Choices in i18n web pages

Choices

To create a locale-aware set of web pages, the choices are

Using a server such as Apache with type-maps
Using a server such as Apache with multi-views
Using a servlet only
Using a JSP with scripting commands and expressions
Using a JSP with standard tags and expression language
Using a JSP with custom-built and standard tags and expression language
Using a servlet and JSP (with scripting or tags)

Server negotiation using Apache type-map

The server decides on the web page based on the Accept-language HTTP header

It uses a type-map such as hello.var


URI: hello

URI: en/hello.html
Content-type: text/html; charset=iso-8859-1
Content-language: en

URI: fr/hello.html
Content-type: text/html;charset=iso-8859-1
Content-language: fr

The URI's are interpreted as URLs relative to the map file; they must be on the same server (!), and they must refer to files to which the client would be granted access if they were to be requested directly.
The directory structure can keep different language files in the same directory or in separate directories. Here we choose separate directories en and fr
```
      ..../hello.var
      ..../en/hello.html
      ..../fr/hello.html
      
```

The English hello.html is


<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Draft//EN">
<html> <head>
<title>Hello</title>
</head>

<body>
<h1>Hello in English</h1>
</body>
</html>

The French hello.html is


<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Draft//EN">
<html> <head>
<title>Bonjour</title>
</head>

<body>
<h1>Bonjour en Francais</h1>
</body>
</html>

This can be tested here

Server negotiation using Apache multiviews

A directory is marked for multiviews in the Apache configuration file e.g.


      <Directory "/home/httpd/html/i18n/webchoices/server-multiviews">
          Options MultiViews
      </Directory>

or by having a file .htaccess in the directory with contents


      options MultiViews

The directory contains files


      .htaccess
      hello.en.html
      hello.fr.html

The pages are accessed by e.g server-multiviews/hello Note: no .html extension!

Apache server negotiation callng JSP/servlets?

The above call HTML pages. Could they call servlets?
The URLs appear to be relative to the current directory
An Apache server couldn't call a Tomcat servlet because it would need an absolute URL
If you integrate Tomcat into Apache (possible) then maybe it could be done

Server-side negotiation using servlets

A servlet can examine the Accept-Language header and return a preferred locale or a list of all locales
Given a locale, it could create a JSP name e.g. from hello and fr_FR it could create a name of fr_FR/hello.jsp

If the JSP exists, then you can forward to it


package jan;

import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
import java.util.Locale;

public class ServletForwardNoCheck extends HttpServlet {
    public void doGet(HttpServletRequest request,
		      HttpServletResponse response)
	throws ServletException, IOException {

	Locale preferredLocale = request.getLocale();
	RequestDispatcher dispatcher = request.
	    getRequestDispatcher("/jsp/" + preferredLocale.toString() + 
			       "/hello.jsp");
	PrintWriter out = response.getWriter();
	if (dispatcher != null) {
	    out.println("Dispatcher not null " + dispatcher.toString());
	    try {
		dispatcher.forward(request, response);		 
	    } catch (Exception e) {
		out.println("JSP Not found" + e.toString());
	    }
	} else {
	    out.println("Dispatcher is null");
	}
    }

    public void doPost(HttpServletRequest request,
		      HttpServletResponse response)
	throws ServletException, IOException {
	doGet(request, response);
    }
}

If the JSP does not exist, then an error is raised which normally returns a "404 not found". To remove this, you need to install an error handler, which will return say a page in a default locale
The above program only handles the preferred locale, and does not fallback to less preferred ones. It should be possible to test if a JSP exists before calling it, but this needs use of ServletContext.getNamedDispatcher() which uses the name of a JSP

The web.xml file in WEB-INF can map names to JSP compiled classes


    <servlet>
        <servlet-name>hello_fr_jsp</servlet-name>
        <servlet-class>org.apache.jsp.jsp.hello_fr_jsp</servlet-class>
    </servlet>

    <servlet-mapping>
        <servlet-name>fr_hello_jsp</servlet-name>
        <url-pattern>/jsp/fr/hello.jsp</url-pattern>
    </servlet-mapping>

A servlet such as this should be able to call the JSP page


package jan;

import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
import java.util.Locale;
import java.util.Enumeration;

public class ServletForward extends HttpServlet {

    private ServletContext context;
    private HttpServletRequest request;
    private HttpServletResponse response;

    public void doGet(HttpServletRequest request,
		      HttpServletResponse response)
	throws ServletException, IOException {
	boolean found = false;

	this.request = request;
	this.response = response;

	Enumeration locales = request.getLocales();

	context = request.getSession().getServletContext();

	while (locales.hasMoreElements()) {
	    if (tryDispatchForLocale((Locale) locales.nextElement())) {
		found = true;
		break;
	    }
	}
	if (!found) {
	    // error
	}
	
    }

    private boolean tryDispatchForLocale(Locale locale)
	throws IOException {
	String jspName = locale.toString() + "_hello.jsp";

	RequestDispatcher dispatcher = context.
	    getNamedDispatcher(jspName);
	PrintWriter out = response.getWriter();
	if (dispatcher != null) {
	    out.println("Dispatcher not null " + dispatcher.toString());
	    try {
		dispatcher.forward(request, response);
		return true;
	    } catch (Exception e) {
		out.println("JSP Not found" + e.toString());
	    }
	} else {
	    out.println("Dispatcher is null");
	}
	return false;
    }

    public void doPost(HttpServletRequest request,
		      HttpServletResponse response)
	throws ServletException, IOException {
	doGet(request, response);
    }
}

It forwards to servlets by name ok, but doesn't seem to work for JSP names :-(

User negotiation

The first page presents a choice of languages to continue.
The language for this first page may be chosen by e.g. server-side negotiation or be multilingual

e.g. the page firstpage.html may be


<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Draft//EN">
<html> <head>
<title>First Page</title>
</head>

<body>
<h1>First page</h1>

<p>
Choose the <a href="en/hello.html">English pages</a>
<br>
Choisir les pages <a href="fr/hello.html">Francais</a>
</p>
<!--#include virtual="../copyright" --></body>
</html>

This calls HTML pages in the en and fr directories - it could call servlets or JSP pages, and there could be different directory structures

Passing the locale in a session

There may be a set of HTML pages/servlets/JSP for each locale
This is high maintenance, and dosesn't encourage reuse of material from one locale to another
An alternative may be to have a single set of pages where the locale is passed as a parameter to each of them

This can work if the principal differences can be captured in resource bundles or localised using the locale (e.g. for dates)


<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Draft//EN">
<html> <head>
<title>First Page</title>
</head>

<body>
<h1>First page</h1>

<p>
Choose the <a href="hello.jsp?locale=en">English pages</a>
<br>
Choisir les pages <a href="hello.jsp?locale=fr">Francais</a>
</p>
<!--#include virtual="../copyright" --></body>
</html>

The single JSP page referenced would need to get the locale parameter and then could set its own locale for e.g. date formatting
The JSP page could also store the locale in the session object if there are more pages in this session

Jan Newmarch <jan@newmarch.name>

Last modified: Sun Sep 17 16:13:39 EST 2006
Copyright ©Jan Newmarch
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Copyright © Jan Newmarch, Monash University, 2007

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