Software Practice 3 Today s lecture Today s Task

Transcription

1 1 Software Practice 3 Today s lecture Today s Task Prof. Hwansoo Han T.A. Jeonghwan Park 43

2 FILE I/O IN ANDROID 2

3 3 Android And Linux Android is implemented on Linux OS Also Android filesystem is exactly same with Linux filesystem(ext4) You can handle file I/O with Java basic file I/O as the same path mechanism of accessing Linux filesystem /home/wow/some/directory /usr/share/other/directory

4 Android File I/O 4

5 5 File Object in Java File object contains the metadata of a file Represent not only regular file, but also directory Example of instantiating File object File dir = new File( /path/to/directory ); File file1 = new File( /path/to/file ); File file2 = new File(dir, path/to/file );

6 6 PrintWriter Writer class for writing contents in a file Gets the File object as the parameter of constructor Example of usage PrintWriter pw = new PrintWriter(mFile); for (String string : strings) { pw.append(string).append("\n"); } append() method gets the input as String pw.flush(); and returns PrintWriter so you can chain the methods pw.close(); flush() method has to be invoked after all contents are appended

7 7 Scanner Reader class for reading contents in a file Gets the File object as the same way in PrintWriter Example of usage StringBuilder helps building up String object with appending contents Scanner sc = new Scanner(mFile); StringBuilder text = new StringBuilder(); while (sc.hasnext()) { text.append(sc.nextline()).append("\n"); } Check whether the scanner can read more sc.close(); mtext = text.tostring(); Read next line as String object Build the content in StringBuilder object as String object

8 8 Context object of Application All applications have their own context Activity inherits Context class You can get the context with getapplicationcontext() method only in Activity This Context object only can be used in Main Thread like UI related works Please check how to use context in AsyncTask or other class with the given example source code

9 9 Extra directory for Application File getdir(string name, int mode); name: directory name mode: operating mode; more details File getfilesdir(); Retrieve, creating if needed, a new directory in which the application can place its own custom data files

10 10 Special Directories for Application Data directory Store persistent data in Android built-in storage Access with getdatadir() method of Context Cache directory Store temporary data in Android built-in storage Access with getdatadir() method of Context External storage directory Store persistent data in SD card Access with the example in next slide

11 11 Example of Each Directory // Access file in general directory File generaldir = getdir("path/to/directory", MODE_APPEND); File generalfile = new File(generalDir, "file/in/directory"); // Access file in data directory File datadir = getdatadir(); File fileindatadir = new File(dataDir, "file/in/directory"); // Access file in cache directory File cachedir = getcachedir(); File fileincachedir = new File(cacheDir, "file/in/directory"); // Access file in external storage File externalstorage = Environment.getExternalStorageDirectory(); File fileinexternalstorage = new File(externalStorage, "file/in/directory");

12 12 Example of File I/O Please check the attachment on the i-campus

13 CSV FORMAT 13

14 14 CSV format Comma-separated values file stores tabular data in plain text Each line of the file is a data record Each record consists of one or more fields, separated by commas The use of the comma as a field separator is the source of the name for the file format

15 15 Example of CSV format Biochemical Oxygen Demand "","Time","demand" "1",1,8.3 "2",2,10.3 "3",3,19 "4",4,16 "5",5,15.6 "6",7,19.8

16 16 Example of CSV format Student Admissions at UC Berkeley "","Admit","Gender","Dept","Freq" "1","Admitted","Male","A",512 "2","Rejected","Male","A",313 "3","Admitted","Female","A",89 "4","Rejected","Female","A",19

17 17 Example of CSV format Matrix Representation 1,2,3,4,5 2,3,4,5,6 3,4,5,6,7

18 18 How to read them? Optionally if the file contains the label, read them first in the outside of loop body Read the contents in the loop body with readline() method of Scanner class Use StringTokenizer class to split the string with comma Handle the I/O related exceptions for missed contents reading or etc.

19 19 [Lab Practice #10] Modify given project to show the contents stored in.csv file as TextView File must be named as students.csv in data directory File must contain the following sequence of columns student_id, name, department, gpa The name of each column is up to you The comma as delimiter should be replaced in tab space

20 20 [Lab Practice #10] Example of appending contents to existing file Second argument of FileOutputStream constructor decides to open file output stream with appending mode or not PrintWriter constructor is also able to get FileOutputStream as its argument FileOutputStream fos = new FileOutputStream(mFile, true); PrintWriter pw = new PrintWriter(fos);

21 21 [Lab Practice #10] Example for inserting first sentence Don t care about The text will not be removed message

22 22 [Lab Practice #10] Example for inserting second sentence

23 23 [Lab Practice #10] Example for inserting last sentences

24 24 APPENDIX SOCKET I/O IN ANDROID

25 25 Socket An internal endpoint for sending or receiving data at a single node in a computer network Concretely, it is a representation of this endpoint in networking software, such as an entry in a table, and is a form of system resource

26 26 Java class for TCP ServerSocket ocket.html?is-external=true Socket html

27 27 Socket programming 5 steps for communication 1. Create server 2. Create client 3. Establish connection 4. Data transport 5. Close connection

28 28 TCP server side ServerSocket ss = new ServerSocket(5000); while (true) { Port number for Socket connection Socket soc = ss.accept(); OutputStream out = soc.getoutputstream(); PrintWriter pw = new PrintWriter(out); } pw.append("message from server"); pw.flush(); Output stream for Socket pw.close(); soc.close();

29 29 TCP client side IP address of Socket server Port number of Socket server String serverip = "localhost"; Socket soc = new Socket(serverIP, 5000); InputStream in = soc.getinputstream(); Scanner sc = new Scanner(in); System.out.println(sc.nextLine()); Input stream for Socket sc.close(); soc.close();

30 30 Manifest for Socket uses-permission tag before application tag <?xml version="1.0" encoding="utf-8"?> <manifest xmlns:android=" package="edu.skku.swp3.fileio"> <uses-permission android:name="android.permission.internet" /> <application android:allowbackup="true" android:supportsrtl="true" <activity android:name=".mainactivity"> <intent-filter> <action android:name="android.intent.action.main" /> <category android:name="android.intent.category.launcher" /> </intent-filter> </activity> </application> </manifest>

31 31 Socket & File I/O No major difference exists in usage use stream based communication recommended to be processed in Service handle exception via IOException The few differences between them are socket needs the INTERNET permission of Android socket always requires server