JarCastingOverview log-file
A Java library for working with append-only files (also known as the log files). The main methods of such files are:
- append - for appending arbitary data;
- load - for fully file read from the begining till the end.
Usage example
import java.nio.file.Paths;
import com.xxlabaza.utils.log.file.Config;
import com.xxlabaza.utils.log.file.LogFile;
import io.appulse.utils.Bytes;
import io.appulse.utils.HexUtil;
// let's instantiate a log file:
Config config = Config.builder()
.path(Paths.get("./my.log"))
.blockBufferSizeBytes(32)
.forceFlush(false)
.build();
LogFile logFile = new LogFile(config);
// than, write some data to log file
Bytes record = Bytes.resizableArray()
.write4B(42);
logFile.append(record);
// now, read all records from the file and print them to STDOUT
logFile.load((buffer, position) -> {
String dump = HexUtil.prettyHexDump(buffer);
System.out.println(dump);
return true; // true - continue reading, false - stop reading
});
// flush and close the file
logFile.close();
Under the hood
A log file has the next structure:
| log file structure | ||||
|---|---|---|---|---|
| file header | blocks | |||
| version | block size | block 0 | ... | block n |
| 1 byte | 4 bytes | blocks count * block size | ||
File header
File header's description:
- version
- The file's format version, which tells the features set is used in the file.
- block size
- The size of a block buffer, in bytes, which is used in the current file.
Block
Each block consist of the records set:
| block | ||
|---|---|---|
| record 1 | ... | record n |
The records have the following structure:
| record | |||
|---|---|---|---|
| checksum | type | body length | body |
| 4 bytes | 1 byte | 2 bytes | body length |
- checksum
- The checksum value, which is calculated from type, body length and body values.
- type
-
One of the record's types:
- FULL - the data is presented entirely in this record;
- FIRST - it is the first chunk of data;
- MIDDLE - one of the middle parts of data;
- LAST - the last piece of data.
- body length
- The length of the next body section, in bytes.
- body
- the record's payload.