如何使用Maven scope

maven 有6个scope类型，下面简单总结备忘下

<dependency>
    <groupId>javax.servlet</groupId>
    <artifactId>servlet-api</artifactId>
    <version>2.4</version>
    <scope>provided</scope>
</dependency>

maven官方描述

Dependency Scope
Dependency scope is used to limit the transitivity of a depedency, and also to affect the classpath used for various build tasks.

There are 6 scopes available:

compile
This is the default scope, used if none is specified. Compile dependencies are available in all classpaths of a project. Furthermore, those dependencies are propagated to dependent projects. 
provided
This is much like compile, but indicates you expect the JDK or a container to provide the dependency at runtime. For example, when building a web application for the Java Enterprise Edition, you would set the dependency on the Servlet API and related Java EE APIs to scope provided because the web container provides those classes. This scope is only available on the compilation and test classpath, and is not transitive. 
runtime
This scope indicates that the dependency is not required for compilation, but is for execution. It is in the runtime and test classpaths, but not the compile classpath. 
test
This scope indicates that the dependency is not required for normal use of the application, and is only available for the test compilation and execution phases. 
system
This scope is similar to provided except that you have to provide the JAR which contains it explicitly. The artifact is always available and is not looked up in a repository. 
import (only available in Maven 2.0.9 or later)
This scope is only used on a dependency of type pom in the <dependencyManagement> section. It indicates that the specified POM should be replaced with the dependencies in that POM's <dependencyManagement> section. Since they are replaced, dependencies with a scope of import do not actually participate in limiting the transitivity of a dependency.

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翻译下（以下内容载自：http://acooly.iteye.com/blog/1788890）

1.compile

编译范围，默认scope，在工程环境的classpath（编译环境）和打包（如果是WAR包，会包含在WAR包中）时候都有效。

2.provided

容器或JDK已提供范围，表示该依赖包已经由目标容器（如tomcat）和JDK提供，只在编译的classpath中加载和使用，打包的时候不会包含在目标包中。最常见的是j2ee规范相关的servlet-api和jsp-api等jar包，一般由servlet容器提供，无需在打包到war包中，如果不配置为provided，把这些包打包到工程war包中，在tomcat6以上版本会出现冲突无法正常运行程序（版本不符的情况）。

3.runtime

一般是运行和测试环境使用，编译时候不用加入classpath，打包时候会打包到目标包中。一般是通过动态加载或接口反射加载的情况比较多。也就是说程序只使用了接口，具体的时候可能有多个，运行时通过配置文件或jar包扫描动态加载的情况。典型的包括：JDBC驱动等。

4.test

测试范围，一般是单元测试场景使用，在编译环境加入classpath，但打包时不会加入，如junit等。

5.system

系统范围，与provided类似，只是标记为该scope的依赖包需要明确指定基于文件系统的jar包路径。因为需要通过systemPath指定本地jar文件路径，所以该scope是不推荐的。如果是基于组织的，一般会建立本地镜像，会把本地的或组织的基础组件加入本地镜像管理，避过使用该scope的情况。

实践：

• provided是没有传递性的，也就是说，如果你依赖的某个jar包，它的某个jar的范围是provided，那么该jar不会在你的工程中依靠jar依赖传递加入到你的工程中。
• provided具有继承性，上面的情况，如果需要统一配置一个组织的通用的provided依赖，可以使用parent，然后在所有工程中继承。