External storage

Basic:

have private and public, if private,when the app delete,the file will be deleted too. Save at both place ,other application can read too.

Important:

it is because the external storage will be hang up,so when to read or write , we need to check first

How to check:

Environment.getExternalStorageState()

Summary
Constants
String MEDIA_BAD_REMOVAL
Storage state if the media was removed before it was unmounted.
String MEDIA_CHECKING
Storage state if the media is present and being disk-checked.
String MEDIA_EJECTING
Storage state if the media is in the process of being ejected.
String MEDIA_MOUNTED
Storage state if the media is present and mounted at its mount point with read/write access.
String MEDIA_MOUNTED_READ_ONLY
Storage state if the media is present and mounted at its mount point with read-only access.
String MEDIA_NOFS
Storage state if the media is present but is blank or is using an unsupported filesystem.
String MEDIA_REMOVED
Storage state if the media is not present.
String MEDIA_SHARED
Storage state if the media is present not mounted, and shared via USB mass storage.
String MEDIA_UNKNOWN
Unknown storage state, such as when a path isn't backed by known storage media.
String MEDIA_UNMOUNTABLE
Storage state if the media is present but cannot be mounted.
String MEDIA_UNMOUNTED
Storage state if the media is present but not mounted.

Permission need:

write

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

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

Write:

//        if private

        File externalDir = this.getExternalFilesDir(null);

//        if public

//        File externalPublicDir = Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOCUMENTS);

        File file = new File(externalDir, name);

FileOutputStream outPutStraem = new FileOutputStream(file, false);

            outPutStraem.write(input.getBytes());

            outPutStraem.close();

Read:

File externalDir = this.getExternalFilesDir(null);

        File file = new File(externalDir, name);

        try {

            StringBuilder sb = new StringBuilder();

            FileInputStream inputStream = new FileInputStream(file);

            int charr;

            while ((charr = inputStream.read()) != -1) {

                sb.append((char)charr);

            }

            inputStream.close();

            return sb.toString();