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分享空指针异常怎么处理 求高人帮忙啊！！！1急在线等
本人用Myeclipse做一个管理系统在调试时 一直发生报错 求各位大神 帮忙啊
exception
org.apache.jasper.JasperException: java.lang.NullPointerException
org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:549)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:470)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:390)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:334)
javax.servlet.http.HttpServlet.service(HttpServlet.java:727)
org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
root cause
java.lang.NullPointerException
org.apache.jsp.index_jsp._jspService(index_jsp.java:337)
org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
javax.servlet.http.HttpServlet.service(HttpServlet.java:727)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:432)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:390)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:334)
javax.servlet.http.HttpServlet.service(HttpServlet.java:727)
org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
本人是个菜鸟 不懂怎么修改 不求帮忙修改下 谢谢各位了！！！
这是报错的后台 index_jsp.java 文件 （377）代码：
out.write("\"><img src=\"images/flower/文学类/假如给我三天光明.jpg\" width=\"183\" height=\"244\" /></a> </p>\r\n");
out.write(" <form id=\"form4\" name=\"form4\" method=\"post\" action=\"BuyCart.jsp?action=add&flowerid=");
out.print(flower2.getFlowerId() );
exception
org.apache.jasper.JasperException: java.lang.NullPointerException
org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:549)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:470)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:390)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:334)
javax.servlet.http.HttpServlet.service(HttpServlet.java:727)
org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
root cause
java.lang.NullPointerException
org.apache.jsp.index_jsp._jspService(index_jsp.java:337)
org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
javax.servlet.http.HttpServlet.service(HttpServlet.java:727)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:432)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:390)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:334)
javax.servlet.http.HttpServlet.service(HttpServlet.java:727)
org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
本人是个菜鸟 不懂怎么修改 不求帮忙修改下 谢谢各位了！！！
这是报错的后台 index_jsp.java 文件 （377）代码：
out.write("\"><img src=\"images/flower/文学类/假如给我三天光明.jpg\" width=\"183\" height=\"244\" /></a> </p>\r\n");
out.write(" <form id=\"form4\" name=\"form4\" method=\"post\" action=\"BuyCart.jsp?action=add&flowerid=");
out.print(flower2.getFlowerId() );
...全文
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Juedaifanghua 2014-05-14
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打断点，调试着看，锁定问题所在
sdjzyuxinburen 2014-05-11
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先找到空指针错误在哪一行，用debug调试，或者打印输出。然后将代码注释，看确定是哪一行出现的错误。方法就是：先找到病根，在开方子。这样贴代码，没有意义呀
a632752281 2014-05-10
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应该怎么该这个JSP 求代码 
BeautfulSoup 2014-05-09
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往页面刷出内容 out.flush();
a632752281 2014-05-08
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out.write(" <td width=\"266\" height=\"342\" align=\"center\" valign=\"top\" bgcolor=\"#CCCCCC\">\r\n");
out.write("\t\t <form id=\"form5\" name=\"form5\" method=\"post\" action=\"ShowFlowers.jsp?flowername=");
out.print(str );
out.write("&flowerkind=");
out.print(flower1.getFlowerKind());
lichao_java 2014-05-08
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后台那个是jsp编译的java文件，你改jsp
a632752281 2014-05-08
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我现在就是想知道 我应该改那个文件 是当前的 index.JSP 文件 还是 后台路径下找到 jsp 的java文件 ......
