封装一个帮助类来写文件到android外置存储器上

项目地址：点击打开

项目简介：写文件到android外置存储器的一个帮助类，和它的demo程序

它是如何工作的呢？

1.创建 AppExternalFileWriter 对象并传递context(上下文);

2.按照你的要求使用 writeDataToFile 或者 writeDataToTimeStampedFile 不同的方法;

3.如果你想写入的文件需要有时间标注的数据，那么使用writeDataToTimeStampedFile类型

4.如果你想创建一个下级目录，那么可以使用灵活的 createSubDirectory类型

5.如果外置存储设比有任何的问题，比如设备没有挂载，作为大容量存储设备，空间容量不足，或者甚至是创建一个已经存在的库文件，该类运行的时候会抛出一个ExternalFileWriterException异常信息。

6.如果你想在外部缓存中写入数据，那么做如下操作：

*检查所有方法的变体（variants），它需要一个boolean类型的参数，如果你传进一个true值，文件操作在cpu缓存中已经完成了，否则将在标准外部存储器中完成。

*如果你在cpu缓存中已经通过createDirectory方法创建了一个目录，把这个目录传递给任何父类需要的方法。这些方法不管父类是在外置存储器或者cpu缓存中工作是一样的。

7.检查某些目录或者文件是否存在某些位置或者不借助isFileExists、isDirectoryExists方法。

8.用deleteDirectory方法删除整个目录。（注意：该方法之关心删除整个目录与它相关的上级目录，如果您想要检查目录是否为空并使用一些错误的消息，我推荐使用 File.delete() 方法。）

关于Variants的描述

1.writeDataToFile--没有父级目录

writeDataToFile(String fileName, byte[] data,boolean inCache);
writeDataToFile(String fileName, String data,boolean inCache);

在程序的目录将数据写入自定义的文件

a.writeDataToFile---在父级路径

writeDataToFile(File parent, String fileName, byte[] data);
writeDataToFile(File parent, String fileName, String data);

b.在其他的路径写入数据到自定义文件名称

b1 writeDataToTimeStampedFile方法---没有父级路径

writeDataToTimeStampedFile(String extension, byte[] data,boolean inCache)
writeDataToTimeStampedFile(String extension, String data,boolean inCache)

b2 writeDataToTimeStampedFile方法----带有父级路径

writeDataToTimeStampedFile(String extension, byte[] data)
writeDataToTimeStampedFile(String extension, String data)

在其他目录下写入数据到指定文件，并伴有时间标识扩展

c1 createSubDirectory方法

createSubDirectory(File parent, String directoryName)

在其他目录下创建上级目录

createSubDirectory(String directoryName,boolean inCache)

在应用程序目录创建上级目录

isDirectoryExists方法

isDirectoryExists(String directoryName, boolean checkInCache)

检查赋予的目录名称是否存在在程序目录下或者缓存目录

isDirectoryExists(String directoryName, File parentDirectory)

检查给予名称的目录是否存在与父路径

a isFileExists 方法

isFileExists(String fileName, boolean checkInCache)

检查给予的文件名称是否存在在程序目录下（parentDirectory ）

isFileExists(String fileName, File parentDirectory)

删除目录

deleteDirectory(File directory)

删除指定指定的目录和它上级的所有文件（翻译的还是很别扭）

一些好的建议（some goodies）

1.getAppDirectory() : 创建app目录的文件对象
 
2.getExternalStorageDirectory() : 获取外置存储目录文件对象
 
3.getExternalCacheDirectory() : 获取外置缓存目录对象

完整类的AppExternalFileWriter.java

 package com.example.filewrite;
 
 import java.io.File;
 import java.io.FileOutputStream;
 import java.io.IOException;
 
 import android.content.Context;
 import android.os.Environment;
 import android.os.StatFs;
 import android.text.TextUtils;
 
 /**
  * @author Prasham Trivedi
  * @version 2.5
  *          <p>
  *          This class will create a directory having same name as your
  *          application. With all the states handled and reported back to
  *          developer.
  *          </p>
  */
 public class AppExternalFileWriter {
 
     private static final String canNotWriteFile = "Can not write file: ";
     private static final String canNotCreateDirectory = "Can not create directory: ";
     private final File externalStorageDirectory;
     private final File externalCacheDirectory;
     private Context context;
     private File appDirectory;
     private File appCacheDirectory;
 
