Getting started with Android: file storage

Document directory

• 1.
• Step 1: Set the simulator to support sdcard
• Step 2: Set permissions in the Application
• Note:
• Suggestion:

There are multiple ways to store data, such as database storage, sharedpreferences storage, and file storage;

Here we will introduce the simplest file storage method;

In simple terms, file storage is the IO stream in the general javase, but it is only applied to Android phones;

I. Core code of file storage

File Storage

(1) fileoutputstream out = context. openfileoutput (string filename, int mode); get the file output stream in Mode

(2) Out. Write (byte [] B );

FileOutputStream out = null;out = context.openFileOutput(filename, Context.MODE_***);out.write(filecontent.getBytes("UTF-8"));out.close();

Note: files are stored in/data/package/files by default;

File Reading

(1) fileinputstream in = context. openfileinput (string filename); get the file stream of a file

(2) int length = in. Read (byte []);

/* Each time a fixed byte is read and the byte is output to the byte output stream. After all the data is read, the content in the byte stream is output together */fileinputstream in = NULL; bytearrayoutputstream bout = NULL; byte [] Buf = new byte [1024]; bout = new bytearrayoutputstream (); int length = 0; In = context. openfileinput (filename); // get the input stream while (length = in. read (BUF ))! =-1) {bout. write (BUF, 0, length);} byte [] content = bout. tobytearray (); filecontentet. settext (new string (content, "UTF-8"); // set the text box to read content in. close (); bout. close ();

Note: files of/data/package/files are read by default;

II. Introduction to file Mode

1. Context. mode_private:Private overwrite Mode
-RW ----

It can only be accessed by the current application and overwritten if it is written;

2. Context. mode_append:Private append Mode
-RW ----

It can only be accessed by the current application, and if it is written, it will be appended;

3. Context, mode_world_readable:Public read-only mode-RW-r --

Can be read by other applications;

4. Context. mode_world_writeable:Public writable mode-RW--w-

Can be written by other applications, but cannot be read;

Note: If you want others to make the file mode overlay, you can use the plus sign to connect;

For example, context. mode_world_readable+Context. mode_world_writeable indicates that other applications read and write data;

3. Simple Application Example 1.

Purpose: When you click "save", the content will be saved with a specific file name and specific file content. When you click "read", the file content read from a specific file will be displayed in the file content text box;

After you click Save, the effect is as follows:

Mainactivity. Java

Package Org. xiazdong. file; import Java. io. bytearrayoutputstream; import Java. io. fileinputstream; import Java. io. filenotfoundexception; import Java. io. fileoutputstream; import android. app. activity; import android. content. context; import android. OS. bundle; import android. view. view; import android. view. view. onclicklistener; import android. widget. button; import android. widget. edittext; public class mainactivity ex Tends activity {private button savebutton, readbutton; private edittext filenameet, filecontentet; private context = This; private onclicklistener listener = new onclicklistener () {@ overridepublic void onclick (view V) {If (V = savebutton) {string filename = filenameet. gettext (). tostring (); string filecontent = filecontentet. gettext (). tostring (); fileoutputstream out = NULL; try {out = context. openfile Output (filename, context. mode_private); out. write (filecontent. getbytes ("UTF-8");} catch (exception e) {e. printstacktrace ();} finally {try {out. close ();} catch (exception e) {e. printstacktrace () ;}} else if (V = readbutton) {string filename = filenameet. gettext (). tostring (); // The name of the file to be read. fileinputstream in = NULL; bytearrayoutputstream bout = NULL; byte [] Buf = new byte [1024]; bout = new bytearrayoutputstream (); Int length = 0; try {In = context. openfileinput (filename); // get the input stream while (length = in. Read (BUF ))! =-1) {bout. write (BUF, 0, length);} byte [] content = bout. tobytearray (); filecontentet. settext (new string (content, "UTF-8"); // set the text box to read content} catch (exception e) {e. printstacktrace ();} filecontentet. invalidate (); // refresh the screen try {In. close (); bout. close () ;}catch (exception e) {}};@ override public void oncreate (bundle savedinstancestate) {super. oncreate (savedinstancestate); setcontentview (R. layout. main); savebutton = (button) This. findviewbyid (R. id. savebutton); readbutton = (button) This. findviewbyid (R. id. readbutton); filenameet = (edittext) This. findviewbyid (R. id. filename); filecontentet = (edittext) This. findviewbyid (R. id. filecontent); savebutton. setonclicklistener (listener); readbutton. setonclicklistener (listener );}}

4. Save the file to sdcard

If a file is large, it is not applicable to storage on mobile phones;

If the mobile phone has an sdcard, the Directory of the sdcard is/Mnt/sdcardDirectory;

Step 1: Set the simulator to support sdcard

Now the simulator supports sdcard;

Step 2: Set permissions in the Application

Set in androidmanifest. xml:

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

Core code stored in sdcard:

File f = new File(Environment.getExternalStorageDirectory(),filename);out = new FileOutputStream(f,true);out.write(filecontent.getBytes("UTF-8"));

Read the core sdcard code:

File f = new File(Environment.getExternalStorageDirectory(),filename);in = new FileInputStream(f);while((length=in.read(buf))!=-1){bout.write(buf,0,length);}byte[] content = bout.toByteArray();

In fact, it is mainly about the storage directory;

Note:

In Android, The sdcard directory of 1.5 and 1.6 is/sdcard, while android2.0 and above are all/mnt/sdcard. Therefore, if we directly write a specific directory during storage, we can use:

Environment. getexternalstoragedirectory ();Obtain the sdcard directory;

Suggestion:

(1) You cannot simply use the sdcard deposit method, because if you cannot determine whether a mobile phone has an sdcard, if not, you need to provide other solutions, such

Save to mobile phone storage;

The system prompts that the sdcard does not exist;

You can use:

If (environment. getexternalstoragestate (). Equals (environment. media_mounted) {// execute the storage sdcard method} else {// store it to your phone, or prompt}