Mastering Redis Replication in Java: How Redis‑Replicator Works and Extends

Overview

Redis‑replicator is a Java library that implements the Redis master‑slave synchronization protocol, allowing a client to act as a slave and receive data from a master. It also parses RDB files, splits and merges them, and parses AOF data for remote backup.

Supported Versions

Since version 2.3.0, the library supports all Redis versions from 2.6.x up to 4.0.x, including modules introduced in Redis 4.0.

Advantages and Disadvantages

Pros : a single 297 KB JAR with only a commons‑logging dependency, easy to embed in any project without jar conflicts.

Cons : only point‑to‑point synchronization; any additional features must be implemented manually, lacking an all‑in‑one solution.

Comparable Projects

redis‑rdb‑tool – parses RDB but does not support data synchronization.

x‑pipe – not lightweight; offers better HA and monitoring.

redis‑migrate‑tool – written in C, does not support Redis 4.0 modules but can sync clusters.

Quick Start Example

Replicator replicator = new RedisReplicator("127.0.0.1", 6379, Configuration.defaultSetting());
replicator.addRdbListener(new RdbListener.Adaptor() {
    @Override
    public void handle(Replicator replicator, KeyValuePair<?> kv) {
        System.out.println(kv);
    }
});
replicator.addCommandListener(new CommandListener() {
    @Override
    public void handle(Replicator replicator, Command command) {
        System.out.println(command);
    }
});
replicator.open();

Extending Commands

When a new Redis command appears that the library does not recognize, developers can add custom command classes, parsers, and listeners as shown below.

// Implement an unrecognized command
public class YourAppendCommand implements Command {
    public final String key;
    public final String value;
    public YourAppendCommand(String key, String value) {
        this.key = key;
        this.value = value;
    }
}

// Parser for the command
public class YourAppendParser implements CommandParser<YourAppendCommand> {
    @Override
    public YourAppendCommand parse(Object command) {
        return new YourAppendCommand(new String((byte) command[1], UTF_8),
                                    new String((byte) command[2], UTF_8));
    }
}

// Register parser and handle events
Replicator replicator = new RedisReplicator("127.0.0.1",6379,Configuration.defaultSetting());
replicator.addCommandParser(CommandName.name("APPEND"), new YourAppendParser());
replicator.addCommandListener(new CommandListener() {
    @Override
    public void handle(Replicator replicator, Command command) {
        if (command instanceof YourAppendCommand) {
            YourAppendCommand append = (YourAppendCommand) command;
            // your code here
        }
    }
});

Module Extension

Redis 4.0 introduced module support, allowing users to define custom commands and RDB storage formats. Module extensions require implementing the Module and ModuleParser interfaces and registering them via Replicator.addModuleParser.

Adoption

Companies and projects such as Dongfang Caifu, 51 Credit Card, and incubator‑rocketmq‑externals have used or plan to use Redis‑replicator.