Scope usage in POM file dependency

scope

stay Maven The dependent domains in are ：compile、provided、runtime、system、test、import

1. compile（ Default ）

When dependent scope by compile When , So the current dependent package , Will be added when compiling ⼊ Come in , And packing （mvn package） Will also be added ⼊ Come in .

The compilation scope is valid , It will be added when compiling and packaging ⼊ go in .

2. provided

When dependent scope by provided When , It works when compiling and testing , Holding on to ⾏（mvn package） Into the ⾏ You won't add ⼊.

for example ： We develop ⼀ individual web Should be ⽤, At compile time, we need to rely on servlet-api.jar, But in transit ⾏ We don't need to jar package , Because of this jar Package already by web Provided by the server , If when packing ⼜ Be added ⼊ go in , Then it may produce ⽣ Conflict . At this point we can make ⽤ provided Into the ⾏ Range modification .

3. system

And provided identical , But being dependent doesn't come from maven Warehouse access ,⽽ It's from local ⽂ The system takes , Need to cooperate with systemPath Attributes use .

such as ：

<dependency>
    <groupId>org.open</groupId>
    <artifactId>open-core</artifactId>
    <version>1.5</version>
    <scope>system</scope>
    <systemPath>${basedir}/WebContent/WEB-INF/lib/open-core.jar</systemPath>
</dependency>

4. runtime

When dependent scope by runtime When , In transit ⾏ Will rely on , When compiling, it will not rely on .⽐ Such as , We don't need to compile JDBC API Of jar package ,⽽ In transit ⾏ When we need JDBC Drive pack . You can use runtime modification .

5. test

When dependent scope by test When , It means that it is valid in the test scope , It won't make ⽤ This dependence .

6. import

maven Multi module items ⽬ In structure , You can make ⽤parent Definition ⽗ term ⽬, from ⽗ term ⽬ Inheritance dependency . but maven Only inheritance , namely ⼀ The item ⽬ Can only make ⽤⼀ individual parent Tag definition ⽗ term ⽬.

maven2.9 Later versions cite ⼊ 了 ⼀ A new feature , Multiple inheritance on dependencies can be realized . This function can make dependency configuration complex pom⽂ Pieces are split into multiple pieces ⽴ Of pom⽂ Pieces of . This treatment can make maven Of pom More concise configuration , At the same time, you can reply ⽤ these pom rely on .
⽐ Such as , We are developing spring boot term ⽬ When ,pom There will be the following configuration in ：

<parent>
	<groupId>org.springframework.boot</groupId>
	<artifactId>spring-boot-starter-parent</artifactId>
	<version>1.3.3.RELEASE</version>
</parent>

however , If this item ⽬ It's a maven⼦ Module , There will be problems . because maven similar java It's single inheritance , There can't be two parent, Now? <parent></parent> The label has ⽤ To quote ⽤⽗ modular , Now? ⼜⽤ To quote ⽤springboot, You'll have ⽣ Conflict .

The solution is ： send ⽤dependencyManagement lead ⼊dependency, And the scope Attribute to import. as follows ：

<dependencyManagement>
	<dependencies>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-dependencies</artifactId>
			<version>2.1.6.RELEASE</version>
			<type>pom</type>
			<scope>import</scope>
		</dependency>
	</dependencies>
</dependencyManagement>

<dependencies>
	<dependency>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-web</artifactId>
	</dependency>
</dependencies>

Be careful ：scope Of import Property can only be <dependencyManagement> Chinese envoy ⽤, surface ⽰ From other pom⽂ It's a guide in the process ⼊dependency To configure .