Android 框架简介
扫描二维码
随时随地手机看文章
======================= 第一节 ===========================
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
|-- vpn
`-- 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
/**
* Copyright (C) 2006 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.util;
import com.Android.internal.os.RuntimeInit;
import java.io.PrintWriter;
import java.io.StringWriter;
/**
* API for sending log output.
*
*
Generally, use the Log.v() Log.d() Log.i() Log.w() and Log.e()
* methods.
*
*
The order in terms of verbosity, from least to most is
* ERROR, WARN, INFO, DEBUG, VERBOSE. Verbose should never be compiled
* into an application except during development. Debug logs are compiled
* in but stripped at runtime. Error, warning and info logs are always kept.
*
*
Tip: A good convention is to declare a TAG constant
* in your class:
*
*
private static final String TAG = "MyActivity";
*
* and use that in subsequent calls to the log methods.
*
*
*
Tip: Don't forget that when you make a call like
*
Log.v(TAG, "index=" + i);
* that when you're building the string to pass into Log.d, the compiler uses a
* StringBuilder and at least three allocations occur: the StringBuilder
* itself, the buffer, and the String object. Realistically, there is also
* another buffer allocation and copy, and even more pressure on the gc.
* That means that if your log message is filtered out, you might be doing[!--empirenews.page--]
* significant work and incurring significant overhead.
*/
public final class Log {
/**
* Priority constant for the println method; use Log.v.
*/
public static final int VERBOSE = 2;
/**
* Priority constant for the println method; use Log.d.
*/
public static final int DEBUG = 3;
/**
* Priority constant for the println method; use Log.i.
*/
public static final int INFO = 4;
/**
* Priority constant for the println method; use Log.w.
*/
public static final int WARN = 5;
/**
* Priority constant for the println method; use Log.e.
*/
public static final int ERROR = 6;
/**
* Priority constant for the println method.
*/
public static final int ASSERT = 7;
/**
* Exception class used to capture a stack trace in {@link #wtf()}.
*/
private static class TerribleFailure extends Exception {
TerribleFailure(String msg, Throwable cause) { super(msg, cause); }
}
private Log() {
}
/**
* Send a {@link #VERBOSE} log message.
* @param tag Used to identify the source of a log message. It usually identifies
* the class or activity where the log call occurs.
* @param msg The message you would like logged.
*/
public static int v(String tag, String msg) {
return println_native(LOG_ID_MAIN, VERBOSE, tag, msg);
}
/**
* Send a {@link #VERBOSE} log message and log the exception.
* @param tag Used to identify the source of a log message. It usually identifies
* the class or activity where the log call occurs.
* @param msg The message you would like logged.
* @param tr An exception to log
*/
public static int v(String tag, String msg, Throwable tr) {
return println_native(LOG_ID_MAIN, VERBOSE, tag, msg + '/n' + getStackTraceString(tr));
}
/**
* Send a {@link #DEBUG} log message.
* @param tag Used to identify the source of a log message. It usually identifies
* the class or activity where the log call occurs.
* @param msg The message you would like logged.
*/
public static int d(String tag, String msg) {
return println_native(LOG_ID_MAIN, DEBUG, tag, msg);
}
/**
* Send a {@link #DEBUG} log message and log the exception.
* @param tag Used to identify the source of a log message. It usually identifies
* the class or activity where the log call occurs.
* @param msg The message you would like logged.
* @param tr An exception to log
*/
public static int d(String tag, String msg, Throwable tr) {
return println_native(LOG_ID_MAIN, DEBUG, tag, msg + '/n' + getStackTraceString(tr));
}
/**
* Send an {@link #INFO} log message.
* @param tag Used to identify the source of a log message. It usually identifies
* the class or activity where the log call occurs.
* @param msg The message you would like logged.
*/
public static int i(String tag, String msg) {
return println_native(LOG_ID_MAIN, INFO, tag, msg);
}
/**
* Send a {@link #INFO} log message and log the exception.
* @param tag Used to identify the source of a log message. It usually identifies
* the class or activity where the log call occurs.
* @param msg The message you would like logged.
* @param tr An exception to log
*/
public static int i(String tag, String msg, Throwable tr) {
return println_native(LOG_ID_MAIN, INFO, tag, msg + '/n' + getStackTraceString(tr));
}
/**
* Send a {@link #WARN} log message.
* @param tag Used to identify the source of a log message. It usually identifies
* the class or activity where the log call occurs.
* @param msg The message you would like logged.
*/
public static int w(String tag, String msg) {
return println_native(LOG_ID_MAIN, WARN, tag, msg);
}
/**
* Send a {@link #WARN} log message and log the exception.
* @param tag Used to identify the source of a log message. It usually identifies
* the class or activity where the log call occurs.
* @param msg The message you would like logged.
* @param tr An exception to log
*/
public static int w(String tag, String msg, Throwable tr) {
return println_native(LOG_ID_MAIN, WARN, tag, msg + '/n' + getStackTraceString(tr));
}
/**
* Checks to see whether or not a log for the specified tag is loggable at the specified level.
*
* The default level of any tag is set to INFO. This means that any level above and including[!--empirenews.page--]
* INFO will be logged. Before you make any calls to a logging method you should check to see
* if your tag should be logged. You can change the default level by setting a system property:
* 'setprop log.tag.