     /**
      * Creates external file writer
      *
      * @param context
      *            : Context
      */
     public AppExternalFileWriter(Context context) {
         this.context = context;
         externalStorageDirectory = Environment.getExternalStorageDirectory();
         externalCacheDirectory = context.getExternalCacheDir();
 
     }
 
     private File createFile(String fileName, boolean inCache)
             throws ExternalFileWriterException {
         return createFile(fileName, getAppDirectory(inCache));
     }
 
     /**
      * Create a file in the app directory with given file name.
      *
      * @param fileName
      *            : Desired name of the file
      * @param parent
      *            parent of the file
      *
      * @return : File with desired name
      */
     private File createFile(String fileName, File parent)
             throws ExternalFileWriterException {
         if (isExternalStorageAvailable(true)) {
             try {
 
                 if (parent.isDirectory()) {
 
                     File detailFile = new File(parent, fileName);
                     if (!detailFile.exists())
                         detailFile.createNewFile();
                     else {
                         String messege = "File already there ";
                         throwException(messege);
                     }
                     return detailFile;
                 } else {
                     throwException(parent + " should be a directory");
                 }
             } catch (IOException e) {
                 e.printStackTrace();
                 String errorMessege = "IOException " + e;
                 throwException(errorMessege);
             } catch (Exception e) {
                 e.printStackTrace();
                 String errorMessege = "Exception " + e;
                 throwException(errorMessege);
             }
         }
         return null;
     }
 
     /** Creates app directory */
     private void createAppDirectory() throws ExternalFileWriterException {
         String directoryName = context
                 .getString(context.getApplicationInfo().labelRes);
 
         if (isExternalStorageAvailable(false)) {
 
             appDirectory = new File(Environment.getExternalStorageDirectory()
                     .toString(), directoryName);
             createDirectory(appDirectory);
 
             appCacheDirectory = new File(externalCacheDirectory, directoryName);
             createDirectory(appCacheDirectory);
 
         }
 
     }
 
     private double getAvailableSpace() {
         StatFs stat = new StatFs(Environment.getExternalStorageDirectory()
                 .getPath());
         double sdAvailSize = (double) stat.getAvailableBlocks()
                 * (double) stat.getBlockSize();
         return sdAvailSize;
     }
 
     private boolean isExternalStorageAvailable(boolean isForFile)
             throws ExternalFileWriterException {
         String errorStarter = (isForFile) ? canNotWriteFile
                 : canNotCreateDirectory;
 
         String storageState = Environment.getExternalStorageState();
 
         if (storageState.equals(Environment.MEDIA_MOUNTED)) {
             return true;
         } else if (storageState.equals(Environment.MEDIA_BAD_REMOVAL)) {
             throwException(errorStarter
                     + "Media was removed before it was unmounted.");
         } else if (storageState.equals(Environment.MEDIA_CHECKING)) {
             throwException(errorStarter
                     + "Media is present and being disk-checked, "
                     + "Please wait and try after some time");
         } else if (storageState.equals(Environment.MEDIA_MOUNTED_READ_ONLY)) {
             throwException(errorStarter + "Presented Media is read only");
         } else if (storageState.equals(Environment.MEDIA_NOFS)) {
             throwException(errorStarter + "Blank or unsupported file media");
         } else if (storageState.equals(Environment.MEDIA_SHARED)) {
             throwException(errorStarter
                     + "Media is shared with USB mass storage");
         } else if (storageState.equals(Environment.MEDIA_REMOVED)) {
             throwException(errorStarter + "Media is not present");
         } else if (storageState.equals(Environment.MEDIA_UNMOUNTABLE)) {
             throwException(errorStarter
                     + "Media is present but cannot be mounted");
         } else if (storageState.equals(Environment.MEDIA_UNMOUNTED)) {
             throwException(errorStarter + "Media is present but not mounted");
         }
 
         return false;
     }
 
     private void throwException(String errorMessege)
             throws ExternalFileWriterException {
         throw new ExternalFileWriterException(errorMessege);
     }
 
     private File createDirectory(File directory)
             throws ExternalFileWriterException {
         if (!directory.exists() || !directory.isDirectory()) {
             if (directory.mkdirs()) {
                 String messege = "directory " + directory + " created : Path "
                         + directory.getPath();
                 System.out.println(messege);
 
