Android在framework层添加自定义服务的流程

环境说明

ubuntu16.04
android4.1
java version “1.6.0_45”
GNU Make 3.81
gcc version 5.4.0 20160609 (Ubuntu 5.4.0-6ubuntu1~16.04.12)

可能有人会问，现在都2024了怎么还在用android4版本，早都过时了。确实，现在最新的都是Android13、Android14了，不过我这里主要是用于demo的演示学习使用，只要整个的流程掌握了，哪个版本的流程都是大同小异；再一个就拿Android13来说，源码100G多非常庞大，代码clone、源码编译都是很慢的，而Android4.1源码才4G多，编译运行就快多了，省时省力。

编写AIDL文件

如果不了解aidl，建议先看看：android AIDL使用demo
仿照系统中现有服务的编写方式，新增服务需要编写aidl接口（也就是提供什么服务），在frameworks/base/core/java/android/helloservice/新建aidl文件，
在这里插入图片描述
ICallBack.aidl内容如下

package android.helloservice;
interface ICallBack {void onReceive(String serverMsg);
}

IHelloService.aidl内容如下

package android.helloservice;
import android.helloservice.ICallBack;
interface IHelloService {String getHello(String send);void registerCallback(ICallBack callback);void unRegisterCallback(ICallBack callback);
}

修改frameworks/base/Android.mk，在LOCAL_SRC_FILES变量中加入新增的aidl文件

## READ ME: ########################################################
##
## When updating this list of aidl files, consider if that aidl is
## part of the SDK API.  If it is, also add it to the list below that
## is preprocessed and distributed with the SDK.  This list should
## not contain any aidl files for parcelables, but the one below should
## if you intend for 3rd parties to be able to send those objects
## across process boundaries.
##
## READ ME: ########################################################
LOCAL_SRC_FILES += \core/java/android/accessibilityservice/IAccessibilityServiceConnection.aidl \core/java/android/accessibilityservice/IAccessibilityServiceClient.aidl \core/java/com/android/internal/widget/IRemoteViewsFactory.aidl \core/java/com/android/internal/widget/IRemoteViewsAdapterConnection.aidl \//省略部分core/java/android/helloservice/ICallBack.aidl \core/java/android/helloservice/IHelloService.aidl \

执行mmm frameworks/base单编，编译成功之后会在out/target/common/obj/JAVA_LIBRARIES/framework_intermediates/src/core/java/android/helloservice/生成如下文件在这里插入图片描述
IHelloService.java内容(androidstudio生成，aosp生成的代码紧凑不方便阅读)

