为什么 maven-enforcer-plugin 在 travis-ci.org 上检测到 maven 3.2.5 运行和 3.1.1？

Question

我有一个项目 document-scanner-aggregator which runs fine locally when run with Maven 3.1.1, i.e. ~/apache-maven-3.1.1/bin/mvn clean install, but doesn't on travis-ci.org，它在其中检测到 Maven 3.2.5，这可疑地是由 travis-ci.org 提供的版本。然而，它不应该这样做，因为运行构建的 Maven 版本应该被强制执行，对吗？

失败是

[WARNING] Rule 0: org.apache.maven.plugins.enforcer.RequireMavenVersion failed with message:
Detected Maven Version: 3.2.5 is not in the allowed range (,3.2).
...
[ERROR] Failed to execute goal org.apache.maven.plugins:maven-enforcer-plugin:1.4:enforce (enforce-versions) on project javaocr-parent: Some Enforcer rules have failed. Look above for specific messages explaining why the rule failed. -> [Help 1]

配置为

<plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-enforcer-plugin</artifactId>
    <version>1.4</version>
    <executions>
        <execution>
            <id>enforce-versions</id>
            <goals>
                <goal>enforce</goal>
            </goals>
            <configuration>
                <rules>
                    <requireMavenVersion>
                        <!--different rules for different issues-->
                        <!--3.3.x causes `java.lang.NoClassDefFoundError: org/eclipse/aether/spi/connector/Transfer$State` which is caused by certain maven versions, see https://cwiki.apache.org/confluence/display/MAVEN/AetherClassNotFound for details-->
                        <version>(,3.3)</version>
                        <!--3.2.x causes `No implementation for org.eclipse.aether.connector.wagon.WagonConfigurator was bound.`-->
                        <version>(,3.2)</version>
                    </requireMavenVersion>
                </rules>
            </configuration>
        </execution>
    </executions>
</plugin>

在 javaocr.

.travis.yml是

language: java
install:
- wget http://mirrors.ae-online.de/apache/maven/maven-3/3.1.1/binaries/apache-maven-3.1.1-bin.tar.gz && tar xf apache-maven-3.1.1-bin.tar.gz
- apache-maven-3.1.1/bin/mvn clean install

Answer 1

您误解了 Enforcer Plugin 的作用：

The Enforcer plugin provides goals to control certain environmental constraints such as Maven version, JDK version and OS family along with many more standard rules and user created rules.

它的目标不是变魔术来验证配置的规则，而是当其中一条规则未被验证时构建失败。换句话说，它会检查已配置规则的列表，这样如果其中一个未被验证，构建就无法继续。原因是如果构建的先决条件之一不满足，还不如趁早失败。

在您的情况下，requireMavenVersion rule enforces that the build is done with a Maven version strictly lower than 3.2. It will not spawn a new Maven instance if you're running the build with a Maven 3.2.5 so that the rule is verified; which version should it use, and where would it get it? Instead, it detects that the build is done with a Maven version that is disallowed, and fails accordingly. Since the Travis build is configured to use Maven 3.2.5预计会失败，您需要为 Travis 构建安装低于 3.2 的 Maven 版本。

要在 Travis CI 上使用不同的 Maven 版本，例如 3.1.1，您可以在 .travis.yml 中添加以下内容：

before_install:
  - wget http://mirrors.ae-online.de/apache/maven/maven-3/3.1.1/binaries/apache-maven-3.1.1-bin.tar.gz
  - tar xf apache-maven-3.1.1-bin.tar.gz
  - export M2_HOME=$PWD/apache-maven-3.1.1
  - export PATH=$M2_HOME/bin:$PATH 

install: /bin/true

script: mvn clean install

作为旁注，您当前的

配置

<requireMavenVersion>
    <version>(,3.3)</version>
    <version>(,3.2)</version>
</requireMavenVersion>

完全等同于

<requireMavenVersion>
    <version>(,3.2)</version>
</requireMavenVersion>

严格匹配3.2以下版本的范围(,3.2)means。因此，要求它也严格低于 3.3 是多余的（因为 3.2 在 3.3 之前）。

为什么 maven-enforcer-plugin 在 travis-ci.org 上检测到 maven 3.2.5 运行 和 3.1.1？

Why does maven-enforcer-plugin detect maven 3.2.5 when it's run with 3.1.1 on travis-ci.org?

java

version

maven

maven-enforcer-plugin

travis-ci

为什么 maven-enforcer-plugin 在 travis-ci.org 上检测到 maven 3.2.5 运行和 3.1.1？