java - 为什么 Maven 总是要下载一堆东西

Question

按照 Maven getting started 上的指南开始使用 Maven ，创建他的第一个 my-app 项目，其中包含一个空目录，并发出命令来创建一个 Maven 项目:

mvn -B archetype:generate \
  -DarchetypeGroupId=org.apache.maven.archetypes \
  -DgroupId=com.mycompany.app \
  -DartifactId=my-app

现在为他下载了以下 hell 般的东西:

[INFO] Scanning for projects...
[INFO] Downloading: https://repo.maven.apache.org/maven2/org/apache/maven/plugins/maven-archetype-plugin/maven-metadata.xml
[INFO] Downloaded: https://repo.maven.apache.org/maven2/org/apache/maven/plugins/maven-archetype-plugin/maven-metadata.xml (759 B at 0.8 KB/sec)
[INFO] Downloading: https://repo.maven.apache.org/maven2/org/apache/maven/plugins/maven-archetype-plugin/2.4/maven-archetype-plugin-2.4.pom
[INFO] Downloaded: https://repo.maven.apache.org/maven2/org/apache/maven/plugins/maven-archetype-plugin/2.4/maven-archetype-plugin-2.4.pom (9 KB at 52.2 KB/sec)
[INFO] Downloading: https://repo.maven.apache.org/maven2/org/apache/maven/archetype/maven-archetype/2.4/maven-archetype-2.4.pom
[INFO] Downloaded: https://repo.maven.apache.org/maven2/org/apache/maven/archetype/maven-archetype/2.4/maven-archetype-2.4.pom (13 KB at 62.0 KB/sec)
[INFO] Downloading: https://repo.maven.apache.org/maven2/org/apache/maven/plugins/maven-archetype-plugin/2.4/maven-archetype-plugin-2.4.jar
[INFO] Downloaded: https://repo.maven.apache.org/maven2/org/apache/maven/plugins/maven-archetype-plugin/2.4/maven-archetype-plugin-2.4.jar (92 KB at 74.5 KB/sec)
[INFO]                                                                         
[INFO] ------------------------------------------------------------------------
[INFO] Building Maven Stub Project (No POM) 1
[INFO] ------------------------------------------------------------------------
[INFO] 
[INFO] >>> maven-archetype-plugin:2.4:generate (default-cli) > generate-sources @ standalone-pom >>>
[INFO] 
[INFO] <<< maven-archetype-plugin:2.4:generate (default-cli) < generate-sources @ standalone-pom <<<
[INFO] 
[INFO] --- maven-archetype-plugin:2.4:generate (default-cli) @ standalone-pom ---
[INFO] Downloading: https://repo.maven.apache.org/maven2/org/apache/maven/archetype/archetype-catalog/2.4/archetype-catalog-2.4.pom
[INFO] Downloaded: https://repo.maven.apache.org/maven2/org/apache/maven/archetype/archetype-catalog/2.4/archetype-catalog-2.4.pom (2 KB at 11.1 KB/sec)
[INFO] Downloading: https://repo.maven.apache.org/maven2/org/apache/maven/archetype/archetype-models/2.4/archetype-models-2.4.pom
[INFO] Downloaded: https://repo.maven.apache.org/maven2/org/apache/maven/archetype/archetype-models/2.4/archetype-models-2.4.pom (3 KB at 12.8 KB/sec)
[INFO] Downloading: https://repo.maven.apache.org/maven2/org/apache/maven/archetype/archetype-descriptor/2.4/archetype-descriptor-2.4.pom
[INFO] Downloaded: https://repo.maven.apache.org/maven2/org/apache/maven/archetype/archetype-descriptor/2.4/archetype-descriptor-2.4.pom (2 KB at 7.9 KB/sec)
[INFO] Downloading: https://repo.maven.apache.org/maven2/org/apache/maven/archetype/archetype-registry/2.4/archetype-registry-2.4.pom
[INFO] Downloaded: https://repo.maven.apache.org/maven2/org/apache/maven/archetype/archetype-registry/2.4/archetype-registry-2.4.pom (2 KB at 7.2 KB/sec)
[INFO] Downloading: https://repo.maven.apache.org/maven2/org/apache/maven/archetype/archetype-common/2.4/archetype-common-2.4.pom
[INFO] Downloaded: https://repo.maven.apache.org/maven2/org/apache/maven/archetype/archetype-common/2.4/archetype-common-2.4.pom (16 KB at 42.3 KB/sec)
[INFO] Downloading: https://repo.maven.apache.org/maven2/net/sourceforge/jchardet/jchardet/1.0/jchardet-1.0.pom
