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android基础架构

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 楼主| 心愿wish 发表于 2013-9-30 10:34 | 显示全部楼层 |阅读模式
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 楼主| 心愿wish 发表于 2013-9-30 10:36 | 显示全部楼层
本帖最后由 心愿wish 于 2013-9-30 10:37 编辑

Android 框架简介
这里简单的介绍了Android的java环境基础，在后面一节中会结合具体的实例来理解这一节的内容。
一、Dalvik虚拟机
Dalvik是Android的程序的java虚拟机，代码在dalvik/下，
./
|-- Android.mk
|-- CleanSpec.mk
|-- MODULE_LICENSE_APACHE2
|-- NOTICE


|-- README.txt
|-- dalvikvm 虚拟机的实现库  
|-- dexdump  
|-- dexlist
|-- dexopt
|-- docs
|-- dvz
|-- dx
|-- hit
|-- libcore
|-- libcore-disabled
|-- libdex
|-- libnativehelper 使用JNI调用本地代码时用到这个库
|-- run-core-tests.sh
|-- tests
|-- tools
`-- vm二、Android的java框架
Android层次中第3层是java框架，第四层就是java应用程序。
Android的java类代码，主要是在frameworks/base/core/java/下，
./
|-- Android
|-- com
|-- jarjar-rules.txt
`-- overview.html
我们再看一下frameworks/base/目录
./
|-- Android.mk
|-- CleanSpec.mk
|-- MODULE_LICENSE_APACHE2
|-- NOTICE
|-- api
|-- awt
|-- build
|-- camera
|-- cmds
|-- common
|-- core
|-- data
|-- docs
|-- graphics
|-- include
|-- keystore
|-- libs
|-- location
|-- media
|-- native
|-- obex
|-- opengl
|-- packages
|-- preloaded-classes
|-- sax
|-- services
|-- telephony
|-- test-runner
|-- tests
|-- tools
|-- ***
`-- wifi
这里也有Android的java框架代码。
三、JNI
在Android中，通过JNI，java可以调用C写的代码，主要的实现是在frameworks/base/core/jni，通过查看Android.mk，我们可以看到最后生成了libandroid_runtime.so，具体实现JNI功能需要上面我们介绍的libnativehelper.so，
四、系统服务之java
1、binder，提供Android的IPC功能
2、servicemanager，服务管理的服务器端
3、系统进程zygote，负责孵化所有的新应用
======================= 第二节 ==========================
  在我平时工作中主要是进行linux网络子系统的模块开发、linux应用程序（C/C++）开发。在学习和从事驱动模块开发的过程中，如果你对linux系统本身，包括应用程序开发都不了解，那么读内核代码就如同天书，毫无意义，所以我分析框架也是从基本系统api开始的，当然也不会太多涉及到应用程序开发。
好，开始这节主要是讲一个简单的adnroid应用程序，从应用程序出发，到框架代码。

分析的应用程序我们也奉行拿来主义:froyo/development/samples/HelloActivity
./
|-- Android.mk
|-- AndroidManifest.xml
|-- res
|-- src
`-- tests
其他的就多说了，看代码
  
01/*

02 * Copyright (C) 2007 The Android Open Source Project

03 *

04 * Licensed under the Apache License, Version 2.0 (the "License");

05 * you may not use this file except in compliance with the License.

06 * You may obtain a copy of the License at

07 *

08 *      http://www.apache.org/licenses/LICENSE-2.0

09 *

10 * Unless required by applicable law or agreed to in writing, software

11 * distributed under the License is distributed on an "AS IS" BASIS,

12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

13 * See the License for the specific language governing permissions and

14 * limitations under the License.

15 */  

16package com.example.Android.helloactivity;  

17import Android.app.Activity;  

18import Android.os.Bundle;  

19/**

20 * A minimal "Hello, World!" application.

21 */  

22public class HelloActivity extends Activity {  

23    public HelloActivity() {  

24    }  

25    /**

26     * Called with the activity is first created.

