APN，这东西对于刚接触的人来说并非那么好理解。对于3G移植上网不可缺少，这里记录一下。
撰写不易,转载请注明出处：
概念：
APN(Access Point Name),也就是 接入点 ，移动设备使用数据流量上网必须配置的一个參数，代表以何种方式来连接服务台开启数据流量功能.
一般有訪问WAP或者connect 因特网，国内的运营商2G，3G标识例如以下：
移动公司：2G:GSM、3G:TD-SCDMA
联通公司：2G:GSM、3G:WCDMA 电信公司：2G:CDMA、3G:CDMA2000关于详细某个运营商的几G网络 的APN 是什么详细可參考/device/sample/etc/apns-full-conf.xml
这个xml文件里有google预置的多国经常使用的APN
使用：
apns-full-conf.xml
上面说道了apns-full-conf.xml 这个配置文件，这里面基本上是这种模块：
其他选项都是网络參数，当中的apn就是我们最重要的接入点.也可自行加入apn属性模块.
移植3G时，就须要用到这个xml配置文件了。在android的device.mk 里面加个PRODUCT_COPY_FILES：
PRODUCT_COPY_FILES += \ device/sample/etc/apns-full-conf.xml:system/etc/apns-conf.xml
telephony.db
这个文件被载入的地方可參考/packages/providers/TelephonyProvider/src/com/android/providers/telephony/TelephonyProvider.java：
private static final String DATABASE_NAME = "telephony.db"; //数据库db文件 private static final String PARTNER_APNS_PATH = "etc/apns-conf.xml"; //上面说到的copy到系统system/etc文件夹下... private static class DatabaseHelper extends SQLiteOpenHelper { // Context to access resources with private Context mContext; /** * DatabaseHelper helper class for loading apns into a database. * * @param context of the user. */ public DatabaseHelper(Context context) { super(context, DATABASE_NAME, null, getVersion(context)); mContext = context; }... @Override public void onCreate(SQLiteDatabase db) { // Set up the database schema db.execSQL("CREATE TABLE " + CARRIERS_TABLE + //建表 "(_id INTEGER PRIMARY KEY," + "name TEXT," + "numeric TEXT," + "mcc TEXT," + "mnc TEXT," + "apn TEXT," + "user TEXT," + "server TEXT," + "password TEXT," + "proxy TEXT," + "port TEXT," + "mmsproxy TEXT," + "mmsport TEXT," + "mmsc TEXT," + "authtype INTEGER," + "type TEXT," + "current INTEGER," + "protocol TEXT," + "roaming_protocol TEXT," + "carrier_enabled BOOLEAN," + "bearer INTEGER);"); initDatabase(db); } private void initDatabase(SQLiteDatabase db) {... // Environment.getRootDirectory() is a fancy way of saying ANDROID_ROOT or "/system". File confFile = new File(Environment.getRootDirectory(), PARTNER_APNS_PATH); //这里就是载入解析 load进db 了 FileReader confreader = null; try { confreader = new FileReader(confFile); confparser = Xml.newPullParser(); confparser.setInput(confreader); XmlUtils.beginDocument(confparser, "apns"); // Sanity check. Force internal version and confidential versions to agree int confversion = Integer.parseInt(confparser.getAttributeValue(null, "version")); if (publicversion != confversion) { throw new IllegalStateException("Internal APNS file version doesn't match " + confFile.getAbsolutePath()); } loadApns(db, confparser); } ... }} 由于Content Provider採用的是懒载入机制，所以仅仅有检測load上sim卡的时候才会被创建这个db：
可使用sqlite3查看：
createAllApnList
在android中数据流量由/frameworks/opt/telephony/src/java/com/android/internal/telephony/DataConnectionTracker.java
以及它的子类GsmDataConnectionTracker.java(GSM模式) 或者 CdmaDataConnectionTracker.java(CDMA模式)，(前者为移动，联通，后者为电信专用)
来控制，当中启动数据流量开关为onSetUserDataEnabled(boolean enabled).
