netbeans总是在运行项目时下载文件

Question

我有一个基于maven的java spring mvc项目。每当我第一次尝试运行这个项目时，控制台都会告诉我netbeans正在下载很多文件，比如

Downloading: http://maven.springframework.org/milestone/org/springframework/spring-asm/3.1.0-SPR7420.BUILD-SNAPSHOT/maven-metadata.xml
Downloading: http://mirrors.ibiblio.org/pub/mirrors/maven2/org/springframework/spring-asm/3.1.0-SPR7420.BUILD-SNAPSHOT/maven-metadata.xml
Downloading: http://maven.springframework.org/snapshot/org/springframework/spring-asm/3.1.0-SPR7420.BUILD-SNAPSHOT/maven-metadata.xml
Downloading: http://repo1.maven.org/maven2/org/springframework/spring-asm/3.1.0-SPR7420.BUILD-SNAPSHOT/maven-metadata.xml

每次退出netbeans并再次启动时都会下载。