android 利用反射获取当前系统sdk版本等属性

    在android系统中，/system/build.prop中含有大量系统相关的信息：

# begin build properties# autogenerated by buildinfo.shro.build.id=FRF91ro.build.display.id=sdk-eng 2.2 FRF91 43546 test-keysro.build.version.incremental=43546ro.build.version.sdk=8ro.build.version.codename=RELro.build.version.release=2.2ro.build.date=Wed Jun 30 13:58:00 PDT 2010ro.build.date.utc=1277931480ro.build.type=engro.build.user=android-buildro.build.host=android-test-25.mtv.corp.google.comro.build.tags=test-keysro.product.model=sdkro.product.brand=genericro.product.name=sdkro.product.device=genericro.product.board=ro.product.cpu.abi=armeabiro.product.manufacturer=unknownro.product.locale.language=ldpiro.product.locale.region=ro.wifi.channels=ro.board.platform=# ro.build.product is obsolete; use ro.product.devicero.build.product=generic# Do not try to parse ro.build.description or .fingerprintro.build.description=sdk-eng 2.2 FRF91 43546 test-keysro.build.fingerprint=generic/sdk/generic/:2.2/FRF91/43546:eng/test-keys# end build properties## system.prop for generic sdk#rild.libpath=/system/lib/libreference-ril.sorild.libargs=-d /dev/ttyS0## ADDITIONAL_BUILD_PROPERTIES#ro.config.notification_sound=OnTheHunt.oggro.config.alarm_alert=Alarm_Classic.oggmedia.stagefright.enable-player=truemedia.stagefright.enable-meta=truemedia.stagefright.enable-scan=truemedia.stagefright.enable-http=truero.kernel.android.checkjni=1ro.setupwizard.mode=OPTIONALxmpp.auto-presence=truero.config.nocheckin=yesnet.bt.name=Androiddalvik.vm.stack-trace-file=/data/anr/traces.txt

    想要针对不同sdk版本，进行不同的处理，就要获取sdk的版本，即ro.build.version.sdk对应的值，本来想用下面的方法获取属性值，但是获取不成功：

System.getenv("ro.build.version.sdk")

   在系统源码中发现SystemProperties可以获取这些属性值，但是SystemProperties没有公布出来，于是想到用反射的办法来调用SystemProperties的方法：

package org.ckl.reflect;import java.lang.reflect.Method;import android.util.Log;public class MySystemProperties {private static final String TAG = "MySystemProperties";// String SystemProperties.get(String key){}public static String get(String key) {init();String value = null;try {value = (String) mGetMethod.invoke(mClassType, key);} catch (Exception e) {e.printStackTrace();}return value;}//int SystemProperties.get(String key, int def){}public static int getInt(String key, int def) {init();int value = def;try {Integer v = (Integer) mGetIntMethod.invoke(mClassType, key, def);value = v.intValue();} catch (Exception e) {e.printStackTrace();}return value;}public static int getSdkVersion() {return getInt("ro.build.version.sdk", -1);}//-------------------------------------------------------------------private static Class<?> mClassType = null;private static Method mGetMethod = null;private static Method mGetIntMethod = null;private static void init() {try {if (mClassType == null) {mClassType = Class.forName("android.os.SystemProperties");mGetMethod = mClassType.getDeclaredMethod("get", String.class);mGetIntMethod = mClassType.getDeclaredMethod("getInt", String.class, int.class);}} catch (Exception e) {e.printStackTrace();}}}

上面的方法确实可以获取到sdk的版本：

Log.i(TAG, MySystemProperties.get("ro.build.version.sdk"));Log.i(TAG, "" + MySystemProperties.getInt("ro.build.version.sdk", -1));

