这些天我开始学习Spring,Iam得到以下异常:我只是想从登录页面导航(稍后将使用DAO在db中插入opeartion)到一些index.jsp页面
exception
org.apache.jasper.JasperException: An exception occurred processing JSP page /login.jsp at line 11
8: </head>
9: <body>
10: <form:form method="post" commandName="user" action="login">
11: <form:label path="uname" /> <form:input path="uname" />
12: <form:label path="password" /> <form:input path="password" />
13: <input type="submit" value="Submit" />
14: </form:form>
Stacktrace:
org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:521)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:424)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:313)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:260)
javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
root cause
java.lang.IllegalStateException: Neither BindingResult nor plain target object for bean name 'user' available as request attribute
org.springframework.web.servlet.support.BindStatus.<init>(BindStatus.java:141)
org.springframework.web.servlet.tags.form.AbstractDataBoundFormElementTag.getBindStatus(AbstractDataBoundFormElementTag.java:179)
org.springframework.web.servlet.tags.form.AbstractDataBoundFormElementTag.getPropertyPath(AbstractDataBoundFormElementTag.java:199)
org.springframework.web.servlet.tags.form.LabelTag.autogenerateFor(LabelTag.java:130)
org.springframework.web.servlet.tags.form.LabelTag.resolveFor(LabelTag.java:120)
org.springframework.web.servlet.tags.form.LabelTag.writeTagContent(LabelTag.java:90)
org.springframework.web.servlet.tags.form.AbstractFormTag.doStartTagInternal(AbstractFormTag.java:103)
org.springframework.web.servlet.tags.RequestContextAwareTag.doStartTag(RequestContextAwareTag.java:80)
org.apache.jsp.login_jsp._jspx_meth_form_005flabel_005f0(login_jsp.java:157)
org.apache.jsp.login_jsp._jspx_meth_form_005fform_005f0(login_jsp.java:111)
org.apache.jsp.login_jsp._jspService(login_jsp.java:71)
org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:388) …我对例外有一些疑问.
任何人都可以告诉我为什么java不允许我们在子类中创建Checked Exception,同时它允许子类中的Unchecked异常
下面的示例抛出当我使用'throws IOException'时编译时错误,但是当我在子类中使用'throws ArithmeticException'时它不会抛出任何错误..我只是想知道它背后的实际原因,你能不能这样做？
这是代码(你会得到编译时错误)
package com.exception.test;
import java.io.IOException;
public class Parent {
void msg() {
System.out.println("Parent...");
}
public static void main(String[] args) {
Parent parent = new Child();
parent.msg();
}
}
class Child extends Parent {
void msg() throws IOException {
System.out.println("Child...");
}
}
//使用unCheckedException
package com.exception.test;
import java.io.IOException;
public class Parent {
void msg() {
System.out.println("Parent...");
}
public static void main(String[] args) {
Parent parent = new Child();
parent.msg();
}
}
class Child extends Parent { …