我不熟悉在 Servlet 中使用 Java Bean，并且在从 HttpServletRequest 对象访问 bean 时遇到问题。当我使用 getAttribute() 时，它返回 null。这是我的代码:
Station.jsp - JSP:
<!--
@author - Dylan Stout
7/19/2016
Description: Station Screen -- Takes scanner input to three fields: fromStation, toStation, toLoad
Javascript is used to handle cursor position,incrementing fields, and button-press for load releasing.
PickProcess java bean holds the session information necessary to verify and send/recieve messages to wrxj
back-end.
Each input field is it's own form so no handling for carriage returns is needed (symbol guns usually
send carriage return after scan)
-->
<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
pageEncoding="ISO-8859-1"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<jsp:useBean id="pickProcess" class="com.wynright.scanui.model.PickProcess" scope="session"/>
<jsp:useBean id="fromStation" class="com.wynright.scanui.model.FromStation" scope="request"/>
<jsp:useBean id="toStation" class="com.wynright.scanui.model.ToStation" scope="request"/>
<jsp:useBean id="toLoad" class="com.wynright.scanui.model.ToLoad" scope="request"/>
<html>
<head>
<meta name="viewport" content="width=240, height=320, user-scalable=no,
initial-scale=1.0, maximum-scale=1.0, minimum-scale=1.0" />
<link type="text/css" rel="stylesheet" href="css/scanui.css">
<script type="text/javascript" src="scripts/jquery-3.1.0.min.js"></script>
<script type="text/javascript" src="scripts/formController.js"></script>
<script type="text/javascript" src="scripts/station.js"></script>
<noscript>JavaScript is off. Please enable to use ScanUI.</noscript>
<title>Station Pick - Scan UI</title>
</head>
<%
if(fromStation.hasErrors()){
%>
<body OnLoad="onBodyLoad();focusFromStation();">
<%
}else if(toStation.hasErrors()) {
%>
<body OnLoad="onBodyLoad();focusToStation();">
<%
}else if(toLoad.hasErrors()){
%>
<body OnLoad="onBodyLoad();focusToLoad();">
<%
}else{
%>
<body OnLoad="onBodyLoad();focusNext();">
<%
}
%>
<table cellpadding=4 cellspacing=2>
<th bgcolor="#CCCCFF" colspan=2><font size=2>Station Pick</font></th>
<tr bgcolor="#c8d8f8">
<td valign=top><form name="fromStation" action="ValidateFromStation" method=post>
From Station: <input type="text" name="value"
value='<%=pickProcess.getFromStation()%>' size=5 maxlength=5 tabindex="1">
<br>
<font size=2 color=red><%=fromStation.getErrorMsg("fromStation")%></font>
</form></td>
<td valign=top><form name="toStation" action="validateToStation.jsp" method=post>
To Station: <input type="text" name="value"
value='<%=pickProcess.getToStation()%>' size=5 maxlength=5 tabindex="2">
<br>
<font size=2 color=red><%=toStation.getErrorMsg("toStation")%></font>
</form></td>
</tr>
<tr bgcolor="#c8d8f8">
<td valign=top colspan="2"><form name="toLoad" action="validateToLoad.jsp" method=post>
To Load: <input type="text" name="value"
value='<%=pickProcess.getToLoad()%>' size=34 maxlength=30 tabindex="3">
<br>
<font size=2 color=red><%=toLoad.getErrorMsg("toLoad")%></font>
</form></td>
</tr>
</table>
</body>
</html>
ValidateFromStation - Servlet:
/**
*
*/
package com.wynright.scanui.action;
import java.io.IOException;
import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.apache.log4j.Logger;
import com.scanui.model.FromStation;
/**
* @author dystout
* Date: Jul 21, 2016
*
* Description: TODO
*/
public class ValidateFromStation extends HttpServlet{
/**
*
*/
private static final long serialVersionUID = 6201980136409592032L;
protected static Logger logger = Logger.getLogger(ValidateFromStation.class);
protected FromStation fromStation = null;
@Override
public void doPost(HttpServletRequest request, HttpServletResponse response) throws IOException,ServletException{
