解析android framework下利用app_process来调用java写的命令及示例

解析android framework下利用app_process来调用java写的命令及示例

在android SDK的framework/base/cmds目录下了，有不少目录，这些目的最终都是build出一个bin文件，再存放到/system/bin目录下，对于C/CPP写的命令，我们还是比较好理解的，都有一个main函数作为入口，但是在cmds目录下还有一些原生代码是java的，比如input、settings，那么这种类型的命令是怎么实现的呢？

笔者研习了原生的命令实现，写了一个demo，抛砖引玉吧！暂时叫strong吧！我们都知道java写的文件最后都是编译成了class文件，java类里面也有很多接口，在android平台上cmds目录下的各模块的java文件都实现了一个共同的方法，还是叫main（），真是情有独钟啊！当然从技术角度看叫其他名字也是可以的。那我们就简单实现以下这个class吧！如下：

    virtual void onVmCreated(JNIEnv* env)    {        if (mClassName == NULL) {            return; // Zygote. Nothing to do here.        }        /*         * This is a little awkward because the JNI FindClass call uses the         * class loader associated with the native method we're executing in.         * If called in onStarted (from RuntimeInit.finishInit because we're         * launching "am", for example), FindClass would see that we're calling         * from a boot class' native method, and so wouldn't look for the class         * we're trying to look up in CLASSPATH. Unfortunately it needs to,         * because the "am" classes are not boot classes.         *         * The easiest fix is to call FindClass here, early on before we start         * executing boot class Java code and thereby deny ourselves access to         * non-boot classes.         */        char* slashClassName = toSlashClassName(mClassName);        mClass = env->FindClass(slashClassName);        if (mClass == NULL) {            ALOGE("ERROR: could not find class '%s'\n", mClassName);        }        free(slashClassName);        mClass = reinterpret_cast<jclass>(env->NewGlobalRef(mClass));    }    virtual void onStarted()    {        sp<ProcessState> proc = ProcessState::self();        ALOGV("App process: starting thread pool.\n");        proc->startThreadPool();        AndroidRuntime* ar = AndroidRuntime::getRuntime();        ar->callMain(mClassName, mClass, mArgC, mArgV);        IPCThreadState::self()->stopProcess();    }if (className) {        // Remainder of args get passed to startup class main()        runtime.mClassName = className;        runtime.mArgC = argc - i;        runtime.mArgV = argv + i;        runtime.start("com.android.internal.os.RuntimeInit",                application ? "application" : "tool");    }

Android平台提供的app_process，还是相当不错的，比较实用，利用好app_process还是可以写成很多供我们自己开发、测试、定制一些特殊的程序，给开发带来了很大的便利。