jsp出错：a null object.

dellon_z 2002-05-08 04:27:21
jsp出错信息如下：
type Exception report

message Internal Server Error

description The server encountered an internal error (Internal Server Error) that prevented it from fulfilling this request.

exception

org.apache.jasper.JasperException: Attempted a bean operation on a null object.


原码：
<jsp:useBean id="myCar" class="com.wrox.cars.CarBean" />
i have a <jsp:getProperty name="mycar" property="make" /> <br />
my car cost $<jsp:getProperty name="mycar" property="price" />

javaBean源码：
package com.wrox.cars;
import java.io.Serializable;
public class CarBean implements Serializable {
public CarBean() {
}
private String make = "ford";
public String getMake() {
return make;
}
public void setMake(String make) {
this.make = make;
}
private double cost = 1000.00;
private double taxRate = 17.5;

public double getPrice() {
double price = (cost + (cost * (taxRate/100)));
return price;
}
private void setPrice(double newPrice) {
}
}
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dellon_z 2002-05-08
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不好意思，，谢谢你了，呵呵
可乐加水 2002-05-08
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你的下面这段代码里问题很多
<jsp:useBean id="myCar" class="com.wrox.cars.CarBean" />
i have a <jsp:getProperty name="mycar" property="make" /> <br />
my car cost $<jsp:getProperty name="mycar" property="price" />
myCar的大小写应该写对的，不然是找不到的
id="myCar" 与name="mycar" 应该是一样的
所以name="myCar" 才对
可乐加水 2002-05-08
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我给改成这样了
import java.io.Serializable;
public class CarBean implements Serializable {
public CarBean() {
}
String make = "ford";
double price=0;
public String getMake() {
return make;
}
public void setMake(String make) {
this.make = make;
}
private double cost = 1000.00;
private double taxRate = 17.5;

public double getPrice() {
price = (cost + (cost * (taxRate/100)));
return price;
}
private void setPrice(double newPrice) {
this.price = newPrice;
}
}

jsp文件
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<HTML>
<HEAD>
<META http-equiv="Content-Type" content="text/html; charset=GB2312">
<META name="GENERATOR" content="IBM WebSphere Studio">
<TITLE>test.jsp</TITLE>
</HEAD>
<%@ page language="java"%>
<%@ page import="CarBean"%>

<BODY>
<jsp:useBean id="myCar" class="CarBean"/>
i have a <jsp:getProperty name="myCar" property="make"/> <br/>
my car cost $<jsp:getProperty name="myCar" property="price"/>

<%
int i=1;
if( i >0){
out.print("i>0");
}
if( i< 0){
out.print("i<0");
}
out.println(myCar.getPrice());
out.println(myCar.getMake());
%>
</BODY>
</HTML>
调试通过，运行结果如下：
i have a ford
my car cost $1175.0 i>01175.0 ford
，你也试一下吧
dellon_z 2002-05-08
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realyfly(含泪海)
改过了，重起了，还是那个错误，怎么办？


description The server encountered an internal error (Internal Server Error) that prevented it from fulfilling this request.

exception

org.apache.jasper.JasperException: Attempted a bean operation on a null object.
at org.apache.jasper.runtime.JspRuntimeLibrary.handleGetProperty(JspRuntimeLibrary.java:510)
at org.apache.jsp.carPage2$jsp._jspService(carPage2$jsp.java:87)
at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:107)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:853)
at org.apache.jasper.servlet.JspServlet$JspServletWrapper.service(JspServlet.java:202)
at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:382)
at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:474)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:853)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:247)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:193)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:243)
at org.apache.catalina.core.StandardPipeline.invokeNext(StandardPipeline.java:566)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:472)
at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:943)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:190)
at org.apache.catalina.core.StandardPipeline.invokeNext(StandardPipeline.java:566)
at org.apache.catalina.valves.CertificatesValve.invoke(CertificatesValve.java:246)
at org.apache.catalina.core.StandardPipeline.invokeNext(StandardPipeline.java:564)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:472)
at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:943)
at org.apache.catalina.core.StandardContext.invoke(StandardContext.java:2343)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:180)
at org.apache.catalina.core.StandardPipeline.invokeNext(StandardPipeline.java:566)
at org.apache.catalina.valves.ErrorDispatcherValve.invoke(ErrorDispatcherValve.java:170)
at org.apache.catalina.core.StandardPipeline.invokeNext(StandardPipeline.java:564)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:170)
at org.apache.catalina.core.StandardPipeline.invokeNext(StandardPipeline.java:564)
at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:468)
at org.apache.catalina.core.StandardPipeline.invokeNext(StandardPipeline.java:564)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:472)
at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:943)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:174)
at org.apache.catalina.core.StandardPipeline.invokeNext(StandardPipeline.java:566)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:472)
at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:943)
at org.apache.catalina.connector.http.HttpProcessor.process(HttpProcessor.java:1012)
at org.apache.catalina.connector.http.HttpProcessor.run(HttpProcessor.java:1107)
at java.lang.Thread.run(Thread.java:536)

