# 6 Causes of Maven "Could not resolve dependencies" Build Failures and How to Fix Them with settings.xml ## If a build that worked yesterday suddenly broke You probably landed here after copying that red console line—`Failed to execute goal ... Could not resolve dependencies`—straight into a search engine. Short version: that message only reports the *result* ("couldn't fetch a dependency"). **The real cause is hiding a few lines below it.** This happens a lot on locked-down networks with an internal Nexus/Artifactory, a corporate proxy, and a private CA—even when you didn't change a single line of code. This post is **Maven-only**. We'll pinpoint and recover from the failure in about five minutes using just the mirror/proxy/server tags in `settings.xml`, the `~/.m2` layout, and a few `mvn` flags. > Scope: Maven CLI, settings.xml, and the local repository (.m2). We don't cover IDE-embedded builds or other build tools. ## Read the error properly first — find the real cause with `mvn -X` The most common mistake is staring at the last `Failed to execute goal` line and giving up. That line always looks the same. What you actually need is the **`Caused by` or `Could not transfer artifact` line above it**. Turn on debug logging and run it again. ```bash # 전체 통신/저장소 접근 로그까지 출력 mvn -X clean install ``` With `mvn -X`, Maven prints which repository it tried, which URL it hit, and why it failed. Which of the keywords below shows up is your branch point. | Phrase in the log | Mapped cause | One-line meaning | | --- | --- | --- | | `Could not transfer artifact ... Connection refused / timed out` | ② Proxy/firewall / ① Wrong mirror URL | Can't reach the repository at all | | `PKIX path building failed` / `unable to find valid certification path` | ③ Private-CA SSL failure | TLS handshake rejected | | `Could not find artifact ...:jar:1.2.3 in central (404)` | ⑤ Bad version / SNAPSHOT never deployed | Reached the repo, but that version isn't there | | `Failed to read artifact descriptor` / mention of `.lastUpdated` | ④ Corrupted local cache | Stuck on a broken cache entry | | `Cannot access ... in offline mode` | ⑥ Misused `-o` flag | Offline mode, but a new dependency is required | If you suspect a conflict, start with the dependency tree. ```bash # 전체 의존성 트리 mvn dependency:tree # 특정 라이브러리가 어디서 끌려오는지, 버전 충돌이 어떻게 정리됐는지 추적 mvn dependency:tree -Dverbose -Dincludes=org.springframework:spring-core ``` ## Cause ① Misconfigured internal Nexus/Artifactory mirror in settings.xml If you see `Connection refused` and the URL is your internal Nexus (`nexus.company.co.kr`) rather than Maven Central, it's almost certainly a mirror misconfiguration in `settings.xml`. Typical triggers: Nexus is down for maintenance, the URL changed, or credentials expired. Open `~/.m2/settings.xml` and check what `` points at. Mirroring only `central` vs. mirroring `*` (everything) behaves completely differently. ```xml company-nexus ${env.NEXUS_USER} ${env.NEXUS_PASS} company-nexus Company Nexus https://nexus.example.co.kr/repository/maven-public/ * ``` The key point: **the `` id and the `` id must match exactly**, or the auth header never gets attached. If you get 401/403, suspect an id mismatch or an expired password first. ## Cause ② Corporate proxy/firewall blocking Maven Central If `` is only `central`, so Maven has to go out to Maven Central directly, and you get `Connection timed out`, the corporate firewall is likely blocking you because you didn't go through the proxy. Diagnose the block first. ```bash # 프록시 없이 직접 닿는지 확인 (timeout이면 차단) curl -I https://repo.maven.apache.org/maven2/ # 프록시를 거치면 되는지 확인 curl -I -x http://proxy.example.co.kr:8080 https://repo.maven.apache.org/maven2/ ``` If you get a 200 through the proxy, register the proxy in settings.xml. ```xml company-proxy true http proxy.example.co.kr 8080 proxyUser proxyPass nexus.example.co.kr|localhost|127.0.0.1 ``` If you omit ``, Maven will try to send even internal Nexus traffic through the external proxy and fail again. Also note that Maven Central blocks HTTP and **allows HTTPS only**, so any leftover `http://...central` URLs in old configs need to be changed to `https://`. ## Cause ③ PKIX/SSL handshake failure from a private CA If you see `PKIX path building failed` or `unable to find valid certification path to requested target`, it's an SSL trust problem. The internal proxy/Nexus presents a cert signed by a private CA that isn't in the JDK trust store (`cacerts`), so the handshake is rejected. This is the fastest-growing case as more teams adopt zero-trust and air-gapped networks. The core fix is importing the private CA certificate into the JDK. ```bash # 사내 CA 인증서를 JDK 신뢰 저장소에 등록 keytool -import -trustcacerts -alias company-ca \ -file company-ca.crt \ -keystore "$JAVA_HOME/lib/security/cacerts" \ -storepass changeit ``` > Certificate extraction for PKIX errors, chain assembly, and JDK-version-specific paths are covered in a separate **PKIX troubleshooting post**. Here we only hit the essentials. ## Cause ④ Corrupted local repository cache (~/.m2/repository) If you can reach the repository fine but one specific library keeps failing and the log mentions `.lastUpdated`, a download was interrupted and the cache is corrupted. Maven leaves a failure marker (`*.lastUpdated`) and won't retry for a while. Before wiping all of `.m2`, **clear just the failure markers**—it's much faster. ```bash # 1) 실패 마커만 삭제 (가장 가볍고 안전) find ~/.m2 -name "*.lastUpdated" -delete # 2) 특정 의존성만 정리 후 재다운로드 mvn dependency:purge-local-repository -Dinclude=org.springframework:spring-core # 3) 그래도 안 되면 강제 업데이트로 재시도 mvn -U clean install ``` A full `rm -rf ~/.m2/repository` is a last resort. You'll re-download several GB, which is especially wasteful in CI. ## Cause ⑤ Version conflict, nonexistent version, or undeployed SNAPSHOT If you clearly see a **404** like `Could not find artifact ...:jar:1.2.3 in central (404)`, this is not a connectivity problem. You reached the repository; that coordinate (groupId:artifactId:version) simply doesn't exist. The three usual causes: - A typo or a version that doesn't exist (e.g. a nonexistent `1.2.3`) - A colleague ran `mvn install` locally but never `deploy`ed the **SNAPSHOT to Nexus** - A version conflict from a transitive dependency pulled in by another library ```bash # 어떤 라이브러리가 문제의 버전을 끌고 오는지 정확히 추적 mvn dependency:tree -Dverbose -Dincludes=com.example:problem-lib ``` Distinguishing `Connection refused` (②) from `404` (⑤) is the key. The former means "couldn't open the door"; the latter means "the door opened, but the item isn't there." ## Cause ⑥ Misused `-U` / `-o` flags Finally, flags trip people up more often than you'd think. - `-o` (offline): Offline mode. Maven can't fetch new dependencies; if they aren't in the cache you get `Cannot access ... in offline mode`. **Don't leave it on out of habit.** - `-U` (update): Forces SNAPSHOTs to be re-fetched. Useful in CI when you need the latest SNAPSHOT, but turning it on for every build adds unnecessary network calls and intermittent failures. ```bash # SNAPSHOT 최신본이 필요할 때만 mvn -U clean install ``` ## 5-minute diagnostic flowchart Walk the error text down this list in order and you'll land on your case. 1. **Does the log contain `PKIX` or `valid certification path`?** → Yes: cause ③ (import the certificate) 2. **Is there a `404` or `Could not find artifact`?** → Yes: cause ⑤ (check version / SNAPSHOT) 3. **`Connection refused / timed out` and the failing URL is internal Nexus?** → Yes: cause ① (check mirror and auth) 4. **`Connection timed out` and the URL is Maven Central?** → Yes: cause ② (configure the proxy) 5. **Is `.lastUpdated` mentioned, or do only one or two artifacts fail?** → Yes: cause ④ (`find ~/.m2 -name "*.lastUpdated" -delete`) 6. **Is there an `offline mode` message?** → Yes: cause ⑥ (remove `-o`) If these six steps don't catch it, temporarily disable settings.xml and run once in a vanilla environment to isolate environment variables. ## What I've learned in practice In my experience, 80% of "new hire's laptop won't build" failures on air-gapped projects were causes ① and ③. Once teams started shipping a known-good `settings.xml` plus the internal CA cert via an onboarding script, the "the build doesn't work" tickets almost disappeared. **Version-controlling a standard settings.xml** is far cheaper than having every individual debug it. ## Recurrence-prevention checklist - Version-control a team-standard `settings.xml`; keep passwords in environment variables - Cache `~/.m2/repository` in CI (GitHub Actions/Jenkins), but exclude `*.lastUpdated` from the cache key - Use `-U` only on jobs that must refresh SNAPSHOTs; leave it off for regular builds - Standardize every repository URL on `https://` (Maven Central no longer allows HTTP) - Bake the internal CA certificate into the JDK image / onboarding script ## FAQ **Q. Are `Could not resolve dependencies` and `Failed to execute goal` different errors?** A. They're effectively one package. `Failed to execute goal` is the outer message that a plugin stopped; `Could not resolve dependencies` is the direct cause. Always look one level down at the `Caused by` or `Could not transfer artifact` line for the real reason. **Q. Is it okay to delete all of `~/.m2/repository`?** A. Yes, but it's a last resort. First delete only the failure markers with `find ~/.m2 -name "*.lastUpdated" -delete`, or purge just the bad dependency with `mvn dependency:purge-local-repository`. A full wipe forces a multi-GB re-download and is especially inefficient in CI. **Q. How do I tell a 404 from Connection refused?** A. A 404 means "reached the repository, but that version isn't there" (cause ⑤). Connection refused/timed out means "couldn't reach the repository at all" (causes ① and ②). For 404, check the version and whether the SNAPSHOT was deployed; for refused, check the mirror URL and proxy settings.

#Could not resolve dependencies

6 Causes of Maven "Could not resolve dependencies" Build Failures and How to Fix Them with settings.xml