[INFO] Downloaded: https://repo.maven.apache.org/maven2/net/sourceforge/jchardet/jchardet/1.0/jchardet-1.0.pom (2 KB at 7.1 KB/sec)
[INFO] Downloading: https://repo.maven.apache.org/maven2/org/hamcrest/hamcrest-core/1.3/hamcrest-core-1.3.pom
[INFO] Downloaded: https://repo.maven.apache.org/maven2/org/hamcrest/hamcrest-core/1.3/hamcrest-core-1.3.pom (0 B at 0.0 KB/sec)
[INFO] Downloading: https://repo.maven.apache.org/maven2/org/codehaus/plexus/plexus-velocity/1.1.8/plexus-velocity-1.1.8.pom
[INFO] Downloaded: https://repo.maven.apache.org/maven2/org/codehaus/plexus/plexus-velocity/1.1.8/plexus-velocity-1.1.8.pom (2 KB at 10.0 KB/sec)
[INFO] Downloading: https://repo.maven.apache.org/maven2/org/codehaus/plexus/plexus-component-api/1.0-alpha-16/plexus-component-api-1.0-alpha-16.pom
[INFO] Downloaded: https://repo.maven.apache.org/maven2/org/codehaus/plexus/plexus-component-api/1.0-alpha-16/plexus-component-api-1.0-alpha-16.pom (3 KB at 11.9 KB/sec)
[INFO] Downloading: https://repo.maven.apache.org/maven2/org/codehaus/plexus/plexus-containers/1.0-alpha-16/plexus-containers-1.0-alpha-16.pom
[INFO] Downloaded: https://repo.maven.apache.org/maven2/org/codehaus/plexus/plexus-containers/1.0-alpha-16/plexus-containers-1.0-alpha-16.pom (2 KB at 9.7 KB/sec)
[INFO] Downloading: https://repo.maven.apache.org/maven2/org/codehaus/groovy/groovy/1.8.3/groovy-1.8.3.pom
[INFO] Downloaded: https://repo.maven.apache.org/maven2/org/codehaus/groovy/groovy/1.8.3/groovy-1.8.3.pom (32 KB at 65.8 KB/sec)
[INFO] Downloading: https://repo.maven.apache.org/maven2/antlr/antlr/2.7.7/antlr-2.7.7.pom
[INFO] Downloaded: https://repo.maven.apache.org/maven2/antlr/antlr/2.7.7/antlr-2.7.7.pom (0 B at 0.0 KB/sec)
[INFO] Downloading: https://repo.maven.apache.org/maven2/asm/asm/3.2/asm-3.2.pom
[INFO] Downloaded: https://repo.maven.apache.org/maven2/asm/asm/3.2/asm-3.2.pom (264 B at 1.0 KB/sec)
[INFO] Downloading: https://repo.maven.apache.org/maven2/asm/asm-parent/3.2/asm-parent-3.2.pom
[INFO] Downloaded: https://repo.maven.apache.org/maven2/asm/asm-parent/3.2/asm-parent-3.2.pom (5 KB at 18.2 KB/sec)
[INFO] Downloading: https://repo.maven.apache.org/maven2/asm/asm-commons/3.2/asm-commons-3.2.pom
[INFO] Downloaded: https://repo.maven.apache.org/maven2/asm/asm-commons/3.2/asm-commons-3.2.pom (415 B at 2.1 KB/sec)
[INFO] Downloading: https://repo.maven.apache.org/maven2/asm/asm-tree/3.2/asm-tree-3.2.pom
[INFO] Downloaded: https://repo.maven.apache.org/maven2/asm/asm-tree/3.2/asm-tree-3.2.pom (404 B at 2.2 KB/sec)
[INFO] Downloading: https://repo.maven.apache.org/maven2/asm/asm-util/3.2/asm-util-3.2.pom
[INFO] Downloaded: https://repo.maven.apache.org/maven2/asm/asm-util/3.2/asm-util-3.2.pom (409 B at 2.2 KB/sec)
[INFO] Downloading: https://repo.maven.apache.org/maven2/asm/asm-analysis/3.2/asm-analysis-3.2.pom
[INFO] Downloaded: https://repo.maven.apache.org/maven2/asm/asm-analysis/3.2/asm-analysis-3.2.pom (417 B at 2.2 KB/sec)
[INFO] Downloading: https://repo.maven.apache.org/maven2/org/beanshell/bsh/2.0b4/bsh-2.0b4.pom
[INFO] Downloaded: https://repo.maven.apache.org/maven2/org/beanshell/bsh/2.0b4/bsh-2.0b4.pom (2 KB at 5.8 KB/sec)
[INFO] Downloading: https://repo.maven.apache.org/maven2/org/beanshell/beanshell/2.0b4/beanshell-2.0b4.pom
[INFO] Downloaded: https://repo.maven.apache.org/maven2/org/beanshell/beanshell/2.0b4/beanshell-2.0b4.pom (2 KB at 5.1 KB/sec)
[INFO] Downloading: https://repo.maven.apache.org/maven2/org/apache/maven/shared/maven-script-interpreter/1.0/maven-script-interpreter-1.0.pom
[INFO] Downloaded: https://repo.maven.apache.org/maven2/org/apache/maven/shared/maven-script-interpreter/1.0/maven-script-interpreter-1.0.pom (4 KB at 14.6 KB/sec)
