Using JaCoCo to Analyze Online Java Code Coverage and Eliminate Zombie Code

As business systems evolve rapidly, large amounts of legacy or "zombie" code often remain in production, increasing maintenance costs and hindering development efficiency. By leveraging JaCoCo probes, teams can obtain precise runtime coverage data, pinpoint unused functionalities, and safely decommission or delete dead code.

The proposed solution consists of several concrete measures:

4.1 Add JaCoCo Ant Dependency

<dependency>
    <groupId>org.jacoco</groupId>
    <artifactId>org.jacoco.ant</artifactId>
    <version>0.8.3</version>
</dependency>
<dependency>
    <groupId>org.apache.ant</groupId>
    <artifactId>ant</artifactId>
    <version>1.9.9</version>
</dependency>

4.2 Expose a REST Dump Endpoint

@RestController
@RequestMapping("/coverage")
public class CoverageController {
    @PostMapping("dump")
    @NoCheckMenuPermission
    public Result<Boolean> dumpCoverageFile() {
        DumpTask dumpTask = new DumpTask();
        // dump file location
        dumpTask.setDestfile(new File("/export/Data/coverage/code-cover.exec"));
        // append on multiple dumps
        dumpTask.setAppend(true);
        // choose an idle port
        dumpTask.setPort(8840);
        // default to localhost
        dumpTask.setAddress("127.0.0.1");
        dumpTask.execute();
        return Result.succeed(true);
    }
}

4.3 Embed JaCoCo Agent Decompress the agent JAR to avoid involving operations personnel: jar -xvf $BASEDIR/lib/org.jacoco.agent-0.8.3.jar Add the javaagent parameter to the startup script:

-javaagent:$BASEDIR/bin/jacocoagent.jar=includes=com.jdwl.*,output=tcpserver,port=8840,address=127.0.0.1 -Xverify:none

4.4 Reserve JDOS Resources (custom export directory) – see JDOS documentation for details.

4.5 Clean Export Directory

#! /bin/bash
ls -lh /export | awk 'NR >1 {print}' | awk '{if ($9 != "Data") print $9}' | xargs -i /bin/rm -rf /export/{} > /dev/null 2>&1
ls -lh /export/Data | awk 'NR >1 {print}' | awk '{if ($9 != "jdos.jd.com" && $9 != "coverage") print $9}' | xargs -i /bin/rm -rf /export/Data/{} > /dev/null 2>&1

4.6 Download and Analyze Coverage File – after dumping, retrieve /export/Data/coverage/code-cover.exec via bastion host and use IDE (e.g., IntelliJ) to view coverage data.

The practical outcomes are significant: delivery cycle shortened from ~15 to ~12 days, development stage duration reduced by ~31%, duplicate code blocks decreased from 31 to 27, per‑person demand throughput rose from 1.5 to 2.5, and unit test line coverage improved from 51.33% to 52.28%.

References

1. JaCoCo Documentation – https://www.jacoco.org/jacoco/trunk/doc/index.html 2. Java Agent Guide – https://www.cnblogs.com/rickiyang/p/11368932.html 3. Jacoco Coverage Practice – https://www.cnblogs.com/ccoder/p/15369719.html#4946710 4. Bytecode Manipulation with ASM/Javassist – https://newrelic.com/blog/best-practices/java-performance-monitoring