Search code examples
javajsp

Why util.prefs.Preferences is not working in JSP script?

I have an example using java.util.prefs.Preferences store and get value from registry in windows server, this is my class.

//File Winreg.java
package oneconect;
import java.util.prefs.*;

public class Winreg {
    Preferences prefs;
    String defaultValue = "NA";
    String InstalledDate ="",version="";
    
    //contrucsiton
    public Winreg()
        {
            try
            { 
               prefs= Preferences.userNodeForPackage(oneconect.Winreg.class); 
            }
            catch (Exception E)
            {
                System.out.println(E);
            }    
        } 
    
        //functio set value
        public void setValue(String vKey,String vValue)
        {
            try
            {                
            prefs.put(vKey,vValue); 
            }
            catch (Exception E)
            {
                E.printStackTrace();
            }
        }
        
        //function get value
        public String getValue(String vKey,String defaultValue)
        {
             try
             {
                 String vGetValues =prefs.get(vKey, defaultValue);
                 prefs.flush();
                 return vGetValues; 
                
             }
             catch (Exception E)
             {
                 E.printStackTrace();
                 return defaultValue;
             }
        }
    }

Working property in java file class,

    public static void main(String[] args) throws IOException {
        // TODO Auto-generated method stub   
        try {  
                    Winreg iWin = new Winreg();
                    iWin.setValue("filepath", "Program file") ;
    System.out.println( iWin.getValue("filepath", null) );    /// out put  Program file
} catch (Exception exp) {  
            System.out.print(exp.toString()); 
        }
    }

But when i want to this method in jsp file, server Tomcat 6.0

    <%@page import="oneconect.Winreg"%>
    <%@page import="java.util.prefs.*"%>

    <%@ 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 http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">

    <title>..:: Test a</title>

    </head>

    <body>

    Winreg iWin = new Winreg();         

    out.println( iWin.getValue("filepath", null) ); 

    %>

    </body>

    </html>

method getValue do not return value stored before, out put always return null (default value).

Please give me what we wrong, and how to fix this case ?

Thanks,

Solution

  • Root cause of the problem:

    You installed it using apache-tomcat-6.0.xx.exe and set it as a Windows service.

    When Tomcat is a Windows service, its default user execution account is not the account you currently log into the system.

    S1

    enter image description here

    S3

    enter image description here

    It uses Local System account as the user account to start Tomcat. Therefore, if you use your login account (XXX) to store the java.util.prefs settings, and use the user account Local System account to read the java.util.prefs settings in Tomcat, it will not be read, because these are the java.util.prefs settings under two different user accounts.

    Solution:

    Add index8.jsp to your webapp (assuming the name is hello),

    index8.jsp

    <%@page contentType="text/html" pageEncoding="UTF-8"%>
<%@page import="oneconect.Winreg"%>
<%@page import="java.util.prefs.*"%>
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Greeting JSP</title>
</head>

<body>

<%
    Winreg iWin = new Winreg();
    iWin.setValue("filepath", "Program file") ;
    out.println( iWin.getValue("filepath", null) );    /// out put  Program file
%>
</body>
</html>

    then open the Browser at http://localhost:8080/hello/index8.jsp

    index7.jsp

    <%@page contentType="text/html" pageEncoding="UTF-8"%>
<%@page import="oneconect.Winreg"%>
<%@page import="java.util.prefs.*"%>
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Test a</title>
</head>

<body>

<%
    Winreg iWin = new Winreg();

    out.println( iWin.getValue("filepath", null) );

%>
</body>
</html>

    then open the Browser at http://localhost:8080/hello/index7.jsp

    P.S.

    If you do not use Windows services to start tomcat, but use C:\Program Files\Apache Software Foundation\Tomcat 6.0\startup.bat to start Tomcat, then open http://localhost:8080/hello/index7.jsp, the java.util.prefs settings it reads will be the java.util.prefs settings of your current user login account, which is what you execute the main method to set.

    Reminder again: Root cause of the problem:

    You installed it using apache-tomcat-6.0.xx.exe and set it as a Windows service.

    When Tomcat is a Windows service, its default user execution account is not the account you currently log into the system.