一、練習-數字對應的中文

找出 E5 B1 8C 這3個十六進位制對應UTF-8編碼的漢字

參考程式碼1

		// 找出 E5 B1 8C 這3個十六進位制對應UTF-8編碼的漢字
		byte[] bs = new byte[3];
		bs[0] = (byte) 0xE5;
		bs[1] = (byte) 0xB1;
		bs[2] = (byte) 0x8C;

		String str = new String(bs, "UTF-8");
		System.out.println("E5B18C 對應的字元是：" + str);

參考程式碼2

		String s =
 
 "E5B18C";
		int total = s.length() / 2;
		byte[] buffer = new byte[total];
		for (int i = 0; i < total; i++) {

			int start = i * 2;
			//先將字元轉換為16進位制數字，再強制轉換為位元組
			buffer[i] = (byte) Integer.parseInt(s.substring(start, start + 2), 16);
		}

		String result = new String(buffer, "UTF-8");
		System.
 
out.println("E5B18C 對應的字元是：" + result);

運作結果

二、練習-移除BOM

如果用記事本根據UTF-8編碼儲存漢字就會在最前面生成一段標示符，這個標示符用於表示該檔案是使用UTF-8編碼的，找出這段標示符對應的十六進位制，並且開發一個方法，自動去除這段標示符

在移除BOM之前，我們首先要知道UTF-8的BOM對應的編碼是多少，測試程式碼如下

package test;

import java.io.File;
import java.io.FileInputStream;

public class Test1 {
	public
 
 static void main(String[] args) {
		File f = new File("D:/Test/test1.txt");
		try(FileInputStream fis = new FileInputStream(f)) {
			byte[] bytes = new byte[(int) f.length()];
			fis.read(bytes);
			System.out.println("檔案text1.txt中的內容："+new String(bytes,"UTF-8"));
			System.out.print("對應的16進製表示：");
			for(byte b : bytes) {
				int a = b & 0x0000ff;
				String hexString = Integer.toHexString(a).toUpperCase();
				System.out.print(hexString+" ");
			}
		} catch (Exception e) {
			// TODO: handle exception
			e.printStackTrace();
		}
	}
}

測試結果

從測試結果以及上一個練習題可以知道，UTF-8的BOM對應的編碼為：EF BB BF,且為前三個，到這裡就可以開始解決我們的問題了

參考程式碼1

package review4;

import java.io.File;
import java.io.FileInputStream;
import java.util.Arrays;

public class RemoveBOM {
	public static void main(String[] args) {
		File f = new File("D:/Test/test1.txt");
		try(FileInputStream fis = new FileInputStream(f)) {
			byte[] read = new byte[(int) f.length()];		
			fis.read(read);
			System.out.print("檔案中讀出來的資料是:");
					
			System.out.println(new String(read,"UTF-8"));
			
			removeBom(f);
			
		} catch (Exception e) {
			// TODO: handle exception
			e.printStackTrace();
		}
		
	}
	
	public static void removeBom(File f) {
		try(FileInputStream fis = new FileInputStream(f)) {
			byte[] read = new byte[(int) f.length()];
			byte[] result = new byte[(int) f.length()-3];
			fis.read(read);
			System.out.print("除去BOM後的結果:");
			for(int i = 3; i < read.length; i++) {
				int a = read[i] & 0x000000ff;
				result[i-3] = (byte) a;
			}			
			System.out.println(new String(result,"UTF-8"));
			
		} catch (Exception e) {
			// TODO: handle exception
			e.printStackTrace();
		}
	}
	
	
}

參考程式碼2

package review4;

import java.io.File;
import java.io.FileInputStream;
import java.util.Arrays;

public class RemoveBOM {
	public static void main(String[] args) {
		File f = new File("D:/Test/test1.txt");
		try(FileInputStream fis = new FileInputStream(f)) {
			byte[] read = new byte[(int) f.length()];		
			fis.read(read);
			System.out.print("檔案中讀出來的資料是:");				
			System.out.println(new String(read,"UTF-8"));		
			byte[] result = removeBom(read);		
			System.out.println("除去BOM後的結果:"+new String(result,"UTF-8"));
				
		} catch (Exception e) {
			// TODO: handle exception
			e.printStackTrace();
		}
		
	}
	
	public static byte[] removeBom(byte[] read) {
		return Arrays.copyOfRange(read, 3,read.length);
	}
}

執行結果