为什么必须Maven的总是不能下载的东西

Question

一开始使用maven在Maven getting started指导下地狱，造成它由一个空目录并发出命令来创建Maven项目的他的第一个我的应用程序内的项目：

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

现在的东西下面到底是下载了他：

[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] ------------------------------------------------------------------------ 

确实看起来正常吗？我再次谈到一个由空目录组成的项目，如果不是因为github上的每个Java项目都使用maven这个事实，这对我来说很可笑！

Answer 1

这就是maven的工作原理。 所有可以是第三方jar的依赖关系，插件的插件依赖关系以及一般来说运行项目可能需要的任何jar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。这些就像一个包含各种罐子和元数据的大文件系统。

在maven中，您可以免费获得依赖关系管理。 这意味着它可以自己管理所有的依赖关系。这包括从这些远程位置下载到某个预定义的文件夹（称为本地回购），并“为你的项目安排”类路径。 如果依赖关系具有自己的依赖关系，那么它们也会被下载。这个概念被称为“传递依赖”。

现在，为了“填充”本地repo maven必须将jar下载到本地硬盘，这就是为什么你看到它下载了很多东西。

所以，回答你的问题，是它的正常maven行为。另外，maven足够聪明，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，如果它找到依赖项，它将不会再次下载它。

也许我可以在这里添加一点： 有一种方法可以告诉maven“在离线模式下运行”。这意味着它将无法访问网络。 为了做到这一点，只需指定'-o选项'。例如：

mvn install -o 

希望这有助于