后来发现sdk中的android.os.Build完全可以提供这些信息：

/* * Copyright (C) 2007 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.os;import com.android.internal.telephony.TelephonyProperties;/** * Information about the current build, extracted from system properties. */public class Build {    /** Value used for when a build property is unknown. */    public static final String UNKNOWN = "unknown";    /** Either a changelist number, or a label like "M4-rc20". */    public static final String ID = getString("ro.build.id");    /** A build ID string meant for displaying to the user */    public static final String DISPLAY = getString("ro.build.display.id");    /** The name of the overall product. */    public static final String PRODUCT = getString("ro.product.name");    /** The name of the industrial design. */    public static final String DEVICE = getString("ro.product.device");    /** The name of the underlying board, like "goldfish". */    public static final String BOARD = getString("ro.product.board");    /** The name of the instruction set (CPU type + ABI convention) of native code. */    public static final String CPU_ABI = getString("ro.product.cpu.abi");    /** The name of the second instruction set (CPU type + ABI convention) of native code. */    public static final String CPU_ABI2 = getString("ro.product.cpu.abi2");    /** The manufacturer of the product/hardware. */    public static final String MANUFACTURER = getString("ro.product.manufacturer");    /** The brand (e.g., carrier) the software is customized for, if any. */    public static final String BRAND = getString("ro.product.brand");    /** The end-user-visible name for the end product. */    public static final String MODEL = getString("ro.product.model");    /** The system bootloader version number. */    public static final String BOOTLOADER = getString("ro.bootloader");    /**     * The radio firmware version number.     *     * @deprecated The radio firmware version is frequently not     * available when this class is initialized, leading to a blank or     * "unknown" value for this string.  Use     * {@link #getRadioVersion} instead.     */    @Deprecated    public static final String RADIO = getString(TelephonyProperties.PROPERTY_BASEBAND_VERSION);    /** The name of the hardware (from the kernel command line or /proc). */    public static final String HARDWARE = getString("ro.hardware");    /** A hardware serial number, if available.  Alphanumeric only, case-insensitive. */     public static final String SERIAL = getString("ro.serialno");      /** Various version strings. */    public static class VERSION {        /**         * The internal value used by the underlying source control to         * represent this build.  E.g., a perforce changelist number         * or a git hash.         */        public static final String INCREMENTAL = getString("ro.build.version.incremental");        /**         * The user-visible version string.  E.g., "1.0" or "3.4b5".         */        public static final String RELEASE = getString("ro.build.version.release");        /**         * The user-visible SDK version of the framework in its raw String         * representation; use {@link #SDK_INT} instead.         *          * @deprecated Use {@link #SDK_INT} to easily get this as an integer.         */        @Deprecated        public static final String SDK = getString("ro.build.version.sdk");        /**         * The user-visible SDK version of the framework; its possible         * values are defined in {@link Build.VERSION_CODES}.         */        public static final int SDK_INT = SystemProperties.getInt(                "ro.build.version.sdk", 0);        /**         * The current development codename, or the string "REL" if this is         * a release build.         */        public static final String CODENAME = getString("ro.build.version.codename");        /**         * The SDK version to use when accessing resources.         * Use the current SDK version code.  If we are a development build,         * also allow the previous SDK version + 1.         * @hide         */        public static final int RESOURCES_SDK_INT = SDK_INT                + ("REL".equals(CODENAME) ? 0 : 1);    }    /**     * Enumeration of the currently known SDK version codes.  These are the     * values that can be found in {@link VERSION#SDK}.  Version numbers     * increment monotonically with each official platform release.     */    public static class VERSION_CODES {        /**         * Magic version number for a current development build, which has         * not yet turned into an official release.         */        public static final int CUR_DEVELOPMENT = 10000;                /**         * October 2008: The original, first, version of Android.  Yay!         */        public static final int BASE = 1;                /**         * February 2009: First Android update, officially called 1.1.         */        public static final int BASE_1_1 = 2;                /**         * May 2009: Android 1.5.         */        public static final int CUPCAKE = 3;                /**         * September 2009: Android 1.6.         *          * <p>Applications targeting this or a later release will get these         * new changes in behavior:</p>         * <ul>         * <li> They must explicitly request the         * {@link android.Manifest.permission#WRITE_EXTERNAL_STORAGE} permission to be         * able to modify the contents of the SD card.  (Apps targeting         * earlier versions will always request the permission.)         * <li> They must explicitly request the         * {@link android.Manifest.permission#READ_PHONE_STATE} permission to be         * able to be able to retrieve phone state info.  (Apps targeting         * earlier versions will always request the permission.)         * <li> They are assumed to support different screen densities and         * sizes.  (Apps targeting earlier versions are assumed to only support         * medium density normal size screens unless otherwise indicated).         * They can still explicitly specify screen support either way with the         * supports-screens manifest tag.         * </ul>         */        public static final int DONUT = 4;                /**         * November 2009: Android 2.0         *          * <p>Applications targeting this or a later release will get these         * new changes in behavior:</p>         * <ul>         * <li> The {@link android.app.Service#onStartCommand         * Service.onStartCommand} function will return the new         * {@link android.app.Service#START_STICKY} behavior instead of the         * old compatibility {@link android.app.Service#START_STICKY_COMPATIBILITY}.         * <li> The {@link android.app.Activity} class will now execute back         * key presses on the key up instead of key down, to be able to detect         * canceled presses from virtual keys.         * <li> The {@link android.widget.TabWidget} class will use a new color scheme         * for tabs. In the new scheme, the foreground tab has a medium gray background         * the background tabs have a dark gray background.         * </ul>         */        public static final int ECLAIR = 5;                /**         * December 2009: Android 2.0.1         */        public static final int ECLAIR_0_1 = 6;                /**         * January 2010: Android 2.1         */        public static final int ECLAIR_MR1 = 7;                /**         * June 2010: Android 2.2         */        public static final int FROYO = 8;                /**         * November 2010: Android 2.3         */        public static final int GINGERBREAD = 9;                /**         * February 2011: Android 2.3.3.         */        public static final int GINGERBREAD_MR1 = 10;        /**         * February 2011: Android 3.0.         *         * <p>Applications targeting this or a later release will get these         * new changes in behavior:</p>         * <ul>         * <li> The default theme for applications is now dark holographic:         *      {@link android.R.style#Theme_Holo}.         * <li> The activity lifecycle has changed slightly as per         * {@link android.app.Activity}.         * <li> When an application requires a permission to access one of         * its components (activity, receiver, service, provider), this         * permission is no longer enforced when the application wants to         * access its own component.  This means it can require a permission         * on a component that it does not itself hold and still access that         * component.         * </ul>         */        public static final int HONEYCOMB = 11;                /**         * May 2011: Android 3.1.         */        public static final int HONEYCOMB_MR1 = 12;                /**         * June 2011: Android 3.2.         *         * <p>Update to Honeycomb MR1 to support 7 inch tablets, improve         * screen compatibility mode, etc.</p>         *         * <p>As of this version, applications that don't say whether they         * support XLARGE screens will be assumed to do so only if they target         * {@link #HONEYCOMB} or later; it had been {@link #GINGERBREAD} or         * later.  Applications that don't support a screen size at least as         * large as the current screen will provide the user with a UI to         * switch them in to screen size compatibility mode.</p>         *         * <p>This version introduces new screen size resource qualifiers         * based on the screen size in dp: see         * {@link android.content.res.Configuration#screenWidthDp},         * {@link android.content.res.Configuration#screenHeightDp}, and         * {@link android.content.res.Configuration#smallestScreenWidthDp}.         * Supplying these in <supports-screens> as per         * {@link android.content.pm.ApplicationInfo#requiresSmallestWidthDp},         * {@link android.content.pm.ApplicationInfo#compatibleWidthLimitDp}, and         * {@link android.content.pm.ApplicationInfo#largestWidthLimitDp} is         * preferred over the older screen size buckets and for older devices         * the appropriate buckets will be inferred from them.