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Servlet过滤字符串的HTML特殊字符

news 来源：原创 2024/5/8 9:00:15

（1）在一些情况下我们在用户输入数据的时候我们要判断一下是否合法，就是要过滤一下用户输入的信息是否含有特殊字符；

（2）直接上代码，以供大家参考学习：

ServletUtilities类：

package com.lc.ch04Biaodanshuju;

import javax.servlet.http.HttpServletRequest;


public class ServletUtilities {
 
  public static String filter(String input) {
    if (!hasSpecialChars(input)) {
      return(input);
    }
    StringBuffer filtered = new StringBuffer(input.length());
    char c;
    for(int i=0; i<input.length(); i++) {
      c = input.charAt(i);
      switch(c) {
        case '<': filtered.append("<"); break;
        case '>': filtered.append(">"); break;
        case '"': filtered.append("""); break;
        case '&': filtered.append("&"); break;
        default: filtered.append(c);
      }
    }
    return(filtered.toString());
  }

  private static boolean hasSpecialChars(String input) {
    boolean flag = false;
    if ((input != null) && (input.length() > 0)) {
      char c;
      for(int i=0; i<input.length(); i++) {
        c = input.charAt(i);
        switch(c) {
          case '<': flag = true; break;
          case '>': flag = true; break;
          case '"': flag = true; break;
          case '&': flag = true; break;
        }
      }
    }
    return(flag);
  }
}

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<!-- 
Front end to BadCodeServlet.

Taken from Core Servlets and JavaServer Pages 2nd Edition
from Prentice Hall and Sun Microsystems Press,
http://www.coreservlets.com/.
(C) 2003 Marty Hall; may be freely used or adapted.
-->
<HTML><HEAD><TITLE>Submit Code Sample</TITLE></HEAD>
<BODY BGCOLOR="#FDF5E6">
<CENTER>
<H1 ALIGN="CENTER">Submit Code Sample</H1>
<FORM ACTION="/servlet/coreservlets.BadCodeServlet">
  Code:<BR>
  <TEXTAREA ROWS="6" COLS="40" NAME="code"></TEXTAREA><P>
  <INPUT TYPE="SUBMIT" VALUE="Submit Code">
</FORM>
</CENTER></BODY></HTML>

package com.lc.ch04Biaodanshuju;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class BadCodeServlet extends HttpServlet {
  public void doGet(HttpServletRequest request,
                    HttpServletResponse response)
      throws ServletException, IOException {
    response.setContentType("text/html");
    PrintWriter out = response.getWriter();
    String title = "Code Sample";
    String docType =
      "<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.0 " +
      "Transitional//EN\">\n";
    out.println(docType +
                "<HTML>\n" +
                "<HEAD><TITLE>" + title + "</TITLE></HEAD>\n" +
                "<BODY BGCOLOR=\"#FDF5E6\">\n" +
                "<H1 ALIGN=\"CENTER\">" + title + "</H1>\n" +
                "<PRE>\n" +
                getCode(request) +
                "</PRE>\n" +
                "Now, wasn't that an interesting sample\n" +
                "of code?\n" +
                "</BODY></HTML>");
  }

  protected String getCode(HttpServletRequest request) {
    return(request.getParameter("code"));
  }
}