Java and Android file operations

File This is the base class of files, which represent a file entity abstractly, and it has four different construction methods:

File (file dir, String name)
File (String Path)
File (String Dirpath, string name)
File (URI Uri)
The essence of these constructs is the same, that is, to construct a file instance, you must provide a complete path to the files.
Constructs a file instance, does not say that creates a new files or the folder, the file instance, is only one representative of the actual system inside the document entity.
Important: Public Boolean exists () determines whether a file or folder exists

public boolean isfile () determines whether the file

Public Boolean isdirectory determines whether the folder

public Boolean createnewfile () creates a new, empty file based on the path and file name you have established

public boolean mkdir () creates a folder based on the path established (first-level operation)

public Boolean mkdirs () creates folders based on established paths (multilevel operations)
public boolean Delete () deletes a file or folder

public boolean Renameto (file dest) renaming files or folders

public long length () Gets the length of the file in bytes (folder is not available)



Public String GetName () Gets the name of the file or folder

Public String GetAbsolutePath () Gets the absolute path to the file or folder

Pubic String GetPath () to get the path to a file or folder


Public file[] Listfiles () returns all file objects within a folder

Public string[] List () returns the name of all files or folders within a folder

File storage mechanisms within Android apps:

Activity provides two ways to obtain byte-based input and output streams, respectively:

Public FileOutputStream openfileoutput (String name, int mode) to get the output stream

Public FileInputStream openfileinput (String name) gets the input stream

Both of these methods create or read files in data/data/<applicatin-package>/files/, which means that this is similar to sharedpreference, specifically for a file storage mechanism that is provided within an application. (not shared between different apps by default)

Mode has the following four modes:
Use 0 or mode_private (the default operation): uses 0 to indicate the default value, only the application that can create the file accesses the file, each time the file is written as an overlay.
Mode_append: Each time a file is written as an append, similar to the APPEND () method in StringBuffer.
Mode_world_readable: only Read permission.
Mode_world_writeable: Only write permission.
If you want to have read and write permission at the same time, you can create it in mode by: Mode_world_readable+ mode_world_writeable

File name Filter General usage

1. Implement FilenameFilter interface;

2. Implement the Boolean accept (File dir,string name); Dir indicates the current directory of the file, and name indicates the filename;

Class Myfilter implements filenamefilter{
Private String type; Type is a condition that needs to be filtered, such as if type= ". jpg", only files with the suffix JPG can be returned
Public myfilter (String type) {
This.type = type;
}

Public boolean accept (file Dir,string name) {//returns true for files qualified
}
}

The Android file operation should have permission:

Determine if the SD card is plugged in

Environment.getexternalstoragestate (). Equals (

Android.os.Environment.MEDIA_MOUNTED);

Get the SD card root directory

File skroot = Environment.getexternalstoragedirectory ();

Get the private root directory

File fileroot = Context.getfilesdir () + "";

Determining or obtaining folder and file paths

String path = File.getpath ();//Relative

String path = File.getabsoultepath ();//Absolute

Get the parent directory of a file or folder

String Parentpath = File.getparent ()

Get the name of the file or folder:

String Name = File.getname ();

Create a file or folder

File.createnewfile ();//Build file

Judging is a file or folder

File.isdirectory ()

List all file and folder names under a folder

file[] files = file.listfiles ();

Modify folder and file name

File.renameto (dest);

Delete a folder or file

File.delete ();

File read/write operation mode

Context.mode_private: New content overwrites original content

Context.mode_append: After new content is appended to the original content

Context.mode_world_readable: Allow other applications to read

Context.mode_world_writeable: Allows other applications to write, overwriting the original data

Java and Android file operations