/** This file is auto-generated.  DO NOT MODIFY.*/
package android.helloservice;
public interface IHelloService extends android.os.IInterface
{/** Default implementation for IHelloService. */public static class Default implements android.helloservice.IHelloService{@Override public java.lang.String getHello(java.lang.String send) throws android.os.RemoteException{return null;}@Override public void registerCallback(android.helloservice.ICallBack callback) throws android.os.RemoteException{}@Override public void unRegisterCallback(android.helloservice.ICallBack callback) throws android.os.RemoteException{}@Overridepublic android.os.IBinder asBinder() {return null;}}/** Local-side IPC implementation stub class. */public static abstract class Stub extends android.os.Binder implements android.helloservice.IHelloService{/** Construct the stub at attach it to the interface. */public Stub(){this.attachInterface(this, DESCRIPTOR);}/*** Cast an IBinder object into an android.helloservice.IHelloService interface,* generating a proxy if needed.*/public static android.helloservice.IHelloService asInterface(android.os.IBinder obj){if ((obj==null)) {return null;}android.os.IInterface iin = obj.queryLocalInterface(DESCRIPTOR);if (((iin!=null)&&(iin instanceof android.helloservice.IHelloService))) {return ((android.helloservice.IHelloService)iin);}return new android.helloservice.IHelloService.Stub.Proxy(obj);}@Override public android.os.IBinder asBinder(){return this;}@Override public boolean onTransact(int code, android.os.Parcel data, android.os.Parcel reply, int flags) throws android.os.RemoteException{java.lang.String descriptor = DESCRIPTOR;if (code >= android.os.IBinder.FIRST_CALL_TRANSACTION && code <= android.os.IBinder.LAST_CALL_TRANSACTION) {data.enforceInterface(descriptor);}switch (code){case INTERFACE_TRANSACTION:{reply.writeString(descriptor);return true;}}switch (code){case TRANSACTION_getHello:{java.lang.String _arg0;_arg0 = data.readString();java.lang.String _result = this.getHello(_arg0);reply.writeNoException();reply.writeString(_result);break;}case TRANSACTION_registerCallback:{android.helloservice.ICallBack _arg0;_arg0 = android.helloservice.ICallBack.Stub.asInterface(data.readStrongBinder());this.registerCallback(_arg0);reply.writeNoException();break;}case TRANSACTION_unRegisterCallback:{android.helloservice.ICallBack _arg0;_arg0 = android.helloservice.ICallBack.Stub.asInterface(data.readStrongBinder());this.unRegisterCallback(_arg0);reply.writeNoException();break;}default:{return super.onTransact(code, data, reply, flags);}}return true;}private static class Proxy implements android.helloservice.IHelloService{private android.os.IBinder mRemote;Proxy(android.os.IBinder remote){mRemote = remote;}@Override public android.os.IBinder asBinder(){return mRemote;}public java.lang.String getInterfaceDescriptor(){return DESCRIPTOR;}@Override public java.lang.String getHello(java.lang.String send) throws android.os.RemoteException{android.os.Parcel _data = android.os.Parcel.obtain();android.os.Parcel _reply = android.os.Parcel.obtain();java.lang.String _result;try {_data.writeInterfaceToken(DESCRIPTOR);_data.writeString(send);boolean _status = mRemote.transact(Stub.TRANSACTION_getHello, _data, _reply, 0);_reply.readException();_result = _reply.readString();}finally {_reply.recycle();_data.recycle();}return _result;}@Override public void registerCallback(android.helloservice.ICallBack callback) throws android.os.RemoteException{android.os.Parcel _data = android.os.Parcel.obtain();android.os.Parcel _reply = android.os.Parcel.obtain();try {_data.writeInterfaceToken(DESCRIPTOR);_data.writeStrongInterface(callback);boolean _status = mRemote.transact(Stub.TRANSACTION_registerCallback, _data, _reply, 0);_reply.readException();}finally {_reply.recycle();_data.recycle();}}@Override public void unRegisterCallback(android.helloservice.ICallBack callback) throws android.os.RemoteException{android.os.Parcel _data = android.os.Parcel.obtain();android.os.Parcel _reply = android.os.Parcel.obtain();try {_data.writeInterfaceToken(DESCRIPTOR);_data.writeStrongInterface(callback);boolean _status = mRemote.transact(Stub.TRANSACTION_unRegisterCallback, _data, _reply, 0);_reply.readException();}finally {_reply.recycle();_data.recycle();}}}static final int TRANSACTION_getHello = (android.os.IBinder.FIRST_CALL_TRANSACTION + 0);static final int TRANSACTION_registerCallback = (android.os.IBinder.FIRST_CALL_TRANSACTION + 1);static final int TRANSACTION_unRegisterCallback = (android.os.IBinder.FIRST_CALL_TRANSACTION + 2);}public static final java.lang.String DESCRIPTOR = "android.helloservice.IHelloService";public java.lang.String getHello(java.lang.String send) throws android.os.RemoteException;public void registerCallback(android.helloservice.ICallBack callback) throws android.os.RemoteException;public void unRegisterCallback(android.helloservice.ICallBack callback) throws android.os.RemoteException;
}

ICallBack.java内容(androidstudio生成)

