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 ”写入到名为charData.txt的文件中。
 1 import static java.nio.file.StandardOpenOption.*;
 2 import java.nio.file.*;
 3 import java.nio.channels.*;
 4 
 5 import java.util.EnumSet;
 6 import java.io.IOException;
 7 import java.nio.ByteBuffer;
 8 
 9 public class BufferStateTrace {
10   public static void main(String[] args) {
11     String phrase = "Garbage in, garbage out.
";
12 
13     Path file = Paths.get(System.getProperty("user.home")).resolve("Beginning Java Struff").resolve("charData.txt"); // Path object for the file
14     try {
15       Files.createDirectories(file.getParent());                       // Make sure we have the directory
16     } catch (IOException e) {
17       e.printStackTrace();
18       System.exit(1);
19     }
20 
21     try (WritableByteChannel channel = Files.newByteChannel(file, EnumSet.of(WRITE, CREATE, APPEND))) {
22       ByteBuffer buf = ByteBuffer.allocate(1024);
23       System.out.printf(
24         "
New buffer:           position = %1$2d   Limit = %2$4d   capacity = %3$4d",
25                         buf.position(), buf.limit(), buf.capacity());
26       // Load the data into the buffer
27       for(char ch : phrase.toCharArray())
28         buf.putChar(ch);
29       System.out.printf(
30         "
Buffer after loading: position = %1$2d   Limit = %2$4d   capacity = %3$4d",
31                         buf.position(), buf.limit(), buf.capacity());
32       buf.flip();                                                      // Flip the buffer ready for file write
33       System.out.printf(
34         "
Buffer after flip:    position = %1$2d   Limit = %2$4d   capacity = %3$4d",
35                         buf.position(), buf.limit(), buf.capacity());
36       channel.write(buf);                                              // Write the buffer to the file channel
37 
38 // Uncomment the following to get the size of the file in the output
39 //      System.out.println("
The file contains " + ((FileChannel)channel).size() + " bytes.");
40 
41       buf.flip();
42       channel.write(buf);                // Write the buffer again to the file channel
43       System.out.println("
Buffer contents written to the file.");
44     } catch (IOException e) {
45       e.printStackTrace();
46     }
47   }
48 }