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HashDiskPersistenceListener.java | 0% | 0% | 0% | 0% |
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/*
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* Copyright (c) 2002-2003 by OpenSymphony
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* All rights reserved.
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*/
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package com.opensymphony.oscache.plugins.diskpersistence;
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import com.opensymphony.oscache.base.Config;
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import com.opensymphony.oscache.base.persistence.PersistenceListener;
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import java.security.MessageDigest;
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import java.security.NoSuchAlgorithmException;
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/**
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* Persists cache data to disk. Provides a hash of the standard key name as the file name.
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*
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* A configurable hash algorithm is used to create a digest of the cache key for the
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* disk filename. This is to allow for more sane filenames for objects which dont generate
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* friendly cache keys.
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*
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* @author <a href="mailto:jparrott@soe.sony.com">Jason Parrott</a>
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*/
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public class HashDiskPersistenceListener extends AbstractDiskPersistenceListener { |
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public final static String HASH_ALGORITHM_KEY = "cache.persistence.disk.hash.algorithm"; |
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public final static String DEFAULT_HASH_ALGORITHM = "MD5"; |
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protected MessageDigest md = null; |
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/**
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* Initializes the <tt>HashDiskPersistenceListener</tt>. Namely this involves only setting up the
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* message digester to hash the key values.
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* @see com.opensymphony.oscache.base.persistence.PersistenceListener#configure(com.opensymphony.oscache.base.Config)
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*/
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public PersistenceListener configure(Config config) {
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try {
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if (config.getProperty(HashDiskPersistenceListener.HASH_ALGORITHM_KEY) != null) { |
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try {
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md = MessageDigest.getInstance(config.getProperty(HashDiskPersistenceListener.HASH_ALGORITHM_KEY)); |
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} catch (NoSuchAlgorithmException e) {
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md = MessageDigest.getInstance(HashDiskPersistenceListener.DEFAULT_HASH_ALGORITHM); |
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} |
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} else {
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md = MessageDigest.getInstance(HashDiskPersistenceListener.DEFAULT_HASH_ALGORITHM); |
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} |
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} catch (NoSuchAlgorithmException e) {
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e.printStackTrace(); |
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throw new RuntimeException("No hash algorithm available for disk persistence", e); |
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} |
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return super.configure(config); |
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} |
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/**
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* Generates a file name for the given cache key. In this case the file name is attempted to be
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* generated from the hash of the standard key name. Cache algorithm is configured via the
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* <em>cache.persistence.disk.hash.algorithm</em> configuration variable.
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* @param key cache entry key
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* @return char[] file name
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*/
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protected char[] getCacheFileName(String key) { |
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byte[] digest;
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if ((key == null) || (key.length() == 0)) { |
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throw new IllegalArgumentException("Invalid key '" + key + "' specified to getCacheFile."); |
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} |
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digest = md.digest(key.getBytes()); |
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String hexString = byteArrayToHexString(digest); |
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return hexString.toCharArray();
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} |
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/**
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* Nibble conversion. Thanks to our friends at:
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* http://www.devx.com/tips/Tip/13540
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* @param in the byte array to convert
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* @return a java.lang.String based version of they byte array
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*/
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static String byteArrayToHexString(byte[] in) { |
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byte ch = 0x00;
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int i = 0;
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if ((in == null) || (in.length <= 0)) { |
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return null; |
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} |
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String[] pseudo = { |
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"0", "1", "2", "3", "4", "5", "6", "7", "8", "9", "A", "B", "C", "D", |
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"E", "F" |
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}; |
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StringBuffer out = new StringBuffer(in.length * 2);
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while (i < in.length) {
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ch = (byte) (in[i] & 0xF0); // Strip off high nibble |
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ch = (byte) (ch >>> 4);
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// shift the bits down
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ch = (byte) (ch & 0x0F);
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// must do this is high order bit is on!
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out.append(pseudo[(int) ch]); // convert the nibble to a String Character |
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ch = (byte) (in[i] & 0x0F); // Strip off low nibble |
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out.append(pseudo[(int) ch]); // convert the nibble to a String Character |
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i++; |
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} |
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String rslt = new String(out);
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return rslt;
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} |
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} |
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