI线程中调用，用来初始化Handler */  
    public static void init() {  
        sHandler.getLooper();  
    }  

    /** 隐藏API：为AsyncTask设置默认执行器 */  
    public static void setDefaultExecutor(Executor exec) {  
        sDefaultExecutor = exec;  
    }  

    /** 
     * Creates a new asynchronous task. This constructor must be invoked on the UI thread. 
     */  
    public AsyncTask() {  
        mWorker = new WorkerRunnable<Params, Result>() {  
            public Result call() throws Exception {  
                mTaskInvoked.set(true);  

                Process.setThreadPriority(Process.THREAD_PRIORITY_BACKGROUND);  
                //noinspection unchecked  
                return postResult(doInBackground(mParams));  
            }  
        };  

        mFuture = new FutureTask<Result>(mWorker) {  
            @Override  
            protected void done() {  
                try {  
                    postResultIfNotInvoked(get());  
                } catch (InterruptedException e) {  
                    android.util.Log.w(LOG_TAG, e);  
                } catch (ExecutionException e) {  
                    throw new RuntimeException("An error occured while executing doInBackground()",  
                            e.getCause());  
                } catch (CancellationException e) {  
                    postResultIfNotInvoked(null);  
                }  
            }  
        };  
    }  

    private void postResultIfNotInvoked(Result result) {  
        final boolean wasTaskInvoked = mTaskInvoked.get();  
        if (!wasTaskInvoked) {  
            postResult(result);  
        }  
    }  
    //doInBackground执行完毕，发送消息  
    private Result postResult(Result result) {  
        @SuppressWarnings("unchecked")  
        Message message = sHandler.obtainMessage(MESSAGE_POST_RESULT,  
                new AsyncTaskResult<Result>(this, result));  
        message.sendToTarget();  
        return result;  
    }  

    /** 
     * 返回任务的状态 
     */  
    public final Status getStatus() {  
        return mStatus;  
    }  

    /** 
     * 这个方法是我们必须要重写的，用来做后台计算 
     * 所在线程：后台线程 
     */  
    protected abstract Result doInBackground(Params... params);  

    /** 
     * 在doInBackground之前调用，用来做初始化工作 
     * 所在线程：UI线程 
     */  
    protected void onPreExecute() {  
    }  

    /** 
     * 在doInBackground之后调用，用来接受后台计算结果更新UI 
     * 所在线程：UI线程 
     */  
    protected void onPostExecute(Result result) {  
    }  

    /** 
     * Runs on the UI thread after {@link #publishProgress} is invoked. 
     /** 
     * 在publishProgress之后调用，用来更新计算进度 
     * 所在线程：UI线程 
     */  
    protected void onProgressUpdate(Progress... values) {  
    }  

     /** 
     * cancel被调用并且doInBackground执行结束，会调用onCancelled，表示任务被取消 
     * 这个时候onPostExecute不会再被调用，二者是互斥的，分别表示任务取消和任务执行完成 
     * 所在线程：UI线程 
     */  
    @SuppressWarnings({"UnusedParameters"})  
    protected void onCancelled(Result result) {  
        onCancelled();  
    }      

    protected void onCancelled() {  
    }  

    public final boolean isCancelled() {  
        return mCancelled.get();  
    }  

    public final boolean cancel(boolean mayInterruptIfRunning) {  
        mCancelled.set(true);  
        return mFuture.cancel(mayInterruptIfRunning);  
    }  

    public final Result get() throws InterruptedException, ExecutionException {  
        return mFuture.get();  
    }  

    public final Result get(long timeout, TimeUnit unit) throws InterruptedException,  
            ExecutionException, TimeoutException {  
        return mFuture.get(timeout, unit);  
    }  

    /** 
     * 这个方法如何执行和系统版本有关，在AsyncTask的使用规则里已经说明，如果你真的想使用并行AsyncTask， 
     * 也是可以的，只要稍作修改 
     * 必须在UI线程调用此方法 
     */  
    public final AsyncTask<Params, Progress, Result> execute(Params... params) {  
        //串行执行  
        return executeOnExecutor(sDefaultExecutor, params);  
        //如果我们想并行执行，这样改就行了，当然这个方法我们没法改  
        //return executeOnExecutor(THREAD_POOL_EXECUTOR, params);  
    }  

    /** 
     * 通过这个方法我们可以自定义AsyncTask的执行方式，串行or并行，甚至可以采用自己的Executor 
     * 为了实现并行，我们可以在外部这么用AsyncTask： 
     * asyncTask.executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR, Params... params); 
     * 必须在UI线程调用此方法 
     */  
    public final AsyncTask<Params, Progress, Result> executeOnExecutor(Executor exec,  
            Params... params) {  
        if (mStatus != Status.PENDING) {  
            switch (mStatus) {  
                case RUNNING:  
                    throw new IllegalStateException("Cannot execute task:"  
                            + " the task is already running.");  
                case FINISHED:  
                    throw new IllegalStateException("Cannot execute task:"  
                            + " the task has already been executed "  
                            + "(a task can be executed only once)");  
            }  
        }  

        mStatus = Status.RUNNING;  
        //这里#onPreExecute会最先执行  
        onPreExecute();  

        mWorker.mParams = params;  
        //然后后台计算#doInBackground才真正开始  
        exec.execute(mFuture);  
        //接着会有#onProgressUpdate被调用，最后是#onPostExecute  

        return this;  
    }  

    /** 
     * 这是AsyncTask提供的一个静态方法，方便我们直接执行一个runnable 
     */  
    public static void execute(Runnable runnable) {  
        sDefaultExecutor.execute(runnable);  
    }  

    /** 
     * 打印后台计算进度，onProgressUpdate会被调用 
     */  
    protected final void publishProgress(Progress... values) {  
        if (!isCancelled()) {  
            sHandler.obtainMessage(MESSAGE_POST_PROGRESS,  
                    new AsyncTaskResult<Progress>(this, values)).sendToTarget();  
        }  
    }  

    //任务结束的时候会进行判断，如果任务没有被取消，则onPostExecute会被调用  
    private void finish(Result result) {  
        if (isCancelled()) {  
            onCancelled(result);  
        } else {  
            onPostExecute(result);  
        }  
        mStatus = Status.FINISHED;  
    }  

    //AsyncTask内部Handler，用来发送后台计算进度更新消息和计算完成消息  
    private static class InternalHandler extends Handler {  
        @SuppressWarnings({"unchecked", "RawUseOfParameterizedType"})  
        @Override  
        public void handleMessage(Message msg) {  
            AsyncTaskResult result = (AsyncTaskResult) msg.obj;  
            switch (msg.what) {  
                case MESSAGE_POST_RESULT:  
                    // There is only one result  
                    result.mTask.finish(result.mData[0]);  
                    break;  
                case MESSAGE_POST_PROGRESS:  
                    result.mTask.onProgressUpdate(result.mData);  
                    break;  
            }  
        }  
    }  

    private static abstract class WorkerRunnable<Params, Result> implements Callable<Result> {  
        Params[] mParams;  
    }  

    @SuppressWarnings({"RawUseOfParameterizedType"})  
    private static class AsyncTaskResult<Data> {  
        final AsyncTask mTask;  
        final Data[] mData;  

        AsyncTaskResult(AsyncTask task, Data... data) {  
            mTask = task;  
            mData = data;  
        }  
    }  
} 

两篇很有启发的博文

http://blog.csdn.net/singwhatiwanna/article/details/17596225
http://blog.csdn.net/guolin_blog/article/details/11711405