爲什麼必須Maven的總是不能下載的東西

Question

一開始使用maven在Maven getting started指導下地獄，造成它由一個空目錄併發出命令來創建Maven項目的他的第一個我的應用程序內的項目：

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

現在的東西下面到底是下載了他：

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

確實看起來正常嗎？我再次談到一個由空目錄組成的項目，如果不是因爲github上的每個Java項目都使用maven這個事實，這對我來說很可笑！

Answer 1

這就是maven的工作原理。 所有可以是第三方jar的依賴關係，插件的插件依賴關係以及一般來說運行項目可能需要的任何jar應該可以在本地訪問。 因此，maven通過連接到一個或多個「遠程位置」（存儲庫）來管理它們。這些就像一個包含各種罐子和元數據的大文件系統。

在maven中，您可以免費獲得依賴關係管理。 這意味着它可以自己管理所有的依賴關係。這包括從這些遠程位置下載到某個預定義的文件夾（稱爲本地回購），並「爲你的項目安排」類路徑。 如果依賴關係具有自己的依賴關係，那麼它們也會被下載。這個概念被稱爲「傳遞依賴」。

現在，爲了「填充」本地repo maven必須將jar下載到本地硬盤，這就是爲什麼你看到它下載了很多東西。

所以，回答你的問題，是它的正常maven行爲。另外，maven足夠聰明，只需下載一次依賴項，第二次使用它時，它應該檢查本地存儲庫，如果它找到依賴項，它將不會再次下載它。

也許我可以在這裏添加一點： 有一種方法可以告訴maven「在離線模式下運行」。這意味着它將無法訪問網絡。 爲了做到這一點，只需指定'-o選項'。例如：

mvn install -o 

希望這有助於