27     */

28    @Override

29    public void onCreate(Bundle savedInstanceState) {  

30        super.onCreate(savedInstanceState);  

31        // Set the layout for this activity.  You can find it   

32        // in res/layout/hello_activity.xml   

33        setContentView(R.layout.hello_activity);  

34    }  

35}




每一个写过Android程序的人都应该是从这个代码起步的吧？那好，那么我们研究android框架也从这里启航。
首先是
  
1import Android.app.Activity;  

2import Android.os.Bundle;



  记住，我们这里不是讲JAVA，我们要讲的是Android.app.Activity，回顾上节的内容，android的JAVA框架代码放在froyo/frameworks/base/，

其中Activity的代码放在框架代码的core/java/Android/app/Activity.java，大概看一下
01public class Activity extends ContextThemeWrapper  

02        implements LayoutInflater.Factory,  

03        Window.Callback, KeyEvent.Callback,  

04        OnCreateContextMenuListener, ComponentCallbacks {  

05    private static final String TAG = "Activity";  

06    /** Standard activity result: operation canceled. */

07    public static final int RESULT_CANCELED    = 0;  

08    /** Standard activity result: operation succeeded. */

09    public static final int RESULT_OK           = -1;  

10    /** Start of user-defined activity results. */

11    public static final int RESULT_FIRST_USER   = 1;  

12    private static long sInstanceCount = 0;



  同样的Bundle的代码core/java/Android/os/Bundle.java
1public final class Bundle implements Parcelable, Cloneable {  

2    private static final String LOG_TAG = "Bundle";  

3    public static final Bundle EMPTY;




呵呵，其实写多应用程序，然后看看这些代码，会有更加豁然开朗的感觉，所以列出以上目录给大家参考，所有的java框架代码都在那个目录下，到这里今天要讨论的第一个问题就到这里了。
我所在的公司是网络设备供应商，其实和Android本身不搭边，android只是平时的爱好而已，所以很多地方如果写错了敬请原谅，当然也计划去做做android系统开发，例如驱动或者是框架开发，这是后话。
======================== 第三节 ========================
  上节讲到了JAVA框架代码和应用程序的关系，那么框架代码和驱动层是怎么联系的呢？这就是这一节的内容：JNI
java使用一种叫做jni的技术来支持对C/C++代码的调用，在anroid中jni的代码放在froyo/frameworks/base/core/jni下，当然在java框架代码的目录下还有其他地方也多多少少放了jni代码，大家可以打开源码来看看。
整体关系如下图：

| java应用程序
--------------------------------------- Android系统api
| java框架
     ｜本地接口声明
--------------------------------------
| JNI
--------------------------------------
| C/C++代码

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 楼主| 心愿wish 发表于 2013-9-30 10:39 | 显示全部楼层
本帖最后由 心愿wish 于 2013-9-30 10:42 编辑

继续拿来主义，C/C++中调试用printf，内核调试用printk，呵呵，Android调试用log，那么我们就分析log的实现。
log的java代码froyo/frameworks/base/core/java/Android/util/Log.java，
001/**

002 * Copyright (C) 2006 The Android Open Source Project

003 *

004 * Licensed under the Apache License, Version 2.0 (the "License");

005 * you may not use this file except in compliance with the License.

006 * You may obtain a copy of the License at

007 *

008 *      http://www.apache.org/licenses/LICENSE-2.0

009 *

010 * Unless required by applicable law or agreed to in writing, software

011 * distributed under the License is distributed on an "AS IS" BASIS,

012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

013 * See the License for the specific language governing permissions and

014 * limitations under the License.

015 */

016package Android.util;  

017import com.Android.internal.os.RuntimeInit;  

018import java.io.PrintWriter;  

019import java.io.StringWriter;  

020/**

021 * API for sending log output.

022 *

023 * <p>Generally, use the Log.v() Log.d() Log.i() Log.w() and Log.e()

024 * methods.

025 *

026 * <p>The order in terms of verbosity, from least to most is

027 * ERROR, WARN, INFO, DEBUG, VERBOSE.  Verbose should never be compiled

028 * into an application except during development.  Debug logs are compiled

029 * in but stripped at runtime.  Error, warning and info logs are always kept.

030 *

031 * <p><b>Tip:</b> A good convention is to declare a <code>TAG</code> constant

032 * in your class:

033 *

034 * <pre>private static final String TAG = "MyActivity";</pre>

035 *

036 * and use that in subsequent calls to the log methods.

037 * </p>

038 *

039 * <p><b>Tip:</b> Don't forget that when you make a call like

040 * <pre>Log.v(TAG, "index=" + i);</pre>

041 * that when you're building the string to pass into Log.d, the compiler uses a

042 * StringBuilder and at least three allocations occur: the StringBuilder

043 * itself, the buffer, and the String object.  Realistically, there is also

044 * another buffer allocation and copy, and even more pressure on the gc.

