案例1. 利用Servlet的过滤器Filter进行完成脏话过滤

package cn.javabs.filter;

import java.io.IOException;

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletRequestWrapper;
import javax.servlet.http.HttpServletResponse;

public class DirtyWordsFilterDemo implements Filter {

  public void init(FilterConfig filterConfig) throws ServletException {

  }

  public void doFilter(ServletRequest req, ServletResponse resp,
      FilterChain chain) throws IOException, ServletException {
    HttpServletRequest request;
    HttpServletResponse response;
    try{
      request = (HttpServletRequest)req;
      response = (HttpServletResponse)resp;
    }catch(Exception e){
      throw new RuntimeException("non-http request");
    }
    DirtyWordHttpServletRequest dwrequest = new DirtyWordHttpServletRequest(request);
    chain.doFilter(dwrequest, response);


  }

  public void destroy() {

  }

}
class DirtyWordHttpServletRequest extends HttpServletRequestWrapper{
  private String strs[] = {"傻逼","畜生","我去年买了个包"};
  private HttpServletRequest request;
  public DirtyWordHttpServletRequest(HttpServletRequest request){
    super(request);
    this.request = request;
  }
  @Override
  public String getParameter(String name) {
    String value = request.getParameter(name);
    if(value==null)
      return null;
    for(String s:strs){
      if(value.contains(s)){
        value = value.replace(s, "**");
      }
    }
    return value;
  }

}

案例2. 利用Servlet的过滤器Filter进行完成Html编码过滤

package cn.javabs.filter;

import java.io.IOException;

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletRequestWrapper;
import javax.servlet.http.HttpServletResponse;

public class HtmlFilterDemo implements Filter {

  public void init(FilterConfig filterConfig) throws ServletException {

  }

  public void doFilter(ServletRequest req, ServletResponse resp,
      FilterChain chain) throws IOException, ServletException {
    HttpServletRequest request;
    HttpServletResponse response;
    try{
      request = (HttpServletRequest)req;
      response = (HttpServletResponse)resp;
    }catch(Exception e){
      throw new RuntimeException("non-http request");
    }

    HtmlHttpServletRequest hrequest = new HtmlHttpServletRequest(request);
    chain.doFilter(hrequest, response);

  }

  public void destroy() {

  }

}
class HtmlHttpServletRequest extends HttpServletRequestWrapper{
  private HttpServletRequest request;
  public HtmlHttpServletRequest(HttpServletRequest request){
    super(request);
    this.request = request;
  }
  @Override
  public String getParameter(String name) {
    String value = request.getParameter(name);
    if(value==null)
      return null;
    value = htmlFilter(value);
    return value;
  }
  private String htmlFilter(String message) {
    if (message == null)
            return (null);

        char content[] = new char[message.length()];
        message.getChars(0, message.length(), content, 0);
        StringBuffer result = new StringBuffer(content.length + 50);
        for (int i = 0; i < content.length; i++) {
            switch (content[i]) {
            case '<':
                result.append("<");
                break;
            case '>':
                result.append(">");
                break;
            case '&':
                result.append("&");
                break;
            case '"':
                result.append(""");
                break;
            default:
                result.append(content[i]);
            }
        }
        return (result.toString());
  }

}

案例3. 利用Servlet的过滤器Filter进行完成字符编码过滤(Get及Post方式)

package cn.javabs.filter;

  import java.io.IOException;
  import java.io.UnsupportedEncodingException;

  import javax.servlet.Filter;
  import javax.servlet.FilterChain;
  import javax.servlet.FilterConfig;
  import javax.servlet.ServletException;
  import javax.servlet.ServletRequest;
  import javax.servlet.ServletResponse;
  import javax.servlet.http.HttpServletRequest;
  import javax.servlet.http.HttpServletRequestWrapper;
  import javax.servlet.http.HttpServletResponse;
  /**
       * 同时解决GET及POST请求参数和响应输出的编码过滤器
       */
  public class SetAllEncodingFilterDemo implements Filter {
    private FilterConfig filterConfig;
    public void init(FilterConfig filterConfig) throws ServletException {
      this.filterConfig = filterConfig;
    }

    public void doFilter(ServletRequest req, ServletResponse resp,
        FilterChain chain) throws IOException, ServletException {
      HttpServletRequest request;
      HttpServletResponse response;
      try{
        request = (HttpServletRequest)req;
        response = (HttpServletResponse)resp;
      }catch(Exception e){
        throw new RuntimeException("non-http request");
      }
      String encoding = "UTF-8";
      String value = filterConfig.getInitParameter("encoding");
      if(value!=null){
        encoding = value;
      }

      request.setCharacterEncoding(encoding);//POST请求方式
      response.setContentType("text/html;charset="+encoding);
      MyHttpServletRequest mrequest = new MyHttpServletRequest(request);
      chain.doFilter(mrequest, response);
    }

    public void destroy() {

    }

  }
  class MyHttpServletRequest extends HttpServletRequestWrapper{
    private HttpServletRequest request;
    public MyHttpServletRequest(HttpServletRequest request){
      super(request);
      this.request = request;
    }
    public String getParameter(String name) {
      String value = request.getParameter(name);
      if(value==null)
        return value;
      try {
        if("get".equalsIgnoreCase(request.getMethod()))
          value = new String(value.getBytes("ISO-8859-1"),request.getCharacterEncoding());
      } catch (UnsupportedEncodingException e) {
        e.printStackTrace();
      }
      return value;
    }

  }