[INFO] Downloading: https://repo.maven.apache.org/maven2/org/apache/ant/ant/1.8.1/ant-1.8.1.pom
[INFO] Downloaded: https://repo.maven.apache.org/maven2/org/apache/ant/ant/1.8.1/ant-1.8.1.pom (9 KB at 16.7 KB/sec)
[INFO] Downloading: https://repo.maven.apache.org/maven2/org/apache/ant/ant-parent/1.8.1/ant-parent-1.8.1.pom
[INFO] Downloaded: https://repo.maven.apache.org/maven2/org/apache/ant/ant-parent/1.8.1/ant-parent-1.8.1.pom (5 KB at 23.5 KB/sec)
[INFO] Downloading: https://repo.maven.apache.org/maven2/org/apache/maven/archetype/archetype-descriptor/2.4/archetype-descriptor-2.4.jar
[INFO] Downloading: https://repo.maven.apache.org/maven2/org/apache/maven/archetype/archetype-catalog/2.4/archetype-catalog-2.4.jar
[INFO] Downloading: https://repo.maven.apache.org/maven2/org/apache/maven/archetype/archetype-common/2.4/archetype-common-2.4.jar
[INFO] Downloading: https://repo.maven.apache.org/maven2/org/apache/maven/archetype/archetype-registry/2.4/archetype-registry-2.4.jar
[INFO] Downloading: https://repo.maven.apache.org/maven2/net/sourceforge/jchardet/jchardet/1.0/jchardet-1.0.jar
[INFO] Downloaded: https://repo.maven.apache.org/maven2/org/apache/maven/archetype/archetype-catalog/2.4/archetype-catalog-2.4.jar (19 KB at 88.9 KB/sec)
[INFO] Downloading: https://repo.maven.apache.org/maven2/dom4j/dom4j/1.6.1/dom4j-1.6.1.jar
[INFO] Downloaded: https://repo.maven.apache.org/maven2/dom4j/dom4j/1.6.1/dom4j-1.6.1.jar (0 B at 0.0 KB/sec)
[INFO] Downloading: https://repo.maven.apache.org/maven2/org/codehaus/plexus/plexus-velocity/1.1.8/plexus-velocity-1.1.8.jar
[INFO] Downloaded: https://repo.maven.apache.org/maven2/org/codehaus/plexus/plexus-velocity/1.1.8/plexus-velocity-1.1.8.jar (8 KB at 13.8 KB/sec)
[INFO] Downloading: https://repo.maven.apache.org/maven2/org/codehaus/plexus/plexus-interactivity-api/1.0-alpha-6/plexus-interactivity-api-1.0-alpha-6.jar
[INFO] Downloaded: https://repo.maven.apache.org/maven2/org/apache/maven/archetype/archetype-registry/2.4/archetype-registry-2.4.jar (17 KB at 28.0 KB/sec)
[INFO] Downloading: https://repo.maven.apache.org/maven2/org/codehaus/plexus/plexus-component-api/1.0-alpha-16/plexus-component-api-1.0-alpha-16.jar
[INFO] Downloaded: https://repo.maven.apache.org/maven2/org/codehaus/plexus/plexus-interactivity-api/1.0-alpha-6/plexus-interactivity-api-1.0-alpha-6.jar (12 KB at 14.6 KB/sec)
[INFO] Downloading: https://repo.maven.apache.org/maven2/org/codehaus/plexus/plexus-classworlds/1.2-alpha-7/plexus-classworlds-1.2-alpha-7.jar
[INFO] Downloaded: https://repo.maven.apache.org/maven2/org/codehaus/plexus/plexus-component-api/1.0-alpha-16/plexus-component-api-1.0-alpha-16.jar (33 KB at 35.4 KB/sec)
[INFO] Downloading: https://repo.maven.apache.org/maven2/org/codehaus/groovy/groovy/1.8.3/groovy-1.8.3.jar
[INFO] Downloaded: https://repo.maven.apache.org/maven2/net/sourceforge/jchardet/jchardet/1.0/jchardet-1.0.jar (26 KB at 26.5 KB/sec)
[INFO] Downloading: https://repo.maven.apache.org/maven2/antlr/antlr/2.7.7/antlr-2.7.7.jar
[INFO] Downloaded: https://repo.maven.apache.org/maven2/org/apache/maven/archetype/archetype-descriptor/2.4/archetype-descriptor-2.4.jar (23 KB at 21.0 KB/sec)
[INFO] Downloading: https://repo.maven.apache.org/maven2/asm/asm/3.2/asm-3.2.jar
[INFO] Downloaded: https://repo.maven.apache.org/maven2/antlr/antlr/2.7.7/antlr-2.7.7.jar (0 B at 0.0 KB/sec)
[INFO] Downloading: https://repo.maven.apache.org/maven2/asm/asm-commons/3.2/asm-commons-3.2.jar
[INFO] Downloaded: https://repo.maven.apache.org/maven2/asm/asm-commons/3.2/asm-commons-3.2.jar (33 KB at 23.5 KB/sec)