045 * That means that if your log message is filtered out, you might be doing

046 * significant work and incurring significant overhead.

047 */

048public final class Log {  

049    /**

050     * Priority constant for the println method; use Log.v.

051     */

052    public static final int VERBOSE = 2;  

053    /**

054     * Priority constant for the println method; use Log.d.

055     */

056    public static final int DEBUG = 3;  

057    /**

058     * Priority constant for the println method; use Log.i.

059     */

060    public static final int INFO = 4;  

061    /**

062     * Priority constant for the println method; use Log.w.

063     */

064    public static final int WARN = 5;  

065    /**

066     * Priority constant for the println method; use Log.e.

067     */

068    public static final int ERROR = 6;  

069    /**

070     * Priority constant for the println method.

071     */

072    public static final int ASSERT = 7;  

073    /**

074     * Exception class used to capture a stack trace in {@ link #wtf()}.

075     */

076    private static class TerribleFailure extends Exception {  

077        TerribleFailure(String msg, Throwable cause) { super(msg, cause); }  

078    }  

079    private Log() {  

080    }  

081    /**

082     * Send a {@link #VERBOSE} log message.

083     * @param tag Used to identify the source of a log message.  It usually identifies

084     *        the class or activity where the log call occurs.

085     * @param msg The message you would like logged.

086     */

087    public static int v(String tag, String msg) {  

088        return println_native(LOG_ID_MAIN, VERBOSE, tag, msg);  

089    }  

090    /**

091     * Send a {@link #VERBOSE} log message and log the exception.

092     * @param tag Used to identify the source of a log message.  It usually identifies

093     *        the class or activity where the log call occurs.

094     * @param msg The message you would like logged.

095     * @param tr An exception to log

096     */

097    public static int v(String tag, String msg, Throwable tr) {  

098        return println_native(LOG_ID_MAIN, VERBOSE, tag, msg + '/n' + getStackTraceString(tr));  

099    }  

100    /**

101     * Send a {@link #DEBUG} log message.

102     * @param tag Used to identify the source of a log message.  It usually identifies

103     *        the class or activity where the log call occurs.

104     * @param msg The message you would like logged.

105     */

106    public static int d(String tag, String msg) {  

107        return println_native(LOG_ID_MAIN, DEBUG, tag, msg);  

108    }  

109    /**

110     * Send a {@link #DEBUG} log message and log the exception.

111     * @param tag Used to identify the source of a log message.  It usually identifies

112     *        the class or activity where the log call occurs.

113     * @param msg The message you would like logged.

114     * @param tr An exception to log

115     */

116    public static int d(String tag, String msg, Throwable tr) {  

117        return println_native(LOG_ID_MAIN, DEBUG, tag, msg + '/n' + getStackTraceString(tr));  

118    }  

119    /**

120     * Send an {@link #INFO} log message.

121     * @param tag Used to identify the source of a log message.  It usually identifies

122     *        the class or activity where the log call occurs.

123     * @param msg The message you would like logged.

124     */

125    public static int i(String tag, String msg) {  

126        return println_native(LOG_ID_MAIN, INFO, tag, msg);  

127    }  

128    /**

129     * Send a {@link #INFO} log message and log the exception.

130     * @param tag Used to identify the source of a log message.  It usually identifies

131     *        the class or activity where the log call occurs.

132     * @param msg The message you would like logged.

133     * @param tr An exception to log

134     */

135    public static int i(String tag, String msg, Throwable tr) {  

136        return println_native(LOG_ID_MAIN, INFO, tag, msg + '/n' + getStackTraceString(tr));  

137    }  

138    /**

139     * Send a {@link #WARN} log message.

140     * @param tag Used to identify the source of a log message.  It usually identifies

141     *        the class or activity where the log call occurs.

142     * @param msg The message you would like logged.

143     */

144    public static int w(String tag, String msg) {  

145        return println_native(LOG_ID_MAIN, WARN, tag, msg);  

146    }  

147    /**

148     * Send a {@link #WARN} log message and log the exception.

149     * @param tag Used to identify the source of a log message.  It usually identifies

150     *        the class or activity where the log call occurs.

151     * @param msg The message you would like logged.

