Question

我有一个简单的代码，可以使用servlet和JSP。通常它在我使用以下代码时有效。然而，这是一些可能性，我得到了这个意外的错误，无法弄清楚问题是什么

Caused by:
javax.el.ELException - Cannot convert testID of type class java.lang.String to    
class java.lang.Integer

我的结果课

public class Result {
    private String testID ; 
    private String date ; 
    private String result ;
    private String grade ;

    public String getTestID() {
        return testID;
    }
    public String getDate() {
        return date;
    }
    public String getResult() {
        return result;
    }
    public String getGrade() {
        return grade;
    }
    public void setTestID(String testID) {
        this.testID = testID;
    }
    public void setDate(String date) {
        this.date = date;
    }
    public void setResult(String result) {
        this.result = result;
    }
    public void setGrade(String grade) {
        this.grade = grade;
    }

}

我的Servlet

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
     String testID = request.getParameter("Action").trim();
     User user = (User) request.getSession().getAttribute("currentSessionUser");
     String sql = "select * from result where testID =" + testID + " and userID = " + user.getUserID();   
     PreparedStatement ps = DBconnection.getPreparedStatement(sql); 
     List <Result> results = new ArrayList<Result>(); 

     try {

        ResultSet rs = ps.executeQuery();

        while(rs.next())
        {
            Result result = new Result();

            result.setTestID(rs.getString("testID"));
            result.setGrade(rs.getString("grade"));
            result.setDate(rs.getString("dates"));
            result.setResult(rs.getString("result"));
            results.add(result);

        }


    } catch (SQLException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
     finally
     {
         DBconnection.close();
     }


     request.getSession().setAttribute("results", results);
        response.sendRedirect(request.getContextPath() +"/faces/subResult.jsp");

我的JSP

<?xml version="1.0" encoding="ISO-8859-1" ?>
<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
    pageEncoding="ISO-8859-1"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"     "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
 <html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1" />
   <title>Insert title here</title>

<%@taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
</head>
<body>


<ul>

<c:forEach items="${results}" var="results">
 <li> ${results.testID} </li>
 <li><c:out value="${result.grade}" /></li>
  <li><c:out value="${result.result}" /></li>
  <li>Hello</li>
 </c:forEach>