/** This file is auto-generated.  DO NOT MODIFY.*/
package android.helloservice;
public interface ICallBack extends android.os.IInterface
{/** Default implementation for ICallBack. */public static class Default implements android.helloservice.ICallBack{@Override public void onReceive(java.lang.String serverMsg) throws android.os.RemoteException{}@Overridepublic android.os.IBinder asBinder() {return null;}}/** Local-side IPC implementation stub class. */public static abstract class Stub extends android.os.Binder implements android.helloservice.ICallBack{/** Construct the stub at attach it to the interface. */public Stub(){this.attachInterface(this, DESCRIPTOR);}/*** Cast an IBinder object into an android.helloservice.ICallBack interface,* generating a proxy if needed.*/public static android.helloservice.ICallBack asInterface(android.os.IBinder obj){if ((obj==null)) {return null;}android.os.IInterface iin = obj.queryLocalInterface(DESCRIPTOR);if (((iin!=null)&&(iin instanceof android.helloservice.ICallBack))) {return ((android.helloservice.ICallBack)iin);}return new android.helloservice.ICallBack.Stub.Proxy(obj);}@Override public android.os.IBinder asBinder(){return this;}@Override public boolean onTransact(int code, android.os.Parcel data, android.os.Parcel reply, int flags) throws android.os.RemoteException{java.lang.String descriptor = DESCRIPTOR;if (code >= android.os.IBinder.FIRST_CALL_TRANSACTION && code <= android.os.IBinder.LAST_CALL_TRANSACTION) {data.enforceInterface(descriptor);}switch (code){case INTERFACE_TRANSACTION:{reply.writeString(descriptor);return true;}}switch (code){case TRANSACTION_onReceive:{java.lang.String _arg0;_arg0 = data.readString();this.onReceive(_arg0);reply.writeNoException();break;}default:{return super.onTransact(code, data, reply, flags);}}return true;}private static class Proxy implements android.helloservice.ICallBack{private android.os.IBinder mRemote;Proxy(android.os.IBinder remote){mRemote = remote;}@Override public android.os.IBinder asBinder(){return mRemote;}public java.lang.String getInterfaceDescriptor(){return DESCRIPTOR;}@Override public void onReceive(java.lang.String serverMsg) throws android.os.RemoteException{android.os.Parcel _data = android.os.Parcel.obtain();android.os.Parcel _reply = android.os.Parcel.obtain();try {_data.writeInterfaceToken(DESCRIPTOR);_data.writeString(serverMsg);boolean _status = mRemote.transact(Stub.TRANSACTION_onReceive, _data, _reply, 0);_reply.readException();}finally {_reply.recycle();_data.recycle();}}}static final int TRANSACTION_onReceive = (android.os.IBinder.FIRST_CALL_TRANSACTION + 0);}public static final java.lang.String DESCRIPTOR = "android.helloservice.ICallBack";public void onReceive(java.lang.String serverMsg) throws android.os.RemoteException;
}

编写系统服务

上面aidl是定义服务接口，下面开始编写一个系统服务来实现接口。参考系统服务MountService.java的路径编写frameworks/base/services/java/com/android/server/HelloService.java

package com.android.server;import android.content.Context;
import android.os.RemoteCallbackList;
import android.os.RemoteException;
import android.util.Log;
import android.helloservice.ICallBack;
import android.helloservice.IHelloService;
public class HelloService extends IHelloService.Stub {private static final String TAG = "HelloService";private RemoteCallbackList<ICallBack> callbackList = new RemoteCallbackList();private Context context;public HelloService(Context context) {this.context = context;Log.d(TAG, "HelloService() init");}@Overridepublic String getHello(String send) throws RemoteException {Log.d(TAG, "getHello() called with: send = [" + send + "]");int num = callbackList.beginBroadcast();for (int i = 0; i < num; i++) {ICallBack callback = callbackList.getBroadcastItem(i);if (callback != null) {callback.onReceive("callback from HelloService with:" + send);}}callbackList.finishBroadcast();return send + ",server receive ok";}@Overridepublic void registerCallback(ICallBack callback) throws RemoteException {callbackList.register(callback);Log.d(TAG, "registerCallback() called with: callback = [" + callback + "]");}@Overridepublic void unRegisterCallback(ICallBack callback) throws RemoteException {callbackList.unregister(callback);Log.d(TAG, "unRegisterCallback() called with: callback = [" + callback + "]");}
}

