IntentService:异步处理服务，新开一个线程：handlerThread在线程中发消息，然后接受处理完成后，会清理线程，并且关掉服务。
IntentService有以下特点：
（1） 它创建了一个独立的工作线程来处理所有的通过onStartCommand()传递给服务的intents。
（2） 创建了一个工作队列，来逐个发送intent给onHandleIntent()。
（3） 不需要主动调用stopSelft()来结束服务。因为，在所有的intent被处理完后，系统会自动关闭服务。
（4） 默认实现的onBind()返回null
（5） 默认实现的onStartCommand()的目的是将intent插入到工作队列中
/* * 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.app; import android.annotation.WorkerThread; import android.content.Intent; import android.os.Handler; import android.os.HandlerThread; import android.os.IBinder; import android.os.Looper; import android.os.Message; /** * IntentService is a base class for {@link Service}s that handle asynchronous * requests (expressed as {@link Intent}s) on demand. Clients send requests * through {@link android.content.Context#startService(Intent)} calls; the * service is started as needed, handles each Intent in turn using a worker * thread, and stops itself when it runs out of work. * * <p>This "work queue processor" pattern is commonly used to offload tasks * from an application's main thread. The IntentService class exists to * simplify this pattern and take care of the mechanics. To use it, extend * IntentService and implement {@link #onHandleIntent(Intent)}. IntentService * will receive the Intents, launch a worker thread, and stop the service as * appropriate. * * <p>All requests are handled on a single worker thread -- they may take as * long as necessary (and will not block the application's main loop), but * only one request will be processed at a time. * * <div class="special reference"> * <h3>Developer Guides</h3> * <p>For a detailed discussion about how to create services, read the * <a href="{@docRoot}guide/topics/fundamentals/services.html">Services</a> developer guide.</p> * </div> * * @see android.os.AsyncTask */ public abstract class IntentService extends Service { private volatile Looper mServiceLooper; private volatile ServiceHandler mServiceHandler; private String mName; private boolean mRedelivery; private final class ServiceHandler extends Handler { public ServiceHandler(Looper looper) { super(looper); } @Override public void handleMessage(Message msg) { onHandleIntent((Intent)msg.obj); stopSelf(msg.arg1); } } /** * Creates an IntentService. Invoked by your subclass's constructor. * * @param name Used to name the worker thread, important only for debugging. */ public IntentService(String name) { super(); mName = name; } /** * Sets intent redelivery preferences. Usually called from the constructor * with your preferred semantics. * * <p>If enabled is true, * {@link #onStartCommand(Intent, int, int)} will return * {@link Service#START_REDELIVER_INTENT}, so if this process dies before * {@link #onHandleIntent(Intent)} returns, the process will be restarted * and the intent redelivered. If multiple Intents have been sent, only * the most recent one is guaranteed to be redelivered. * * <p>If enabled is false (the default), * {@link #onStartCommand(Intent, int, int)} will return * {@link Service#START_NOT_STICKY}, and if the process dies, the Intent * dies along with it. */ public void setIntentRedelivery(boolean enabled) { mRedelivery = enabled; } @Override public void onCreate() { // TODO: It would be nice to have an option to hold a partial wakelock // during processing, and to have a static startService(Context, Intent) // method that would launch the service & hand off a wakelock. super.onCreate(); HandlerThread thread = new HandlerThread("IntentService[" + mName + "]"); thread.start(); mServiceLooper = thread.getLooper(); mServiceHandler = new ServiceHandler(mServiceLooper); } @Override public void onStart(Intent intent, int startId) { Message msg = mServiceHandler.obtainMessage(); msg.arg1 = startId; msg.obj = intent; mServiceHandler.sendMessage(msg); } /** * You should not override this method for your IntentService. Instead, * override {@link #onHandleIntent}, which the system calls when the IntentService * receives a start request. * @see android.app.Service#onStartCommand */ <strong>@Override public int onStartCommand(Intent intent, int flags, int startId) { onStart(intent, startId); return mRedelivery ? START_REDELIVER_INTENT : START_NOT_STICKY; }</strong> @Override public void onDestroy() { mServiceLooper.quit(); } /** * Unless you provide binding for your service, you don't need to implement this * method, because the default implementation returns null. * @see android.app.Service#onBind */ @Override public IBinder onBind(Intent intent) { return null; } /** * This method is invoked on the worker thread with a request to process. * Only one Intent is processed at a time, but the processing happens on a * worker thread that runs independently from other application logic. * So, if this code takes a long time, it will hold up other requests to * the same IntentService, but it will not hold up anything else. * When all requests have been handled, the IntentService stops itself, * so you should not call {@link #stopSelf}. * * @param intent The value passed to {@link * android.content.Context#startService(Intent)}. */ @WorkerThread protected abstract void onHandleIntent(Intent intent); } 加上一个实现的子类： import android.app.IntentService; import android.content.Context; import android.content.Intent; import android.net.Uri; import com.google.samples.apps.guangdong.BuildConfig; import com.google.samples.apps.guangdong.R; import com.google.samples.apps.guangdong.io.JSONHandler; import com.google.samples.apps.guangdong.provider.ScheduleContract; import com.google.samples.apps.guangdong.settings.SettingsUtils; import com.google.samples.apps.guangdong.sync.ConferenceDataHandler; import com.google.samples.apps.guangdong.sync.SyncHelper; import com.google.samples.apps.guangdong.util.AccountUtils; import com.google.samples.apps.guangdong.util.LogUtils; import java.io.IOException; import static com.google.samples.apps.guangdong.util.LogUtils.LOGD; import static com.google.samples.apps.guangdong.util.LogUtils.LOGE; import static com.google.samples.apps.guangdong.util.LogUtils.LOGI; import static com.google.samples.apps.guangdong.util.LogUtils.LOGW; /** * An {@code IntentService} that performs the one-time data bootstrap. It takes the prepackaged * conference data from the R.raw.bootstrap_data resource, and populates the database. This data * contains the sessions, speakers, etc. */ public class DataBootstrapService extends IntentService { private static final String TAG = LogUtils.makeLogTag(DataBootstrapService.class); /** * Start the {@link DataBootstrapService} if the bootstrap is either not done or complete yet. * * @param context The context for starting the {@link IntentService} as well as checking if the * shared preference to mark the process as done is set. */ public static void startDataBootstrapIfNecessary(Context context) { if (!SettingsUtils.isDataBootstrapDone(context)) { LOGW(TAG, "One-time data bootstrap not done yet. Doing now."); context.startService(new Intent(context, DataBootstrapService.class)); } } /** * Creates a DataBootstrapService. */ public DataBootstrapService() { super(TAG); } /** 根据app自带数据，从file或者网上下载相关文件 */ @Override protected void onHandleIntent(Intent intent) { Context appContext = getApplicationContext(); if (SettingsUtils.isDataBootstrapDone(appContext)) { LOGD(TAG, "Data bootstrap already done."); return; } try { LOGD(TAG, "Starting data bootstrap process."); // Load data from bootstrap raw resource. String bootstrapJson = JSONHandler .parseResource(appContext, R.raw.bootstrap_data); // Apply the data we read to the database with the help of the ConferenceDataHandler. /** * 利用ConferenceDataHandler将获得的数据处理并写入数据库中 */ ConferenceDataHandler dataHandler = new ConferenceDataHandler(appContext); dataHandler.applyConferenceData(new String[]{bootstrapJson}, BuildConfig.BOOTSTRAP_DATA_TIMESTAMP, false); SyncHelper.performPostSyncChores(appContext); LOGI(TAG, "End of bootstrap -- successful. Marking bootstrap as done."); SettingsUtils.markSyncSucceededNow(appContext); SettingsUtils.markDataBootstrapDone(appContext); getContentResolver().notifyChange(Uri.parse(ScheduleContract.CONTENT_AUTHORITY), null, false); } catch (IOException ex) { // This is serious -- if this happens, the app won't work :-( // This is unlikely to happen in production, but IF it does, we apply // this workaround as a fallback: we pretend we managed to do the bootstrap // and hope that a remote sync will work. LOGE(TAG, "*** ERROR DURING BOOTSTRAP! Problem in bootstrap data?", ex); LOGE(TAG, "Applying fallback -- marking boostrap as done; sync might fix problem."); SettingsUtils.markDataBootstrapDone(appContext); } finally { // Request a manual sync immediately after the bootstrapping process, in case we // have an active connection. Otherwise, the scheduled sync could take a while. SyncHelper.requestManualSync(AccountUtils.getActiveAccount(appContext)); } } }