Java Servlet NumberFormatException

Posted 2023-04-13

【中文标题】Java Servlet NumberFormatException

【英文标题】：

【发布时间】：2020-05-06 09:19:25

【问题描述】：

我的代码中出现 NumberFormatException，应该更新 SQL 列。当我尝试将其从字符串解析为 int 时，对 id 的异常引用为空。我不确定我做错了什么，因为我使用的代码在插入和删除子句之前起作用，如果有人可以提供帮助，这里是错误和代码。

堆栈跟踪：

INFO: Starting ProtocolHandler ["http-nio-8080"]
java.lang.NumberFormatException: null
    at java.base/java.lang.Integer.parseInt(Integer.java:620)
    at java.base/java.lang.Integer.parseInt(Integer.java:776)
    at control.EditScoreServlet.doPost(EditScoreServlet.java:34)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:660)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:741)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:202)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:541)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:139)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:74)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343)
    at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:367)
    at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65)
    at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:868)
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1639)
    at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
    at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
    at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    at java.base/java.lang.Thread.run(Thread.java:830)

代码：

    package control;

    import java.io.IOException;

    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 model.Score;
    import model.dao.ScoreDAO;

    @WebServlet("/editscore")
    public class EditScoreServlet extends HttpServlet 
        @Override
        protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException 
            req.getRequestDispatcher("WEB-INF/editscore.jsp").forward(req, resp);

        

        @Override
        protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException 

            try 
                String name = req.getParameter("name");
                String strDiff= req.getParameter("diff");
                int diff= Integer.parseInt(strDiff);
                String song = req.getParameter("song");
                String grade = req.getParameter("grade");
                String score = req.getParameter("score");
                String groove = req.getParameter("groove");
                int id = Integer.parseInt(req.getParameter("id"));

                Score score = new Score(id, name, diff, song, grade, score, groove);
                ScoreDAO scoredao = new ScoreDAO();
                System.out.println(score.toString());

                boolean updateSuccess= scoredao.editScore(tulos);

                if (updateSuccess)
                    resp.sendRedirect("/listscores");
                else 
                    req.setAttribute("message", "An error occurred when updating a score");
                    req.getRequestDispatcher("WEB-INF/actionreport.jsp").forward(req, resp);
                

             catch (NumberFormatException e) 
                // TODO Auto-generated catch block
                e.printStackTrace();
             catch (IOException e) 
                // TODO Auto-generated catch block
                e.printStackTrace();
             catch (ServletException e) 
                // TODO Auto-generated catch block
                e.printStackTrace();
            

        
    

【问题讨论】：

id 的值为 null。请检查您是否在请求中传递了 id。

【参考方案1】：

看看这些对你有没有帮助：

在 NumberFormatException 的 catch 块中做一些事情 可能会添加一个执行 parseInt 的方法，并在 parse-failures 的情况下返回默认值 在调用 parseInt() 之前进行空检查