如何在Java NIO解码过程中剔除错误符号？

import java.nio.ByteBuffer;
import java.nio.CharBuffer;
import java.nio.charset.Charset;
import java.nio.charset.CharsetDecoder;
import java.nio.charset.CharsetEncoder;
import java.nio.charset.CoderResult;

public class NIOEncodingExample {
    public static void main(String[] args) {
        // 原始数据
        ByteBuffer inputBuffer = ByteBuffer.wrap(new byte[]{104, 101, 108, 108, -30, -126, -84, 119, 111, 114, 108, 100});
        
        // 字符集
        Charset charset = Charset.forName("UTF-8");
        CharsetDecoder decoder = charset.newDecoder();
        CharsetEncoder encoder = charset.newEncoder();
        
        // 解码
        CharBuffer charBuffer = CharBuffer.allocate(10);
        CoderResult result = decoder.decode(inputBuffer, charBuffer, true);
        charBuffer.flip();
        
        // 剔除错误符号
        StringBuilder sb = new StringBuilder();
        while (charBuffer.hasRemaining()) {
            char c = charBuffer.get();
            if (isSymbolValid(c)) {
                sb.append(c);
            }
        }
        
        // 重新编码
        charBuffer.clear();
        charBuffer.put(sb.toString());
        charBuffer.flip();
        ByteBuffer outputBuffer;
        try {
            outputBuffer = encoder.encode(charBuffer);
            
            // 输出结果
            while (outputBuffer.hasRemaining()) {
                System.out.print(outputBuffer.get());
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
    
    private static boolean isSymbolValid(char c) {
        // 自定义判断逻辑，剔除不符合要求的错误符号
        return (c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z');
    }
}