注册系统服务

所有系统服务都运行在名为 system_server 的进程中，我们也要把服务加入进去。系统中已有很多服务了，我们把它加入到最后，修改frameworks/base/services/java/com/android/server/SystemServer.java

 	@Overridepublic void run() {...省略部分try {Slog.i(TAG, "Entropy Mixer");ServiceManager.addService("entropy", new EntropyMixer());//HelloService的name必须唯一Slog.i(TAG, "HelloService");ServiceManager.addService("HelloService", new HelloService(context));}}

执行mmm frameworks/base/services/java/编译service模块
执行make snod重新打包system.img
执行emulator重启模拟器，发现一直停留在重启界面。在这里插入图片描述
无奈，执行make -j30(本机16核32线程)重编也报错，提示如下

PRODUCT_COPY_FILES device/generic/goldfish/data/etc/apns-conf.xml:system/etc/apns-conf.xml ignored.
Checking API: checkapi-current
target Java: services (out/target/common/obj/JAVA_LIBRARIES/services_intermediates/classes)
out/target/common/obj/PACKAGING/public_api.txt:10084: error 2: Added package android.helloservice******************************
You have tried to change the API from what has been previously approved.To make these errors go away, you have two choices:1) You can add "@hide" javadoc comments to the methods, etc. listed in theerrors above.2) You can update current.txt by executing the following command:make update-apiTo submit the revised current.txt to the main Android repository,you will need approval.
******************************

根据错误提示执行下面命令

make update-api
make -j30
emulator

模拟器重启成功，且看到HelloService相关日志，说明HelloService服务添加成功。

I/InputManager(  147): Starting input manager
D/PermissionCache(   35): checking android.permission.ACCESS_SURFACE_FLINGER for uid=1000 => granted (1193 us)
I/WindowManager(  147): Enabled StrictMode logging for WMThread's Looper
I/SystemServer(  147): HelloService
D/HelloService(  147): HelloService() init
I/SystemServer(  147): No Bluetooh Service (emulator)

App调用服务

framework层添加服务成功后，app如何使用服务呢？有两种方式，下面一一讲解

方式1：拿到AIDL文件直接访问

为了方便开发，用androidstudio新建一个项目名字就叫Hello。把上面的两个aidl文件复制到项目，保持aidl的包名结构，在这里插入图片描述

MainActivity内容如下,其中ServiceManager会报红不用管，因为等下我们要拷贝项目到aosp源码环境下编译，源码环境下可以正常编过。

package com.hai.hello;import android.app.Activity;
import android.helloservice.ICallBack;
import android.helloservice.IHelloService;
import android.os.Bundle;
import android.os.RemoteException;
import android.os.ServiceManager;
import android.util.Log;
import android.view.View;public class MainActivity extends Activity {private static final String TAG = "MainActivity";IHelloService mService;ICallBack.Stub callback = new ICallBack.Stub() {@Overridepublic void onReceive(String serverMsg) throws RemoteException {Log.d(TAG, "onReceive() called with: serverMsg = [" + serverMsg + "]");}};@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);mService = IHelloService.Stub.asInterface(ServiceManager.getService("HelloService"));Log.d(TAG, "onCreate: " + mService);try {mService.registerCallback(callback);} catch (RemoteException e) {throw new RuntimeException(e);}try {mService.getHello("client say hello");} catch (RemoteException e) {throw new RuntimeException(e);}try {mService.unRegisterCallback(callback);} catch (RemoteException e) {throw new RuntimeException(e);}}
}

把项目拷贝到packages/experimental/目录下。参考此目录下的其他app的项目结构，移除不要的文件，最终Hello的目录结构如图在这里插入图片描述
Android.mk内容如下

