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("
View 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();
    }
  }
}