这里单以GSM模式来说，在SIM 被load时调用：
private void onRecordsLoaded() { if (DBG) log("onRecordsLoaded: createAllApnList"); createAllApnList(); if(!mUserDataEnabled) return;//jscese add judgement if (mPhone.mCM.getRadioState().isOn()) { if (DBG) log("onRecordsLoaded: notifying data availability"); notifyOffApnsOfAvailability(Phone.REASON_SIM_LOADED); } setupDataOnReadyApns(Phone.REASON_SIM_LOADED); } 调用进createAllApnList
/** * Based on the sim operator numeric, create a list for all possible * Data Connections and setup the preferredApn. */ private void createAllApnList() { mAllApns = new ArrayList (); IccRecords r = mIccRecords.get(); String operator = (r != null) ? r.getOperatorNumeric() : ""; if (operator != null) { String selection = "numeric = '" + operator + "'"; // query only enabled apn. // carrier_enabled : 1 means enabled apn, 0 disabled apn. selection += " and carrier_enabled = 1"; if (DBG) log("createAllApnList: selection=" + selection); Cursor cursor = mPhone.getContext().getContentResolver().query( //用当前SIM卡相应的运营商查询系统的全部APN。往下调用createApnList Telephony.Carriers.CONTENT_URI, null, selection, null, null); if (cursor != null) { if (cursor.getCount() > 0) { mAllApns = createApnList(cursor); //能够跟进去看查询Telephony.Carriers并返回一个Apn的list } cursor.close(); } } if (mAllApns.isEmpty()) { if (DBG) log("createAllApnList: No APN found for carrier: " + operator); mPreferredApn = null; // TODO: What is the right behaviour? //notifyNoData(GsmDataConnection.FailCause.MISSING_UNKNOWN_APN); } else { mPreferredApn = getPreferredApn(); if (mPreferredApn != null && !mPreferredApn.numeric.equals(operator)) { mPreferredApn = null; setPreferredApn(-1); } if (DBG) log("createAllApnList: mPreferredApn=" + mPreferredApn); } if (DBG) log("createAllApnList: X mAllApns=" + mAllApns); }
onSetUserDataEnabled(true)：
代表打开数据流量。终于调用到
private boolean trySetupData(ApnContext apnContext){... if (apnContext.getState() == DctConstants.State.IDLE) { ArrayList waitingApns = buildWaitingApns(apnContext.getApnType());//使用用户设置的preferred APN构建一个可用于数据连接的备选APN列表，即waitingApns列表（当有preferred APN，该列表就仅仅有一个）。 //若用户没有设置preferred APN，则将全部类型匹配的APN加入到waitingApns列表（如default类型） if (waitingApns.isEmpty()) { if (DBG) log("trySetupData: No APN found"); notifyNoData(GsmDataConnection.FailCause.MISSING_UNKNOWN_APN, apnContext); notifyOffApnsOfAvailability(apnContext.getReason()); return false; } else { apnContext.setWaitingApns(waitingApns); if (DBG) { log ("trySetupData: Create from mAllApns : " + apnListToString(mAllApns)); } } } if (DBG) { log ("Setup watingApns : " + apnListToString(apnContext.getWaitingApns())); } // apnContext.setReason(apnContext.getReason()); boolean retValue = setupData(apnContext); // waitingApns列表中有可用的APN时，尝试建立连接 notifyOffApnsOfAvailability(apnContext.getReason()); return retValue; ... }
另外几个对apn操作的几个函数都在这个文件中面。分别的作用例如以下：onApnChanged：当APN被用户更改时，将调用到此函数，又一次建立数据连接
setPreferredApn：当用户没有设置preferred APN时，将当前数据连接成功的那个APN设置为preferred APN。
能够去看onDataSetupComplete时的操作。
getPreferredApn：用户获取用户设置的preferred APN，这个在上面说到的createAllApnList时会去获取一次。看是否存在.
对于这个preferredApn会以xml的形式保存在：
shell@android:/data/data/com.android.providers.telephony/shared_prefs # cat preferred-apn.xmlml <
xml version='1.0' encoding='utf-8' standalone='yes' ?> <map> <long name="apn_id" value="1124" /> </map>
这是代表打开数据流量成功之后保存的apn map。能够像上面一样去 telephony.db里面查查看看：sqlite> select * from carriers where _id='1124';1124|沃3G连接互联网 (China Unicom)|46001|460|01|3gnet|||||||||-1|default,supl|1|IP|IP|1|0这里仅仅是分析了一下apn的由来以及在framework层的使用，终于是通过RIL.java 的setupDataCall通过一个rild 的socket发请求到hardware的ril.cpp：
public void setupDataCall(String radioTechnology, String profile, String apn, /*上面传下来的apn*/ String user, String password, String authType, String protocol, Message result) { RILRequest rr = RILRequest.obtain(RIL_REQUEST_SETUP_DATA_CALL, result); rr.mp.writeInt(7); rr.mp.writeString(radioTechnology); rr.mp.writeString(profile); rr.mp.writeString(apn); rr.mp.writeString(user); rr.mp.writeString(password); rr.mp.writeString(authType); rr.mp.writeString(protocol); if (RILJ_LOGD) riljLog(rr.serialString() + "> " + requestToString(rr.mRequest) + " " + radioTechnology + " " + profile + " " + apn + " " + user + " " + password + " " + authType + " " + protocol); send(rr); //里面就是 socket了 } 再之后怎么获取到这个socket event处理而且交给reference-ril 发送这个apn接入网路可參考我前面的博客：