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https://issues.apache.org/jira/browse/CONFIGURATION-136?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13218027#comment-13218027
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Laurent Michelet edited comment on CONFIGURATION-136 at 2/28/12 10:30 AM:
--------------------------------------------------------------------------
THe problem here is that filesystem is not transactional. When an exception is
raised, there is no rollback on the file which is written.
A proposal of correction is to save in memory the file before any
modifications. When an exception is raised we replace the current file with the
original one.
The 2 following patches has been tested successfully with XMLConfiguration file.
{code:title=AbstractFileConfiguration.java|borderStyle=solid}
/**
* Save the configuration to the specified URL. This doesn't change the
* source of the configuration, use setURL() if you need it.
*
* @param url
* the URL
*
* @throws ConfigurationException
* if an error occurs during the save operation
*/
public void save(URL url) throws ConfigurationException {
OutputStream out = null;
ByteArrayInputStream originalFile = null;
try {
final File file = new File(url.getFile());
// Save original file if existing
if (file.exists()) {
InputStream inputStreamOfOrignalFile =
fileSystem
.getInputStream(url);
originalFile =
saveOriginalFile(inputStreamOfOrignalFile);
}
out = fileSystem.getOutputStream(url);
save(out);
if (out instanceof VerifiableOutputStream) {
((VerifiableOutputStream) out).verify();
}
} catch (IOException e) {
// Rollback for IOException if existing
if (originalFile != null) {
reloadOriginalFile(url, originalFile, out);
}
throw new ConfigurationException("Could not save to URL
" + url, e);
} catch (Exception e) {
// Rollback when any kind of Exception is raised if
existing
if (originalFile != null) {
reloadOriginalFile(url, originalFile, out);
}
throw new ConfigurationException(e);
} finally {
closeSilent(out);
}
}
/**
* Save the original file before any modifications
*
* @param in
* @return
* @throws IOException
* @since 1.9
*/
private ByteArrayInputStream saveOriginalFile(
InputStream inputStreamOfOrignalFile) throws
IOException {
ByteArrayOutputStream baos = new ByteArrayOutputStream();
byte[] buffer = new byte[1024];
int len;
while ((len = inputStreamOfOrignalFile.read(buffer)) > -1) {
baos.write(buffer, 0, len);
}
baos.flush();
return new ByteArrayInputStream(baos.toByteArray());
}
/**
* Replace the current file with the original one before any
modifications
*
* @param url
* @param originalFile
* @param outOfCurrentFile
* @throws ConfigurationException
* @since 1.9
*/
private void reloadOriginalFile(URL url, ByteArrayInputStream
originalFile,
OutputStream outOfCurrentFile) throws
ConfigurationException {
if (outOfCurrentFile != null && originalFile != null) {
try {
int nextChar;
while ((nextChar = originalFile.read()) != -1)
outOfCurrentFile.write((char) nextChar);
outOfCurrentFile.write('\n');
outOfCurrentFile.flush();
} catch (IOException ioe) {
throw new ConfigurationException(
"Could not save to URL " + url,
ioe);
}
}
}
{code}
was (Author: l.michelet):
THe problem here is that filesystem is not transactional. When an exception
is raised, there is no rollback on the file which is written.
A proposal of correction is to save in memory the file before any
modifications. When an exception is raised we replace the current file with the
original one.
The 2 previous patches has been tested successfully with XMLConfiguration file.
{code:title=AbstractFileConfiguration.java|borderStyle=solid}
/**
* Save the configuration to the specified URL. This doesn't change the
* source of the configuration, use setURL() if you need it.
*
* @param url
* the URL
*
* @throws ConfigurationException
* if an error occurs during the save operation
*/
public void save(URL url) throws ConfigurationException {
OutputStream out = null;
ByteArrayInputStream originalFile = null;
try {
final File file = new File(url.getFile());
// Save original file if existing
if (file.exists()) {
InputStream inputStreamOfOrignalFile =
fileSystem
.getInputStream(url);
originalFile =
saveOriginalFile(inputStreamOfOrignalFile);
}
out = fileSystem.getOutputStream(url);
save(out);
if (out instanceof VerifiableOutputStream) {
((VerifiableOutputStream) out).verify();
}
} catch (IOException e) {
// Rollback for IOException if existing
if (originalFile != null) {
reloadOriginalFile(url, originalFile, out);
}
throw new ConfigurationException("Could not save to URL
" + url, e);
} catch (Exception e) {
// Rollback when any kind of Exception is raised if
existing
if (originalFile != null) {
reloadOriginalFile(url, originalFile, out);
}
throw new ConfigurationException(e);
} finally {
closeSilent(out);
}
}
/**
* Save the original file before any modifications
*
* @param in
* @return
* @throws IOException
* @since 1.9
*/
private ByteArrayInputStream saveOriginalFile(
InputStream inputStreamOfOrignalFile) throws
IOException {
ByteArrayOutputStream baos = new ByteArrayOutputStream();
byte[] buffer = new byte[1024];
int len;
while ((len = inputStreamOfOrignalFile.read(buffer)) > -1) {
baos.write(buffer, 0, len);
}
baos.flush();
return new ByteArrayInputStream(baos.toByteArray());
}
/**
* Replace the current file with the original one before any
modifications
*
* @param url
* @param originalFile
* @param outOfCurrentFile
* @throws ConfigurationException
* @since 1.9
*/
private void reloadOriginalFile(URL url, ByteArrayInputStream
originalFile,
OutputStream outOfCurrentFile) throws
ConfigurationException {
if (outOfCurrentFile != null && originalFile != null) {
try {
int nextChar;
while ((nextChar = originalFile.read()) != -1)
outOfCurrentFile.write((char) nextChar);
outOfCurrentFile.write('\n');
outOfCurrentFile.flush();
} catch (IOException ioe) {
throw new ConfigurationException(
"Could not save to URL " + url,
ioe);
}
}
}
{code}
> Reloading may corrupt the configuration
> ---------------------------------------
>
> Key: CONFIGURATION-136
> URL: https://issues.apache.org/jira/browse/CONFIGURATION-136
> Project: Commons Configuration
> Issue Type: Bug
> Components: File reloading
> Affects Versions: 1.1
> Reporter: nicolas de loof
> Fix For: 1.9
>
> Attachments: commons-configuration-1.5_patch_CONFIGURATION-136.jar,
> commons-configuration-1.8_patch_CONFIGURATION-136.jar
>
>
> Current reloading process clears current properties and load updated values
> from
> resource reader. If an IO error occurs (or invalid format), the configuration
> gets corrupted and the application becomes unstable.
> It may be better for hot-reload to put loaded values into a temporary
> Properties
> and replace previous values only when reloading is successful.
> It may also allow to use a 'currentlty-reloading' flag in the synchronized
> 'reload' block to avoid blocking threads during a reload (they could access
> safelly the 'old' properties until reload is finished)
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