Mega Code Archive
Using RandomAccessFile to read file saved DataOutputStream
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/*
This program is a part of the companion code for Core Java 8th ed.
(http://horstmann.com/corejava)
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
import java.io.DataInput;
import java.io.DataOutput;
import java.io.DataOutputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.util.Calendar;
import java.util.Date;
import java.util.GregorianCalendar;
/**
* @version 1.11 2004-05-11
* @author Cay Horstmann
*/
public class RandomFileTest
{
public static void main(String[] args)
{
Employee[] staff = new Employee[3];
staff[0] = new Employee("Carl Cracker", 75000, 1987, 12, 15);
staff[1] = new Employee("Harry Hacker", 50000, 1989, 10, 1);
staff[2] = new Employee("Tony Tester", 40000, 1990, 3, 15);
try
{
// save all employee records to the file employee.dat
DataOutputStream out = new DataOutputStream(new FileOutputStream("employee.dat"));
for (Employee e : staff)
e.writeData(out);
out.close();
// retrieve all records into a new array
RandomAccessFile in = new RandomAccessFile("employee.dat", "r");
// compute the array size
int n = (int)(in.length() / Employee.RECORD_SIZE);
Employee[] newStaff = new Employee[n];
// read employees in reverse order
for (int i = n - 1; i >= 0; i--)
{
newStaff[i] = new Employee();
in.seek(i * Employee.RECORD_SIZE);
newStaff[i].readData(in);
}
in.close();
// print the newly read employee records
for (Employee e : newStaff)
System.out.println(e);
}
catch (IOException e)
{
e.printStackTrace();
}
}
}
class Employee
{
public Employee() {}
public Employee(String n, double s, int year, int month, int day)
{
name = n;
salary = s;
GregorianCalendar calendar = new GregorianCalendar(year, month - 1, day);
hireDay = calendar.getTime();
}
public String getName()
{
return name;
}
public double getSalary()
{
return salary;
}
public Date getHireDay()
{
return hireDay;
}
/**
Raises the salary of this employee.
@byPercent the percentage of the raise
*/
public void raiseSalary(double byPercent)
{
double raise = salary * byPercent / 100;
salary += raise;
}
public String toString()
{
return getClass().getName()
+ "[name=" + name
+ ",salary=" + salary
+ ",hireDay=" + hireDay
+ "]";
}
/**
Writes employee data to a data output
@param out the data output
*/
public void writeData(DataOutput out) throws IOException
{
DataIO.writeFixedString(name, NAME_SIZE, out);
out.writeDouble(salary);
GregorianCalendar calendar = new GregorianCalendar();
calendar.setTime(hireDay);
out.writeInt(calendar.get(Calendar.YEAR));
out.writeInt(calendar.get(Calendar.MONTH) + 1);
out.writeInt(calendar.get(Calendar.DAY_OF_MONTH));
}
/**
Reads employee data from a data input
@param in the data input
*/
public void readData(DataInput in) throws IOException
{
name = DataIO.readFixedString(NAME_SIZE, in);
salary = in.readDouble();
int y = in.readInt();
int m = in.readInt();
int d = in.readInt();
GregorianCalendar calendar = new GregorianCalendar(y, m - 1, d);
hireDay = calendar.getTime();
}
public static final int NAME_SIZE = 40;
public static final int RECORD_SIZE = 2 * NAME_SIZE + 8 + 4 + 4 + 4;
private String name;
private double salary;
private Date hireDay;
}
class DataIO
{
public static String readFixedString(int size, DataInput in)
throws IOException
{
StringBuilder b = new StringBuilder(size);
int i = 0;
boolean more = true;
while (more && i < size)
{
char ch = in.readChar();
i++;
if (ch == 0) more = false;
else b.append(ch);
}
in.skipBytes(2 * (size - i));
return b.toString();
}
public static void writeFixedString(String s, int size, DataOutput out)
throws IOException
{
for (int i = 0; i < size; i++)
{
char ch = 0;
if (i < s.length()) ch = s.charAt(i);
out.writeChar(ch);
}
}
}
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