152     * @param tr An exception to log

153     */

154    public static int w(String tag, String msg, Throwable tr) {  

155        return println_native(LOG_ID_MAIN, WARN, tag, msg + '/n' + getStackTraceString(tr));  

156    }  

157    /**







  
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 楼主| 心愿wish 发表于 2013-9-30 10:39 | 显示全部楼层
本帖最后由 心愿wish 于 2013-9-30 10:41 编辑

158     * Checks to see whether or not a log for the specified tag is loggable at the specified level.
159     *

160     *  The default level of any tag is set to INFO. This means that any level above and including

161     *  INFO will be logged. Before you make any calls to a logging method you should check to see

162     *  if your tag should be logged. You can change the default level by setting a system property:

163     *      'setprop log.tag.<YOUR_LOG_TAG> <LEVEL>'

164     *  Where level is either VERBOSE, DEBUG, INFO, WARN, ERROR, ASSERT, or SUPPRESS. SUPPRESS will

165     *  turn off all logging for your tag. You can also create a local.prop file that with the

166     *  following in it:

167     *      'log.tag.<YOUR_LOG_TAG>=<LEVEL>'

168     *  and place that in /data/local.prop.

169     *

170     * @param tag The tag to check.

171     * @param level The level to check.

172     *  Whether or not that this is allowed to be logged.

173     * @throws IllegalArgumentException is thrown if the tag.length() > 23.

174     */

175    public static native boolean isLoggable(String tag, int level);  

176    /**

177     * Send a { #WARN} log message and log the exception.

178     * @param tag Used to identify the source of a log message.  It usually identifies

179     *        the class or activity where the log call occurs.

180     * @param tr An exception to log

181     */

182    public static int w(String tag, Throwable tr) {  

183        return println_native(LOG_ID_MAIN, WARN, tag, getStackTraceString(tr));  

184    }  

185    /**

186     * Send an {@link #ERROR} log message.

187     * @param tag Used to identify the source of a log message.  It usually identifies

188     *        the class or activity where the log call occurs.

189     * @param msg The message you would like logged.

190     */

191    public static int e(String tag, String msg) {  

192        return println_native(LOG_ID_MAIN, ERROR, tag, msg);  

193    }  

194    /**

195     * Send a {@link #ERROR} log message and log the exception.

196     * @param tag Used to identify the source of a log message.  It usually identifies

197     *        the class or activity where the log call occurs.

198     * @param msg The message you would like logged.

199     * @param tr An exception to log

200     */

201    public static int e(String tag, String msg, Throwable tr) {  

202        return println_native(LOG_ID_MAIN, ERROR, tag, msg + '/n' + getStackTraceString(tr));  

203    }  

204    /**

205     * What a Terrible Failure: Report a condition that should never happen.

206     * The error will always be logged at level ASSERT with the call stack.

207     * Depending on system configuration, a report may be added to the

208     * {@link Android.os.DropBoxManager} and/or the process may be terminated

209     * immediately with an error dialog.

210     * @param tag Used to identify the source of a log message.

211     * @param msg The message you would like logged.

212     */

213    public static int wtf(String tag, String msg) {  

214        return wtf(tag, msg, null);  

215    }  

216    /**

217     * What a Terrible Failure: Report an exception that should never happen.

218     * Similar to {@link #wtf(String, String)}, with an exception to log.

219     * @param tag Used to identify the source of a log message.

220     * @param tr An exception to log.

221     */

222    public static int wtf(String tag, Throwable tr) {  

223        return wtf(tag, tr.getMessage(), tr);  

224    }  

225    /**

226     * What a Terrible Failure: Report an exception that should never happen.

227     * Similar to {@link #wtf(String, Throwable)}, with a message as well.

228     * @param tag Used to identify the source of a log message.

229     * @param msg The message you would like logged.

230     * @param tr An exception to log.  May be null.

231     */

232    public static int wtf(String tag, String msg, Throwable tr) {  

233        tr = new TerribleFailure(msg, tr);  

234        int bytes = println_native(LOG_ID_MAIN, ASSERT, tag, getStackTraceString(tr));  

235        RuntimeInit.wtf(tag, tr);  

236        return bytes;  

237    }  

238    /**

239     * Handy function to get a loggable stack trace from a Throwable

240     * @param tr An exception to log

241     */

242    public static String getStackTraceString(Throwable tr) {  

243        if (tr == null) {  

244            return "";  

245        }  

246        StringWriter sw = new StringWriter();  

247        PrintWriter pw = new PrintWriter(sw);  

248        tr.printStackTrace(pw);  

249        return sw.toString();  

250    }  

251    /**

252     * Low-level logging call.

