abstractdiskpersistencelistener.java

一个不错的cache

    * @return Adjusted cache path
    */
    protected String adjustFileCachePath(String cachePathStr) {
        if (cachePathStr.compareToIgnoreCase(CONTEXT_TMPDIR) == 0) {
            cachePathStr = contextTmpDir.getAbsolutePath();
        }

        return cachePathStr;
    }

    /**
    *        Set caching to file on or off.
    *  If the <code>cache.path</code> property exists, we assume file caching is turned on.
    *        By the same token, to turn off file caching just remove this property.
    */
    protected void initFileCaching(String cachePathStr) {
        if (cachePathStr != null) {
            cachePath = new File(cachePathStr);

            try {
                if (!cachePath.exists()) {
                    if (log.isInfoEnabled()) {
                        log.info("cache.path '" + cachePathStr + "' does not exist, creating");
                    }

                    cachePath.mkdirs();
                }

                if (!cachePath.isDirectory()) {
                    log.error("cache.path '" + cachePathStr + "' is not a directory");
                    cachePath = null;
                } else if (!cachePath.canWrite()) {
                    log.error("cache.path '" + cachePathStr + "' is not a writable location");
                    cachePath = null;
                }
            } catch (Exception e) {
                log.error("cache.path '" + cachePathStr + "' could not be used", e);
                cachePath = null;
            }
        } else {
            // Use default value
        }
    }

    protected void remove(File file) throws CachePersistenceException {
        try {
            // Loop until we are able to delete (No current read).
            // The cache must ensure that there are never two concurrent threads
            // doing write (store and delete) operations on the same item.
            // Delete only should be enough but file.exists prevents infinite loop
            while (!file.delete() && file.exists()) {
                ;
            }
        } catch (Exception e) {
            throw new CachePersistenceException("Unable to remove '" + file + "' from the cache: " + e);
        }
    }

    /**
    * Stores an object using the supplied file object
    *
    * @param file The file to use for storing the object
    * @param obj the object to store
    * @throws CachePersistenceException
    */
    protected void store(File file, Object obj) throws CachePersistenceException {
        // check if the directory structure required exists and create it if it doesn't
        File filepath = new File(file.getParent());

        try {
            if (!filepath.exists()) {
                filepath.mkdirs();
            }
        } catch (Exception e) {
            throw new CachePersistenceException("Unable to create the directory " + filepath);
        }

        // Loop until we are able to delete (No current read).
        // The cache must ensure that there are never two concurrent threads
        // doing write (store and delete) operations on the same item.
        // Delete only should be enough but file.exists prevents infinite loop
        while (file.exists() && !file.delete()) {
            ;
        }

        // Write the object to disk
        FileOutputStream fout = null;
        ObjectOutputStream oout = null;

        try {
            fout = new FileOutputStream(file);
            oout = new ObjectOutputStream(fout);
            oout.writeObject(obj);
            oout.flush();
        } catch (Exception e) {
            while (file.exists() && !file.delete()) {
                ;
            }

            throw new CachePersistenceException("Unable to write '" + file + "' in the cache. Exception: " + e.getClass().getName() + ", Message: " + e.getMessage());
        } finally {
            try {
                fout.close();
            } catch (Exception e) {
            }

            try {
                oout.close();
            } catch (Exception e) {
            }
        }
    }

    /**
    * Build fully qualified cache file for the specified cache entry key.
    *
    * @param key   Cache Entry Key.
    * @return File reference.
    */
    protected File getCacheFile(String key) {
        char[] fileChars = getCacheFileName(key);

        File file = new File(root, new String(fileChars) + "." + CACHE_EXTENSION);

        return file;
    }

    /**
    * Build cache file name for the specified cache entry key.
    *
    * @param key   Cache Entry Key.
    * @return char[] file name.
    */
    protected abstract char[] getCacheFileName(String key);

    /**
    * Builds a fully qualified file name that specifies a cache group entry.
    *
    * @param group The name of the group
    * @return A File reference
    */
    private File getCacheGroupFile(String group) {
        int AVERAGE_PATH_LENGTH = 30;

        if ((group == null) || (group.length() == 0)) {
            throw new IllegalArgumentException("Invalid group '" + group + "' specified to getCacheGroupFile.");
        }

        StringBuffer path = new StringBuffer(AVERAGE_PATH_LENGTH);

        // Build a fully qualified file name for this group
        path.append(GROUP_DIRECTORY).append('/');
        path.append(group).append('.').append(CACHE_EXTENSION);

        return new File(root, path.toString());
    }

    /**
    * This allows to persist different scopes in different path in the case of
    * file caching.
    *
    * @param scope   Cache scope.
    * @return The scope subpath
    */
    private String getPathPart(int scope) {
        if (scope == PageContext.SESSION_SCOPE) {
            return SESSION_CACHE_SUBPATH;
        } else {
            return APPLICATION_CACHE_SUBPATH;
        }
    }

    /**
    * Clears a whole directory, starting from the specified
    * directory
    *
    * @param baseDirName The root directory to delete
    * @throws CachePersistenceException
    */
    private void clear(String baseDirName) throws CachePersistenceException {
        File baseDir = new File(baseDirName);
        File[] fileList = baseDir.listFiles();

        try {
            if (fileList != null) {
                // Loop through all the files and directory to delete them
                for (int count = 0; count < fileList.length; count++) {
                    if (fileList[count].isFile()) {
                        fileList[count].delete();
                    } else {
                        // Make a recursive call to delete the directory
                        clear(fileList[count].toString());
                        fileList[count].delete();
                    }
                }
            }

            // Delete the root directory
            baseDir.delete();
        } catch (Exception e) {
            throw new CachePersistenceException("Unable to clear the cache directory");
        }
    }

    /**
    * Retrives a serialized object from the supplied file, or returns
    * <code>null</code> if the file does not exist.
    *
    * @param file The file to deserialize
    * @return The deserialized object
    * @throws CachePersistenceException
    */
    private Object retrieve(File file) throws CachePersistenceException {
        Object readContent = null;
        boolean fileExist;

        try {
            fileExist = file.exists();
        } catch (Exception e) {
            throw new CachePersistenceException("Unable to verify if " + file + " exists: " + e);
        }

        // Read the file if it exists
        if (fileExist) {
            BufferedInputStream in = null;
            ObjectInputStream oin = null;

            try {
                in = new BufferedInputStream(new FileInputStream(file));
                oin = new ObjectInputStream(in);
                readContent = oin.readObject();
            } catch (Exception e) {
                // We expect this exception to occur.
                // This is when the item will be invalidated (written or deleted)
                // during read.
                // The cache has the logic to retry reading.
                throw new CachePersistenceException("Unable to read '" + file.getAbsolutePath() + "' from the cache: " + e);
            } finally {
                try {
                    oin.close();
                } catch (Exception ex) {
                }

                try {
                    in.close();
                } catch (Exception ex) {
                }
            }
        }

        return readContent;
    }
}