Java基础之写文件——在通道写入过程中的缓冲区状态（BufferStateTrace）

控制台程序，在Junk目录中将字符串“Garbage in, garbage out\n”写入到名为charData.txt的文件中。

 import static java.nio.file.StandardOpenOption.*;
 import java.nio.file.*;
 import java.nio.channels.*;

 import java.util.EnumSet;
 import java.io.IOException;
 import java.nio.ByteBuffer;

 public class BufferStateTrace {
   public static void main(String[] args) {
     String phrase = "Garbage in, garbage out.\n";

     Path file = Paths.get(System.getProperty("user.home")).resolve("Beginning Java Struff").resolve("charData.txt"); // Path object for the file
     try {
       Files.createDirectories(file.getParent());                       // Make sure we have the directory
     } catch (IOException e) {
       e.printStackTrace();
       System.exit(1);
     }

     try (WritableByteChannel channel = Files.newByteChannel(file, EnumSet.of(WRITE, CREATE, APPEND))) {
       ByteBuffer buf = ByteBuffer.allocate(1024);
       System.out.printf(
         "\nNew buffer:           position = %1$2d   Limit = %2$4d   capacity = %3$4d",
                         buf.position(), buf.limit(), buf.capacity());
       // Load the data into the buffer
       for(char ch : phrase.toCharArray())
         buf.putChar(ch);
       System.out.printf(
         "\nBuffer after loading: position = %1$2d   Limit = %2$4d   capacity = %3$4d",
                         buf.position(), buf.limit(), buf.capacity());
       buf.flip();                                                      // Flip the buffer ready for file write
       System.out.printf(
         "\nBuffer after flip:    position = %1$2d   Limit = %2$4d   capacity = %3$4d",
                         buf.position(), buf.limit(), buf.capacity());
       channel.write(buf);                                              // Write the buffer to the file channel

 // Uncomment the following to get the size of the file in the output
 //      System.out.println("\nThe file contains " + ((FileChannel)channel).size() + " bytes.");

       buf.flip();
       channel.write(buf);                // Write the buffer again to the file channel
       System.out.println("\nBuffer contents written to the file.");
     } catch (IOException e) {
       e.printStackTrace();
     }
   }
 }