             } else {
                 if (directory.exists()) {
                     if (directory.isDirectory()) {
                         String messege = "directory " + directory
                                 + " Already exists : Path "
                                 + directory.getPath();
                         System.out.println(messege);
                     } else {
                         String messege = directory
                                 + "should be a directory but found a file : Path "
                                 + directory.getPath();
                         throwException(messege);
                         System.out.println(messege);
                     }
 
                 }
             }
         }
         return directory;
     }
 
     /**
      * Write byte array to file. Will show error if given file is a directory.
      *
      * @param file
      *            : File where data is to be written.
      * @param data
      *            String which you want to write a file. If size of this is
      *            greater than size available, it will show error.
      */
     private void writeDataToFile(File file, String data)
             throws ExternalFileWriterException {
         byte[] stringBuffer = data.getBytes();
         writeDataToFile(file, stringBuffer);
     }
 
     /**
      * Write byte array to file. Will show error if given file is a directory.
      *
      * @param file
      *            : File where data is to be written.
      * @param data
      *            byte array which you want to write a file. If size of this is
      *            greater than size available, it will show error.
      */
     private void writeDataToFile(File file, byte[] data)
             throws ExternalFileWriterException {
         if (isExternalStorageAvailable(true)) {
             if (file.isDirectory()) {
                 throwException(file
                         + " is not a file, can not write data in it");
             } else {
                 if (file != null && data != null) {
                     double dataSize = data.length;
                     double remainingSize = getAvailableSpace();
                     if (dataSize >= remainingSize) {
                         throwException("Not enough size available");
 
                     } else {
                         try {
                             FileOutputStream out = new FileOutputStream(file);
                             out.write(data);
                             out.close();
                         } catch (IOException e) {
                             e.printStackTrace();
                         } catch (Exception e) {
                             e.printStackTrace();
                         }
                     }
                 }
 
             }
         }
     }
 
     private File getAppDirectory(boolean inCache) {
         return (inCache) ? this.appCacheDirectory : this.appDirectory;
     }
 
     /**
      * Creates subdirectory in application directory
      *
      * @param directoryName
      *            name of subdirectory
      *
      * @return File object of created subdirectory
      *
      * @throws ExternalFileWriterException
      *             if external storage is not available
      */
     public File createSubDirectory(String directoryName, boolean inCache)
             throws ExternalFileWriterException {
         if (isExternalStorageAvailable(false)) {
 
             getAppDirectory();
 
             File subDirectory = new File(getAppDirectory(inCache),
                     directoryName);
 
             return createDirectory(subDirectory);
         } else
             return null;
     }
 
     /**
      * Checks whether directory with given name exists in AppDirectory
      *
      * @param directoryName
      *            : Name of the directory to check.
      *
      * @return true if a directory with "directoryName" exists, false otherwise
      */
     public boolean isDirectoryExists(String directoryName, boolean checkInCache) {
         File parentDirectory = (checkInCache) ? appCacheDirectory
                 : appDirectory;
         return isDirectoryExists(directoryName, parentDirectory);
     }
 
     /**
      * Check whether file with given name exists in parentDirectory or not.
      *
      * @param fileName
      *            : Name of the file to check.
      * @param parentDirectory
      *            : Parent directory where directory with "fileName" should be
      *            present
      *
      * @return true if a file with "fileName" exists, false otherwise
      */
     public boolean isFileExists(String fileName, File parentDirectory) {
         File directoryToCheck = new File(parentDirectory, fileName);
         return directoryToCheck.exists() && directoryToCheck.isFile();
     }
 
     /**
      * Checks whether file with given name exists in AppDirectory
      *
      * @param fileName
      *            : Name of the file to check.
      *
      * @return true if a file with "directoryName" exists, false otherwise
      */
     public boolean isFileExists(String fileName, boolean checkInCache) {
         File parentDirectory = (checkInCache) ? appCacheDirectory
                 : appDirectory;
         return isFileExists(fileName, parentDirectory);
     }
 
     /**
      * Check whether directory with given name exists in parentDirectory or not.
      *
      * @param directoryName
      *            : Name of the directory to check.
      * @param parentDirectory
      *            : Parent directory where directory with "directoryName" should
      *            be present
      *
      * @return true if a directory with "directoryName" exists, false otherwise
      */
     public boolean isDirectoryExists(String directoryName, File parentDirectory) {
         File directoryToCheck = new File(parentDirectory, directoryName);
         return directoryToCheck.exists() && directoryToCheck.isDirectory();
     }
 
