Java基础之读文件——使用通道读二进制数据（ReadPrimes）

控制台程序，本例读取Java基础之写文件部分（PrimesToFile）写入的primes.bin。

 import java.nio.file.*;
 import java.nio.*;
 import java.nio.channels.ReadableByteChannel;
 import java.io.IOException;

 public class ReadPrimes {
   public static void main(String[] args) {
     Path file = Paths.get(System.getProperty("user.home")).resolve("Beginning Java Struff").resolve("primes.bin");
     if(!Files.exists(file)) {
       System.out.println(file + " does not exist. Terminating program.");
       System.exit(1);
     }

     final int PRIMECOUNT = 6;
     final int LONG_BYTES = 8;                                          // Number of bytes for type long
     ByteBuffer buf = ByteBuffer.allocate(LONG_BYTES*PRIMECOUNT);
     long[] primes = new long[PRIMECOUNT];
     try (ReadableByteChannel inCh = Files.newByteChannel(file)){
       int primesRead = 0;
       while(inCh.read(buf) != -1) {
         LongBuffer longBuf = ((ByteBuffer)(buf.flip())).asLongBuffer();
         primesRead = longBuf.remaining();
         longBuf.get(primes, 0, primesRead);

         // List the primes read on the same line
         System.out.println();
         for(int i = 0 ; i < primesRead ; ++i) {
           System.out.printf("%10d", primes[i]);
         }
         buf.clear();                                                   // Clear the buffer for the next read
       }
       System.out.println("\nEOF reached.");
     } catch(IOException e) {
       e.printStackTrace();
     }
   }
 }