S117 2014-05-08
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所有对象在使用前先判断是否为null，这样可以避免空指针异常！
一梭子码农 2014-05-08
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先定位错在哪，定位到变量，然后就一目了然了，要养成找错的习惯。
zy_think123 2014-05-08
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flowerid值为空，你检查一下，你传过来的有没有正确值呀
安优小青和他的程序生活 2014-05-08
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把 这句先注释掉
out.print(flower1.getFlowerKind());
// out.print(flower1.getFlowerKind());
然后再跑跑看
tony4geek 2014-05-08
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flower2 没有数据。
点滴寸土 2014-05-08
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话说 方法里需不需要set和get方法呢。。。
请叫我砖家 2014-05-08
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先判断报空指针的是哪一句啊,看看这个空指针对应的内容有没有用啊,捕捉空指针异常就不会报了反正
a632752281 2014-05-08
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337是这个
out.write("&flowerkind=");
out.print(flower1.getFlowerKind());
a632752281 2014-05-08
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这是Java
package org.apache.jsp;
import javax.servlet.*;
import javax.servlet.http.*;
import javax.servlet.jsp.*;
import java.util.*;
import ustc.edu.user.*;
import ustc.edu.flower.*;
import ustc.edu.cart.*;
public final class index_jsp extends org.apache.jasper.runtime.HttpJspBase
implements org.apache.jasper.runtime.JspSourceDependent {
private static final javax.servlet.jsp.JspFactory _jspxFactory =
javax.servlet.jsp.JspFactory.getDefaultFactory();
private static java.util.Map<java.lang.String,java.lang.Long> _jspx_dependants;
private javax.el.ExpressionFactory _el_expressionfactory;
private org.apache.tomcat.InstanceManager _jsp_instancemanager;
public java.util.Map<java.lang.String,java.lang.Long> getDependants() {
return _jspx_dependants;
}
public void _jspInit() {
_el_expressionfactory = _jspxFactory.getJspApplicationContext(getServletConfig().getServletContext()).getExpressionFactory();
_jsp_instancemanager = org.apache.jasper.runtime.InstanceManagerFactory.getInstanceManager(getServletConfig());
}
public void _jspDestroy() {
}
public void _jspService(final javax.servlet.http.HttpServletRequest request, final javax.servlet.http.HttpServletResponse response)
throws java.io.IOException, javax.servlet.ServletException {
final javax.servlet.jsp.PageContext pageContext;
javax.servlet.http.HttpSession session = null;
final javax.servlet.ServletContext application;
final javax.servlet.ServletConfig config;
javax.servlet.jsp.JspWriter out = null;
final java.lang.Object page = this;
javax.servlet.jsp.JspWriter _jspx_out = null;
javax.servlet.jsp.PageContext _jspx_page_context = null;
try {
response.setContentType("text/html; charset=utf-8");
pageContext = _jspxFactory.getPageContext(this, request, response,
null, true, 8192, true);
_jspx_page_context = pageContext;
application = pageContext.getServletContext();
config = pageContext.getServletConfig();
session = pageContext.getSession();
out = pageContext.getOut();
_jspx_out = out;
out.write("\r\n");
out.write("<!DOCTYPE html PUBLIC \"-//W3C//DTD XHTML 1.0 Transitional//EN\" \"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd\">\r\n");
out.write("<html xmlns=\"http://www.w3.org/1999/xhtml\">\r\n");
out.write("\r\n");
request.setCharacterEncoding("utf-8");
Flower flower1 = FlowerMgr.getInstance().loadFlowerByFlowerId(1);
Flower flower2 = FlowerMgr.getInstance().loadFlowerByFlowerId(17);
Flower flower3 = FlowerMgr.getInstance().loadFlowerByFlowerId(18);
Flower flower4 = FlowerMgr.getInstance().loadFlowerByFlowerId(16);
String action = request.getParameter("action");
if(action != null && action.equals("exit")) {
session.removeAttribute("user");
session.removeAttribute("cart");
}
else if(action != null && action.equals("login")) {
User user = (User)session.getAttribute("user");
if(user!=null){
response.sendRedirect("AlreadyLogin.jsp");
return;
}
String username = request.getParameter("username");
String password = request.getParameter("password");
User u = null;
Cart c=null;
try {
u = User.check(username, password);
} catch (UserNotFoundException e) {
response.sendRedirect("LoginFailure.jsp");
return;
} catch (PasswordNotCorrectException e) {
response.sendRedirect("LoginFailure.jsp");
return;
}
session.setAttribute("user", u);
session.setAttribute("cart", c);
}
String guest = "游客";
User user = (User)session.getAttribute("user");
if(user != null){
guest = user.getUserName();
}
ArrayList<String> flowerkinds = FlowerMgr.getInstance().getFlowerKinds();
String str = "";
别闹腰不好 2014-05-08
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flower2这个定义了吗
别闹腰不好 2014-05-08
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index_jsp.java:337
apache-tomcat-6.0.37\work\Catalina\localhost 这个路径下找到 jsp 的java文件 。看看337 是什么 ，就找到错了