</p>         *         * <p>New {@link android.content.pm.PackageManager#FEATURE_SCREEN_PORTRAIT}         * and {@link android.content.pm.PackageManager#FEATURE_SCREEN_LANDSCAPE}         * features are introduced in this release.  Applications that target         * previous platform versions are assumed to require both portrait and         * landscape support in the device; when targeting Honeycomb MR1 or         * greater the application is responsible for specifying any specific         * orientation it requires.</p>         */        public static final int HONEYCOMB_MR2 = 13;        /**         * Android 4.0.         *         * <p>Applications targeting this or a later release will get these         * new changes in behavior:</p>         * <ul>         * <li> For devices without a dedicated menu key, the software compatibility         * menu key will not be shown even on phones.  By targeting Ice Cream Sandwich         * or later, your UI must always have its own menu UI affordance if needed,         * on both tablets and phones.  The ActionBar will take care of this for you.         * <li> 2d drawing hardware acceleration is now turned on by default.         * You can use         * {@link android.R.attr#hardwareAccelerated android:hardwareAccelerated}         * to turn it off if needed, although this is strongly discouraged since         * it will result in poor performance on larger screen devices.         * <li> The default theme for applications is now the "device default" theme:         *      {@link android.R.style#Theme_DeviceDefault}. This may be the         *      holo dark theme or a different dark theme defined by the specific device.         *      The {@link android.R.style#Theme_Holo} family must not be modified         *      for a device to be considered compatible. Applications that explicitly         *      request a theme from the Holo family will be guaranteed that these themes         *      will not change character within the same platform version. Applications         *      that wish to blend in with the device should use a theme from the         *      {@link android.R.style#Theme_DeviceDefault} family.         * <li> Managed cursors can now throw an exception if you directly close         * the cursor yourself without stopping the management of it; previously failures         * would be silently ignored.         * <li> The fadingEdge attribute on views will be ignored (fading edges is no         * longer a standard part of the UI).  A new requiresFadingEdge attribute allows         * applications to still force fading edges on for special cases.         * </ul>         */        public static final int ICE_CREAM_SANDWICH = 14;    }        /** The type of build, like "user" or "eng". */    public static final String TYPE = getString("ro.build.type");    /** Comma-separated tags describing the build, like "unsigned,debug". */    public static final String TAGS = getString("ro.build.tags");    /** A string that uniquely identifies this build.  Do not attempt to parse this value. */    public static final String FINGERPRINT = getString("ro.build.fingerprint");    // The following properties only make sense for internal engineering builds.    public static final long TIME = getLong("ro.build.date.utc") * 1000;    public static final String USER = getString("ro.build.user");    public static final String HOST = getString("ro.build.host");    /**     * Returns the version string for the radio firmware.  May return     * null (if, for instance, the radio is not currently on).     */    public static String getRadioVersion() {        return SystemProperties.get(TelephonyProperties.PROPERTY_BASEBAND_VERSION, null);    }    private static String getString(String property) {        return SystemProperties.get(property, UNKNOWN);    }    private static long getLong(String property) {        try {            return Long.parseLong(SystemProperties.get(property));        } catch (NumberFormatException e) {            return -1;        }    }}

    也是调用SystemProperties实现的：

    private static String getString(String property) {        return SystemProperties.get(property, UNKNOWN);    }

package org.ckl.reflect;import android.os.Build;import android.util.Log;public class AndroidInfo {private static final String TAG = "AndroidInfo";private AndroidInfo() {}public static void info() {String info =       "Product: "              + Build.PRODUCT    + ", CPU_ABI: "            + Build.CPU_ABI    + ", TAGS: "               + Build.TAGS    + ", VERSION_CODES.BASE: " + Build.VERSION_CODES.BASE    + ", MODEL: "              + Build.MODEL    + ", SDK: "                + Build.VERSION.SDK    + ", VERSION.RELEASE: "    + Build.VERSION.RELEASE    + ", DEVICE: "             + Build.DEVICE    + ", DISPLAY: "            + Build.DISPLAY    + ", BRAND: "              + Build.BRAND    + ", BOARD: "              + Build.BOARD    + ", FINGERPRINT: "        + Build.FINGERPRINT    + ", ID: "                 + Build.ID    + ", MANUFACTURER: "       + Build.MANUFACTURER    + ", USER: "               + Build.USER;    Log.i(TAG, info);}}