fromStation = (FromStation)request.getSession(false).getAttribute("fromStation");
fromStation.setValue(request.getParameter("value"));
if(fromStation.validate()){
logger.debug("From Station Validated: " + fromStation.getValue());
RequestDispatcher rd = request.getRequestDispatcher("Station.jsp");
rd.include(request, response);
}else{
logger.debug("From Station INVALID, not validated: " + fromStation.getValue());
RequestDispatcher rd = request.getRequestDispatcher("Station.jsp");
rd.include(request,response);
}
}
}
FromStation Java Bean:
package com.wynright.scanui.model;
import java.util.Hashtable;
import com.daifukuamerica.wrxj.application.Application;
import com.daifukuamerica.wrxj.application.PropertiesStack;
import com.daifukuamerica.wrxj.custom.piolax.dataserver.PiolaxPickServer;
import com.daifukuamerica.wrxj.jdbc.DBCommException;
import com.daifukuamerica.wrxj.jdbc.DBException;
import com.daifukuamerica.wrxj.jdbc.DBResultSet;
import com.wynright.scanui.connectionFactory.DBConnection;
public class FromStation extends ScanField{
@Override
public boolean validate(){
if(value.equals("")){
errors.put("fromStationNumber", "Please scan/enter valid station");
}
String sql = "SELECT SDESTINATIONSTATION FROM ORDERHEADER WHERE SDESTINATIONSTATION = '" + getValue() + "'";
DBResultSet results = null;
if(DBConnection.getWrxjConnection().isConnectionActive()){
try {
results= DBConnection.getWrxjConnection().execute(sql, null);
} catch (DBCommException | DBException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
if(results != null && results.getRowCount()!=0){
isValidated = true;
}
//TODO -- Add WRXJ server validate (JSON)
return isValidated;
}
}
Tomcat 7 Web.xml:
<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" id="WebApp_ID" version="3.0">
<display-name>RFUI</display-name>
<listener>
<listener-class>com.wynright.scanui.connectionFactory.DBConnectionService</listener-class>
</listener>
<servlet>
<servlet-name>ValidateFromStation</servlet-name>
<servlet-class>com.wynright.scanui.action.ValidateFromStation
</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>ValidateFromStation</servlet-name>
<url-pattern>/ValidateFromStation/*</url-pattern>
</servlet-mapping>
<servlet>
<servlet-name>ValidateLogin</servlet-name>
<servlet-class>com.wynright.scanui.action.ValidateLogin
</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>ValidateLogin</servlet-name>
<url-pattern>/ValidateLogin/*</url-pattern>
</servlet-mapping>
<servlet>
<servlet-name>ValidatePickingFromStation</servlet-name>
<servlet-class>com.wynright.scanui.action.ValidatePickingFromStation
</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>ValidatePickingFromStation</servlet-name>
<url-pattern>/ValidatePickingFromStation/*</url-pattern>
</servlet-mapping>
<servlet>
<servlet-name>ValidatePickingToStation</servlet-name>
<servlet-class>com.wynright.scanui.action.ValidatePickingToStation
</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>ValidatePickingToStation</servlet-name>
<url-pattern>/ValidatePickingToStation/*</url-pattern>
</servlet-mapping>
<servlet>
<servlet-name>ValidateSerialNumber</servlet-name>
<servlet-class>com.wynright.scanui.action.ValidateSerialNumber
</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>ValidateSerialNumber</servlet-name>
<url-pattern>/ValidateSerialNumber/*</url-pattern>
</servlet-mapping>
<servlet>
<servlet-name>ValidateToLoad</servlet-name>
<servlet-class>com.wynright.scanui.action.ValidateToLoad
</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>ValidateToLoad</servlet-name>
<url-pattern>/ValidateToLoad/*</url-pattern>
