android 内外置SD卡的研究

来源：互联网发布：java打印杨辉三角10行编辑：程序博客网时间：2024/04/28 03:32

最近网站后台监控上传的app崩溃记录，最常见的一条就是获取手机sd卡根目录出现崩溃。所以有查找各方面的资料，以及看android api源码。

以前的Android(4.1之前的版本)中，SDcard跟路径通过“/sdcard”或者“/mnt/sdcard”来表示存储卡，而在Jelly Bean系统中修改为了“/storage/sdcard0”，以后可能还会有多个SDcard的情况。

目前为了保持和之前代码的兼容，sdcard路径做了link映射。

为了使您的代码更加健壮并且能够兼容以后的Android版本和新的设备，请通过Environment.getExternalStorageDirectory().getPath()来获取sdcard路径。

1、通用的获取语句

Environment.getExternalStorageDirectory().getPath()

当外置sd卡不存在的情况下，这条语句是获取的内置sd卡的路径。外置sd卡存在，获取是外置sd卡。获取出来的值是/storage/sdcard0

2、那么内置sd卡是怎样的

public static String getSoftwareStorageDirectory() {Map<String,String> sysInfo=System.getenv();//获取外置的sd卡String sd_defult = sysInfo.get("SECONDARY_STORAGE");    return sd_defult;}

获取出来的值是/storage/sdcard1，看序号一个是0，一个是1。我在网上看到有人说，这种获取方法，在api23中将不存在，我还没验证，没有相应的机子测试，以及查看api23的源码。就是这个字段在API 23版本中 SECONDARY_STORAGE 被移除。这种获取方法也是类似于源码获取方式。

调试时候Map<String,String> sysInfo=System.getenv();，这句语句获取出来的值如下：

{ANDROID_SOCKET_zygote=9, SECONDARY_STORAGE=/storage/sdcard1,ANDROID_STORAGE=/storage, ANDROID_BOOTLOGO=1,EXTERNAL_STORAGE=/storage/sdcard0,ANDROID_ASSETS=/system/app,ASEC_MOUNTPOINT=/mnt/asec, PATH=/sbin:/vendor/bin:/system/sbin:/system/bin:/system/xbin,LOOP_MOUNTPOINT=/mnt/obb, BOOTCLASSPATH=/system/framework/core.jar:/system/framework/core-junit.jar:/system/framework/bouncycastle.jar:/system/framework/ext.jar:/system/framework/framework.jar:/system/framework/telephony-common.jar:/system/framework/mms-common.jar:/system/framework/android.policy.jar:/system/framework/services.jar:/system/framework/apache-xml.jar:/system/framework/mediatek-common.jar:/system/framework/mediatek-framework.jar:/system/framework/secondary-framework.jar:/system/framework/CustomProperties.jar:/system/framework/mediatek-telephony-common.jar:/system/framework/mediatek-op.jar, ANDROID_DATA=/data, ANDROID_PROPERTY_WORKSPACE=8,49664,ANDROID_ROOT=/system,LD_LIBRARY_PATH=/vendor/lib:/system/lib}

api17源码，部分源码Environment

    private static final String ENV_EXTERNAL_STORAGE = "EXTERNAL_STORAGE";    private static final String ENV_EMULATED_STORAGE_SOURCE = "EMULATED_STORAGE_SOURCE";    private static final String ENV_EMULATED_STORAGE_TARGET = "EMULATED_STORAGE_TARGET";    private static final String ENV_MEDIA_STORAGE = "MEDIA_STORAGE";

        public UserEnvironment(int userId) {            // See storage config details at http://source.android.com/tech/storage/            String rawExternalStorage = System.getenv(ENV_EXTERNAL_STORAGE);            String rawEmulatedStorageTarget = System.getenv(ENV_EMULATED_STORAGE_TARGET);            String rawMediaStorage = System.getenv(ENV_MEDIA_STORAGE);            if (TextUtils.isEmpty(rawMediaStorage)) {                rawMediaStorage = "/data/media";            }            if (!TextUtils.isEmpty(rawEmulatedStorageTarget)) {                // Device has emulated storage; external storage paths should have                // userId burned into them.                final String rawUserId = Integer.toString(userId);                final File emulatedBase = new File(rawEmulatedStorageTarget);                final File mediaBase = new File(rawMediaStorage);                // /storage/emulated/0                mExternalStorage = buildPath(emulatedBase, rawUserId);                // /data/media/0                mMediaStorage = buildPath(mediaBase, rawUserId);            } else {                // Device has physical external storage; use plain paths.                if (TextUtils.isEmpty(rawExternalStorage)) {                    Log.w(TAG, "EXTERNAL_STORAGE undefined; falling back to default");                    rawExternalStorage = "/storage/sdcard0";                }                // /storage/sdcard0                mExternalStorage = new File(rawExternalStorage);                // /data/media                mMediaStorage = new File(rawMediaStorage);            }            mExternalStorageAndroidObb = buildPath(mExternalStorage, DIRECTORY_ANDROID, "obb");            mExternalStorageAndroidData = buildPath(mExternalStorage, DIRECTORY_ANDROID, "data");            mExternalStorageAndroidMedia = buildPath(mExternalStorage, DIRECTORY_ANDROID, "media");        }

在上面的源码当中String sdcardPath = System.getenv("EXTERNAL_STORAGE"); 获取也是外置sd卡。

可是在源码中也是没有看到String extSdcardPath = System.getenv("SECONDARY_STORAGE"); 。SECONDARY_STORAGE这个变量是没有，我也纳闷，怎么也可以使用。这就有点疑问了。