LOCAL_PATH:= $(call my-dir)
include $(CLEAR_VARS)
LOCAL_MODULE_TAGS := optional
#LOCAL_SRC_FILES := $(call all-java-files-under, src)
LOCAL_SRC_FILES := $(call all-subdir-java-files)
LOCAL_SRC_FILES += aidl/android/helloservice/IHelloService.aidl
LOCAL_SRC_FILES += aidl/android/helloservice/ICallBack.aidl
LOCAL_PACKAGE_NAME := Hello
LOCAL_CERTIFICATE := platform
include $(BUILD_PACKAGE)

执行以下命令单编Hello项目，重启模拟器，

mmm packages/experimental/Hello
make snod
emulator

在这里插入图片描述
点击启动app，从日志可以看到Hello app启动成功并和HelloService正确交互了。

方式2：通过getSystemService访问

为了方便开发者使用，我们也提供通用接口context.getSystemService()方式获取服务。仿照AccountManager我们也写一个类就叫HelloManager吧，
frameworks/base/core/java/android/helloservice/HelloManager.java内容如下

package android.helloservice;
import android.content.Context;
import android.helloservice.ICallBack;
import android.helloservice.IHelloService;
import android.os.RemoteException;
import android.util.Log;public class HelloManager {private static final String TAG = "HelloManager";private Context context;private IHelloService service;public HelloManager(Context context, IHelloService service) {this.context = context;this.service = service;Log.d(TAG, "HelloManager()");}public String getHello(String send) {try {return service.getHello(send);} catch (RemoteException ex) {throw new RuntimeException(ex);}}public void registerCallback(ICallBack callback) {try {service.registerCallback(callback);} catch (RemoteException ex) {throw new RuntimeException(ex);}}public void unRegisterCallback(ICallBack callback) {try {service.unRegisterCallback(callback);} catch (RemoteException ex) {throw new RuntimeException(ex);}}
}

HelloManager写好之后需要注册到context中，修改frameworks/base/core/java/android/app/ContextImpl.java如下：

import android.helloservice.IHelloService;
import android.helloservice.HelloManager; 
static {...省略部分   registerService(ACCESSIBILITY_SERVICE, new ServiceFetcher() {public Object getService(ContextImpl ctx) {return AccessibilityManager.getInstance(ctx);}});registerService("HelloService", new ServiceFetcher() {public Object createService(ContextImpl ctx) {IBinder b = ServiceManager.getService("HelloService");IHelloService service = IHelloService.Stub.asInterface(b);return new HelloManager(ctx, service);}});registerService(ACTIVITY_SERVICE, new ServiceFetcher() {public Object createService(ContextImpl ctx) {return new ActivityManager(ctx.getOuterContext(), ctx.mMainThread.getHandler());}});

然后是app使用，这里还是使用Hello项目，修改MainActivity内容如下

package com.hai.hello;
import android.app.Activity;
import android.helloservice.ICallBack;
import android.helloservice.IHelloService;
import android.helloservice.HelloManager;
import android.os.Bundle;
import android.os.RemoteException;
import android.os.ServiceManager;
import android.util.Log;
import android.view.View;public class MainActivity extends Activity {private static final String TAG = "MainActivity";IHelloService mService;ICallBack.Stub callback = new ICallBack.Stub() {@Overridepublic void onReceive(String serverMsg) throws RemoteException {Log.d(TAG, "onReceive() called with: serverMsg = [" + serverMsg + "]");}};@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);HelloManager helloManager=(HelloManager) getSystemService("HelloService");Log.d(TAG, "HelloManager onCreate: " + mService);helloManager.registerCallback(callback);helloManager.getHello("client say hello");helloManager.unRegisterCallback(callback);}
}

执行下面命令

mmm packages/experimental/Hello/
make update-api
make -j30
emulator

模拟器重启后看到如下日志，说明getSystemService的方式也访问成功。
在这里插入图片描述
参考：
Android 添加系统服务的完整流程SystemService
为Android系统的Application Frameworks层增加硬件访问服务
为Android硬件抽象层（HAL）模块编写JNI方法提供Java访问硬件服务接口