Maven 教程— Maven之pom.xml文件简单说明
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原文地址:https://blog.csdn.net/liupeifeng3514/article/details/79543963
通过前面几部分知识,我们对maven已经有了初步的印象,就像Make的Makefile、Ant的build.xml一样,Maven项目的核心是pom.xml。POM(Project Object Model,项目对象模型)定义了项目的基本信息,用于描述项目如何构建,声明依赖,等等。我们来看看maven中pom.xml文件主要标签的意思及其用法,来看一下pom.xml文件的结构:
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"> <modelVersion>4.0.0</modelVersion> <groupId>com.uidp</groupId> <artifactId>UidpParent</artifactId> <version>0.0.1-SNAPSHOT</version> <packaging>pom</packaging> <!--当前项目的全称(名称) --> <name>UidpParent</name> <!--当前项目的主页的URL --> <url>http://maven.apache.org</url> <!--配置常用属性或定义一系列版本号 --> <properties> <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding> <repository-url>http://192.168.0.70:8081/content/groups/public/</repository-url> <maven-compiler-plugin.version>3.1</maven-compiler-plugin.version> <maven-war-plugin.version>2.4</maven-war-plugin.version> <maven-javadoc-plugin.version>2.9.1</maven-javadoc-plugin.version> <maven-release-plugin.version>2.4.1</maven-release-plugin.version> <maven-deploy-plugin.version>2.7</maven-deploy-plugin.version> <junit.version>4.11</junit.version> <oracle.version>10.2.0.4</oracle.version> <springframework.version>3.2.8.RELEASE</springframework.version> <mybatis.version>3.2.2</mybatis.version> <mybatis-spring.version>1.2.0</mybatis-spring.version> <mysql-driver.version>5.1.25</mysql-driver.version> <aspectjweaver.version>1.7.3</aspectjweaver.version> <commons-dbcp.version>1.4</commons-dbcp.version> <commons-pool.version>1.5.5</commons-pool.version> <commons-fileupload.version>1.2.2</commons-fileupload.version> <log4j.version>1.2.17</log4j.version> <slf4j-api.version>1.7.5</slf4j-api.version> <slf4j-log4j12.version>1.7.5</slf4j-log4j12.version> <freemarker.version>2.3.19</freemarker.version> <jackson-core.version>2.5.0</jackson-core.version> <jackson-mapper-asl.version>1.9.7</jackson-mapper-asl.version> <javax.servlet-api.version>3.0.1</javax.servlet-api.version> <jsp-api.version>2.2</jsp-api.version> <kryo.version>1.04</kryo.version> <snakeyaml.version>1.8</snakeyaml.version> <jedis.version>2.0.0</jedis.version> <commons-lang.version>2.6</commons-lang.version> <mockito-core.version>1.8.5</mockito-core.version> <powermock-core.version>1.4.9</powermock-core.version> <powermock-api-mockito.version>1.4.9</powermock-api-mockito.version> <powermock-module-junit4.version>1.4.9</powermock-module-junit4.version> </properties> <!--依赖管理 --> <dependencyManagement> <dependencies> <dependency> <groupId>junit</groupId> <artifactId>junit</artifactId> <version>$junit.version</version> <scope>test</scope> </dependency> <!-- spring jar begin --> <dependency> <groupId>org.springframework</groupId> <artifactId>spring-web</artifactId> <version>$springframework.version</version> </dependency> <dependency> <groupId>org.springframework</groupId> <artifactId>spring-webmvc</artifactId> <version>$springframework.version</version> </dependency> <dependency> <groupId>org.springframework</groupId> <artifactId>spring-beans</artifactId> <version>$springframework.version</version> </dependency> <dependency> <groupId>org.springframework</groupId> <artifactId>spring-context</artifactId> <version>$springframework.version</version> </dependency> <dependency> <groupId>org.springframework</groupId> <artifactId>spring-context-support</artifactId> <version>$springframework.version</version> </dependency> <dependency> <groupId>org.springframework</groupId> <artifactId>spring-core</artifactId> <version>$springframework.version</version> </dependency> <dependency> <groupId>org.springframework</groupId> <artifactId>spring-jdbc</artifactId> <version>$springframework.version</version> </dependency> <dependency> <groupId>org.springframework</groupId> <artifactId>spring-tx</artifactId> <version>$springframework.version</version> </dependency> <dependency> <groupId>org.springframework</groupId> <artifactId>spring-test</artifactId> <version>$springframework.version</version> </dependency> <dependency> <groupId>org.springframework</groupId> <artifactId>spring-expression</artifactId> <version>$springframework.version</version> </dependency> <dependency> <groupId>org.springframework</groupId> <artifactId>spring-aop</artifactId> <version>$springframework.version</version> </dependency> <!-- spring jar end --> <dependency> <groupId>org.mybatis</groupId> <artifactId>mybatis</artifactId> <version>$mybatis.version</version> </dependency> <dependency> <groupId>org.mybatis</groupId> <artifactId>mybatis-spring</artifactId> <version>$mybatis-spring.version</version> </dependency> <dependency> <groupId>mysql</groupId> <artifactId>mysql-connector-java</artifactId> <version>$mysql-driver.version</version> </dependency> <dependency> <groupId>com.oracle</groupId> <artifactId>ojdbc14</artifactId> <version>$oracle.version</version> </dependency> <dependency> <groupId>org.aspectj</groupId> <artifactId>aspectjweaver</artifactId> <version>$aspectjweaver.version</version> </dependency> <dependency> <groupId>commons-dbcp</groupId> <artifactId>commons-dbcp</artifactId> <version>$commons-dbcp.version</version> </dependency> <dependency> <groupId>commons-pool</groupId> <artifactId>commons-pool</artifactId> <version>$commons-pool.version</version> </dependency> <dependency> <groupId>commons-fileupload</groupId> <artifactId>commons-fileupload</artifactId> <version>$commons-fileupload.version</version> </dependency> <!-- log jar --> <dependency> <groupId>log4j</groupId> <artifactId>log4j</artifactId> <version>$log4j.version</version> </dependency> <dependency> <groupId>org.slf4j</groupId> <artifactId>slf4j-api</artifactId> <version>$slf4j-api.version</version> </dependency> <dependency> <groupId>org.slf4j</groupId> <artifactId>slf4j-log4j12</artifactId> <version>$slf4j-log4j12.version</version> </dependency> <!-- freemarker --> <dependency> <groupId>org.freemarker</groupId> <artifactId>freemarker</artifactId> <version>$freemarker.version</version> </dependency> <!-- jackson --> <dependency> <groupId>com.fasterxml.jackson.core</groupId> <artifactId>jackson-core</artifactId> <version>$jackson-core.version</version> </dependency> <dependency> <groupId>org.codehaus.jackson</groupId> <artifactId>jackson-mapper-asl</artifactId> <version>$jackson-mapper-asl.version</version> </dependency> <dependency> <groupId>javax.servlet</groupId> <artifactId>javax.servlet-api</artifactId> <version>$javax.servlet-api.version</version> <scope>provided</scope> </dependency> <dependency> <groupId>javax.servlet.jsp</groupId> <artifactId>jsp-api</artifactId> <version>$jsp-api.version</version> <scope>provided</scope> </dependency> <dependency> <groupId>com.googlecode</groupId> <artifactId>kryo</artifactId> <version>$kryo.version</version> </dependency> <dependency> <groupId>org.yaml</groupId> <artifactId>snakeyaml</artifactId> <version>$snakeyaml.version</version> </dependency> <dependency> <groupId>redis.clients</groupId> <artifactId>jedis</artifactId> <version>$jedis.version</version> </dependency> <dependency> <groupId>commons-lang</groupId> <artifactId>commons-lang</artifactId> <version>$commons-lang.version</version> </dependency> <dependency> <groupId>org.mockito</groupId> <artifactId>mockito-core</artifactId> <version>$mockito-core.version</version> <scope>test</scope> </dependency> <dependency> <groupId>org.powermock</groupId> <artifactId>powermock-core</artifactId> <version>$powermock-core.version</version> <scope>test</scope> </dependency> <dependency> <groupId>org.powermock</groupId> <artifactId>powermock-api-mockito</artifactId> <version>$powermock-api-mockito.version</version> <scope>test</scope> </dependency> <dependency> <groupId>org.powermock</groupId> <artifactId>powermock-module-junit4</artifactId> <version>$powermock-module-junit4.version</version> <scope>test</scope> </dependency> </dependencies> </dependencyManagement> <distributionManagement> <repository> <id>releases</id> <name>public</name> <url>http://59.50.95.66:8081/nexus/content/repositories/releases</url> </repository> <snapshotRepository> <id>snapshots</id> <name>Snapshots</name> <url>http://59.50.95.66:8081/nexus/content/repositories/snapshots</url> </snapshotRepository> </distributionManagement> <!--构建管理 --> <build> <plugins> <plugin> <groupId>org.apache.maven.plugins</groupId> <artifactId>maven-compiler-plugin</artifactId> <version>$maven-compiler-plugin.version</version> <configuration> <source>1.7</source> <!-- 源代码使用的开发版本 --> <target>1.7</target> <!-- 需要生成的目标class文件的编译版本 --> </configuration> </plugin> <plugin> <groupId>org.apache.maven.plugins</groupId> <artifactId>maven-javadoc-plugin</artifactId> <version>$maven-javadoc-plugin.version</version> </plugin> <plugin> <groupId>org.apache.maven.plugins</groupId> <artifactId>maven-release-plugin</artifactId> <version>$maven-release-plugin.version</version> </plugin> <plugin> <groupId>org.apache.maven.plugins</groupId> <artifactId>maven-deploy-plugin</artifactId> <version>$maven-deploy-plugin.version</version> <configuration> <updateReleaseInfo>true</updateReleaseInfo> </configuration> </plugin> </plugins> </build> <pluginRepositories> <pluginRepository> <id>nexus</id> <name>nexus</name> <url>$repository-url</url> <releases> <enabled>true</enabled> </releases> <snapshots> <enabled>true</enabled> </snapshots> </pluginRepository> </pluginRepositories> </project>
我们可以看到maven的pom.xml文件结构非常清晰,把项目创建好后,我们基本上是在dependencies元素下添加一些子元素及plugins元素下添加一些插件,下面我们来介绍一下各个元素的含义:
- project:是所有pom.xml的根元素,并且在里面定义了命名空间和xsd元素;
- modelVersion:当前pom模型的版本;
- groupId:定义当前maven项目隶属的实际项目,并会根据这给项目建立包结构;
- artifactId:定义项目中的某个模块名称,如果只有一个模块那就是项目的名称;
- version:定义maven项目当前所处的版本号,默认0.0.1-SNAPSHOT为快照版本;
- packaging:定义maven项目的打包方式,可以是jar包、war包、pom;
- dependencies:元素底下就是加入依赖包的地方,那么我们从哪里查询依赖包呢,可以查询的地方比较多,我给出一个大家用得比较多的仓库:http://mvnrepository.com;
- 每个dependency都是一个依赖包,依赖包也就是在dependency里面定义各个依赖包的坐标,这样maven就会从网上下载依赖包到你本地仓库中,有所不同的是dependency元素包含了一个子元素,这个就是对maven生命周期的一个说明,当然除了上面四个子元素外,还包含几个其他的元素。
- type:说明依赖的类型;
- optional:标记依赖是否可选;
- exclusions:用来排斥传递依赖。
我们具体来看看这个结构:
<dependency> <groupId>实际项目</groupId> <artifactId>模块</artifactId> <version>版本</version> <type>依赖类型</type> <scope>依赖范围</scope> <optional>依赖是否可选</optional> <!-- 主要用于排除传递性依赖 --> <exclusions> <exclusion> <groupId>…</groupId> <artifactId>…</artifactId> </exclusion> </exclusions> </dependency>
Maven是通过groupId、artifactId、version这三个类似于坐标的元素来确定唯一性的,因此这三个元素对于每个依赖大多是必须的,后面会详细介绍依赖、聚合、继承等知识点。
没有任何实际的Java代码,我们能够定义一个Maven项目的POM,这体现了Maven的一大优点,它能让项目对象模型最大程度地与实际代码相独立,我们可以称之为解耦。这在很大程度上避免了Java代码和POM代码的相互影响。只要我们定义的POM稳定后,日常的Java代码开发工作中基本不会涉及到POM的修改。
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