scarab 2002-05-08
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很可能是BEAN的路径不对，没有找到该BEAN
可乐加水 2002-05-08
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<jsp:getProperty name="mycar" property="price" />
这一句里面指出了bean中有一个price，但是你的
bean里（不是函数里）没有声明它，在

private String make = "ford";下面加一句
double price=0;
并且把
public double getPrice() {
double price = (cost + (cost * (taxRate/100)));
return price;
}
改成
public double getPrice() {
price = (cost + (cost * (taxRate/100)));
return price;
}

spring_MVC源码
弃用了struts，用spring mvc框架做了几个项目，感觉都不错，而且使用了注解方式，可以省掉一大堆配置文件。本文主要介绍使用注解方式配置的spring mvc，之前写的spring3.0 mvc和rest小例子没有介绍到数据层的内容，现在这一篇补上。下面开始贴代码。 文中用的框架版本：spring 3,hibernate 3,没有的，自己上网下。 先说web.xml配置： [java] view plaincopy 01.<?xml version="1.0" encoding="UTF-8"?> 02. 03. s3h3 04. 05. contextConfigLocation 06. classpath:applicationContext*.xml 07. 08. 09. org.springframework.web.context.ContextLoaderListener 10. 11. 12. 13. spring 14. org.springframework.web.servlet.DispatcherServlet 15. 1 16. 17. 18. spring <!-- 这里在配成spring,下边也要写一个名为spring-servlet.xml的文件，主要用来配置它的controller --> 19. *.do 20. 21. 22. index.jsp 23. 24. spring-servlet,主要配置controller的信息 [java] view plaincopy 01.<?xml version="1.0" encoding="UTF-8"?> 02. 09. 10. 11. <!-- 把标记了@Controller注解的类转换为bean --> 12. 13. <!-- 启动Spring MVC的注解功能，完成请求和注解POJO的映射 --> 14. 15. 16. <!-- 对模型视图名称的解析，即在模型视图名称添加前后缀 --> 17. 19. 20. 23. applicationContext.xml代码 [java] view plaincopy 01.<?xml version="1.0" encoding="UTF-8"?> 02. 11. 12. 13. <!-- 自动扫描所有注解该路径 --> 14. 15. 16. 17. 19. 20. 21. 22. ${dataSource.dialect} 23. ${dataSource.hbm2ddl.auto} 24. update 25. 26. 27. 28. 29. com.mvc.entity<!-- 扫描实体类，也就是平时所说的model --> 30. 31. 32. 33. 34. 36. 37. 38. 39. 40. 42. 43. 44. 45. 46. 47. <!-- Dao的实现 --> 48. 49. 50. 51. 52. 53. 54. 55. hibernate.properties数据库连接配置 [java] view plaincopy 01.dataSource.password=123 02.dataSource.username=root 03.dataSource.databaseName=test 04.dataSource.driverClassName=com.mysql.jdbc.Driver 05.dataSource.dialect=org.hibernate.dialect.MySQL5Dialect 06.dataSource.serverName=localhost:3306 07.dataSource.url=jdbc:mysql://localhost:3306/test 08.dataSource.properties=user=${dataSource.username};databaseName=${dataSource.databaseName};serverName=${dataSource.serverName};password=${dataSource.password} 09.dataSource.hbm2ddl.auto=update 配置已经完成，下面开始例子 先在数据库建表，例子用的是mysql数据库 [java] view plaincopy 01.CREATE TABLE `test`.`student` ( 02. `id` int(10) unsigned NOT NULL AUTO_INCREMENT, 03. `name` varchar(45) NOT NULL, 04. `psw` varchar(45) NOT NULL, 05. PRIMARY KEY (`id`) 06.) 建好表后，生成实体类 [java] view plaincopy 01.package com.mvc.entity; 02. 03.import java.io.Serializable; 04. 05.import javax.persistence.Basic; 06.import javax.persistence.Column; 07.import javax.persistence.Entity; 08.import javax.persistence.GeneratedValue; 09.import javax.persistence.GenerationType; 10.import javax.persistence.Id; 11.import javax.persistence.Table; 12. 13.@Entity 14.@Table(name = "student") 15.public class Student implements Serializable { 16. private static final long serialVersionUID = 1L; 17. @Id 18. @Basic(optional = false) 19. @GeneratedValue(strategy = GenerationType.IDENTITY) 20. @Column(name = "id", nullable = false) 21. private Integer id; 22. @Column(name = "name") 23. private String user; 24. @Column(name = "psw") 25. private String psw; 26. public Integer getId() { 27. return id; 28. } 29. public void setId(Integer id) { 30. this.id = id; 31. } 32. 33. public String getUser() { 34. return user; 35. } 36. public void setUser(String user) { 37. this.user = user; 38. } 39. public String getPsw() { 40. return psw; 41. } 42. public void setPsw(String psw) { 43. this.psw = psw; 44. } 45.} Dao层实现 [java] view plaincopy 01.package com.mvc.dao; 02. 03.import java.util.List; 04. 05.public interface EntityDao { 06. public List<Object> createQuery(final String queryString); 07. public Object save(final Object model); 08. public void update(final Object model); 09. public void delete(final Object model); 10.