import javax.servlet.*;
import javax.servlet.annotation.WebFilter;
import java.io.BufferedReader;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.util.ArrayList;
import java.util.List;
//過濾敏感詞匯
@WebFilter("/*")
public class FilterDemo8 implements Filter {
    //讀取txt文件時將詞匯存入列表
    private List<String> list = new ArrayList<String>();
    public void destroy() {
    }
    public void doFilter(ServletRequest req, ServletResponse resp, FilterChain chain) throws ServletException, IOException {
        //通過代理增強方法
        ServletRequest proxy = (ServletRequest) Proxy.newProxyInstance(req.getClass().getClassLoader(), req.getClass().getInterfaces(), new InvocationHandler() {
            @Override
            public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
                //判斷方法是否為getParameter
                if (method.getName().equals("getParameter")){
                    String obj = (String) method.invoke(req, args);
                    if (obj != null){
                        //遍歷后替換詞匯
                        for (String s : list) {
                            if (obj.contains(s)){
                                obj = obj.replaceAll(s,"***");
                            }
                        }
                    }
                    return obj;
                }
                return method.invoke(req,args);
            }
        });
        //放行
        chain.doFilter(proxy,resp);
    }
    public void init(FilterConfig config) throws ServletException {
        //讀取文件
        ServletContext context = config.getServletContext();
        //src下的文件真實位置是在WEN-INF/classes下的
        String realPath = context.getRealPath("/WEB-INF/classes/bad.txt");
        BufferedReader reader = null;
        try {
            reader = new BufferedReader(new FileReader(realPath));
            String line = null;
            while ((line = reader.readLine()) != null){
                list.add(line);
            }
        } catch (IOException e) {
            e.printStackTrace();
        }finally {
            if (reader != null){
                try {
                    reader.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }
}

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
@WebServlet("/servletDemo")
public class ServletDemo extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String name = request.getParameter("name");
        String what = request.getParameter("what");
        System.out.println(name + " : " + what);
    }
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request, response);
    }
}