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我正在关注本教程 http://netbeans.org/kb/docs/web/quickstart-webapps.html

如前所述，我创建了两个 jsp 页面。我的 index.jsp 页面看起来像这样

%@page contentType="text/html" pageEncoding="UTF-8"%>
<!DOCTYPE html>
<html>
    <head>
        <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
        <title>JSP Page</title>
    </head>
    <body>

        Name<form name="Name Input Form" action="response.jsp">
            <input type="text" name="name" value="" />
            <input type="submit" value="OK" />
        </form>

    </body>
</html>

我的 response.jsp 看起来像这样

<%@page contentType="text/html" pageEncoding="UTF-8"%>
<!DOCTYPE html>
<html>
    <head>
        <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
        <title>JSP Page</title>
    </head>
    <body>

        <jsp:useBean id="useBean" scope="session" class="abc.NameHandler" />

        <jsp:setProperty name="myBean" property="name" /><h1>Hello</h1>
        <jsp:getProperty name="myBean" property="name" />

    </body>
</html>

我创建了一个名为 abc 的包，其中我定义了一个名为 NameHandler 的类。

package abc;

public class NameHandler 
{

    private String name;

    public NameHandler() 
    {
        name =null;

    }

    /**
     * @return the name
     */
    public String getName() {
        return name;
    }

    /**
     * @param name the name to set
     */
    public void setName(String name) {
        this.name = name;
    }
}

当我运行项目时 index.jsp 正确显示并且它命令输入名称并且它有一个提交按钮。现在当我按下提交按钮时出现以下错误。

HTTP Status 500 -

type Exception report

message

descriptionThe server encountered an internal error () that prevented it from fulfilling this request.

exception

org.apache.jasper.JasperException: java.lang.NullPointerException

root cause

java.lang.NullPointerException

note The full stack traces of the exception and its root causes are available in the GlassFish Server Open Source Edition 3.1 logs.
GlassFish Server Open Source Edition 3.1

而且我不知道为什么会出现此错误。有人可以解释一下吗？

[更新]

这个错误是什么意思？

WARNING: StandardWrapperValve[jsp]: PWC1406: Servlet.service() for servlet jsp threw exception
java.lang.NullPointerException
    at org.apache.jasper.runtime.JspRuntimeLibrary.internalIntrospecthelper(JspRuntimeLibrary.java:368)
    at org.apache.jasper.runtime.JspRuntimeLibrary.introspecthelper(JspRuntimeLibrary.java:354)
    at org.apache.jsp.response_jsp._jspService(response_jsp.java from :68)
    at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:111)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:848)
    at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:403)
    at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:492)
    at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:378)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:848)
    at org.apache.catalina.core.StandardWrapper.service(StandardWrapper.java:1534)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:281)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:175)
    at org.apache.catalina.core.StandardPipeline.doInvoke(StandardPipeline.java:655)
    at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:595)
    at com.sun.enterprise.web.WebPipeline.invoke(WebPipeline.java:98)
    at com.sun.enterprise.web.PESessionLockingStandardPipeline.invoke(PESessionLockingStandardPipeline.java:91)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:162)
    at org.apache.catalina.connector.CoyoteAdapter.doService(CoyoteAdapter.java:326)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:227)
    at com.sun.enterprise.v3.services.impl.ContainerMapper.service(ContainerMapper.java:170)
    at com.sun.grizzly.http.ProcessorTask.invokeAdapter(ProcessorTask.java:822)
    at com.sun.grizzly.http.ProcessorTask.doProcess(ProcessorTask.java:719)
    at com.sun.grizzly.http.ProcessorTask.process(ProcessorTask.java:1013)
    at com.sun.grizzly.http.DefaultProtocolFilter.execute(DefaultProtocolFilter.java:225)
    at com.sun.grizzly.DefaultProtocolChain.executeProtocolFilter(DefaultProtocolChain.java:137)
    at com.sun.grizzly.DefaultProtocolChain.execute(DefaultProtocolChain.java:104)
    at com.sun.grizzly.DefaultProtocolChain.execute(DefaultProtocolChain.java:90)
    at com.sun.grizzly.http.HttpProtocolChain.execute(HttpProtocolChain.java:79)
    at com.sun.grizzly.ProtocolChainContextTask.doCall(ProtocolChainContextTask.java:54)
    at com.sun.grizzly.SelectionKeyContextTask.call(SelectionKeyContextTask.java:59)
    at com.sun.grizzly.ContextTask.run(ContextTask.java:71)
    at com.sun.grizzly.util.AbstractThreadPool$Worker.doWork(AbstractThreadPool.java:532)
    at com.sun.grizzly.util.AbstractThreadPool$Worker.run(AbstractThreadPool.java:513)
    at java.lang.Thread.run(Thread.java:619)
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1 回答 1

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jsp:useBean和jsp:setProperty/中的 bean 的 ID 和名称jsp:getProperty应匹配：

   <jsp:useBean id="myBean" scope="session" class="abc.NameHandler" />

   <jsp:setProperty name="myBean" property="name" /><h1>Hello</h1>
   <jsp:getProperty name="myBean" property="name" />
于 2012-11-23T08:37:31.517 回答