Java DFA算法实现示例代码

import java.util.*;
public class DFAFilter {
    // 根节点
    private Map<Character, Object> rootNode = new HashMap<>();
    // 敏感词结束标识
    private static final String END_FLAG = "isEnd";
    /**
     * 添加关键词到DFA中
     * @param keyword 关键词
     */
    public void addKeyword(String keyword) {
        if (keyword == null || keyword.isEmpty()) return;
        Map<Character, Object> currentMap = rootNode;
        for (int i = 0; i < keyword.length(); i++) {
            char c = keyword.charAt(i);
            // 获取下一层节点
            Map<Character, Object> nextMap = 
                (Map<Character, Object>) currentMap.get(c);
            if (nextMap == null) {
                nextMap = new HashMap<>();
                currentMap.put(c, nextMap);
            }
            currentMap = nextMap;
            // 最后一个字符标记结束
            if (i == keyword.length() - 1) {
                currentMap.put(END_FLAG, true);
            }
        }
    }
    /**
     * 批量添加关键词
     */
    public void addKeywords(List<String> keywords) {
        for (String keyword : keywords) {
            addKeyword(keyword);
        }
    }
}

/**
 * 检查文本是否包含敏感词，并返回第一个匹配的敏感词
 */
public String check(String text) {
    if (text == null || text.isEmpty()) return null;
    for (int i = 0; i < text.length(); i++) {
        int matchCount = 0;
        Map<Character, Object> currentMap = rootNode;
        char c;
        for (int j = i; j < text.length(); j++) {
            c = text.charAt(j);
            currentMap = (Map<Character, Object>) currentMap.get(c);
            if (currentMap == null) {
                break; // 匹配失败，重新从下一个字符开始
            }
            matchCount++;
            // 检查是否匹配到完整关键词
            if (currentMap.containsKey(END_FLAG)) {
                return text.substring(i, i + matchCount);
            }
        }
    }
    return null;
}
/**
 * 替换文本中的敏感词
 * @param text 原始文本
 * @param replaceChar 替换字符
 * @return 替换后的文本
 */
public String replace(String text, char replaceChar) {
    if (text == null || text.isEmpty()) return text;
    StringBuilder result = new StringBuilder(text);
    List<int[]> positions = new ArrayList<>();
    for (int i = 0; i < text.length(); i++) {
        int matchCount = 0;
        Map<Character, Object> currentMap = rootNode;
        char c;
        for (int j = i; j < text.length(); j++) {
            c = text.charAt(j);
            currentMap = (Map<Character, Object>) currentMap.get(c);
            if (currentMap == null) break;
            matchCount++;
            if (currentMap.containsKey(END_FLAG)) {
                positions.add(new int[]{i, i + matchCount});
                i = i + matchCount - 1; // 跳过已匹配部分
                break;
            }
        }
    }
    // 执行替换
    for (int[] pos : positions) {
        for (int i = pos[0]; i < pos[1]; i++) {
            result.setCharAt(i, replaceChar);
        }
    }
    return result.toString();
}

public class DFATest {
    public static void main(String[] args) {
        DFAFilter filter = new DFAFilter();
        // 添加敏感词
        filter.addKeywords(Arrays.asList(
            "色情", "暴力", "赌博", "毒品", "法轮功"
        ));
        // 测试文本
        String text = "这个网站包含色情和暴力内容，还有赌博信息。";
        // 检查敏感词
        String sensitive = filter.check(text);
        System.out.println("检测到敏感词: " + sensitive);
        // 替换敏感词
        String filtered = filter.replace(text, '*');
        System.out.println("过滤后: " + filtered);
    }
}
输出：
检测到敏感词: 色情
过滤后: 这个网站包含**和**内容，还有**信息。

/**
 * 增强版：支持忽略特殊字符（如空格、标点）
 */
public class AdvancedDFAFilter {
    private Map<Character, Object> rootNode = new HashMap<>();
    private static final String END_FLAG = "isEnd";
    // 忽略字符集合（空格、标点符号等）
    private Set<Character> ignoreChars = new HashSet<>(
        Arrays.asList(' ', ',', '.', '!', '?', ';', ':', '、', '，', '。', '！', '？')
    );
    public void addKeyword(String keyword) {
        Map<Character, Object> currentMap = rootNode;
        for (char c : keyword.toCharArray()) {
            currentMap = (Map<Character, Object>) currentMap.computeIfAbsent(
                c, k -> new HashMap<>()
            );
        }
        currentMap.put(END_FLAG, true);
    }
    public String check(String text) {
        for (int i = 0; i < text.length(); i++) {
            int matchCount = 0;
            Map<Character, Object> currentMap = rootNode;
            for (int j = i; j < text.length(); j++) {
                char c = text.charAt(j);
                // 跳过忽略字符
                if (ignoreChars.contains(c)) {
                    continue;
                }
                currentMap = (Map<Character, Object>) currentMap.get(c);
                if (currentMap == null) break;
                matchCount++;
                if (currentMap.containsKey(END_FLAG)) {
                    return text.substring(i, j + 1);
                }
            }
        }
        return null;
    }
}