info.unterrainer.commons.jreutils.DoubleBufferedFile Maven / Gradle / Ivy
package info.unterrainer.commons.jreutils;
import java.io.BufferedWriter;
import java.io.IOException;
import java.nio.charset.Charset;
import java.nio.file.Files;
import java.nio.file.LinkOption;
import java.nio.file.Path;
import java.nio.file.attribute.BasicFileAttributes;
import java.time.LocalDateTime;
import java.util.Objects;
import lombok.Data;
import lombok.experimental.Accessors;
/**
* Allows to access (read/write) a 'doubleBuffered file', meaning that there are
* two files which get written to alternately.
* The files are named pathToFile/file1.fileExtension and
* pathToFile/file2.fileExtension
*
* This allows for some fault-tolerance when it comes to corrupted files, since
* you always have, at least, the other, albeit older file at your disposal.
*
* You create this with a path to a virtual file that should not exist, since it
* misses the numbers.
* Use the methods to retrieve a write-handle to the correct (older) file and a
* read-handle as well (newer).
*
* Throws an IOException if something happens it cannot handle any longer (both
* files are locked for write-access and you're requesting write-access for
* example).
*/
@Accessors(fluent = true)
public class DoubleBufferedFile {
@FunctionalInterface
public interface ConsumerWithIoException {
/**
* Performs this operation on the given argument.
*
* @param t the input argument
* @throws IOException if one occurs
*/
void accept(T t) throws IOException;
/**
* Returns a composed {@code Consumer} that performs, in sequence, this
* operation followed by the {@code after} operation. If performing either
* operation throws an exception, it is relayed to the caller of the composed
* operation. If performing this operation throws an exception, the
* {@code after} operation will not be performed.
*
* @param after the operation to perform after this operation
* @return a composed {@code Consumer} that performs in sequence this operation
* followed by the {@code after} operation
* @throws NullPointerException if {@code after} is null
* @throws IOException if one occurs
*/
default ConsumerWithIoException andThen(final ConsumerWithIoException after) throws IOException {
Objects.requireNonNull(after);
return (final T t) -> {
accept(t);
after.accept(t);
};
}
}
@Data
class DoubleBufferedFileData {
private final Path path;
private boolean exists;
private LocalDateTime modified;
private boolean readable;
private boolean writable;
DoubleBufferedFileData(final Path path) {
super();
this.path = path;
probe();
}
void delete() throws IOException {
if (Files.exists(path, LinkOption.NOFOLLOW_LINKS))
Files.delete(path);
}
void probe() {
exists = Files.exists(path, LinkOption.NOFOLLOW_LINKS);
writable = Files.isWritable(path);
readable = Files.isReadable(path);
modified = null;
if (exists)
try {
modified = DateUtils.fileTimeToUtcLocalDateTime(
Files.readAttributes(path, BasicFileAttributes.class).lastModifiedTime());
} catch (IOException e) {
modified = null;
readable = false;
writable = false;
}
}
DoubleBufferedFileData withCheckedWrite() throws IOException {
if (!writable)
throw new IOException(String.format("There is no write-access for the given path [%s].", path));
return this;
}
DoubleBufferedFileData withCheckedRead() throws IOException {
if (!readable)
throw new IOException(String.format("There is no read-access for the given path [%s].", path));
return this;
}
BufferedWriter getBufferedWriter() throws IOException {
return Files.newBufferedWriter(path, Charset.forName("UTF-8"));
}
}
protected DoubleBufferedFileData path1;
protected DoubleBufferedFileData path2;
public DoubleBufferedFile(final Path pathWithoutNumber, final String fileExtension) {
path1 = new DoubleBufferedFileData(Path.of(pathWithoutNumber.toString() + "1." + fileExtension));
path2 = new DoubleBufferedFileData(Path.of(pathWithoutNumber.toString() + "2." + fileExtension));
}
public void delete() throws IOException {
path1.delete();
path2.delete();
}
public boolean exists() {
return path1.exists() || path2.exists();
}
public LocalDateTime getNewestModifiedTime() {
if (path1.modified() == null && path2.modified() == null)
return null;
if (path1.modified() == null)
return path2.modified();
if (path2.modified() == null)
return path1.modified();
if (path1.modified().compareTo(path2.modified()) > 0)
return path1.modified();
return path2.modified();
}
public LocalDateTime getOldestModifiedTime() {
if (path1.modified() == null && path2.modified() == null)
return null;
if (path1.modified() == null)
return path2.modified();
if (path2.modified() == null)
return path1.modified();
if (path1.modified().compareTo(path2.modified()) <= 0)
return path1.modified();
return path2.modified();
}
private DoubleBufferedFileData getOldestForWriteAccess() throws IOException {
path1.probe();
path2.probe();
if (!path1.exists() && !path2.exists())
return path1;
if (!path1.exists())
return path1;
if (!path2.exists())
return path2;
if (!path1.writable() && !path2.writable())
throw new IOException("Both files are locked for write-access.");
if (!path1.writable())
throw new IOException("File1 is locked for write-access.");
if (!path2.writable())
throw new IOException("File2 is locked for write-access.");
if (path1.modified() == null || path2.modified() == null)
throw new IOException("Could not read the modified-date from one of the files.");
if (path1.modified().compareTo(path2.modified()) <= 0)
return path1;
return path2;
}
private DoubleBufferedFileData getNewestForReadAccess() throws IOException {
path1.probe();
path2.probe();
if (!path1.exists() && !path2.exists())
throw new IOException("There is no file to read from, because both files are missing.");
if (!path1.exists())
return path2.withCheckedRead();
if (!path2.exists())
return path1.withCheckedRead();
if (!path1.readable() && !path2.readable())
throw new IOException("Both files are locked for read-access.");
if (!path1.readable())
throw new IOException("File1 is locked for read-access.");
if (!path2.readable())
throw new IOException("File2 is locked for read-access.");
if (path1.modified() == null || path2.modified() == null)
throw new IOException("Could not read the modified-date from one of the files.");
if (path1.modified().compareTo(path2.modified()) > 0)
return path1;
return path2;
}
public void write(final ConsumerWithIoException writeContentDelegate) throws IOException {
DoubleBufferedFileData p = getOldestForWriteAccess();
if (p.exists())
Files.delete(p.path());
try (BufferedWriter writer = p.getBufferedWriter()) {
writeContentDelegate.accept(writer);
}
p.probe();
}
public String read() throws IOException {
DoubleBufferedFileData p = getNewestForReadAccess();
return Files.readString(p.path());
}
}