Estoy creando una aplicación Blackberry para mostrar una vista web a pantalla completa de un determinado sitio. Tengo un campo de navegador que funciona correctamente, pero la navegación de una página a otra es más lenta que la del navegador nativo. El campo del navegador no parece tener una memoria caché integrada, lo que hace que el tiempo de carga sea lento. Cuando agrego el siguiente código para administrar el caché, el sitio ya no se muestra correctamente.

BrowserFieldScreen.java:

import net.rim.device.api.browser.field2.*;
import net.rim.device.api.script.ScriptEngine;
import net.rim.device.api.system.*;
import net.rim.device.api.ui.*;
import net.rim.device.api.ui.component.*;
import net.rim.device.api.ui.container.*;
import org.w3c.dom.Document;

class BrowserFieldScreen extends MainScreen
{
    BrowserField browserField;
    LoadingScreen load = new LoadingScreen();;

    public BrowserFieldScreen()
    {   
        browserField = new BrowserField();
        browserField.getConfig().setProperty(
            BrowserFieldConfig.JAVASCRIPT_ENABLED, 
            Boolean.TRUE);
        browserField.getConfig().setProperty(
            BrowserFieldConfig.NAVIGATION_MODE, 
            BrowserFieldConfig.NAVIGATION_MODE_POINTER);
        browserField.getConfig().setProperty(
            BrowserFieldConfig.CONTROLLER, 
            new CacheProtocolController(browserField));

        browserField.requestContent("http://www.stackoverflow.com");
        add(browserField);
    }
}

CacheProtocolController.java:

import javax.microedition.io.HttpConnection;
import javax.microedition.io.InputConnection;

import net.rim.device.api.browser.field2.BrowserField;
import net.rim.device.api.browser.field2.BrowserFieldRequest;
import net.rim.device.api.browser.field2.ProtocolController;

public class CacheProtocolController extends ProtocolController{

    // The BrowserField instance
    private BrowserField browserField;

    // CacheManager will take care of cached resources 
    private CacheManager cacheManager;

    public CacheProtocolController(BrowserField browserField) {
        super(browserField);
        this.browserField = browserField;
    }

    private CacheManager getCacheManager() {
        if ( cacheManager == null ) {
            cacheManager = new CacheManagerImpl();
        }
        return cacheManager;
    }

    /**
     * Handle navigation requests (e.g., link clicks)
     */
    public void handleNavigationRequest(BrowserFieldRequest request) 
        throws Exception 
    {
        InputConnection ic = handleResourceRequest(request);
        browserField.displayContent(ic, request.getURL());
    }

    /**
     * Handle resource request 
     * (e.g., images, external css/javascript resources)
     */
    public InputConnection handleResourceRequest(BrowserFieldRequest request) 
        throws Exception 
    {
        // if requested resource is cacheable (e.g., an "http" resource), 
            // use the cache
        if (getCacheManager() != null 
            && getCacheManager().isRequestCacheable(request)) 
            {
                InputConnection ic = null;
                // if requested resource is cached, retrieve it from cache
                if (getCacheManager().hasCache(request.getURL()) 
                    && !getCacheManager().hasCacheExpired(request.getURL())) 
                {
                    ic = getCacheManager().getCache(request.getURL());
                }
                // if requested resource is not cached yet, cache it
                else 
                {
                ic = super.handleResourceRequest(request);
                    if (ic instanceof HttpConnection) 
                    {
                        HttpConnection response = (HttpConnection) ic;
                        if (getCacheManager().isResponseCacheable(response)) 
                        {
                        ic = getCacheManager().createCache(request.getURL(), 
                             response);
                        }
                }
            }
            return ic;
        }
        // if requested resource is not cacheable, load it as usual
        return super.handleResourceRequest(request);
    }

}

CacheManager.java:

import javax.microedition.io.HttpConnection;
import javax.microedition.io.InputConnection;

import net.rim.device.api.browser.field2.BrowserFieldRequest;

public interface CacheManager {
    public boolean isRequestCacheable(BrowserFieldRequest request);
    public boolean isResponseCacheable(HttpConnection response);
    public boolean hasCache(String url);
    public boolean hasCacheExpired(String url);
    public InputConnection getCache(String url);
    public InputConnection createCache(String url, HttpConnection response);
    public void clearCache(String url);
}

