添加权限：
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/> <uses-permission android:name="android.permission.MOUNT_UNMOUNT_FILESYSTEMS"/> /** 获取SD卡路径 **/ private static String getSDPath() { String sdcardPath = null; boolean sdCardExist = Environment.getExternalStorageState().equals( android.os.Environment.MEDIA_MOUNTED); //判断sd卡是否存在 if (sdCardExist) { sdcardPath = Environment.getExternalStorageDirectory();//获取根目录 } if (sdcardPath != null) { return sdcardPath; } else { return ""; } }
解决方法：获取根目录的代码改为：
sdcardPath = Environment.getExternalStorageDirectory().getAbsolutePath();
这样就可以了。
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附文件缓存类：
package com.etnet.utilities;import java.io.File;import java.io.FileNotFoundException;import java.io.FileOutputStream;import java.io.IOException;import java.io.OutputStream;import java.util.Arrays;import java.util.Comparator;import android.graphics.Bitmap;import android.graphics.BitmapFactory;import android.os.Environment;import android.os.StatFs;import android.util.Log;/** * 图片文件保存、读写类 * @author thdyb */public class FileOperationUtil {private static final String TAG = "FileOperationUtil"; private static final String CACHE_DIRECTORY = "TqProCache"; private static final int MB = 1024*1024; private static final int MAX_CACHE_SIZE = 10 * MB; private static final int LEAST_SIZE_OF_SDCARD = 10 * MB; /** 从缓存中获取图片 **/ public static Bitmap getImage(final String imageUrl) { final String path = getCacheDirectory() + "/" + convertUrlToFileName(imageUrl); // Log.i(TAG, "getImage filepath:" + path); // Log.i(TAG, "getImage url:" + url); File file = new File(path); if (file.exists()) {// Log.i(TAG, "getImage file exists"); Bitmap bmp = null; try { //宽变为原图的1/3，高也变为原图的1/3。这样是为了降低内存的消耗，防止内存溢出 BitmapFactory.Options options=new BitmapFactory.Options(); options.inSampleSize = 3; bmp = BitmapFactory.decodeFile(path,options); LogUtil.d(TAG, "bmp size="+bmp.getByteCount());} catch (Exception e) {e.printStackTrace();} if (bmp == null) { file.delete(); } else { updateFileTime(path); return bmp; } } return null; } /** 将图片存入文件缓存 **/ public static void saveBitmap(String imageUrl, Bitmap bm ) { if (bm == null) { return; } //判断sdcard上的空间 if (getFreeSpaceOfSdcard() < LEAST_SIZE_OF_SDCARD) { //SD空间不足 return; } String filename = convertUrlToFileName(imageUrl); String dir = getCacheDirectory(); File dirFile = new File(dir); if (!dirFile.exists()){ if(!dirFile.mkdirs()){ Log.w(TAG, "create cache file directorys failed"); } } File file = new File(dir +"/" + filename); try { file.createNewFile(); OutputStream outStream = new FileOutputStream(file); bm.compress(Bitmap.CompressFormat.JPEG, 100, outStream); outStream.flush(); outStream.close(); } catch (FileNotFoundException e) { Log.w(TAG, "FileNotFoundException"); } catch (IOException e) { Log.w(TAG, "IOException"); } } /** * 计算存储目录下的文件大小， * 当文件总大小大于指定的MAX_CACHE_SIZE或者sdcard剩余空间小于指定的LEAST_SIZE_OF_SDCARD * 那么删除40%最近没有被使用的文件 */ public static boolean removeExtraCache() { File dir = new File(getCacheDirectory()); File[] files = dir.listFiles(); if (files == null) { return true; } if (!android.os.Environment.getExternalStorageState().equals( android.os.Environment.MEDIA_MOUNTED)) { return false; } int dirSize = 0; for (int i = 0; i < files.length; i++) { dirSize += files[i].length(); }// LogUtil.d("thdyb", "dirSize="+dirSize); if (dirSize > MAX_CACHE_SIZE || getFreeSpaceOfSdcard() < LEAST_SIZE_OF_SDCARD) { int removeNum = (int) ((0.4 * files.length) + 1); /* 根据文件的最后修改时间进行升序排序 */ Arrays.sort(files, new Comparator<File>() { @Override public int compare(File file1, File file2) { if (file1.lastModified() > file2.lastModified()) { return 1; } else if (file1.lastModified() == file2.lastModified()) { return 0; } else { return -1; } }}); /* for (int i = 0; i < files.length; i++) { LogUtil.d("thdyb", "file.modifiedTime="+files[i].lastModified());}*/ for (int i = 0; i < removeNum; i++) { files[i].delete(); } return true; }else{ return false; } } /** 修改文件的最后修改时间 **/ public static void updateFileTime(String path) { File file = new File(path); long newModifiedTime = System.currentTimeMillis(); file.setLastModified(newModifiedTime); } /** 计算sdcard上的剩余空间 **/ private static int getFreeSpaceOfSdcard() { StatFs stat = new StatFs(Environment.getExternalStorageDirectory().getPath()); double sdFreeSize = ((double)stat.getAvailableBlocks() * (double) stat.getBlockSize()); return (int) sdFreeSize; } private static String convertUrlToFileName(String url) { String[] strs = url.split("/"); String savedImageName = strs[strs.length - 1]; return savedImageName; } /** 获得缓存目录 **/ private static String getCacheDirectory() { String dir = getSDPath() + "/" + CACHE_DIRECTORY; return dir; } /** 获取SD卡路径 **/ private static String getSDPath() { String sdcardPath = null; boolean sdCardExist = Environment.getExternalStorageState().equals( android.os.Environment.MEDIA_MOUNTED); //判断sd卡是否存在 if (sdCardExist) { sdcardPath = Environment.getExternalStorageDirectory().getAbsolutePath(); //获取根目录 } if (sdcardPath != null) { return sdcardPath; } else { return ""; } }}