} [java] view plaincopy 01.package com.mvc.dao; 02. 03.import java.util.List; 04. 05.import org.hibernate.Query; 06.import org.springframework.orm.hibernate3.HibernateCallback; 07.import org.springframework.orm.hibernate3.support.HibernateDaoSupport; 08. 09.public class EntityDaoImpl extends HibernateDaoSupport implements EntityDao{ 10. public List<Object> createQuery(final String queryString) { 11. return (List<Object>) getHibernateTemplate().execute( 12. new HibernateCallback<Object>() { 13. public Object doInHibernate(org.hibernate.Session session) 14. throws org.hibernate.HibernateException { 15. Query query = session.createQuery(queryString); 16. List<Object> rows = query.list(); 17. return rows; 18. } 19. }); 20. } 21. public Object save(final Object model) { 22. return getHibernateTemplate().execute( 23. new HibernateCallback<Object>() { 24. public Object doInHibernate(org.hibernate.Session session) 25. throws org.hibernate.HibernateException { 26. session.save(model); 27. return null; 28. } 29. }); 30. } 31. public void update(final Object model) { 32. getHibernateTemplate().execute(new HibernateCallback<Object>() { 33. public Object doInHibernate(org.hibernate.Session session) 34. throws org.hibernate.HibernateException { 35. session.update(model); 36. return null; 37. } 38. }); 39. } 40. public void delete(final Object model) { 41. getHibernateTemplate().execute(new HibernateCallback<Object>() { 42. public Object doInHibernate(org.hibernate.Session session) 43. throws org.hibernate.HibernateException { 44. session.delete(model); 45. return null; 46. } 47. }); 48. } 49.} Dao在applicationContext.xml注入 Dao只有一个类的实现，直接供其它service层调用，如果你想更换为其它的Dao实现，也只需修改这里的配置就行了。 开始写view页面，WEB-INF/view下新建页面student.jsp，WEB-INF/view这路径是在spring-servlet.xml文件配置的，你可以配置成其它，也可以多个路径。student.jsp代码 [xhtml] view plaincopy 01.<%@ page language="java" contentType="text/html; charset=UTF-8" 02. pageEncoding="UTF-8"%> 03.<%@ include file="/include/head.jsp"%> 04. 05.<html> 06.<head> 07.<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 08.<title>添加</title> 09. 11.// --><!-- 13.table{ border-collapse:collapse; } 14.td{ border:1px solid #f00; } 15.--><style mce_bogus="1">table{ border-collapse:collapse; } 16.td{ border:1px solid #f00; }</style> 17.<!-- 18.function add(){ 19. [removed].href="<%=request.getContextPath() %>/student.do?method=add"; 20.} 21. 22.function del(id){ 23.$.ajax( { 24. type : "POST", 25. url : "<%=request.getContextPath()%>/student.do?method=del&id;=" + id, 26. dataType: "json", 27. success : function(data) { 28. if(data.del == "true"){ 29. alert("删除成功！"); 30. $("#" + id).remove(); 31. } 32. else{ 33. alert("删除失败！"); 34. } 35. }, 36. error :function(){ 37. alert("网络连接出错！"); 38. } 39.}); 40.} 41.// --> 47. 48. 序号 49. 姓名 50. 密码 51. 操作 52. 53. 54. "> 55. 56. 57. 58. 59. <input type="button" value="编辑"/> 60. <input type="button" value="${student.id}"/>')" value="删除"/> 61. 62. 63. 64. 65. 66.</body> 67.</html> student_add.jsp [xhtml] view plaincopy 01.<%@ page language="java" contentType="text/html; charset=UTF-8" 02. pageEncoding="UTF-8"%> 03.<%@ include file="/include/head.jsp"%> 04. 05.<html> 06.<head> 07.<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 08.<title>学生添加</title> 09.<!-- 10.function turnback(){ 11. [removed].href="<%=request.getContextPath() %>/student.do"; 12.} 13.// --> 17.
18. 19. 20. 21. 22.
姓名<input id="user" name="user" type="text" /></td>
密码<input id="psw" name="psw" type="text" /></td>
<input type="submit" value="提交"/><input type="button" value="返回" />