CacheManagerImpl.java:

import java.io.IOException;
import java.io.InputStream;
import java.util.Date;
import java.util.Hashtable;

import javax.microedition.io.HttpConnection;
import javax.microedition.io.InputConnection;

import net.rim.device.api.browser.field2.BrowserFieldRequest;
import net.rim.device.api.browser.field2.BrowserFieldResponse;
import net.rim.device.api.io.http.HttpHeaders;


public class CacheManagerImpl implements CacheManager {

    private static final int MAX_STANDARD_CACHE_AGE = 2592000;
    private Hashtable cacheTable;

    public CacheManagerImpl() {
        cacheTable = new Hashtable();
    }

    public boolean isRequestCacheable(BrowserFieldRequest request) {
        // Only HTTP requests are cacheable
        if (!request.getProtocol().equals("http")) {
            return false;
        }

        // Don't cache the request whose method is not "GET".
        if (request instanceof HttpConnection) {
            if (!((HttpConnection) request).getRequestMethod().equals("GET")) 
            {
                return false;
            }
        }

        // Don't cache the request with post data.
        if (request.getPostData() != null) {
                return false;
        }

        // Don't cache authentication request.
        if (request.getHeaders().getPropertyValue("Authorization") != null) {
            return false;
        }        

        return true;        
    }

    public boolean isResponseCacheable(HttpConnection response) {
        try {
            if (response.getResponseCode() != 200) {
                return false;
            }
        } catch (IOException ioe) {
            return false;
        }

        if (!response.getRequestMethod().equals("GET")) {
            return false;
        }

        if (containsPragmaNoCache(response)) {
            return false;
        }

        if (isExpired(response)) {
            return false;
        }

        if (containsCacheControlNoCache(response)) {
            return false;
        }

        if ( response.getLength() <= 0 ) {
            return false;
        }

        // additional checks can be implemented here to inspect
        // the HTTP cache-related headers of the response object

        return true;
    }

    private boolean isExpired(HttpConnection response) {
        try 
        {
            // getExpiration() returns 0 if not known
            long expires = response.getExpiration(); 
            if (expires > 0 && expires <= (new Date()).getTime()) {
                return true;
            }    
            return false;
        } catch (IOException ioe) {
            return true;
        }
    }

    private boolean containsPragmaNoCache(HttpConnection response) {
        try 
        {
            if (response.getHeaderField("pragma") != null 
                && response.getHeaderField("pragma")
                           .toLowerCase()
                           .indexOf("no-cache") >= 0) 
            {
                return true;
            } 

            return false;
        } catch (IOException ioe) {
            return true;
        }
    }

    private boolean containsCacheControlNoCache(HttpConnection response) {
        try {
            String cacheControl = response.getHeaderField("cache-control");
            if (cacheControl != null) {
                cacheControl = removeSpace(cacheControl.toLowerCase());
                if (cacheControl.indexOf("no-cache") >= 0 
                    || cacheControl.indexOf("no-store") >= 0 
                    || cacheControl.indexOf("private") >= 0 
                    || cacheControl.indexOf("max-age=0") >= 0) {
                    return true;        
                }

                long maxAge = parseMaxAge(cacheControl);
                if (maxAge > 0 && response.getDate() > 0) {
                    long date = response.getDate();
                    long now = (new Date()).getTime();                    
                    if (now > date + maxAge) {
                        // Already expired
                        return true;
                    }
                }
            } 

            return false;
        } catch (IOException ioe) {
            return true;
        }
    }    

    public InputConnection createCache(String url, HttpConnection response) {

        byte[] data = null;
        InputStream is = null;
        try {
            // Read data
            int len = (int) response.getLength();
            if (len > 0) {
                is = response.openInputStream();
                int actual = 0;
                int bytesread = 0 ;
                data = new byte[len];
                while ((bytesread != len) && (actual != -1)) {
                    actual = is.read(data, bytesread, len - bytesread);
                    bytesread += actual;
                }
            }       
        } catch (IOException ioe) {
            data = null;
        } finally {
            if (is != null) {
                try {
                    is.close();
                } catch (IOException ioe) {
                }
            }
            if (response != null) {
                try {
                    response.close();
                } catch (IOException ioe) {
                }
            } 
        }

        if (data == null) {
            return null;
        } 

        // Calculate expires
        long expires = calculateCacheExpires(response);

        // Copy headers
        HttpHeaders headers = copyResponseHeaders(response);

        // add item to cache
        cacheTable.put(url, new CacheItem(url, expires, data, headers));

        return new BrowserFieldResponse(url, data, headers);
    }

    private long calculateCacheExpires(HttpConnection response) {
        long date = 0;
        try {
            date = response.getDate();
        } catch (IOException ioe) {
        }

        if (date == 0) {
            date = (new Date()).getTime();
        }

        long expires = getResponseExpires(response);

