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[DL-Learner SVN] SF.net SVN: dl-learner: [458] trunk/src/dl-learner/org/dllearner/kb/sparql/ Cache.java
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From: <jen...@us...> - 2008-01-29 20:05:04
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Revision: 458
http://dl-learner.svn.sourceforge.net/dl-learner/?rev=458&view=rev
Author: jenslehmann
Date: 2008-01-29 12:04:57 -0800 (Tue, 29 Jan 2008)
Log Message:
-----------
finished cache implementation (probably still not working - needs to be tested)
Modified Paths:
--------------
trunk/src/dl-learner/org/dllearner/kb/sparql/Cache.java
Modified: trunk/src/dl-learner/org/dllearner/kb/sparql/Cache.java
===================================================================
--- trunk/src/dl-learner/org/dllearner/kb/sparql/Cache.java 2008-01-29 19:24:02 UTC (rev 457)
+++ trunk/src/dl-learner/org/dllearner/kb/sparql/Cache.java 2008-01-29 20:04:57 UTC (rev 458)
@@ -28,7 +28,7 @@
import java.io.Serializable;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
-import java.util.HashMap;
+import java.util.LinkedList;
import org.apache.log4j.Logger;
@@ -49,6 +49,10 @@
* If a cached result of a SPARQL query exists, but is too old, the cache
* behaves as if the cached result would not exist.
*
+ * TODO: We are doing md5 hashing at the moment, so in rare cases different
+ * SPARQL queries can be mapped to the same file. Support for such scenarios
+ * needs to be included.
+ *
* @author Sebastian Hellmann
* @author Sebastian Knappe
* @author Jens Lehmann
@@ -60,12 +64,12 @@
private static final long serialVersionUID = 843308736471742205L;
// maps hash of a SPARQL queries to JSON representation
- // of its results; this
- private HashMap<String, String> hm;
+ // of its results; this
+ // private HashMap<String, String> hm;
private transient String cacheDir = "";
private transient String fileEnding = ".cache";
- private long timestamp;
+ // private long timestamp;
// specifies after how many seconds a cached result becomes invalid
private long freshnessSeconds = 15 * 24 * 60 * 60;
@@ -85,22 +89,7 @@
}
}
- /**
- * constructor for single cache object(one entry)
- *
- * @param sparqlQuery
- * query
- * @param content
- * that is the sparql query result as xml
- */
- private Cache(String sparqlQuery, String content) {
- // this.content = c;
- // this.sparqlquery = sparql;
- this.timestamp = System.currentTimeMillis();
- this.hm = new HashMap<String, String>();
- hm.put(sparqlQuery, content);
- }
-
+ // compute md5-hash
private String getHash(String string) {
// calculate md5 hash of the string (code is somewhat
// difficult to read, but there doesn't seem to be a
@@ -122,110 +111,92 @@
return hexString.toString();
}
+ // return filename where the query result should be saved
private String getFilename(String sparqlQuery) {
- return getHash(sparqlQuery) + fileEnding;
+ return cacheDir + getHash(sparqlQuery) + fileEnding;
}
-
+
/**
- * Gets the query result for a SPARQL query.
+ * Gets a result for a query if it is in the cache.
*
* @param sparqlQuery
* SPARQL query to check.
* @return Query result or null if no result has been found or it is
* outdated.