23. 24.</form> 25.</body> 26.</html> controller类实现，只需把注解写上，spring就会自动帮你找到相应的bean，相应的注解标记意义，不明白的，可以自己查下@Service，@Controller，@Entity等等的内容。 [java] view plaincopy 01.package com.mvc.controller; 02. 03.import java.util.List; 04. 05.import javax.servlet.http.HttpServletRequest; 06.import javax.servlet.http.HttpServletResponse; 07. 08.import org.apache.commons.logging.Log; 09.import org.apache.commons.logging.LogFactory; 10.import org.springframework.beans.factory.annotation.Autowired; 11.import org.springframework.stereotype.Controller; 12.import org.springframework.ui.ModelMap; 13.import org.springframework.web.bind.annotation.RequestMapping; 14.import org.springframework.web.bind.annotation.RequestMethod; 15.import org.springframework.web.bind.annotation.RequestParam; 16.import org.springframework.web.servlet.ModelAndView; 17. 18.import com.mvc.entity.Student; 19.import com.mvc.service.StudentService; 20. 21.@Controller 22.@RequestMapping("/student.do") 23.public class StudentController { 24. protected final transient Log log = LogFactory 25. .getLog(StudentController.class); 26. @Autowired 27. private StudentService studentService; 28. public StudentController(){ 29. 30. } 31. 32. @RequestMapping 33. public String load(ModelMap modelMap){ 34. List<Object> list = studentService.getStudentList(); 35. modelMap.put("list", list); 36. return "student"; 37. } 38. 39. @RequestMapping(params = "method=add") 40. public String add(HttpServletRequest request, ModelMap modelMap) throws Exception{ 41. return "student_add"; 42. } 43. 44. @RequestMapping(params = "method=save") 45. public String save(HttpServletRequest request, ModelMap modelMap){ 46. String user = request.getParameter("user"); 47. String psw = request.getParameter("psw"); 48. Student st = new Student(); 49. st.setUser(user); 50. st.setPsw(psw); 51. try{ 52. studentService.save(st); 53. modelMap.put("addstate", "添加成功"); 54. } 55. catch(Exception e){ 56. log.error(e.getMessage()); 57. modelMap.put("addstate", "添加失败"); 58. } 59. 60. return "student_add"; 61. } 62. 63. @RequestMapping(params = "method=del") 64. public void del(@RequestParam("id") String id, HttpServletResponse response){ 65. try{ 66. Student st = new Student(); 67. st.setId(Integer.valueOf(id)); 68. studentService.delete(st); 69. response.getWriter().print("{/"del/":/"true/"}"); 70. } 71. catch(Exception e){ 72. log.error(e.getMessage()); 73. e.printStackTrace(); 74. } 75. } 76.} service类实现 [java] view plaincopy 01.package com.mvc.service; 02. 03.import java.util.List; 04. 05.import org.springframework.beans.factory.annotation.Autowired; 06.import org.springframework.stereotype.Service; 07.import org.springframework.transaction.annotation.Transactional; 08. 09.import com.mvc.dao.EntityDao; 10.import com.mvc.entity.Student; 11. 12.@Service 13.public class StudentService { 14. @Autowired 15. private EntityDao entityDao; 16. 17. @Transactional 18. public List<Object> getStudentList(){ 19. StringBuffer sff = new StringBuffer(); 20. sff.append("select a from ").append(Student.class.getSimpleName()).append(" a "); 21. List<Object> list = entityDao.createQuery(sff.toString()); 22. return list; 23. } 24. 25. public void save(Student st){ 26. entityDao.save(st); 27. } 28. public void delete(Object obj){ 29. entityDao.delete(obj); 30. } 31.} OK，例子写完。有其它业务内容，只需直接新建view，并实现相应comtroller和service就行了，配置和dao层的内容基本不变，也就是每次只需写jsp（view），controller和service调用dao就行了。 怎样，看了这个，spring mvc是不是比ssh实现更方便灵活。
https://www.linkedin.com/in/joshuazhu wilson chen
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edit.jsp页面没有加入隐藏字段id ，导致模型驱动封装时缺少id ,，调用update更新数据库时出错! 转载于:https://www.cnblogs.com/Zhusi/p/10296059.html
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org.hibernate.MappingException: Unknown entity: cn.itcast.hibernate717.helloworld.Person hibernate框架根本不知道Person这个持久化类的存在 Caused by: Java.sql.SQLException: Field ‘id’ doesn’t have a default value 如果主键的生
java jsp 报错 Timestamp format must be yyyy-mm-dd hh:mm:ss [.fffffffff]
数据库是timestamp ,jsp里赋值报 Timestamp format must be yyyy-mm-dd hh:mm:ss [.fffffffff] 如何修改 1，修改返回界面的对象的时间字段类型为String。然后，在Object.setXxxx(rs.getTimeSteamp("***")),改为 SimpleDateFormate sdf = new S
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