        // If an expire date has not been specified assumes the maximum time
        if ( expires == 0 ) {
            return date + (MAX_STANDARD_CACHE_AGE * 1000L);
        }

        return expires;
    }

    private long getResponseExpires(HttpConnection response) {
        try {
            // Calculate expires from "expires"
            long expires = response.getExpiration();
            if (expires > 0) {
                return expires;
            }

            // Calculate expires from "max-age" and "date"
            if (response.getHeaderField("cache-control") != null) {
                String cacheControl = removeSpace(response
                                               .getHeaderField("cache-control")
                                               .toLowerCase());
                long maxAge = parseMaxAge(cacheControl);
                long date = response.getDate();

                if (maxAge > 0 && date > 0) {
                    return (date + maxAge);
                }
            }
        } catch (IOException ioe) {
        }

        return 0;
    }

    private long parseMaxAge(String cacheControl) {
        if (cacheControl == null) {
            return 0;
        }

        long maxAge = 0;
        if (cacheControl.indexOf("max-age=") >= 0) {
            int maxAgeStart = cacheControl.indexOf("max-age=") + 8;
            int maxAgeEnd = cacheControl.indexOf(',', maxAgeStart);
            if (maxAgeEnd < 0) {
                maxAgeEnd = cacheControl.length();
            }

            try {
                maxAge = Long.parseLong(cacheControl.substring(maxAgeStart,
                                                               maxAgeEnd));
            } catch (NumberFormatException nfe) {
            }
        }

                // Multiply maxAge by 1000 to convert seconds to milliseconds
                maxAge *= 1000L;
        return maxAge;
    }

    private static String removeSpace(String s) {
        StringBuffer result= new StringBuffer();
        int count = s.length();
        for (int i = 0; i < count; i++) {
            char c = s.charAt(i);
            if (c != ' ') {
                result.append(c);
            }
        }

        return result.toString();
    }

    private HttpHeaders copyResponseHeaders(HttpConnection response) {
        HttpHeaders headers = new HttpHeaders();
        try {
            int index = 0;
            while (response.getHeaderFieldKey(index) != null) {
                headers.addProperty(response.getHeaderFieldKey(index),
                                    response.getHeaderField(index));
                index++;
            }
        } catch (IOException ioe) {
        }

        return headers;
    }    

    public boolean hasCache(String url) {
        return cacheTable.containsKey(url);
    }

    public boolean hasCacheExpired(String url) {
        Object o = cacheTable.get(url);

        if (o instanceof CacheItem) {
            CacheItem ci = (CacheItem) o;
            long date = (new Date()).getTime();
            if (ci.getExpires() > date) {
                return false;
            } else {
                // Remove the expired cache item
                clearCache(url);
            }
        }

        return true;
    }

    public void clearCache(String url) {
        cacheTable.remove(url);
    }    

    public InputConnection getCache(String url) {
        Object o = cacheTable.get(url);        
        if (o instanceof CacheItem) {
            CacheItem ci = (CacheItem) o;
            return new BrowserFieldResponse(url, 
                                            ci.getData(), 
                                            ci.getHttpHeaders());
        }        
        return null;
    }
}

CacheItem.java:

import net.rim.device.api.io.http.HttpHeaders;

public class CacheItem {

    private String  url;    
    private long    expires;    
    private byte[] data;
    private HttpHeaders httpHeaders;

    public CacheItem(String url, 
                     long expires, 
                     byte[] data, 
                     HttpHeaders httpHeaders)
    {
        this.url = url;
        this.expires = expires;
        this.data = data;
        this.httpHeaders = httpHeaders;
    }

    public String getUrl() {
        return url;
    }

    public long getExpires() {
        return expires;
    }

    public byte[] getData() {
        return data;
    }

    public HttpHeaders getHttpHeaders() {
        return httpHeaders;
    }
}

Cualquier ayuda que pueda estar dando para esto será muy apreciada. Esto realmente me tiene perplejo. Gracias

ACTUALIZAR Parece que el almacenamiento en caché solo funciona en cierto nivel de las bibliotecas Blackberry. He agregado lógica para verificar el nivel de software actual y activar el almacenamiento en caché si es compatible con el nivel de software actual del dispositivo. Esto me proporciona una buena solución, pero aún me gustaría saber si hay una mejor manera de que el almacenamiento en caché funcione con todos los dispositivos.

UPDATE 2 Según los comentarios: el sitio que ya no se muestra correctamente pertenece al sitio que no muestra el diseño, las imágenes y el texto adecuados. Básicamente proporciona un fondo blanco con enlaces y texto que se muestran como una lista con viñetas, sin formato alguno.