corejava第10版

corejava第10版/v2ch02/randomAccess2/RandomAccessTest.java

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+package randomAccess2;
+
+import java.io.*;
+import java.nio.*;
+import java.nio.channels.*;
+import java.nio.file.*;
+import java.util.*;
+
+/**
+ * @version 1.12 2012-05-30
+ * @author Cay Horstmann
+ */
+public class RandomAccessTest 
+{  
+   public static void main(String[] args) throws IOException
+   {
+      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);
+
+      Path path = Paths.get("employee.dat");
+      ByteBuffer buffer = ByteBuffer.allocate(Employee.RECORD_SIZE);         
+      
+      try (FileChannel channel = FileChannel.open(path, 
+               StandardOpenOption.CREATE, StandardOpenOption.WRITE, StandardOpenOption.TRUNCATE_EXISTING))
+      {  
+         // save all employee records to the file employee.dat
+         for (Employee e : staff)         
+         {
+            buffer.clear();
+            writeData(buffer, e);
+            buffer.flip();
+            channel.write(buffer);
+         }       
+      }
+      
+      try (FileChannel channel = FileChannel.open(path, StandardOpenOption.READ))
+      {  
+         // compute the array size
+         int n = (int)(Files.size(path)) / 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();
+            channel.position(i * Employee.RECORD_SIZE);
+            buffer.clear();
+            channel.read(buffer);
+            buffer.flip();
+            newStaff[i] = readData(buffer);
+         }
+
+         // print the newly read employee records
+         for (Employee e : newStaff) 
+            System.out.println(e);
+      }
+   }
+   
+
+   /**
+      Writes employee data to a byte buffer
+      @param out the buffer
+      @param e the employee
+   */
+   public static void writeData(ByteBuffer out, Employee e) throws IOException
+   {
+      String name = e.getName();
+      int length = Math.min(name.length(), Employee.NAME_SIZE - 1);
+      // for (int i = 0; i < length; i++) out.putChar(name.charAt(i));
+      out.asCharBuffer().put(name.substring(0, length)).put('\0');
+      out.position(2 * Employee.NAME_SIZE);
+      out.putDouble(e.getSalary());
+      GregorianCalendar calendar = new GregorianCalendar();
+      calendar.setTime(e.getHireDay());
+      out.putInt(calendar.get(Calendar.YEAR));
+      out.putInt(calendar.get(Calendar.MONTH) + 1);
+      out.putInt(calendar.get(Calendar.DAY_OF_MONTH));
+   }
+
+   /**
+      Reads employee data from a byte buffer
+      @param in the buffer
+      @return the employee
+   */
+   public static Employee readData(ByteBuffer in) throws IOException
+   {      
+      StringBuilder name = new StringBuilder();
+      char ch;
+      while ((ch = in.getChar()) != '\0') name.append(ch);
+      in.position(2 * Employee.NAME_SIZE);
+      double salary = in.getDouble();
+      int y = in.getInt();
+      int m = in.getInt();
+      int d = in.getInt();
+      return new Employee(name.toString(), salary, y, m - 1, d);
+   }  
+}