[INFO] Downloading: https://repo.maven.apache.org/maven2/asm/asm-util/3.2/asm-util-3.2.jar
[INFO] Downloaded: https://repo.maven.apache.org/maven2/org/apache/maven/archetype/archetype-common/2.4/archetype-common-2.4.jar (170 KB at 117.0 KB/sec)
[INFO] Downloading: https://repo.maven.apache.org/maven2/asm/asm-analysis/3.2/asm-analysis-3.2.jar
[INFO] Downloaded: https://repo.maven.apache.org/maven2/asm/asm/3.2/asm-3.2.jar (43 KB at 27.2 KB/sec)
[INFO] Downloading: https://repo.maven.apache.org/maven2/asm/asm-tree/3.2/asm-tree-3.2.jar
[INFO] Downloaded: https://repo.maven.apache.org/maven2/asm/asm-util/3.2/asm-util-3.2.jar (36 KB at 22.2 KB/sec)
[INFO] Downloading: https://repo.maven.apache.org/maven2/org/beanshell/bsh/2.0b4/bsh-2.0b4.jar
[INFO] Downloaded: https://repo.maven.apache.org/maven2/asm/asm-analysis/3.2/asm-analysis-3.2.jar (18 KB at 10.6 KB/sec)
[INFO] Downloading: https://repo.maven.apache.org/maven2/org/apache/maven/shared/maven-script-interpreter/1.0/maven-script-interpreter-1.0.jar
[INFO] Downloaded: https://repo.maven.apache.org/maven2/org/codehaus/plexus/plexus-classworlds/1.2-alpha-7/plexus-classworlds-1.2-alpha-7.jar (42 KB at 24.5 KB/sec)
[INFO] Downloading: https://repo.maven.apache.org/maven2/org/apache/ant/ant/1.8.1/ant-1.8.1.jar
[INFO] Downloaded: https://repo.maven.apache.org/maven2/org/apache/maven/shared/maven-script-interpreter/1.0/maven-script-interpreter-1.0.jar (21 KB at 10.6 KB/sec)
[INFO] Downloaded: https://repo.maven.apache.org/maven2/asm/asm-tree/3.2/asm-tree-3.2.jar (22 KB at 11.2 KB/sec)
[INFO] Downloaded: https://repo.maven.apache.org/maven2/org/beanshell/bsh/2.0b4/bsh-2.0b4.jar (276 KB at 90.4 KB/sec)
[INFO] Downloaded: https://repo.maven.apache.org/maven2/org/apache/ant/ant/1.8.1/ant-1.8.1.jar (1479 KB at 124.5 KB/sec)
[INFO] Downloaded: https://repo.maven.apache.org/maven2/org/codehaus/groovy/groovy/1.8.3/groovy-1.8.3.jar (5394 KB at 220.5 KB/sec)
[INFO] Generating project in Batch mode
[INFO] No archetype defined. Using maven-archetype-quickstart (org.apache.maven.archetypes:maven-archetype-quickstart:1.0)
[INFO] Downloading: https://repo.maven.apache.org/maven2/org/apache/maven/archetypes/maven-archetype-quickstart/1.0/maven-archetype-quickstart-1.0.jar
[INFO] Downloaded: https://repo.maven.apache.org/maven2/org/apache/maven/archetypes/maven-archetype-quickstart/1.0/maven-archetype-quickstart-1.0.jar (5 KB at 13.8 KB/sec)
[INFO] Downloading: https://repo.maven.apache.org/maven2/org/apache/maven/archetypes/maven-archetype-quickstart/1.0/maven-archetype-quickstart-1.0.pom
[INFO] Downloaded: https://repo.maven.apache.org/maven2/org/apache/maven/archetypes/maven-archetype-quickstart/1.0/maven-archetype-quickstart-1.0.pom (703 B at 2.0 KB/sec)
[INFO] ----------------------------------------------------------------------------
[INFO] Using following parameters for creating project from Old (1.x) Archetype: maven-archetype-quickstart:1.0
[INFO] ----------------------------------------------------------------------------
[INFO] Parameter: basedir, Value: /home/frgs/mvntest+
[INFO] Parameter: package, Value: com.mycompany.app
[INFO] Parameter: groupId, Value: com.mycompany.app
[INFO] Parameter: artifactId, Value: my-app
[INFO] Parameter: packageName, Value: com.mycompany.app
[INFO] Parameter: version, Value: 1.0-SNAPSHOT
[INFO] project created from Old (1.x) Archetype in dir: /home/frgs/mvntest+/my-app
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 56.119 s
[INFO] Finished at: 2015-11-14T18:00:05+01:00
[INFO] Final Memory: 16M/166M
[INFO] ------------------------------------------------------------------------

