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康美药业三度行贿曝监管漏洞金融反腐停不下来

Greenhorn

Posts: 25

posted 2 years ago

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The error I am getting is:
HTTP Status 500 – Internal Server Error
Type Exception Report

Message Cannot parse null string

Description The server encountered an unexpected condition that prevented it from fulfilling the request.

Exception

java.lang.NumberFormatException: Cannot parse null string
java.base/java.lang.Integer.parseInt(Integer.java:630)
java.base/java.lang.Integer.parseInt(Integer.java:786)
com.servlets.Servlet1.doPost(Servlet1.java:19)
javax.servlet.http.HttpServlet.service(HttpServlet.java:555)
javax.servlet.http.HttpServlet.service(HttpServlet.java:623)
org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:51)
Note The full stack trace of the root cause is available in the server logs.

Servlet1.java

Servlet2.java

index.html

Paul Clapham

Marshal

Posts: 28449

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posted 2 years ago

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You can see that the error occurs in this line of code. If the servlet's request doesn't contain the "num1" parameter then req.getParameter() returns null. This happens when the client doesn't type anything in that input field of the form.

So instead of just trying to parse null as an integer, you need to decide what you want to do with null values and write code to act accordingly. It's also possible the the client will type something that isn't an integer, so you need to catch that exception and act accordingly.

Java 8 (verified skill)
Skill verified by Paul Clapham

Sourabh Chavan

Greenhorn

Posts: 25

posted 2 years ago

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Paul Clapham wrote: int number1=Integer.parseInt(req.getParameter("num1"));

You can see that the error occurs in this line of code. If the servlet's request doesn't contain the "num1" parameter then req.getParameter() returns null. This happens when the client doesn't type anything in that input field of the form.

So instead of just trying to parse null as an integer, you need to decide what you want to do with null values and write code to act accordingly. It's also possible the the client will type something that isn't an integer, so you need to catch that exception and act accordingly.

Will this code fix things?
Servlet1.java

package com.servlets;

import java.io.IOException;

import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

@WebServlet("/servlet1")
public class Servlet1 extends HttpServlet{

@Override
	protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
		// TODO Auto-generated method stub
		RequestDispatcher rd;
		int number1=0;
		int number2=0;
		
		
		try {
			  number1=Integer.parseInt(req.getParameter("num1"));
		    } catch (Exception e) {
		    	rd=req.getRequestDispatcher("/servlet3");
		    	rd.forward(req, resp);
		    }
		
		try {
			  number2=Integer.parseInt(req.getParameter("num2"));
		    } catch (Exception e) {
		    	rd=req.getRequestDispatcher("/servlet3");
		    	rd.forward(req, resp);
		    }
		
		int sum=number1+number2;
		
		req.setAttribute("s", sum);
		rd=req.getRequestDispatcher("/servlet2");
		rd.forward(req, resp);
	}
}

Servlet2.java

package com.servlets;

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

@WebServlet("/servlet2")
public class Servlet2 extends HttpServlet{
	
	
	@Override
	protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
		// TODO Auto-generated method stub
		RequestDispatcher rd;
		int number1=0;
		int number2=0;

try {
			  number1=Integer.parseInt(req.getParameter("num1"));
		    } catch (Exception e) {
		    	rd=req.getRequestDispatcher("/servlet3");
		    	rd.forward(req, resp);
		    }
		
		try {
			  number2=Integer.parseInt(req.getParameter("num2"));
		    } catch (Exception e) {
		    	rd=req.getRequestDispatcher("/servlet3");
		    	rd.forward(req, resp);
		    }
		
		resp.setContentType("index/html");
		
		int product=number1*number2;
		int sum=(int) req.getAttribute("s");
		PrintWriter out=resp.getWriter();
	}

}

Ron McLeod

Sheriff

Posts: 4857

613

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posted 2 years ago

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Sourabh Chavan wrote:Will this code fix things? ...

As Paul mentioned, it depends what you want to do if the client doesn't provide a value, or provides a value which does not represent an int value.

If you just want to handle missing or invalid values by using a default, you could do something like this:

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康美药业三度行贿曝监管漏洞 金融反腐停不下来

康美药业三度行贿曝监管漏洞金融反腐停不下来