maven scope的作用

建立的一个用maven管控的web工程，发现jstl-1.2.jar不会部署到lib下。很是奇怪。但tomcat 7.0里自带的库里又不包括。导致页面一声明jstl标签就报错。
后来才知道是pom里指定的scope。代码如下：

<dependency>
	<groupId>javax.servlet</groupId>
	<artifactId>jstl</artifactId>
	<version>1.2</version>
	<scope>provided</scope>
</dependency>

去掉<scope>provided</scope>就OK了。

查询maven的文档，了解到：

• 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.