</servlet-mapping>
<servlet>
<servlet-name>ValidateToStation</servlet-name>
<servlet-class>com.wynright.scanui.action.ValidateToStation
</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>ValidateToStation</servlet-name>
<url-pattern>/ValidateToStation/*</url-pattern>
</servlet-mapping>
<welcome-file-list>
<welcome-file>index.html</welcome-file>
<welcome-file>index.htm</welcome-file>
<welcome-file>index.jsp</welcome-file>
<welcome-file>default.html</welcome-file>
<welcome-file>default.htm</welcome-file>
<welcome-file>default.jsp</welcome-file>
</welcome-file-list>
</web-app>
最佳答案
我想我已经解决了这个问题。我相信我没有正确使用整个 bean。仍然有可能我使用 HttpSession 和 HttpServletRequest 和 HttpServletResponse 的全部目的是错误的，所以如果我是某人请指教。
我的问题是我正尝试使用 jsp 标记来加载我的 bean，如下所示:
<jsp:useBean id="fromStation" class="com.wynright.scanui.model.FromStation" scope="request"/>
它将我的 bean 设置为“请求”的范围，但该请求实际上将在下一次页面加载时被清除，从而导致空值。我重组了我的代码以允许 session 处理我在页面之间传递的对象。我不确定这是否是好的做法，因为我经常听说 session 只应在绝对必要时保留对象。我在别处读到你也可以使用 cookie 来保存这些信息，但 session 似乎更清晰。
这是我修改后的代码，供其他人引用:
在之前的 servlet - ValidateLogin 中，我使用 PickProcess 对象设置 session 属性，该对象包含我的 FromStation(以及所有其他扫描字段)对象:
/**
*
*/
package com.wynright.scanui.action;
import java.io.IOException;
import java.net.InetAddress;
import java.net.UnknownHostException;
import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import org.apache.log4j.Logger;
import com.daifukuamerica.wrxj.dataserver.standard.StandardUserServer;
import com.daifukuamerica.wrxj.jdbc.DBException;
import com.wynright.scanui.core.UserSession;
import com.wynright.scanui.model.PickProcess;
/**
* @author dystout
* Date: Jul 21, 2016
*
* Description: TODO
*/
public class ValidateLogin extends HttpServlet{
/**
*
*/
private static final long serialVersionUID = 1L;
protected static Logger logger = Logger.getLogger(ValidateLogin.class);
protected UserSession user = new UserSession();
protected int loginCode = -1;
protected StandardUserServer userServer = null;
private PickProcess pickProcess = null;
@Override
public void doPost(HttpServletRequest request, HttpServletResponse response) throws IOException,ServletException{
pickProcess = new PickProcess();
HttpSession session = request.getSession();
user.setSessionId(session.getId());
user.setUserName(request.getParameter("userName"));
user.setPassword(request.getParameter("password"));
if(validateLogin("'" + user.getUserName().toString() + "'", user.getPassword().toString() , user.getSessionId())){
//validate login - redirect (add pickPrcess to session)
logger.debug("Login Successful for: " + user.getUserName() + " Session ID: " + user.getSessionId());
RequestDispatcher rd = request.getRequestDispatcher("station.jsp");
pickProcess.setUserName(user.getUserName());
session.setAttribute("pickProcess", pickProcess);
session.setAttribute("user", user);
rd.include(request, response);
}else{
// retry login with error code
logger.debug("Login Unsuccessful for: " + user.getUserName());
RequestDispatcher rd = request.getRequestDispatcher("login.jsp");
request.setAttribute("user", user);
rd.include(request,response);
}
}
public boolean validateLogin(String username, String password, String sessionId){
InetAddress ip = null;
String machineName = "";
try {
ip = InetAddress.getLocalHost();
machineName = ip.getHostName();
} catch (UnknownHostException e) {
logger.error("*** Could not determine host IP Address during login validation ***");
logger.error(e.getMessage());
}
if(ip!=null){
user.setIpAddress(ip.getHostAddress());
user.setMachineName(machineName);
}else{
logger.error("Unable to retrieve IP Address");
}
try {
logger.debug("Attempting to login user: " + username);
