pjs/grendel/storage/intertwingle/HackDB.java

198 строки
5.4 KiB
Java
Исходник Обычный вид История

1998-09-09 04:52:38 +04:00
/* -*- Mode: java; indent-tabs-mode: nil; c-basic-offset: 2 -*-
*
* The contents of this file are subject to the Mozilla Public License
* Version 1.0 (the "License"); you may not use this file except in
* compliance with the License. You may obtain a copy of the License at
* http://www.mozilla.org/MPL/
*
* Software distributed under the License is distributed on an "AS IS"
* basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
* the License for the specific language governing rights and limitations
* under the License.
*
* The Original Code is the Grendel mail/news client.
*
* The Initial Developer of the Original Code is Netscape Communications
* Corporation. Portions created by Netscape are Copyright (C) 1997
* Netscape Communications Corporation. All Rights Reserved.
*
* Created: Terry Weissman <terry@netscape.com>, 26 Sep 1997.
*/
package grendel.storage.intertwingle;
import calypso.util.Assert;
import calypso.util.NullJavaEnumeration;
import java.io.File;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.util.Enumeration;
import java.util.Hashtable;
import java.util.NoSuchElementException;
/** This is a completely wretched thing that implements a RDF-ish database.
It works by generating zillions of tiny files. We should never ever really
use this; it's just for playing. If we actually ever do ship this, I will
be forced to spend the rest of my life hunting down every copy on every
machine in the world and eradicating it. */
final class HackDB extends BaseDB {
private File top;
private File tmpfile;
private Hashtable slotdirs = new Hashtable();
private Hashtable reverseslotdirs = new Hashtable();
HackDB(File f) throws IOException {
top = f;
ensureDirectory(top);
tmpfile = new File(top, "--tmp--");
}
private void ensureDirectory(File f) throws IOException {
if (!f.exists()) f.mkdirs();
if (!f.isDirectory()) {
throw new IOException("Must be a directory: " + f);
}
}
private File findSlotFile(String name, boolean reverse) throws IOException {
Hashtable table = (reverse ? reverseslotdirs : slotdirs);
File result = (File) table.get(name);
if (result == null) {
result = new File(top, reverse ? "reverse-" + name : name);
ensureDirectory(result);
table.put(name, result);
}
return result;
}
private void putone(File dir, String name, String value) throws IOException {
File n = new File(dir, name);
RandomAccessFile file = new RandomAccessFile(n, "rw");
String line;
long length = file.length();
while (file.getFilePointer() < length) {
line = file.readUTF();
if (line.equals(value)) {
file.close();
return;
}
}
file.writeUTF(value);
file.close();
}
private void nukeone(File dir, String name, String value)
throws IOException
{
File n = new File(dir, name);
if (!n.exists()) return;
RandomAccessFile file = new RandomAccessFile(n, "r");
tmpfile.delete();
RandomAccessFile out = new RandomAccessFile(tmpfile, "rw");
long length = file.length();
boolean found = false;
int count = 0;
while (file.getFilePointer() < length) {
String line = file.readUTF();
if (line.equals(value)) {
found = true;
} else {
out.writeUTF(line);
count++;
}
}
file.close();
out.close();
if (found) {
n.delete();
if (count > 0) {
tmpfile.renameTo(n);
} else {
tmpfile.delete();
}
} else {
tmpfile.delete();
}
}
public synchronized void assert(String name, String slot, String value)
throws IOException
{
File s = findSlotFile(slot, false);
File r = findSlotFile(slot, true);
putone(s, name, value);
putone(r, value, name);
}
public synchronized void unassert(String name, String slot, String value)
throws IOException
{
File s = findSlotFile(slot, false);
File r = findSlotFile(slot, true);
nukeone(s, name, value);
nukeone(r, value, name);
}
public synchronized String findFirst(String name, String slot,
boolean reverse) throws IOException {
File f = new File(findSlotFile(slot, reverse), name);
if (!f.exists()) return null;
RandomAccessFile fid = new RandomAccessFile(f, "r");
String line = null;
if (fid.length() > 0) {
line = fid.readUTF();
}
fid.close();
return line;
}
public Enumeration findAll(String name, String slot, boolean reverse)
throws IOException
{
File f = new File(findSlotFile(slot, reverse), name);
if (!f.exists()) return NullJavaEnumeration.kInstance;
final RandomAccessFile thefid = new RandomAccessFile(f, "r");
return new Enumeration() {
RandomAccessFile fid = thefid;
String next = null;
public boolean hasMoreElements() {
if (next != null) return true;
if (fid == null) return false;
try {
next = fid.readUTF();
} catch (IOException e) {
next = null;
}
if (next == null) {
try {
fid.close();
} catch (IOException e) {
}
fid = null;
return false;
}
return true;
}
public Object nextElement() throws NoSuchElementException {
if (!hasMoreElements()) throw new NoSuchElementException();
String result = next;
next = null;
return result;
}
};
}
};