6. Java basic I/O 2. Files презентация

6. Basic I/O 2. Files

Write to a Text File Example import java.io.*; public void Write(String fileId){ PrintStream outF = null; try{ outF = new PrintStream(fileId); outF.println(”This is a test record”); } catch(IOException e){…processing code } finally{ if (outF != null) outF.close(); } }

Home Exercise: Create Deposit Report Modify 512SortDepo project to get deposit report in a text file.

Read from a Text File Example public void Read(String fileId){ BufferedReader inF = null; try{ inF = new BufferedReader(new FileReader(fileId)); while (txt = inF.readLine() != null){ // code for processing txt } } catch(IOException e) { … processing code } finally{ if (inF != null) inF.close(); } }

Random Access Files Random access files permit nonsequential, or random, access to a file's contents To access a file randomly, you: open the file seek a particular location read from or write to that file

Random Access File Example File f = new File("test.txt"); FileChannel fc = (FileChannel.open(f, READ, WRITE)); fc.position(10); ByteBuffer copy = ByteBuffer.allocate(12); do { nread = fc.read(copy); // processing copy } while (nread != -1 && copy.hasRemaining()); fc.close();

What Is a Path? Java 7 A file is identified by its path through the file system, beginning from the root node The Path class is a programmatic representation of a path in the file system A Path object contains the file name and directory list used to construct the path

Relative and Absolute Path A path is either relative or absolute. The latter contains the root element. A relative path needs to be combined with another path in order to access a file. The character used to separate the directory names (also called the delimiter) is specific to the file system It is used to examine, locate, and manipulate files

Creating a Path A Path instance contains the information used to specify the location of a file or directory A root element or a file name might be included, but neither are required Path p1 = Paths.get("/tmp/foo"); Path p2 = Paths.get(args[0]); Path p3 = Paths.get(URI.create("file:///Users/joe/FileTest.java"));

Path Operations Retrieving Information About a Path Converting a Path Joining Two Paths Creating a Path Between Two Paths Comparing Two Paths

The File Class The Files class is the other primary entrypoint of the java.nio.file package You can get some functionality of Path class from the File class in pre-JDK7.

Some File Operations Verifying the Existence of a File or Directory (exists, notExists) Checking File Accessibility (isReadable, isWritable, isExecutable) Copying / Moving a File or Directory (copy, move) Creating and Reading Directories (createDirectory, newDirectoryStream)

Manuals http://docs.oracle.com/javase/tutorial/essential/io/index.html