Maven依賴版本號引起的血案

項目版本升級用了relase版本，可是發佈之後，依賴的jar包在編譯之後的lib目錄仍是舊版本。

緣由是snapshot版本每次發佈都會更新遠程和本地倉庫的文件，可是release版本會先在本地版本庫中檢查，若是存在就使用本地版本庫的，沒有才拉取遠程倉庫的。一樣的，release版本的代碼在遠程倉庫也是不會更新的。

那麼當發現relase版本的依賴有問題時該怎麼辦呢？

下面是能夠解決問題的幾個方案。

1. 將版本號升級。 新的版本號會在遠程倉庫生成新的文件，本地倉庫會從新下載。

2. 將本地和遠程倉庫中的舊版本刪除，從新打包上去。

3. 更改settings.xml，將updatePolicy改成always。

<profile>
    <id>nexus</id>
    <repositories>
        <repository>
            <id>central</id>
            <url>http://central</url>
            <releases>
                <enabled>true</enabled>
                <updatePolicy>always</updatePolicy>
            </releases>
            <snapshots>
                <enabled>true</enabled>
                <updatePolicy>always</updatePolicy>
            </snapshots>
        </repository>
    </repositories>
</profile>
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4. maven執行打包命令的時候加上 -U 命令強制下載全部依賴的jar包

$ mvn clean install
……
[INFO] --- maven-dependency-plugin:2.1:copy-dependencies (copy-dependencies) @ demo ---
[INFO] aopalliance-1.0.jar already exists in destination.
[INFO] c3p0-0.9.1.1.jar already exists in destination.
[INFO] cglib-3.2.5.jar already exists in destination.
[INFO] druid-1.0.31.jar already exists in destination.
[INFO] fastjson-1.2.31.jar already exists in destination.
[INFO] jackson-annotations-2.5.0.jar already exists in destination.
[INFO] jackson-core-2.5.0.jar already exists in destination.
[INFO] jackson-databind-2.5.0.jar already exists in destination.
[INFO] commons-beanutils-1.8.3.jar already exists in destination.
[INFO] commons-codec-1.2.jar already exists in destination.
[INFO] commons-collections-3.2.1.jar already exists in destination.
[INFO] commons-fileupload-1.3.1.jar already exists in destination.
[INFO] commons-httpclient-3.1.jar already exists in destination.
[INFO] commons-io-2.2.jar already exists in destination.
[INFO] commons-lang-2.5.jar already exists in destination.
[INFO] commons-logging-1.1.3.jar already exists in destination.
[INFO] jstl-1.2.jar already exists in destination.
[INFO] log4j-1.2.17.jar already exists in destination.
[INFO] mysql-connector-java-5.1.40.jar already exists in destination.
[INFO] thumbnailator-0.4.8.jar already exists in destination.
[INFO] ehcache-core-2.6.8.jar already exists in destination.
[INFO] ezmorph-1.0.6.jar already exists in destination.
[INFO] json-lib-2.4-jdk15.jar already exists in destination.
[INFO] ant-1.9.6.jar already exists in destination.
[INFO] ant-launcher-1.9.6.jar already exists in destination.
[INFO] httpclient-4.5.7.jar already exists in destination.
[INFO] httpcore-4.4.11.jar already exists in destination.
[INFO] shiro-core-1.2.2.jar already exists in destination.
[INFO] shiro-web-1.2.2.jar already exists in destination.
[INFO] aspectjweaver-1.8.9.jar already exists in destination.
[INFO] mybatis-3.2.3.jar already exists in destination.
[INFO] mybatis-spring-1.3.1.jar already exists in destination.
[INFO] asm-5.2.jar already exists in destination.
[INFO] lombok-1.16.16.jar already exists in destination.
[INFO] quartz-2.2.1.jar already exists in destination.
[INFO] slf4j-api-1.7.20.jar already exists in destination.
[INFO] slf4j-log4j12-1.7.20.jar already exists in destination.
[INFO] spring-aop-4.2.5.RELEASE.jar already exists in destination.
[INFO] spring-beans-4.2.5.RELEASE.jar already exists in destination.
[INFO] spring-context-4.2.5.RELEASE.jar already exists in destination.
[INFO] spring-context-support-4.2.5.RELEASE.jar already exists in destination.
[INFO] spring-core-4.2.5.RELEASE.jar already exists in destination.
[INFO] spring-expression-4.2.5.RELEASE.jar already exists in destination.
[INFO] spring-jdbc-4.2.5.RELEASE.jar already exists in destination.
[INFO] spring-test-4.2.5.RELEASE.jar already exists in destination.
[INFO] spring-tx-4.2.5.RELEASE.jar already exists in destination.
[INFO] spring-web-4.2.5.RELEASE.jar already exists in destination.
[INFO] spring-webmvc-4.2.5.RELEASE.jar already exists in destination.
[INFO] standard-1.1.2.jar already exists in destination.
……
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