Ref Files and Serialization.ppt

Files and Serialization Files and Serialization Nguyen Thanh Phuoc Files Files Used to transfer data to and from secondary storage Diskette Memory Input file Output file A Portion of Java’s File Classes A Portion of Java’s File Classes Object InputStream OutputStream FileInputStream FileOutputStreamObjectInputStream ObjectOutputStream File These classes are included in the java.io package, which must be imported into any application that uses them Basic Algorithm for File Output Basic Algorithm for File Output Open an output connection to a file Write the data to the file Close the output connection to the file FileOutputStream Disk Basic Algorithm for File Input Basic Algorithm for File Input Open an input connection to a file Read the data from the file and process it Close the input connection to the file FileInputStream Disk Files and Exceptions Files and Exceptions • Java requires the programmer to catch file exceptions • For example, an IOException can be thrown during at attempt to open a file Serializing a Data Model Serializing a Data Model • A data is said to be serialized when it can be permanently saved on a storage medium • Serialization requires file management • Java support object serialization Serializing a Data Serializing a Data • All classes to be serialized must implement the Serializable interface • This interface is defined in the java.io package • Many standard java classes are already serializable import java.io.Serializable; public class Employee implements Serializable{ private String name; private int[] days; public Employee(String name, int[] days){ this.name = name; this.days = days; } } Serializing the Employee System Serializing the Employee System Many of Java’s data classes are already serializable All specialized data classes should be made to be serializable Writing Objects to Output Files Writing Objects to Output Files • Create a new instance of FileOutputStream • Wrap around this object a new instance of ObjectOutputStream • Use the method writeObject to send an object out on the stream [...]...Writing Objects to Output Files A file name new FileOutputStream() new ObjectOutputStream() .writeObject() Writing Objects to Output Files int[] days = {8, 8, 8, 10, 6}; Employee emp = new Employee("Bill", days); try{ FileOutputStream fos = new FileOutputStream("employee.dat");... System.out.println("Error in output:" + e.toString()); } Reading Objects from Input Files • Create a new instance of FileInputStream • Wrap around this object a new instance of ObjectInputStream • Use the method readObject to receive an object from the stream • Cast the received object to its actual class Reading Objects from Input Files A file name new FileInputStream() new ObjectInputStream()... class Reading Objects from Input Files A file name new FileInputStream() new ObjectInputStream() () .readObject() Reading Objects from Input Files Employee emp; try{ FileInputStream fis = new FileInputStream("employee.dat"); ObjectInputStream ois = new ObjectInputStream(fis); emp = (Employee) ois.readObject(); fis.close(); }catch(Exception . Files and Serialization Files and Serialization Nguyen Thanh Phuoc Files Files Used to transfer data to and from secondary storage Diskette Memory Input. connection to a file Read the data from the file and process it Close the input connection to the file FileInputStream Disk Files and Exceptions Files and Exceptions • Java requires the programmer. serialized when it can be permanently saved on a storage medium • Serialization requires file management • Java support object serialization Serializing a Data Serializing a Data • All classes