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"/>