How to reference "global" variable in java function

mfoley · 02-05-2018, 11:17 AM

I have a function, referenced by numerous other programs, whose parameters are not able to be changed:

Code:

static void reportDetail(Statement stmt, BufferedWriter outFile, String detailColumn) throws Exception

However, the body of the function is defined locally in any given program. What I need to do in one particular program is reference a string defined in the main program, e.g.:

String localVar = globalVar;

where globalVar is defined outside the scope of reportDetail().

Is there a way to do this? (this is jsp BTW)

To be specific, I need a way of getting the UserAgent string: (request.getHeader( "User-Agent" ), in a function without passing it as a function parameter.

dugan · 02-05-2018, 12:13 PM

The method is static! Just add the user agent to its class as a static variable.

Code:

class ReportDetail implements IReportDetail
{
    @Override
    public static void reportDetail(Statement stmt, BufferedWriter outFile, String detailColumn) throws Exception
    {
        System.out.println(userAgent);
    }

    public static string userAgent;

public class Main
{
    public static void main(String[] args)
    {
        ReportDetail.userAgent = request.getHeader("User-Agent");
        ReportDetail.reportDetail(/* parameters go here */);
    }
}

mfoley · 02-05-2018, 03:38 PM

Not sure if I did it right:

Code:

IReportDetail cannot be resolved to a type
455: 
456: //HttpSession sessionObject = session;
457: 
458: class ReportDetail implements IReportDetail
459: {
460:     @Override
461: public static void reportDetail(Statement stmt, BufferedWriter outFile, String detailColumn) throws Exception

An error occurred at line: [461] in the jsp file: [/printAPchecks.jsp]
The method reportDetail cannot be declared static; static methods can only be declared in a static or top level type
458: class ReportDetail implements IReportDetail
459: {
460:     @Override
461: public static void reportDetail(Statement stmt, BufferedWriter outFile, String detailColumn) throws Exception
462: {
463:     ResultSet rs = null;
464:     SimpleDateFormat mmddyyyy = new SimpleDateFormat("MM/dd/yyyy");

An error occurred at line: [461] in the jsp file: [/printAPchecks.jsp]
The method reportDetail(Statement, BufferedWriter, String) of type printAPchecks_jsp.ReportDetail must override or implement a supertype method
458: class ReportDetail implements IReportDetail
459: {
460:     @Override
461: public static void reportDetail(Statement stmt, BufferedWriter outFile, String detailColumn) throws Exception
462: {
463:     ResultSet rs = null;
464:     SimpleDateFormat mmddyyyy = new SimpleDateFormat("MM/dd/yyyy");


An error occurred at line: [133] in the jsp file: [/include/pdfMerge.inc]
The method reportDetail(Statement, BufferedWriter, String) is undefined for the type printAPchecks_jsp
130: 
131: 	// Optionally call reportDetail() function to create detail lines on the page
132: 
133: 	if (stmt != null) reportDetail(stmt,outFile,rs.getString(detailColumn)); // note, need maxDetailLines/page
134: 
135: 	outFile.write("<div style=\"page-break-before:always\"></div>\n");
136:     }

Is your example missing a '}'? I've added one after "public static string userAgent;".

This whole thing may not work with jsp per the error at 461. I don't believe JSP has the ability to create classes outside of main.

dugan · 02-05-2018, 03:46 PM

Quote:

Originally Posted by mfoley

Is your example missing a '}'?

Might well be. I wrote it to get the architectural idea across, not to be compileable (and I did not try to compile it).

Note that "IReportDetail" was a placeholder for the name of the superclass that contains the reportDetail method. You did not name it, and it wasn't in your code sample, so I could not use its actual name in my reply. If you're pasting "IReportDetail" into your actual code, you've misunderstood the recommendation.

mfoley · 02-05-2018, 05:24 PM

Well, as mentioned, I'm using JSP which creates the main class as part of its compilation of the jsp. The generated .java code has for the main class:

Code:

public final class printAPchecks_jsp extends org.apache.jasper.runtime.HttpJspBase
     implements org.apache.jasper.runtime.JspSourceDependent,
                  org.apache.jasper.runtime.JspSourceImports { ...}

which is likely the equivalent of your 'public class Main{}'. All jsp code is actually expanded within this printAPchecks_jsp class and you cannot define classes external to this class, which is probably what is needed in your example.