     /**
      * Creates subdirectory in parent directory
      *
      * @param parent
      *            : Parent directory where directory with "directoryName" should
      *            be created
      * @param directoryName
      *            name of subdirectory
      *
      * @return File object of created subdirectory
      *
      * @throws ExternalFileWriterException
      *             if external storage is not available
      */
     public File createSubDirectory(File parent, String directoryName)
             throws ExternalFileWriterException {
         if (isExternalStorageAvailable(false)) {
 
             getAppDirectory();
 
             if (!parent.isDirectory())
                 throwException(parent.getName() + " Must be a directory ");
 
             File subDirectory = new File(parent, directoryName);
 
             return createDirectory(subDirectory);
         } else
             return null;
     }
 
     /**
      * Deletes given directory with all its subdirectories and its files.
      *
      * @param directory
      *            : Directory to delete
      */
     public void deleteDirectory(File directory) {
         if (directory != null) {
             if (directory.isDirectory())
                 for (File child : directory.listFiles()) {
 
                     if (child != null) {
                         if (child.isDirectory())
                             deleteDirectory(child);
                         else
                             child.delete();
                     }
                 }
 
             directory.delete();
         }
         // return false;
     }
 
     /**
      * Get created app directory
      *
      * @return File object of created AppDirectory
      */
     public File getAppDirectory() throws ExternalFileWriterException {
         if (appDirectory == null) {
             createAppDirectory();
         }
         return appDirectory;
     }
 
     /**
      * get External Cache directory
      *
      * @return File object of External Cache directory
      */
     public File getExternalCacheDirectory() {
         return externalCacheDirectory;
     }
 
     /**
      * Get external storage directory
      *
      * @return File object of external storage directory
      */
     public File getExternalStorageDirectory() {
         return externalStorageDirectory;
     }
 
     /**
      * Write data in file of a parent directory
      *
      * @param parent
      *            parent directory
      * @param fileName
      *            desired filename
      * @param data
      *            data
      *
      * @throws ExternalFileWriterException
      *             if external storage is not available or free space is less
      *             than size of the data
      */
     public void writeDataToFile(File parent, String fileName, byte[] data)
             throws ExternalFileWriterException {
         if (isExternalStorageAvailable(true)) {
             getAppDirectory();
 
             File file = createFile(fileName, parent);
 
             writeDataToFile(file, data);
         }
     }
 
     /**
      * Writes data to the file. The file will be created in the directory name
      * same as app.
      *
      * @param fileName
      *            name of the file
      * @param data
      *            data to write
      *
      * @throws ExternalFileWriterException
      *             if external storage is not available or free space is less
      *             than size of the data
      */
     public void writeDataToFile(String fileName, String data, boolean inCache)
             throws ExternalFileWriterException {
         if (isExternalStorageAvailable(true)) {
             getAppDirectory();
 
             File file = createFile(fileName, inCache);
 
             writeDataToFile(file, data);
         }
     }
 
     /**
      * Writes data to the file. The file will be created in the directory name
      * same as app.
      *
      * @param fileName
      *            name of the file
      * @param data
      *            data to write
      *
      * @throws ExternalFileWriterException
      *             if external storage is not available or free space is less
      *             than size of the data
      */
     public void writeDataToFile(String fileName, byte[] data, boolean inCache)
             throws ExternalFileWriterException {
         if (isExternalStorageAvailable(true)) {
             getAppDirectory();
 
             File file = createFile(fileName, inCache);
 
             writeDataToFile(file, data);
         }
     }
 
     /**
      * Write data in file of a parent directory
      *
      * @param parent
      *            parent directory
      * @param fileName
      *            desired filename
      * @param data
      *            data
      *
      * @throws ExternalFileWriterException
      *             if external storage is not available or free space is less
      *             than size of the data
      */
     public void writeDataToFile(File parent, String fileName, String data)
             throws ExternalFileWriterException {
         if (isExternalStorageAvailable(true)) {
             getAppDirectory();
 
