Exception thrown by getter for property, bean org.apache.struts.taglib.html.BEAN

Preface

在浏览本文之前，请确定你是在以下相似environment和condition下遇到相似问题。

Environment:
OS: Windows XP
Language: Java 1.5
Framework: Struts 1.3
IDE: MyEclipse 6.0

Condition:
在jsp page正常，在actionForm中用到object class。

Introduction

本文讲述在actionForm中用到object class时可能会导致的Exception。

Section1 - Problem

HTTP Status 500 -

---

type Exception report

message

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

exception

org.apache.jasper.JasperException: javax.servlet.ServletException: javax.servlet.jsp.JspException: Getter for property countryRegionCode threw exception: java.lang.NullPointerExceptionorg.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:541)org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:417)org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:320)org.apache.jasper.servlet.JspServlet.service(JspServlet.java:266)javax.servlet.http.HttpServlet.service(HttpServlet.java:803)

 

root cause

javax.servlet.ServletException: javax.servlet.jsp.JspException: Getter for property countryRegionCode threw exception: java.lang.NullPointerExceptionorg.apache.jasper.runtime.PageContextImpl.doHandlePageException(PageContextImpl.java:850)org.apache.jasper.runtime.PageContextImpl.handlePageException(PageContextImpl.java:779)org.apache.jsp.fundInformation.fundHouseSearch_jsp._jspService(fundHouseSearch_jsp.java:365)org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)javax.servlet.http.HttpServlet.service(HttpServlet.java:803)org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:393)org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:320)org.apache.jasper.servlet.JspServlet.service(JspServlet.java:266)javax.servlet.http.HttpServlet.service(HttpServlet.java:803)

 

root cause

javax.servlet.jsp.JspException: Getter for property countryRegionCode threw exception: java.lang.NullPointerExceptionorg.apache.struts.taglib.html.SelectTag.calculateMatchValues(SelectTag.java:245)org.apache.struts.taglib.html.SelectTag.doStartTag(SelectTag.java:177)org.apache.jsp.fundInformation.fundHouseSearch_jsp._jspx_meth_html_005fselect_005f0(fundHouseSearch_jsp.java:487)org.apache.jsp.fundInformation.fundHouseSearch_jsp._jspService(fundHouseSearch_jsp.java:197)org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)javax.servlet.http.HttpServlet.service(HttpServlet.java:803)org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:393)org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:320)org.apache.jasper.servlet.JspServlet.service(JspServlet.java:266)javax.servlet.http.HttpServlet.service(HttpServlet.java:803)

 

note The full stack trace of the root cause is available in the Apache Tomcat/6.0.13 logs.

---

Apache Tomcat/6.0.13

Section 2 - Reason

例如首先在jsp page上有这样一个property
<html:text property="fundHouseID" styleClass="text_general"></html:text>

用其default创建下的actionForm是没有问题的，但从reuse和abstract的aspect角度来说，一般在actionForm中define的private property都是仅仅在jsp page有该property而实际的object class中却没有该property，或者该property需要经过经过action去转换成object class需要的property。所以在jsp page上的property和实际object class的property对应时，在actionForm中不再为jsp page上的property define一个新的property，而是通过getter和setter call object class上的getter和setter来操作property，但是这样就经常容易出现一种错误，因为必须要在actionForm中new一个object class的instance，如果没有new到会碰到以上Exception，如一下Code:

actionForm:
 /** fundHouse property */
 private FundHouse fundHouse;
 
 /** fundHouseName property */
 private String fundHouseID;

 /**
  * @return the fundHouse
  */
 public FundHouse getFundHouse() {
  return fundHouse;
 }

 /**
  * @param fundHouse the fundHouse to set
  */
 public void setFundHouse(FundHouse fundHouse) {
  this.fundHouse = fundHouse;
 }

 /**
  * @return the fundHouseID
  */
 public String getFundHouseID() {
  return fundHouseID;
 }

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

Object Class:
private String fundHouseID;

 /**
  * @return the fundHouseID
  */
 public String getFundHouseID() {
  return fundHouseID;
 }
 /**
  * @param fundHouseID the fundHouseID to set
  */
 public void setFundHouseID(String fundHouseID) {
  this.fundHouseID = fundHouseID;
 }

Section 3 - Solution

很简单，只是很容易被忽略，一定要new一个object class的instance，对以上的actionFrom fundHouse property修改如下：
private FundHouse fundHouse = new FundHouse();