* Where level is either VERBOSE, DEBUG, INFO, WARN, ERROR, ASSERT, or SUPPRESS. SUPPRESS will
* turn off all logging for your tag. You can also create a local.prop file that with the
* following in it:
* 'log.tag.
* and place that in /data/local.prop.
*
* @param tag The tag to check.
* @param level The level to check.
* @return Whether or not that this is allowed to be logged.
* @throws IllegalArgumentException is thrown if the tag.length() > 23.
*/
public static native boolean isLoggable(String tag, int level);
/**
* Send a {@link #WARN} log message and log the exception.
* @param tag Used to identify the source of a log message. It usually identifies
* the class or activity where the log call occurs.
* @param tr An exception to log
*/
public static int w(String tag, Throwable tr) {
return println_native(LOG_ID_MAIN, WARN, tag, getStackTraceString(tr));
}
/**
* Send an {@link #ERROR} log message.
* @param tag Used to identify the source of a log message. It usually identifies
* the class or activity where the log call occurs.
* @param msg The message you would like logged.
*/
public static int e(String tag, String msg) {
return println_native(LOG_ID_MAIN, ERROR, tag, msg);
}
/**
* Send a {@link #ERROR} log message and log the exception.
* @param tag Used to identify the source of a log message. It usually identifies
* the class or activity where the log call occurs.
* @param msg The message you would like logged.
* @param tr An exception to log
*/
public static int e(String tag, String msg, Throwable tr) {
return println_native(LOG_ID_MAIN, ERROR, tag, msg + '/n' + getStackTraceString(tr));
}
/**
* What a Terrible Failure: Report a condition that should never happen.
* The error will always be logged at level ASSERT with the call stack.
* Depending on system configuration, a report may be added to the
* {@link Android.os.DropBoxManager} and/or the process may be terminated
* immediately with an error dialog.
* @param tag Used to identify the source of a log message.
* @param msg The message you would like logged.
*/
public static int wtf(String tag, String msg) {
return wtf(tag, msg, null);
}
/**
* What a Terrible Failure: Report an exception that should never happen.
* Similar to {@link #wtf(String, String)}, with an exception to log.
* @param tag Used to identify the source of a log message.
* @param tr An exception to log.
*/
public static int wtf(String tag, Throwable tr) {
return wtf(tag, tr.getMessage(), tr);
}
/**
* What a Terrible Failure: Report an exception that should never happen.
* Similar to {@link #wtf(String, Throwable)}, with a message as well.
* @param tag Used to identify the source of a log message.
* @param msg The message you would like logged.
* @param tr An exception to log. May be null.
*/
public static int wtf(String tag, String msg, Throwable tr) {
tr = new TerribleFailure(msg, tr);
int bytes = println_native(LOG_ID_MAIN, ASSERT, tag, getStackTraceString(tr));
RuntimeInit.wtf(tag, tr);
return bytes;
}
/**
* Handy function to get a loggable stack trace from a Throwable
* @param tr An exception to log
*/
public static String getStackTraceString(Throwable tr) {
if (tr == null) {
return "";
}
StringWriter sw = new StringWriter();
PrintWriter pw = new PrintWriter(sw);
tr.printStackTrace(pw);
return sw.toString();
}
/**
* Low-level logging call.
* @param priority The priority/type of this log message
* @param tag Used to identify the source of a log message. It usually identifies
* the class or activity where the log call occurs.
* @param msg The message you would like logged.
* @return The number of bytes written.
*/
public static int println(int priority, String tag, String msg) {
return println_native(LOG_ID_MAIN, priority, tag, msg);
}
/** @hide */ public static final int LOG_ID_MAIN = 0;
/** @hide */ public static final int LOG_ID_RADIO = 1;
/** @hide */ public static final int LOG_ID_EVENTS = 2;[!--empirenews.page--]
/** @hide */ public static final int LOG_ID_SYSTEM = 3;
/** @hide */ public static native int println_native(int bufID,
int priority, String tag, String msg);
}
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
/*
* In class Android.util.Log:
* public static native int println_native(int buffer, int priority, String tag, String msg)
*/
static jint Android_util_Log_println_native(JNIEnv* env, jobject clazz,
jint bufID, jint priority, jstring tagObj, jstring msgObj)
{
const char* tag = NULL;
const char* msg = NULL;
if (msgObj == NULL) {
jclass npeClazz;
npeClazz = env->FindClass("java/lang/NullPointerException");
assert(npeClazz != NULL);
env->ThrowNew(npeClazz, "println needs a message");
return -1;
}
if (bufID < 0 || bufID >= LOG_ID_MAX) {
jclass npeClazz;
npeClazz = env->FindClass("java/lang/NullPointerException");
assert(npeClazz != NULL);
env->ThrowNew(npeClazz, "bad bufID");
return -1;
}
if (tagObj != NULL)
tag = env->GetStringUTFChars(tagObj, NULL);
msg = env->GetStringUTFChars(msgObj, NULL);
int res = __Android_log_buf_write(bufID, (android_LogPriority)priority, tag, msg);
if (tag != NULL)
env->ReleaseStringUTFChars(tagObj, tag);
env->ReleaseStringUTFChars(msgObj, msg);
return res;
}
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
./system/core/include/cutils/log.h:int __Android_log_buf_write(int bufID, int prio, const char *tag, const char *text);
./system/core/liblog/logd_write.c:int __Android_log_buf_write(int bufID, int prio, const char *tag, const char *msg)
./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。
下载文档