             File file = createFile(fileName, parent);
 
             writeDataToFile(file, data);
         }
     }
 
     /**
      * Writes data to the file. The file will be created in the directory name
      * same as app.
      * <p>
      * Name of the file will be the timestamp.extension
      * </p>
      *
      * @param extension
      *            extension of the file, pass null if you don't want to have
      *            extension.
      * @param data
      *            data to write
      * @param inCache
      *            Pass true if you want to write data in External Cache. false
      *            if you want to write data in external directory.
      *
      * @throws ExternalFileWriterException
      *             if external storage is not available or free space is less
      *             than size of the data
      */
     public void writeDataToTimeStampedFile(String extension, String data,
             boolean inCache) throws ExternalFileWriterException {
         if (isExternalStorageAvailable(true)) {
             getAppDirectory();
 
             String fileExtension = (TextUtils.isEmpty(extension)) ? "" : "."
                     + extension;
             String fileName = System.currentTimeMillis() + fileExtension;
 
             File file = createFile(fileName, getAppDirectory(inCache));
 
             writeDataToFile(file, data);
         }
     }
 
     /**
      * Writes data to the file. The file will be created in the directory name
      * same as app.
      * <p>
      * Name of the file will be the timestamp.extension
      * </p>
      *
      * @param parent
      *            parent directory path
      * @param extension
      *            extension of the file, pass null if you don't want to have
      *            extension.
      * @param data
      *            data to write
      *
      * @throws ExternalFileWriterException
      *             if external storage is not available or free space is less
      *             than size of the data
      */
     public void writeDataToTimeStampedFile(File parent, String extension,
             String data) throws ExternalFileWriterException {
         if (isExternalStorageAvailable(true)) {
             getAppDirectory();
 
             String fileExtension = (TextUtils.isEmpty(extension)) ? "" : "."
                     + extension;
             String fileName = System.currentTimeMillis() + fileExtension;
 
             File file = createFile(fileName, parent);
 
             writeDataToFile(file, data);
         }
     }
 
     /**
      * Writes data to the file. The file will be created in the directory name
      * same as app.
      * <p>
      * Name of the file will be the timestamp.extension
      * </p>
      *
      * @param extension
      *            extension of the file, pass null if you don't want to have
      *            extension.
      * @param data
      *            data to write
      *
      * @throws ExternalFileWriterException
      *             if external storage is not available or free space is less
      *             than size of the data
      */
     public void writeDataToTimeStampedFile(String extension, byte[] data,
             boolean inCache) throws ExternalFileWriterException {
         if (isExternalStorageAvailable(true)) {
             getAppDirectory();
 
             String fileExtension = (TextUtils.isEmpty(extension)) ? "" : "."
                     + extension;
             String fileName = System.currentTimeMillis() + fileExtension;
 
             File file = createFile(fileName, getAppDirectory(inCache));
 
             writeDataToFile(file, data);
         }
     }
 
     /**
      * Writes data to the file. The file will be created in the directory name
      * same as app.
      * <p>
      * Name of the file will be the timestamp.extension
      * </p>
      *
      * @param parent
      *            parent directory path
      * @param extension
      *            extension of the file, pass null if you don't want to have
      *            extension.
      * @param data
      *            data to write
      *
      * @throws ExternalFileWriterException
      *             if external storage is not available or free space is less
      *             than size of the data
      */
     public void writeDataToTimeStampedFile(File parent, String extension,
             byte[] data) throws ExternalFileWriterException {
         if (isExternalStorageAvailable(true)) {
             getAppDirectory();
 
             String fileExtension = (TextUtils.isEmpty(extension)) ? "" : "."
                     + extension;
             String fileName = System.currentTimeMillis() + fileExtension;
 
             File file = createFile(fileName, parent);
 
             writeDataToFile(file, data);
         }
     }
 
     /**
      * Exception to report back developer about media state or storage state if
      * writing is not possible
      */
     public class ExternalFileWriterException extends Exception {
 
         public ExternalFileWriterException(String messege) {
             super(messege);
         }
 
     }
 }

在MainActivity.java中使用的方法如下：

String test = "writer File class test";
if (testFolder == null) {
    testFolder = writer.getExternalStorageDirectory();// 获取sd卡的根目录,testFolder和writer分别为File和AppExternalFileWriter(this)的实例
}
try {
   writer.writeDataToFile(testFolder, "fileName.txt",
                            test.getBytes());// 注意对应的惨胡分别为存储目录，写入的文件名称，byte[]
   } catch (ExternalFileWriterException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
  }

注意添加写入的权限：

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