这看起来正常吗？我再次谈论一个由空目录组成的项目，如果不是因为 github 上几乎每个 Java 项目都使用 maven，这对我来说看起来很荒谬!

Answer 1

这就是 Maven 的工作原理。所有依赖项(可以是 3rdparty jar、插件的插件依赖项以及运行项目可能需要的任何 jar)都应该可以在本地访问。因此，maven 通过连接到一个或多个“远程位置”(存储库)来管理它们。它们就像一个包含各种 jar 和元数据的大文件系统。

在 Maven 中，你可以“免费”获得依赖管理。这意味着它可以自行管理所有依赖项。这包括从这些远程位置下载到一些预定义的文件夹(称为本地存储库)并“安排”项目的类路径。如果依赖项有自己的依赖项，它们也会被下载。这个概念称为“传递依赖”。

现在，为了“填充”本地存储库，maven 必须将 jar 下载到本地硬盘，这就是为什么您会看到它下载了很多东西。

所以，回答你的问题，是的，这是正常的 maven 行为。此外，maven 足够智能，只需下载一次依赖项，第二次使用它时，它应该检查本地存储库，如果找到依赖项，则不会再次下载。

也许我可以在这里补充一点:有一种方法可以告诉maven“以离线模式运行”。这意味着它将无法访问网络。为此，只需指定“-o 选项”。示例:

mvn install -o

希望这有帮助