loginCode = userServer.validateLogin(username, password, "'" + machineName + "'", "'" + user.getIpAddress() + "'");
} catch (DBException e) {
logger.error("Error validating login, Database problem exists.");
e.printStackTrace();
}
if(loginCode == userServer.LOGIN_OKAY){
user.setValidated(true);
}else{
switch(loginCode){
case -1:
user.setLoginError("Login Invalid");
break;
case -2:
user.setLoginError("Login has Expired");
break;
case -3:
user.setLoginError("Login is in use");
break;
}
}
// return user.isValidated();
//TODO DEBUG
return true;
}
public ValidateLogin(){
userServer = new StandardUserServer("OracleDB");
}
public StandardUserServer getUserServer() {
return userServer;
}
public void setUserServer(StandardUserServer userServer) {
this.userServer = userServer;
}
}
然后在我的 JSP station.jsp 中，我可以使用表达式语言使用 ${bean.beanvalue} 的标签访问 bean directyle(有关更多信息:Which variables can be accessed with the ${...} syntax in a Struts tag in a JSP page? ) 这是我在 station.jsp 中用来访问值的代码:
<!--
@author - Dylan Stout
7/19/2016
Description: Station Screen -- Takes scanner input to three fields: fromStation, toStation, toLoad
Javascript is used to handle cursor position,incrementing fields, and button-press for load releasing.
PickProcess java bean holds the session information necessary to verify and send/recieve messages to wrxj
back-end.
Each input field is it's own form so no handling for carriage returns is needed (symbol guns usually
send carriage return after scan)
-->
<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
pageEncoding="ISO-8859-1"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta name="viewport" content="width=240, height=320, user-scalable=no,
initial-scale=1.0, maximum-scale=1.0, minimum-scale=1.0" />
<link type="text/css" rel="stylesheet" href="css/scanui.css">
<script type="text/javascript" src="scripts/jquery-3.1.0.min.js"></script>
<script type="text/javascript" src="scripts/formController.js"></script>
<script type="text/javascript" src="scripts/station.js"></script>
<noscript>JavaScript is off. Please enable to use ScanUI.</noscript>
<title>Station Pick - Scan UI</title>
</head>
<body onload="onBodyLoad()">
<table cellpadding=4 cellspacing=2 id="stationTable">
<th bgcolor="#CCCCFF" colspan=2><font size=2>Station Pick : ${pickProcess.userName}</font></th>
<tr bgcolor="#c8d8f8">
<td valign=top>
<form name="fromStation" action="${pageContext.request.contextPath}/ValidateFromStation" method=post id="fromStationForm">
From Station: <input type="text" name="value" id="fromStation" value='${pickProcess.fromStation}' size=5 maxlength=5 tabindex="1">
<font size=2 color=red><br> ${fromStation.error}</font>
</form>
</td>
<td valign=top>
<form name="toStation" action="${pageContext.request.contextPath}/ValidateToStation" method=post id="toStation">
To Station: <input type="text" name="value" value='${pickProcess.toStation}' size=5 maxlength=5 tabindex="2">
<font size=2 color=red><br> ${toStation.error}</font>
</form>
</td>
</tr>
<tr bgcolor="#c8d8f8">
<td valign=top colspan="2"><form name="toLoad" action="${pageContext.request.contextPath}/ValidateToLoad" method=post id="toLoad">
To Load: <input type="text" name="value"
value='${pickProcess.toLoad}' size=34 maxlength=30 tabindex="3">
<font size=2 color=red><br> ${toLoad.error}</font>
</form></td>
</tr>
</table>
</body>
</html>
此时，由于我在 ValidateLogin servlet 中设置了属性:
session.setAttribute("pickProcess", pickProcess);
然后我可以在这个 session 存在的任何地方检索它:
PickProcess pickProcess = (PickProcess)session.getAttribute("pickProcess");
如果没有收到空值，我将无法检索 session 属性。
关于spring - 无法访问Servlet中的Java Bean，getAttribute()返回null，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/38514897/