In the generated .java code the reportDetail() is simply a function, not a class:

Code:

static void reportDetail(Statement stmt, BufferedWriter outFile, String detailColumn) throws Exception { ... }

So either there is no "super class" or printAPchecks_jsp { ... } is the super class.

Perhaps this cannot be done this way (or at all?) in JSP.

dugan · 02-05-2018, 05:56 PM

Quote:

Originally Posted by mfoley

However, the body of the function is defined locally in any given program.

Post an example of how that would be done.

reportDetail() is part of a class. Your example should include that class.

mfoley · 02-05-2018, 08:13 PM

Here is a complete (probably compilable) .jsp program. Unless escaped with some form of "<%", lines in the code are assumed to be HTML statements, like the 1st 3 lines in the example. Java code is bracket by <% someJavaCode %>. The <%@ ... %> delimiters are for including files or imports. The <%! ... %> delimiters are for function definitions. In this example, the main logic calls the pdfmergeDoc() function which, in-turn, calls reportDetail().

Code:

<!DOCTYPE html>
<html>
<body>

<%@ page import="javax.naming.Context,
  javax.naming.NamingException,
  javax.sql.DataSource,
  javax.servlet.http.Cookie,
  java.sql.*,
  java.lang.String, java.lang.Object,
  java.io.*, java.util.*,
  java.util.Calendar, java.util.Date, java.text.SimpleDateFormat" %>
<%
String ua = (request.getHeader( "User-Agent" ) == null) ? "" : request.getHeader( "User-Agent" );

String pdfURL =  mergeDoc();

out.println("</body></html>");
%>

<%!
static void reportDetail(Statement stmt, BufferedWriter outFile, String detailColumn) throws Exception
{
// doSomething
}
%>

The .java generated from this .jsp is 1,552 lines and begins as follows:

Code:

/*
 * Generated by the Jasper component of Apache Tomcat
 * Version: Apache Tomcat/8.5.23
 * Generated at: 2018-02-05 23:21:50 UTC
 * Note: The last modified time of this file was set to
 *       the last modified time of the source file after
 *       generation to assist with modification tracking.
 */
package org.apache.jsp;

import javax.servlet.*;
import javax.servlet.http.*;
import javax.servlet.jsp.*;
import javax.naming.Context;
import javax.naming.NamingException;
import javax.sql.DataSource;
import javax.servlet.http.Cookie;
import java.sql.*;
import java.lang.String;
import java.lang.Object;
import java.io.*;
import java.util.*;
import java.util.Calendar;
import java.util.Date;
import java.text.SimpleDateFormat;
import java.lang.StringBuffer;
import java.text.FieldPosition;
import java.math.BigDecimal;
import java.text.DecimalFormat;
import java.util.Random;
import java.lang.Runtime;
import java.io.*;
import java.util.Random;

public final class printAPchecks_jsp extends org.apache.jasper.runtime.HttpJspBase
    implements org.apache.jasper.runtime.JspSourceDependent,
                 org.apache.jasper.runtime.JspSourceImports {
:
:
static void reportDetail(Statement stmt, BufferedWriter outFile, String detailColumn) throws Exception
{
:
:
}

}

dugan · 02-05-2018, 09:00 PM

Okay, this demo does work. It prints "the user agent":

Code:

class GlobalData
{
    static String userAgent;
}

final class printAPChecks_jsp
{
    static void reportDetail()
    {
        System.out.println(GlobalData.userAgent);
    }
}

public class GlobalDataDemo
{
    public static void main(String[] args)
    {
        GlobalData.userAgent = "The user agent";
        printAPChecks_jsp.reportDetail();
    }
};

What I have in mind is:

Code:

<%@ page import="GlobalData %>
<%
GlobalData.ua = (request.getHeader( "User-Agent" ) == null) ? "" : request.getHeader( "User-Agent" );
%>

<%!
static void reportDetail(Statement stmt, BufferedWriter outFile, String detailColumn) throws Exception
{
// doSomething with GlobalData.ua
}
%>

This does depend on the "page imports" working consistently across the <%%> and <%!%> sections. If not, then I'm out of ideas.

dugan · 02-05-2018, 09:27 PM

Could you perhaps put the user-agent in a session? That's a global store... A number of the hits I got when I googled this recommended exactly that.