获取外置sd卡是否存在的源码

    /**     * Gets the current state of the primary "external" storage device.     *      * @see #getExternalStorageDirectory()     */    public static String getExternalStorageState() {        try {            IMountService mountService = IMountService.Stub.asInterface(ServiceManager                    .getService("mount"));            final StorageVolume primary = getPrimaryVolume();            return mountService.getVolumeState(primary.getPath());        } catch (RemoteException rex) {            Log.w(TAG, "Failed to read external storage state; assuming REMOVED: " + rex);            return Environment.MEDIA_REMOVED;        }    }

一些映射关系

    private static StorageVolume getPrimaryVolume() {        if (sPrimaryVolume == null) {            synchronized (sLock) {                if (sPrimaryVolume == null) {                    try {                        IMountService mountService = IMountService.Stub.asInterface(ServiceManager                                .getService("mount"));                        final StorageVolume[] volumes = mountService.getVolumeList();                        sPrimaryVolume = StorageManager.getPrimaryVolume(volumes);                    } catch (Exception e) {                        Log.e(TAG, "couldn't talk to MountService", e);                    }                }            }        }        return sPrimaryVolume;    }

那么，在android上是怎么判断的。

/** * getExternalStorageState() returns MEDIA_CHECKING if the media is present and being disk-checked * 要获取SD卡首先要确认SD卡是否装载   * @return */public boolean getExternalStorageState(){return Environment.getExternalStorageState().equals(Environment.MEDIA_CHECKING); }

判断是都可以读写

/** * getExternalStorageState() returns MEDIA_MOUNTED  * if the media is present and mounted at its mount point with read/write access.  * 要获取SD卡是否可以读写 * @return */public boolean getExternalStorageStateMOUNTED(){return Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED); }

这里判断读写跟判断是都存在是有歧义的，我测试时候，没有放sd卡，判断读写是可以的，可是外置sd卡根本不存在。写程序时候是不是先要判断存在，再判断能不能读写。

还有一个问题就是，既然外置sd卡不存在时候Environment.getExternalStorageDirectory().getPath()这条语句获取的是内置的sd卡，那么判断是否是内置sd卡的读写呢？

3、网上看到最多获取外置SD卡路径两个方法

方法一

/** * 获取外置SD卡路径 *  * @return 应该就一条记录或空 */public List getExtSDCardPath() {List lResult = new ArrayList();try {Runtime rt = Runtime.getRuntime();Process proc = rt.exec("mount");InputStream is = proc.getInputStream();InputStreamReader isr = new InputStreamReader(is);BufferedReader br = new BufferedReader(isr);String line;//rootfs / rootfs ro,relatime 0 0while ((line = br.readLine()) != null) {if (line.contains("extSdCard")) {String[] arr = line.split(" ");String path = arr[1];File file = new File(path);if (file.isDirectory()) {lResult.add(path);}}}isr.close();} catch (Exception e) {}return lResult;}

方法二

//获取外置存储卡的根路径，如果没有外置存储卡，则返回null public String getExtSDCardPath2() {String sdcard_path = null;String sd_default = Environment.getExternalStorageDirectory().getAbsolutePath();if (sd_default.endsWith("/")) {sd_default = sd_default.substring(0, sd_default.length() - 1);}// 得到路径try {Runtime runtime = Runtime.getRuntime();Process proc = runtime.exec("mount");InputStream is = proc.getInputStream();InputStreamReader isr = new InputStreamReader(is);String line;BufferedReader br = new BufferedReader(isr);//rootfs / rootfs ro,relatime 0 0while ((line = br.readLine()) != null) {if (line.contains("secure"))continue;if (line.contains("asec"))continue;if (line.contains("fat") && line.contains("/mnt/")) {String columns[] = line.split(" ");if (columns != null && columns.length > 1) {if (sd_default.trim().equals(columns[1].trim())) {continue;}sdcard_path = columns[1];}} else if (line.contains("fuse") && line.contains("/mnt/")) {String columns[] = line.split(" ");if (columns != null && columns.length > 1) {if (sd_default.trim().equals(columns[1].trim())) {continue;}sdcard_path = columns[1];}}}} catch (Exception e) {// TODO Auto-generated catch blocke.printStackTrace();}return sdcard_path;}

我用机子测试时候，获取出来的值都是//rootfs / rootfs ro,relatime 0 0

根本没有想要的。

manifest权限

    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>    <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"/>

最后总结一下

Environment.getExternalStorageDirectory().getPath()是万能的，不管是外置还是内置sd卡都可以获取。

不过app应用来说是需要固定一个路径的。

我现在使用的是

public String getSoftwareStorageDirectory() {String strDirectory;Map<String,String> sysInfo=System.getenv();String sd_defult = sysInfo.get("SECONDARY_STORAGE");if (!CheckDirectoryExists(sd_defult)){sd_defult = Environment.getExternalStorageDirectory().getPath();}    return strDirectory;}//判断检出目录是否存在private boolean CheckDirectoryExists(String fileName) {if (fileName == null || fileName.length()<=0) {return false;}File temFile = new File(fileName);File[] childFiles = null;if (temFile != null)childFiles = temFile.listFiles();if (childFiles == null) {return false;}//目录是否可以写File testFile = new File(temFile, "com_testDir");if (!testFile.exists()) {if (!testFile.mkdir()) {return false;}testFile.delete();}return true;}

欢迎大家测试，提供不同机子的测试结果，还有不同源码下是怎样的。
因为有不同厂商，或者用户是刷机，所以有很多奇葩的路径也不足为奇。

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