</ul>
</body>

堆栈跟踪

javax.faces.FacesException: javax.el.ELException: Cannot convert testID of type class java.lang.String to class java.lang.Integer
at org.apache.myfaces.shared_impl.context.ExceptionHandlerImpl.wrap(ExceptionHandlerImpl.java:241)
at org.apache.myfaces.shared_impl.context.ExceptionHandlerImpl.handle(ExceptionHandlerImpl.java:156)
at org.apache.myfaces.lifecycle.LifecycleImpl.render(LifecycleImpl.java:258)
at javax.faces.webapp.FacesServlet.service(FacesServlet.java:191)
at com.ibm.ws.webcontainer.servlet.ServletWrapper.service(ServletWrapper.java:1229)
at com.ibm.ws.webcontainer.servlet.ServletWrapper.handleRequest(ServletWrapper.java:774)
at com.ibm.ws.webcontainer.servlet.ServletWrapper.handleRequest(ServletWrapper.java:456)
at com.ibm.ws.webcontainer.servlet.ServletWrapperImpl.handleRequest(ServletWrapperImpl.java:178)
at com.ibm.ws.webcontainer.filter.WebAppFilterManager.invokeFilters(WebAppFilterManager.java:1032)
at com.ibm.ws.webcontainer.webapp.WebApp.handleRequest(WebApp.java:3748)
at com.ibm.ws.webcontainer.webapp.WebGroup.handleRequest(WebGroup.java:304)
at com.ibm.ws.webcontainer.WebContainer.handleRequest(WebContainer.java:962)
at com.ibm.ws.webcontainer.WSWebContainer.handleRequest(WSWebContainer.java:1662)
at com.ibm.ws.webcontainer.channel.WCChannelLink.ready(WCChannelLink.java:195)
at com.ibm.ws.http.channel.inbound.impl.HttpInboundLink.handleDiscrimination(HttpInboundLink.java:459)
at com.ibm.ws.http.channel.inbound.impl.HttpInboundLink.handleNewRequest(HttpInboundLink.java:526)
at com.ibm.ws.http.channel.inbound.impl.HttpInboundLink.processRequest(HttpInboundLink.java:312)
at com.ibm.ws.http.channel.inbound.impl.HttpInboundLink.ready(HttpInboundLink.java:283)
at com.ibm.ws.tcp.channel.impl.NewConnectionInitialReadCallback.sendToDiscriminators(NewConnectionInitialReadCallback.java:214)
at com.ibm.ws.tcp.channel.impl.NewConnectionInitialReadCallback.complete(NewConnectionInitialReadCallback.java:113)
at com.ibm.ws.tcp.channel.impl.AioReadCompletionListener.futureCompleted(AioReadCompletionListener.java:165)
at com.ibm.io.async.AbstractAsyncFuture.invokeCallback(AbstractAsyncFuture.java:217)
at com.ibm.io.async.AsyncChannelFuture.fireCompletionActions(AsyncChannelFuture.java:161)
at com.ibm.io.async.AsyncFuture.completed(AsyncFuture.java:138)
at com.ibm.io.async.ResultHandler.complete(ResultHandler.java:204)
at com.ibm.io.async.ResultHandler.runEventProcessingLoop(ResultHandler.java:775)
at com.ibm.io.async.ResultHandler$2.run(ResultHandler.java:905)
at com.ibm.ws.util.ThreadPool$Worker.run(ThreadPool.java:1814)
Caused by: javax.el.ELException: Cannot convert testID of type class java.lang.String to class java.lang.Integer
at org.apache.el.lang.ELSupport.coerceToNumber(ELSupport.java:338)
at org.apache.el.lang.ELSupport.coerceToNumber(ELSupport.java:309)
at org.apache.el.lang.ELSupport.coerceToType(ELSupport.java:422)
at org.apache.el.ExpressionFactoryImpl.coerceToType(ExpressionFactoryImpl.java:47)
at org.apache.myfaces.el.convert.PropertyResolverToELResolver.coerceToInt(PropertyResolverToELResolver.java:271)
at org.apache.myfaces.el.convert.PropertyResolverToELResolver.getValue(PropertyResolverToELResolver.java:157)
at javax.el.CompositeELResolver.getValue(CompositeELResolver.java:55)
at org.apache.myfaces.el.unified.resolver.FacesCompositeELResolver.getValue(FacesCompositeELResolver.java:142)
at javax.el.CompositeELResolver.getValue(CompositeELResolver.java:55)
at org.apache.el.parser.AstValue.getValue(AstValue.java:173)
at org.apache.el.ValueExpressionImpl.getValue(ValueExpressionImpl.java:283)
at org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate(PageContextImpl.java:778)
at com.ibm._jsp._subResult._jspx_meth_c_forEach_0(_subResult.java:182)
at com.ibm._jsp._subResult._jspService(_subResult.java:98)
at com.ibm.ws.jsp.runtime.HttpJspBase.service(HttpJspBase.java:99)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:668)
at com.ibm.ws.webcontainer.servlet.ServletWrapper.service(ServletWrapper.java:1229)
at com.ibm.ws.webcontainer.servlet.ServletWrapper.handleRequest(ServletWrapper.java:774)
at com.ibm.ws.webcontainer.servlet.ServletWrapper.handleRequest(ServletWrapper.java:456)
at com.ibm.ws.webcontainer.servlet.ServletWrapperImpl.handleRequest(ServletWrapperImpl.java:178)
at com.ibm.wsspi.webcontainer.servlet.GenericServletWrapper.handleRequest(GenericServletWrapper.java:122)
at com.ibm.ws.jsp.webcontainerext.AbstractJSPExtensionServletWrapper.handleRequest(AbstractJSPExtensionServletWrapper.java:216)
at com.ibm.ws.webcontainer.filter.WebAppFilterManager.invokeFilters(WebAppFilterManager.java:1032)
at com.ibm.ws.webcontainer.webapp.WebAppRequestDispatcher.dispatch(WebAppRequestDispatcher.java:1384)
at com.ibm.ws.webcontainer.webapp.WebAppRequestDispatcher.forward(WebAppRequestDispatcher.java:193)
at com.FYP.servletGetSubResult.doGet(servletGetSubResult.java:74)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:575)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:668)
at com.ibm.ws.webcontainer.servlet.ServletWrapper.service(ServletWrapper.java:1229)
at com.ibm.ws.webcontainer.servlet.ServletWrapper.handleRequest(ServletWrapper.java:774)
at com.ibm.ws.webcontainer.servlet.ServletWrapper.handleRequest(ServletWrapper.java:456)
at com.ibm.ws.webcontainer.servlet.ServletWrapperImpl.handleRequest(ServletWrapperImpl.java:178)
at com.ibm.ws.webcontainer.filter.WebAppFilterManager.invokeFilters(WebAppFilterManager.java:1032)
at com.ibm.ws.webcontainer.webapp.WebAppRequestDispatcher.dispatch(WebAppRequestDispatcher.java:1384)
at com.ibm.ws.webcontainer.webapp.WebAppRequestDispatcher.forward(WebAppRequestDispatcher.java:193)
at org.apache.myfaces.context.servlet.ServletExternalContextImpl.dispatch(ServletExternalContextImpl.java:367)
at org.apache.myfaces.view.jsp.JspViewDeclarationLanguage.buildView(JspViewDeclarationLanguage.java:94)
at org.apache.myfaces.lifecycle.RenderResponseExecutor.execute(RenderResponseExecutor.java:66)
at org.apache.myfaces.lifecycle.LifecycleImpl.render(LifecycleImpl.java:239)
... 25 more

Answer 1

我想这一行给出了问题

<li> ${results.testID + ""} </li>

我想知道它的目的是什么。为什么要尝试将Integer与空字符串连接起来？

使用el运算符无法实现+中的连接。你只需要将el表达式放在彼此靠近的位置。

以下内容应该有效

<li> ${results.testID} ${""}</li>

这会做同样的事情，但更有意义

<li> ${results.testID}</li>

编辑：

正如JB Nizet在对该问题的评论中指出的那样，该问题是在命名引用当前项目的变量时由错误的选择引起的。

引用他：

不确定这是否与异常有关，但是命名当前项目结果（在var =＆＃34;结果＆＃34;）是一个坏主意：它是与集合本身相同的名称。将其命名为结果，然后更改 $ {results.testID}到$ {result.testID}。

Answer 2

很可能您将Result.testID定义为Integer（在Result类中）。但是在您的数据库中，testID列是String。大多数数据都是数字的，因此result.setTestID(rs.getString("testID"));通常不会失败，但是在某些情况下，testID列中的数据库数据不是数字。因此“无法将java.lang.String类型的testID转换为类java.lang.Integer”错误

无法使用JSTL标记显示值

2 个答案: