lrucachehandler.java

这个weblogging 设计得比较精巧

            }
            catch (Exception e)
            {
                if (mLogger.isDebugEnabled())
                {
                    StringBuffer sb = new StringBuffer();
                    sb.append("Probably a client abort exception, key=");
                    sb.append(key);
                    mLogger.error(sb.toString());
                }
            }
            
        }
    }

    /**
     * Purge entire cache.
     */
    public synchronized void flushCache(HttpServletRequest req)
    {
        mPageCache.clear();
    }

    /**
     * Purge user's entries from cache.
     */
    public synchronized void removeFromCache(HttpServletRequest req, UserData user)
    {
        // TODO: can we make this a little more precise, perhaps via regex?
        String rssString = "/rss/" + user.getUserName(); // user's pages
        String pageString = "/page/" + user.getUserName(); // user's RSS feeds
        String mainRssString = "/rss_"; // main RSS feed
        List purgeList = new ArrayList();
        
        Iterator keys = mPageCache.keySet().iterator();
        while (keys.hasNext())
        {
            String key = (String) keys.next();
            
            if (key.indexOf(rssString)!=-1 || key.indexOf(pageString)!=-1 || key.indexOf(mainRssString)!=-1) 
            {
                purgeList.add(key);
            }
        }
        
        Iterator purgeIter = purgeList.iterator();
        while (purgeIter.hasNext())
        {
            String key = (String) purgeIter.next();
            mPageCache.remove(key);
        }
        
        if (mLogger.isDebugEnabled())
        {
            StringBuffer sb = new StringBuffer();
            sb.append("Purged, count=");
            sb.append(purgeList.size());
            sb.append(", user=");
            sb.append(user.getUserName());
            mLogger.debug(sb.toString());
        }        
    }
    
    public synchronized void timeoutCache() 
    {
        if (mTimeoutRatio == 1.0)
        {
            mLogger.debug("Timing out whole cache: " + mName);
            mPageCache.clear();   
        }
        else 
        {
            int numToTimeout = (int)(mTimeoutRatio * mPageCache.size());
            mLogger.debug(
                "Timing out " + numToTimeout + " of " + mPageCache.size()
                + " entries from cache: " + mName);
            ArrayList allKeys = new ArrayList(mPageCache.keySet());
            for (int i=numToTimeout; i>0; i--) 
            {
                mPageCache.remove(allKeys.get(i));
            }
        }
    }
    
    /** 
     * Get from cache. Synchronized because "In access-ordered linked hash 
     * maps, merely querying the map with get is a structural modification" 
     */
    public synchronized Object getFromCache(String key) 
    {
        Object entry = mPageCache.get(key);
        
        if (entry != null && mLogger.isDebugEnabled())
        {
            hits++;
        }
        return entry;
    }

    public synchronized void putToCache(String key, Object entry) 
    {
        mPageCache.put(key, entry);
        if (mLogger.isDebugEnabled())
        {
            misses++;
            
            StringBuffer sb = new StringBuffer();
            sb.append("Missed, cache size=");
            sb.append(mPageCache.size());
            sb.append(", hits=");
            sb.append(hits);
            sb.append(", misses=");
            sb.append(misses);
            sb.append(", key=");
            sb.append(key);
            mLogger.debug(sb.toString());
        }
    }

    public String generateEntryKey(String key, 
                       HttpServletRequest request, int scope, String language)
    {
        StringBuffer cBuffer = new StringBuffer(AVERAGE_KEY_LENGTH);
        // Append the language if available
        if (language != null)
        {
            cBuffer.append(FILE_SEPARATOR).append(language);
        }
        
        //cBuffer.append(FILE_SEPARATOR).append(request.getServerName());
        
        if (key != null)
        {
            cBuffer.append(FILE_SEPARATOR).append(key);
        }
        else
        {
            String generatedKey = request.getRequestURI();
            if (generatedKey.charAt(0) != FILE_SEPARATOR_CHAR)
            {
                cBuffer.append(FILE_SEPARATOR_CHAR);
            }
            cBuffer.append(generatedKey);
            cBuffer.append("_").append(request.getMethod()).append("_");
            generatedKey = getSortedQueryString(request);
            if (generatedKey != null)
            {
                try
                {
                    java.security.MessageDigest digest = 
                        java.security.MessageDigest.getInstance("MD5");
                    byte[] b = digest.digest(generatedKey.getBytes());
                    cBuffer.append("_");
                    // Base64 encoding allows for unwanted slash characters.
                    cBuffer.append(toBase64(b).replace('/', '_'));
                }
                catch (Exception e)
                {
                    // Ignore query string
                }
            }
        }
        return cBuffer.toString();
    }

    protected String getSortedQueryString(HttpServletRequest request)
    {
        Map paramMap = request.getParameterMap();
        if (paramMap.isEmpty())
        {
            return null;
        }
        Set paramSet = new TreeMap(paramMap).entrySet();
        StringBuffer buf = new StringBuffer();
        boolean first = true;
        for (Iterator it = paramSet.iterator(); it.hasNext();)
        {
            Map.Entry entry = (Map.Entry) it.next();
            String[] values = (String[]) entry.getValue();
            for (int i = 0; i < values.length; i++)
            {
                String key = (String) entry.getKey();
                if ((key.length() != 10) || !"jsessionid".equals(key))
                {
                    if (first)
                    {
                        first = false;
                    }
                    else
                    {
                        buf.append('&');
                    }
                    buf.append(key).append('=').append(values[i]);
                }
            }
        }
        // We get a 0 length buffer if the only parameter was a jsessionid
        if (buf.length() == 0)
        {
            return null;
        }
        else
        {
            return buf.toString();
        }
    }

    /**
     * Convert a byte array into a Base64 string (as used in mime formats)
     */
    private static String toBase64(byte[] aValue)
    {
        int byte1;
        int byte2;
        int byte3;
        int iByteLen = aValue.length;
        StringBuffer tt = new StringBuffer();
        for (int i = 0; i < iByteLen; i += 3)
        {
            boolean bByte2 = (i + 1) < iByteLen;
            boolean bByte3 = (i + 2) < iByteLen;
            byte1 = aValue[i] & 0xFF;
            byte2 = (bByte2) ? (aValue[i + 1] & 0xFF) : 0;
            byte3 = (bByte3) ? (aValue[i + 2] & 0xFF) : 0;
            tt.append(m_strBase64Chars.charAt(byte1 / 4));
            tt.append(m_strBase64Chars.charAt((byte2 / 16)
                            + ((byte1 & 0x3) * 16)));
            tt.append(((bByte2) ? m_strBase64Chars.charAt((byte3 / 64)
                            + ((byte2 & 0xF) * 4)) : '='));
            tt.append(((bByte3) ? m_strBase64Chars.charAt(byte3 & 0x3F) : '='));
        }
        return tt.toString();
    }
}