Rewrote embedded XML database to make it more dependable:
New records are first written to temporary files and only renamed to their actual names when the transaction is committed.
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hns
parent
e512386e9a
commit
6f3d080b34
3 changed files with 188 additions and 77 deletions
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@ -19,9 +19,29 @@ package helma.objectmodel;
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/**
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* This interface is kept for databases that are able
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* to run transactions. Transactions were used for the
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* Berkeley database and might be used in other future
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* databases, so we leave transactions in.
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* to run transactions.
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*/
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public interface ITransaction {
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public final int ADDED = 0;
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public final int UPDATED = 1;
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public final int DELETED = 2;
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/**
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* Complete the transaction by making its changes persistent.
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*/
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public void commit() throws DatabaseException;
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/**
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* Rollback the transaction, forgetting the changed items
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*/
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public void abort() throws DatabaseException;
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/**
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* Adds a resource to the list of resources encompassed by this transaction
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*
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* @param res the resource to add
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* @param status the status of the resource (ADDED|UPDATED|DELETED)
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*/
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public void addResource(Object res, int status) throws DatabaseException;
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}
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@ -92,7 +92,7 @@ public final class NodeManager {
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}
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}
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db = new XmlDatabase(dbHome, null, this);
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db = new XmlDatabase(dbHome, this);
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initDb();
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}
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@ -25,13 +25,14 @@ import org.xml.sax.SAXException;
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import javax.xml.parsers.ParserConfigurationException;
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import java.io.File;
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import java.io.IOException;
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import java.util.ArrayList;
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/**
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* A simple XML-database
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*/
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public final class XmlDatabase implements IDatabase {
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private String dbHome;
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private File dbBaseDir;
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private File dbHomeDir;
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private NodeManager nmgr;
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private IDGenerator idgen;
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@ -43,19 +44,17 @@ public final class XmlDatabase implements IDatabase {
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* Creates a new XmlDatabase object.
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*
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* @param dbHome ...
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* @param dbFilename ...
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* @param nmgr ...
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*
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* @throws DatabaseException ...
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* @throws RuntimeException ...
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*/
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public XmlDatabase(String dbHome, String dbFilename, NodeManager nmgr)
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public XmlDatabase(String dbHome, NodeManager nmgr)
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throws DatabaseException {
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this.dbHome = dbHome;
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this.nmgr = nmgr;
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dbBaseDir = new File(dbHome);
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dbHomeDir = new File(dbHome);
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if (!dbBaseDir.exists() && !dbBaseDir.mkdirs()) {
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if (!dbHomeDir.exists() && !dbHomeDir.mkdirs()) {
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throw new RuntimeException("Couldn't create DB-directory");
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}
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@ -63,48 +62,47 @@ public final class XmlDatabase implements IDatabase {
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}
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/**
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*
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* Shut down the database
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*/
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public void shutdown() {
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// nothing to do
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}
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/**
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* Start a new transaction.
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*
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*
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* @return ...
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*
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* @throws DatabaseException ...
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* @return the new tranaction object
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* @throws DatabaseException
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*/
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public ITransaction beginTransaction() throws DatabaseException {
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return null;
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return new Transaction();
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}
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/**
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* committ the given transaction, makint its changes persistent
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*
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*
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* @param txn ...
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*
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* @throws DatabaseException ...
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* @param txn
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* @throws DatabaseException
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*/
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public void commitTransaction(ITransaction txn) throws DatabaseException {
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txn.commit();
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}
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/**
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* Abort the given transaction
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*
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*
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* @param txn ...
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*
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* @throws DatabaseException ...
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* @param txn
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* @throws DatabaseException
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*/
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public void abortTransaction(ITransaction txn) throws DatabaseException {
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txn.abort();
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}
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/**
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* Get the next free id to use for new objects
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*
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*
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* @return ...
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*
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* @throws ObjectNotFoundException ...
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* @return
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* @throws ObjectNotFoundException
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*/
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public String nextID() throws ObjectNotFoundException {
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if (idgen == null) {
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@ -115,17 +113,15 @@ public final class XmlDatabase implements IDatabase {
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}
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/**
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* Get the id-generator
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*
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*
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* @param txn ...
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*
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* @return ...
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*
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* @throws ObjectNotFoundException ...
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* @param txn
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* @return
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* @throws ObjectNotFoundException
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*/
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public IDGenerator getIDGenerator(ITransaction txn)
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throws ObjectNotFoundException {
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File file = new File(dbBaseDir, "idgen.xml");
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File file = new File(dbHomeDir, "idgen.xml");
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this.idgen = IDGenParser.getIDGenerator(file);
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@ -133,36 +129,39 @@ public final class XmlDatabase implements IDatabase {
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}
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/**
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* Write the id-generator to file
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*
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*
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* @param txn ...
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* @param idgen ...
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*
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* @throws IOException ...
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* @param txn
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* @param idgen
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* @throws IOException
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*/
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public void saveIDGenerator(ITransaction txn, IDGenerator idgen)
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throws IOException {
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File file = new File(dbBaseDir, "idgen.xml");
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File tmp = File.createTempFile("idgen.xml.", ".tmp", dbHomeDir);
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IDGenParser.saveIDGenerator(idgen, file);
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IDGenParser.saveIDGenerator(idgen, tmp);
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this.idgen = idgen;
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File file = new File(dbHomeDir, "idgen.xml");
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Resource res = new Resource(file, tmp);
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txn.addResource(res, ITransaction.ADDED);
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}
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/**
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* Retrieves a Node from the database.
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*
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*
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* @param txn ...
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* @param kstr ...
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*
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* @return ...
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*
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* @throws Exception ...
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* @throws ObjectNotFoundException ...
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* @param txn
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* @param kstr
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* @return
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* @throws IOException
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* @throws ObjectNotFoundException
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* @throws ParserConfigurationException
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* @throws SAXException
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*/
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public INode getNode(ITransaction txn, String kstr)
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throws IOException, ObjectNotFoundException,
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ParserConfigurationException, SAXException {
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File f = new File(dbBaseDir, kstr + ".xml");
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File f = new File(dbHomeDir, kstr + ".xml");
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if (!f.exists()) {
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throw new ObjectNotFoundException("Object not found for key " + kstr + ".");
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@ -174,68 +173,160 @@ public final class XmlDatabase implements IDatabase {
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return node;
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} catch (RuntimeException x) {
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nmgr.app.logEvent("error reading node from XmlDatbase: " + x.toString());
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nmgr.app.logError("Error reading " +f+": " + x.toString());
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throw new ObjectNotFoundException(x.toString());
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}
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}
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/**
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* Write the node to a temporary file.
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*
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*
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* @param txn ...
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* @param kstr ...
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* @param node ...
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*
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* @throws Exception ...
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* @param txn the transaction we're in
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* @param kstr the node's key
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* @param node the node to save
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* @throws IOException
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*/
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public void saveNode(ITransaction txn, String kstr, INode node)
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throws IOException {
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XmlWriter writer = null;
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File file = new File(dbBaseDir, kstr + ".xml");
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File tmp = File.createTempFile(kstr + ".xml.", ".tmp", dbHomeDir);
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if (encoding != null) {
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writer = new XmlWriter(file, encoding);
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writer = new XmlWriter(tmp, encoding);
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} else {
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writer = new XmlWriter(file);
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writer = new XmlWriter(tmp);
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}
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writer.setMaxLevels(1);
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writer.write((Node) node);
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writer.write(node);
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writer.close();
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File file = new File(dbHomeDir, kstr+".xml");
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Resource res = new Resource(file, tmp);
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txn.addResource(res, ITransaction.ADDED);
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}
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/**
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* Marks an element from the database as deleted
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*
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*
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* @param txn ...
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* @param kstr ...
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*
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* @throws Exception ...
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* @param txn
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* @param kstr
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* @throws IOException
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*/
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public void deleteNode(ITransaction txn, String kstr)
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throws IOException {
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File f = new File(dbBaseDir, kstr + ".xml");
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f.delete();
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Resource res = new Resource(new File(dbHomeDir, kstr+".xml"), null);
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txn.addResource(res, ITransaction.DELETED);
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}
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/**
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* set the file encoding to use
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*
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*
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* @param enc ...
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* @param encoding the database's file encoding
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*/
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public void setEncoding(String encoding) {
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this.encoding = encoding;
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}
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/**
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* get the file encoding used by this database
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*
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*
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* @return ...
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* @return the file encoding used by this database
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*/
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public String getEncoding() {
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return encoding;
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}
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class Transaction implements ITransaction {
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ArrayList writeFiles = new ArrayList();
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ArrayList deleteFiles = new ArrayList();
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/**
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* Complete the transaction by making its changes persistent.
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*/
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public void commit() throws DatabaseException {
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// move through updated/created files and persist them
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int l = writeFiles.size();
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for (int i=0; i<l; i++) {
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Resource res = (Resource) writeFiles.get(i);
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try {
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if (res.tmpfile.renameTo(res.file)) {
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nmgr.app.logEvent(res.tmpfile+" -> "+res.file);
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res.tmpfile.delete();
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} else {
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nmgr.app.logError("*** Error committing "+res.file);
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nmgr.app.logError("*** Committed version is in "+res.tmpfile);
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}
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} catch (SecurityException ignore) {
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// shouldn't happen
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}
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}
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// move through deleted files and delete them
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l = deleteFiles.size();
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for (int i=0; i<l; i++) {
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Resource res = (Resource) deleteFiles.get(i);
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try {
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res.file.delete();
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} catch (SecurityException ignore) {
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// shouldn't happen
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}
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}
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// clear registered resources
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writeFiles.clear();
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deleteFiles.clear();
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}
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/**
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* Rollback the transaction, forgetting the changed items
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*/
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public void abort() throws DatabaseException {
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int l = writeFiles.size();
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for (int i=0; i<l; i++) {
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Resource res = (Resource) writeFiles.get(i);
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try {
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res.tmpfile.delete();
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} catch (SecurityException ignore) {
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// shouldn't happen
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}
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}
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// clear registered resources
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writeFiles.clear();
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deleteFiles.clear();
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}
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/**
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* Adds a resource to the list of resources encompassed by this transaction
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*
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* @param res the resource to add
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* @param status the status of the resource (ADDED|UPDATED|DELETED)
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*/
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public void addResource(Object res, int status)
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throws DatabaseException {
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if (status == DELETED) {
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deleteFiles.add(res);
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} else {
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writeFiles.add(res);
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}
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}
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}
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/**
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* A holder class for two files, the temporary file and the permanent one
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*/
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class Resource {
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File tmpfile;
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File file;
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public Resource(File file, File tmpfile) {
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this.file = file;
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this.tmpfile = tmpfile;
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}
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}
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}
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