session防止表单重复提交

阳光穿透心脏的1/2处 2022-08-12 05:29 235阅读 0赞

有一个生成表单号的sevlet

public class FormServlet extends HttpServlet {
    	private static final long serialVersionUID = 1L;
    
    	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    		//产生随机数表单号
    		TokenProcessor tp = TokenProcessor.getInstance();
    		
    		String token = tp.getToken();
    		
    		request.getSession().setAttribute("token", token);
    		
    		request.getRequestDispatcher("/form.jsp").forward(request, response);
    	}
    
    	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    		doGet(request,response);
    	}
    
    }
    
    class TokenProcessor{//令牌
    	/*1，构造方法私有
    	 * 2。自己创建一个
    	 * 3.对外暴露一个方法，允许获取上面对象
    	 */
    	
    	private TokenProcessor(){};
    	private static final TokenProcessor instance = new TokenProcessor();
    	
    	public static TokenProcessor getInstance(){
    		return instance;
    	}
    	
    	public String getToken(){
    		
    		//先生成随机数
    		String token = System.currentTimeMillis()+new Random().nextInt()+"";
    		//使位数固定，摘要算法
    		try {
    			MessageDigest md = MessageDigest.getInstance("md5");
    			byte[] md5 = md.digest(token.getBytes());
    			
    			//base64编码，生成字符串
    			BASE64Encoder encoder = new BASE64Encoder();
    			return encoder.encode(md5);
    			
    		} catch (NoSuchAlgorithmException e) {
    			throw new RuntimeException(e);
    		}
    		
    		
    	}
    }

表单如下

<%@ page language="java" contentType="text/html; charset=utf-8"
        pageEncoding="utf-8"%>
    <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
    <html>
    <head>
    <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
    <title>Form</title>
    </head>
    <body>
    	
    	<form action="/day07/DoForm" method="post">
    		<input type="hidden" name="token" value="${token}"><br>
    		用户名：<input type="text" name="username"><br>
    		<input type="submit" value="提交">
    	</form>
    </body>
    </html>

处理表单的sevlet

public class DoForm extends HttpServlet {
    	private static final long serialVersionUID = 1L;
    	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    		
    		String token = request.getParameter("token");
    		
    		String server_token = (String) request.getSession().getAttribute("token");
    		boolean b = isTokenValid(token,server_token);
    		
    		if(!b){
    			System.out.println("Invalid token");
    			return;
    		}
    		
    		request.getSession().removeAttribute("token");
    		System.out.println("ok");
    		
    	}
    
    	//判断表单是否有效
    	private boolean isTokenValid(String token,String server_token) {
    		if(token==null){
    			return false;
    		}
    		
    		if(server_token==null){
    			return false;
    		}
    		
    		if(!token.equals(server_token)){
    			return false;
    		}
    		
    		return true;
    	}
    
    
    	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    		doGet(request,response);
    	}
    
    }