android往文件中保存和读取数据

/**
* Writes content to internal storage making the content private to
* the application. The method can be easily changed to take the MODE
* as argument and let the caller dictate the visibility:
* MODE_PRIVATE, MODE_WORLD_WRITEABLE, MODE_WORLD_READABLE, etc.
*
* @param filename - the name of the file to create
* @param content - the content to write
*/
public void writeInternalStoragePrivate(
String filename, byte[] content) {
try {
//MODE_PRIVATE creates/replaces a file and makes
//  it private to your application. Other modes:
//    MODE_WORLD_WRITEABLE
//    MODE_WORLD_READABLE
//    MODE_APPEND
FileOutputStream fos =
openFileOutput(filename, Context.MODE_PRIVATE);
fos.write(content);
fos.close();
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}

/**
* Reads a file from internal storage
* @param filename the file to read from
* @return the file content
*/
public byte[] readInternalStoragePrivate(String filename) {
int len = 1024;
byte[] buffer = new byte[len];
try {
FileInputStream fis = openFileInput(filename);
ByteArrayOutputStream baos = new ByteArrayOutputStream();
int nrb = fis.read(buffer, 0, len); // read up to len bytes
while (nrb != -1) {
baos.write(buffer, 0, nrb);
nrb = fis.read(buffer, 0, len);
}
buffer = baos.toByteArray();
fis.close();
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
return buffer;
}

/**
* Delete internal private file
* @param filename - the filename to delete
*/
public void deleteInternalStoragePrivate(String filename) {
File file = getFileStreamPath(filename);
if (file != null) {
file.delete();
}
}

/**
* Helper Method to Test if external Storage is Available
*/
public boolean isExternalStorageAvailable() {
boolean state = false;
String extStorageState = Environment.getExternalStorageState();
if (Environment.MEDIA_MOUNTED.equals(extStorageState)) {
state = true;
}
return state;
}

/**
* Helper Method to Test if external Storage is read only
*/
public boolean isExternalStorageReadOnly() {
boolean state = false;
String extStorageState = Environment.getExternalStorageState();
if (Environment.MEDIA_MOUNTED_READ_ONLY.equals(extStorageState)) {
state = true;
}
return state;
}

/**
* Write to external public directory
* @param filename - the filename to write to
* @param content - the content to write
*/
public void writeToExternalStoragePublic(String filename, byte[] content) {

// API Level 7 or lower, use getExternalStorageDirectory()
//  to open a File that represents the root of the external
// storage, but writing to root is not recommended, and instead
// application should write to application-specific directory, as shown below.

String packageName = this.getPackageName();
String path = "/Android/data/" + packageName + "/files/";

if (isExternalStorageAvailable() &&
!isExternalStorageReadOnly()) {
try {
File file = new File(path, filename);
file.mkdirs();
FileOutputStream fos = new FileOutputStream(file);
fos.write(content);
fos.close();
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
}

/**
* Reads a file from internal storage
* @param filename - the filename to read from
* @return the file contents
*/
public byte[] readExternallStoragePublic(String filename) {
int len = 1024;
byte[] buffer = new byte[len];
String packageName = this.getPackageName();
String path = "/Android/data/" + packageName + "/files/";

if (!isExternalStorageReadOnly()) {
try {
File file = new File(path, filename);
FileInputStream fis = new FileInputStream(file);
ByteArrayOutputStream baos = new ByteArrayOutputStream();
int nrb = fis.read(buffer, 0, len); //read up to len bytes
while (nrb != -1) {
baos.write(buffer, 0, nrb);
nrb = fis.read(buffer, 0, len);
}
buffer = baos.toByteArray();
fis.close();
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
return buffer;
}

/**
* Delete external public file
* @param filename - the filename to write to
*/
void deleteExternalStoragePublicFile(String filename) {
String packageName = this.getPackageName();
String path = "/Android/data/" + packageName + "/files/"+filename;
File file = new File(path, filename);
if (file != null) {
file.delete();
}
}

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

/**
* Helper method to retrieve the absolute path to the application
* specific internal cache directory on the file system. These files
* will be ones that get deleted when the application is uninstalled or when
* the device runs low on storage. There is no guarantee when these
* files will be deleted.
*
* Note: This uses a Level 8+ API.
*
* @return the absolute path to the application specific cache
* directory
*/
public String getInternalCacheDirectory() {
String cacheDirPath = null;
File cacheDir = getCacheDir();
if (cacheDir != null) {
cacheDirPath = cacheDir.getPath();
}
return cacheDirPath;
}

/**
* Helper method to retrieve the absolute path to the application
* specific external cache directory on the file system. These files
* will be ones that get deleted when the application is uninstalled or when
* the device runs low on storage. There is no guarantee when these
* files will be deleted.
*
* Note: This uses a Level 8+ API.
*
* @return the absolute path to the application specific cache
* directory
*/
public String getExternalCacheDirectory() {
String extCacheDirPath = null;
File cacheDir = getExternalCacheDir();
if (cacheDir != null) {
extCacheDirPath = cacheDir.getPath();
}
return extCacheDirPath;
}