253     * @param priority The priority/type of this log message

254     * @param tag Used to identify the source of a log message.  It usually identifies

255     *        the class or activity where the log call occurs.

256     * @param msg The message you would like logged.

257     * @return The number of bytes written.

258     */

259    public static int println(int priority, String tag, String msg) {  

260        return println_native(LOG_ID_MAIN, priority, tag, msg);  

261    }  

262    /** @hide */ public static final int LOG_ID_MAIN = 0;  

263    /** @hide */ public static final int LOG_ID_RADIO = 1;  

264    /** @hide */ public static final int LOG_ID_EVENTS = 2;  

265    /** @hide */ public static final int LOG_ID_SYSTEM = 3;  

266    /** @hide */ public static native int println_native(int bufID,  

267            int priority, String tag, String msg);  

268}


我们看到所有代码都是调用public static native int println_native(int bufID,
             int priority, String tag, String msg);来实现输出的，这个函数的实现就是C++，调用的方式就是JNI
我们看一下对应的jni代码froyo/frameworks/base/core/jni/Android_util_Log.cpp，最终调用的输出函数是
  
01/*

02 * In class Android.util.Log:

03 *  public static native int println_native(int buffer, int priority, String tag, String msg)

04 */

05static jint Android_util_Log_println_native(JNIEnv* env, jobject clazz,  

06        jint bufID, jint priority, jstring tagObj, jstring msgObj)  

07{  

08    const char* tag = NULL;  

09    const char* msg = NULL;  

10    if (msgObj == NULL) {  

11        jclass npeClazz;  

12        npeClazz = env->FindClass("java/lang/NullPointerException");  

13        assert(npeClazz != NULL);  

14        env->ThrowNew(npeClazz, "println needs a message");  

15        return -1;  

16    }  

17    if (bufID < 0 || bufID >= LOG_ID_MAX) {  

18        jclass npeClazz;  

19        npeClazz = env->FindClass("java/lang/NullPointerException");  

20        assert(npeClazz != NULL);  

21        env->ThrowNew(npeClazz, "bad bufID");  

22        return -1;  

23    }  

24    if (tagObj != NULL)  

25        tag = env->GetStringUTFChars(tagObj, NULL);  

26    msg = env->GetStringUTFChars(msgObj, NULL);  

27    int res = __Android_log_buf_write(bufID, (android_LogPriority)priority, tag, msg);  

28    if (tag != NULL)  

29        env->ReleaseStringUTFChars(tagObj, tag);  

30    env->ReleaseStringUTFChars(msgObj, msg);  

31    return res;  

32}



  当然我们发现最终输出是
1int res = __Android_log_buf_write(bufID, (android_LogPriority)priority, tag, msg);



  用力grep了一下代码，结果如下
1./system/core/include/cutils/log.h:int __Android_log_buf_write(int bufID, int prio, const char *tag, const char *text);

2./system/core/liblog/logd_write.c:int __Android_log_buf_write(int bufID, int prio, const char *tag, const char *msg)

3./system/core/liblog/logd_write.c:    return __Android_log_buf_write(bufID, prio, tag, buf);




这个就是和Android专用驱动进行通信的方式，这个分析下去就有点深了，后面分析。
以上三个小节分析了Android的JAVA环境，我这里都是简单的抛砖引玉，希望能给大家一点大体的指引，其他修行靠大家了，能成为是一个android程序员是多么幸福的事情，各位已经在幸福中了，我什么时候也可以幸福一把？？

   
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kekeke 发表于 2013-9-30 10:43 | 显示全部楼层
Android虽然方便，但是各个版本差异很大，应用开发很头疼啊
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monkeypony 发表于 2013-9-30 10:51 | 显示全部楼层
不明觉厉，虽然不太懂，但是还是支持一下，安卓前途远大啊，免费的面包大家都想吃。
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hisong 发表于 2013-9-30 11:34 | 显示全部楼层
现在安卓用户更多啊
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cxljh032302 发表于 2013-10-3 20:06 | 显示全部楼层
好资料，谢谢楼主分享
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cxljh032302 发表于 2013-10-3 20:08 | 显示全部楼层
kekeke 发表于 2013-9-30 10:43
Android虽然方便，但是各个版本差异很大，应用开发很头疼啊

不用考虑那么多，只要在当前版本稳定运行就好，老版本随着硬件的更新，淘汰只是时间问题
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zzx__ 发表于 2013-12-12 19:14 | 显示全部楼层
很详细，好东西！
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