arex-agent-java is an Apache-2.0 licensed Java agent that attaches to any Java 8+ application through the JVM javaagent flag, weaves bytecode into existing code to record real live traffic, and replays that recorded data for mocking, testing and debugging, built for QA, test-automation and DevOps teams that maintain evolving Java services.

What it is

arex-agent-java is the agent component of AREX, described in its README as an open source testing framework built on real world data. The framework follows a deliberately plain principle: it uses the data an application already produces in production — database records, service payloads, cache items and similar — as the input for regression testing. The agent is shipped as an out-of-box agent file that can be attached to any application running Java 8 or above, and it dynamically weaves bytecode into existing code to record the real data of live traffic, which is then reused and replayed for mocking, testing and debugging purposes.

The concrete problem it solves is the cost of testing a system that keeps growing in complexity. As an application evolves, the effort required to test it thoroughly becomes tremendous, and hand-built fixtures and mock data fall out of step with production behaviour. AREX records from live traffic rather than from a proxy: the README states that instead of being a proxy like other similar frameworks, AREX sits in the background without awareness of the application and captures realistic data in live traffic, which means no intrusive code changes are required when integrating it into an existing Java application. It relies on the Java Instrument API and instruments a broad set of widely used libraries and frameworks.

Key capabilities

• Attaches as a JVM javaagent, so instrumentation is enabled without code changes to the target application.
• Uses the Java Instrument API to weave bytecode into running applications on Java 8 through 21.
• Records live traffic data including database records, service payloads and cache items for later replay.
• Replays recorded traffic for mocking, testing and debugging of new builds.
• Covers HTTP clients: Apache HttpClient 4.0+, OkHttp 3.0 to 4.11, Feign 9.0+, Spring OpenFeign, Spring RestTemplate, Spring WebClient 5.0+, ning/async-http-client and Elasticsearch Client 7.x+.
• Covers cache and Redis clients: Caffeine Cache, Guava Cache, Spring Cache, RedisTemplate, Jedis 2.10+ and 4+, Redisson 3.0+ and Lettuce 5.x and 6.x.
• Covers persistence and RPC: MyBatis 3.x, MyBatis-Plus, TkMyBatis, Hibernate 5.x, MongoDB 3.x and 4.x, Apache Dubbo 2.x and 3.x and Alibaba Dubbo 2.x.
• Supports Spring Boot 1.4+ and 2.x+, Servlet API 3+ and 5+, Spring Security 5.x, Apache Shiro 1.x, JCasbin 1.x, Auth0 jwt 3.x, jjwt 0.1+, Netty HTTP server 3.x and 4.x and Apollo Config 1.x and 2.x.

Who uses it and how

• QA and regression-testing teams that need repeatable test data for Java services without writing fixtures by hand.
• Development teams maintaining microservices built on Spring Boot, Dubbo or Spring Cloud HTTP and RPC stacks, where recorded payloads flow across service boundaries.
• DevOps and platform teams that attach the agent at deployment time through the javaagent JVM flag, keeping application artefacts unchanged.
• Applications running on Java 8 through 21, since the agent's supported JDK range matches the build range.
• Local debugging workflows, where the agent is run with its CLI in local mode instead of against a shared storage service.

Getting started

Download the latest binary from the project releases page, or build it with mvn clean install -DskipTests, which places arex-agent.jar in the arex-agent-jar folder. Run the application with java -javaagent:/path/to/arex-agent.jar -Darex.service.name=my-service-name -Darex.storage.service.host= -jar my-application.jar, or put the same settings such as arex.service.name and arex.storage.service.host in an arex.agent.conf file and pass it with -Darex.config.path.

How it compares

The facts provided name no paid products that this project replaces, and no competing tools by name; the README refers only generically to other similar frameworks that act as proxies. On that basis the project stands alone in this registry rather than in a documented replacement set. A comparison against named alternatives cannot be made from the material available.

When to use it — and when not to

A self-hoster must also run the separate AREX storage service, since the agent works alongside it and is configured with its host and port. Teams outside the JVM ecosystem should not pick it, as instrumentation support is entirely Java and library-specific, and the README's own support list is still marked as being added to, so coverage of a given framework version should be checked before adoption. Adopting the agent also means accepting an agent that instruments bytecode inside production applications, which is a heavier trust decision than attaching a read-only log shipper.

java -javaagent:/path/to/arex-agent.jar -Darex.service.name=my-service-name -Darex.storage.service.host=<storage.service.host:port> -jar my-application.jar

arex.service.name=my-service-name
arex.storage.service.host=<storage.service.host:port> 

java -javaagent:/path/to/arex-agent.jar -Darex.config.path=/path/to/arex.agent.conf -jar my-application.jar