Java基础之写文件——使用Formatter对象加载缓冲区（UsingAFormatter)

控制台程序，使用Formatter对象将写入文件的数据准备好。

使用Formatter对象的format()方法，将数据值格式化到视图缓冲区charBuf中。

 import static java.nio.file.StandardOpenOption.*;
 import java.nio.file.*;                                                // Files  and Path
 import java.nio.channels.WritableByteChannel;
 import java.nio.*;                                                     // ByteBuffer and CharBuffer
 import java.util.*;                                                    // Formatter and EnumSet
 import java.io.IOException;

 public class UsingAFormatter {
   public static void main(String[] args) {
     String[] phrases = {"Rome wasn't burned in a day.",
                         "It's a bold mouse that sits in the cat's ear.",
                         "An ounce of practice is worth a pound of instruction."
                        };
     String separator = System.lineSeparator();                         // Get line separator
     Path file = Paths.get(System.getProperty("user.home")).resolve("Beginning Java Struff").resolve("Phrases.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);
       CharBuffer charBuf = buf.asCharBuffer(); // Create a view buffer
       System.out.println("Char view buffer:");
       System.out.printf("position = %2d  Limit = %4d  capacity = %4d%n", charBuf.position(),charBuf.limit(),charBuf.capacity());

       Formatter formatter = new Formatter(charBuf);

       // Write to the view buffer using a formatter
       int number = 0;                        // Proverb number
       for(String phrase : phrases) {
         formatter.format("Proverb%2d: %s%s", ++number, phrase, separator);
         System.out.println("\nView buffer after loading:");
         System.out.printf("position = %2d  Limit = %4d  capacity = %4d%n", charBuf.position(), charBuf.limit(),charBuf.capacity());

         charBuf.flip();                                                // Flip the view buffer
         System.out.println("View buffer after flip:");
         System.out.printf("position = %2d  Limit = %4d  length = %4d%n", charBuf.position(),charBuf.limit(),charBuf.length());

         buf.limit(2*charBuf.length());                                 // Set byte buffer limit

         System.out.println("Byte buffer after limit update:");
         System.out.printf("position = %2d  Limit = %4d  length = %4d%n", buf.position(),buf.limit(), buf.remaining());

         channel.write(buf);                                            // Write buffer to the channel
         System.out.println("Buffer contents written to file.");
         buf.clear();
         charBuf.clear();
       }
     } catch (IOException e) {
        e.printStackTrace();
     }
   }
 }