*/
- public String get(String sparqlQuery) {
- Cache c = readFromFile(getFilename(sparqlQuery));
- if (c == null)
+ @SuppressWarnings({"unchecked"})
+ private String getCacheEntry(String sparqlQuery) {
+ String filename = getFilename(sparqlQuery);
+ File file = new File(filename);
+
+ // return null (indicating no result) if file does not exist
+ if(!file.exists())
return null;
- // System.out.println(" file found");
- if (!c.checkFreshness())
- return null;
- // System.out.println("fresh");
- String xml = "";
+
+ LinkedList<Object> entry = null;
try {
- xml = c.hm.get(sparqlQuery);
- } catch (Exception e) {
+ FileInputStream fos = new FileInputStream(filename);
+ ObjectInputStream o = new ObjectInputStream(fos);
+ entry = (LinkedList<Object>) o.readObject();
+ } catch (IOException e) {
+ e.printStackTrace();
+ } catch (ClassNotFoundException e) {
+ e.printStackTrace();
+ }
+
+ // TODO: we need to check whether the query is correct
+ // (may not always be the case due to md5 hashing)
+
+ // determine whether query is outdated
+ long timestamp = (Long) entry.get(0);
+ boolean fresh = checkFreshness(timestamp);
+
+ if(!fresh) {
+ // delete file
+ file.delete();
+ // return null indicating no result
return null;
}
- return xml;
+
+ return (String) entry.get(2);
}
/**
- * @param key
- * is the resource, the identifier
- * @param sparqlquery
- * is the query used as another identifier
- * @param content
- * is the result of the query
+ * Adds an entry to the cache.
+ *
+ * @param sparqlQuery
+ * The SPARQL query.
+ * @param result
+ * Result of the SPARQL query.
*/
- public void put(String sparqlQuery, String content) {
- String hash = getHash(sparqlQuery);
- Cache c = readFromFile(hash);
- if (c == null) {
- c = new Cache(sparqlQuery, content);
- putIntoFile(hash, c);
- } else {
- c.hm.put(sparqlQuery, content);
- putIntoFile(hash, c);
- }
+ private void addToCache(String sparqlQuery, String result) {
+ String filename = getFilename(sparqlQuery);
+ long timestamp = System.currentTimeMillis();
- }
+ // create the object which will be serialised
+ LinkedList<Object> list = new LinkedList<Object>();
+ list.add(timestamp);
+ list.add(sparqlQuery);
+ list.add(result);
- public void checkFile(String Filename) {
- if (!new File(Filename).exists()) {
- try {
- new File(Filename).createNewFile();
- } catch (Exception e) {
- e.printStackTrace();
- }
+ // create the file we want to use
+ File file = new File(filename);
- }
-
- }
-
- /**
- * puts a cache entry in a file
- *
- * @param filename
- * @param c
- */
- protected void putIntoFile(String filename, Cache c) {
try {
- // FileWriter fw=new FileWriter(new File(Filename),true);
+ file.createNewFile();
FileOutputStream fos = new FileOutputStream(filename, false);
ObjectOutputStream o = new ObjectOutputStream(fos);
- o.writeObject(c);
+ o.writeObject(list);
fos.flush();
fos.close();
- } catch (Exception e) {
- System.out.println("Not in cache creating: " + filename);
- }
- }
-
- /**
- * reads a cache entry from a file
- *
- * @param Filename
- * @return cache entry
- */
- protected Cache readFromFile(String Filename) {
- Cache content = null;
- try {
- FileInputStream fos = new FileInputStream(Filename);
- ObjectInputStream o = new ObjectInputStream(fos);
- content = (Cache) o.readObject();
} catch (IOException e) {
e.printStackTrace();
- } catch (ClassNotFoundException e) {
- e.printStackTrace();
}
- return content;
}
- private boolean checkFreshness() {
- if ((System.currentTimeMillis() - this.timestamp) <= (freshnessSeconds * 1000))
- // fresh
+ // check whether the given timestamp is fresh
+ private boolean checkFreshness(long timestamp) {
+ if ((System.currentTimeMillis() - timestamp) <= (freshnessSeconds * 1000))
return true;
else
return false;
@@ -242,12 +213,15 @@
* @return Jena result set.
*/
public ResultSet executeSparqlQuery(SparqlQuery query) {
- if (hm.containsKey(query.getQueryString())) {
- String result = hm.get(query.getQueryString());
+ String result = getCacheEntry(query.getQueryString());
+ if (result != null) {
return SparqlQuery.JSONtoResultSet(result);
} else {
query.send();
- return query.getResultSet();
+ ResultSet rs = query.getResultSet();
+ String json = SparqlQuery.getAsJSON(rs);
+ addToCache(query.getQueryString(), json);
+ return rs;
}
}
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