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：
1 <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"> 2 <modelVersion>4.0.0</modelVersion> 3 4 <groupId>com.uidp</groupId> 5 <artifactId>UidpParent</artifactId> 6 <version>0.0.1-SNAPSHOT</version> 7 <packaging>pom</packaging> 8 9 <!--当前项目的全称(名称)--> 10 <name>UidpParent</name> 11 <!--当前项目的主页的URL--> 12 <url>http://maven.apache.org</url> 13 14 <!--配置常用属性或定义一系列版本号--> 15 <properties> 16 <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding> 17 18 <repository-url>http://192.168.0.70:8081/content/groups/public/</repository-url> 19 20 <maven-compiler-plugin.version>3.1</maven-compiler-plugin.version> 21 <maven-war-plugin.version>2.4</maven-war-plugin.version> 22 <maven-javadoc-plugin.version>2.9.1</maven-javadoc-plugin.version> 23 <maven-release-plugin.version>2.4.1</maven-release-plugin.version> 24 <maven-deploy-plugin.version>2.7</maven-deploy-plugin.version> 25 26 27 28 <junit.version>4.11</junit.version> 29 <oracle.version>10.2.0.4</oracle.version> 30 <springframework.version>3.2.8.RELEASE</springframework.version> 31 <mybatis.version>3.2.2</mybatis.version> 32 <mybatis-spring.version>1.2.0</mybatis-spring.version> 33 <mysql-driver.version>5.1.25</mysql-driver.version> 34 <aspectjweaver.version>1.7.3</aspectjweaver.version> 35 36 <commons-dbcp.version>1.4</commons-dbcp.version> 37 <commons-pool.version>1.5.5</commons-pool.version> 38 <commons-fileupload.version>1.2.2</commons-fileupload.version> 39 40 <log4j.version>1.2.17</log4j.version> 41 <slf4j-api.version>1.7.5</slf4j-api.version> 42 <slf4j-log4j12.version>1.7.5</slf4j-log4j12.version> 43 44 <freemarker.version>2.3.19</freemarker.version> 45 46 <jackson-core.version>2.5.0</jackson-core.version> 47 <jackson-mapper-asl.version>1.9.7</jackson-mapper-asl.version> 48 49 <javax.servlet-api.version>3.0.1</javax.servlet-api.version> 50 <jsp-api.version>2.2</jsp-api.version> 51 <kryo.version>1.04</kryo.version> 52 <snakeyaml.version>1.8</snakeyaml.version> 53 <jedis.version>2.0.0</jedis.version> 54 <commons-lang.version>2.6</commons-lang.version> 55 56 57 <mockito-core.version>1.8.5</mockito-core.version> 58 <powermock-core.version>1.4.9</powermock-core.version> 59 <powermock-api-mockito.version>1.4.9</powermock-api-mockito.version> 60 <powermock-module-junit4.version>1.4.9</powermock-module-junit4.version> 61 62 63 </properties> 64 65 <!--依赖管理--> 66 <dependencyManagement> 67 <dependencies> 68 69 <dependency> 70 <groupId>junit</groupId> 71 <artifactId>junit</artifactId> 72 <version>${junit.version}</version> 73 <scope>test</scope> 74 </dependency> 75 76 <!-- spring jar begin --> 77 <dependency> 78 <groupId>org.springframework</groupId> 79 <artifactId>spring-web</artifactId> 80 <version>${springframework.version}</version> 81 </dependency> 82 83 <dependency> 84 <groupId>org.springframework</groupId> 85 <artifactId>spring-webmvc</artifactId> 86 <version>${springframework.version}</version> 87 </dependency> 88 89 <dependency> 90 <groupId>org.springframework</groupId> 91 <artifactId>spring-beans</artifactId> 92 <version>${springframework.version}</version> 93 </dependency> 94 95 <dependency> 96 <groupId>org.springframework</groupId> 97 <artifactId>spring-context</artifactId> 98 <version>${springframework.version}</version> 99 </dependency> 100 101 <dependency> 102 <groupId>org.springframework</groupId> 103 <artifactId>spring-context-support</artifactId> 104 <version>${springframework.version}</version> 105 </dependency> 106 107 <dependency> 108 <groupId>org.springframework</groupId> 109 <artifactId>spring-core</artifactId> 110 <version>${springframework.version}</version> 111 </dependency> 112 113 <dependency> 114 <groupId>org.springframework</groupId> 115 <artifactId>spring-jdbc</artifactId> 116 <version>${springframework.version}</version> 117 </dependency> 118 119 <dependency> 120 <groupId>org.springframework</groupId> 121 <artifactId>spring-tx</artifactId> 122 <version>${springframework.version}</version> 123 </dependency> 124 125 <dependency> 126 <groupId>org.springframework</groupId> 127 <artifactId>spring-test</artifactId> 128 <version>${springframework.version}</version> 129 </dependency> 130 131 <dependency> 132 <groupId>org.springframework</groupId> 133 <artifactId>spring-expression</artifactId> 134 <version>${springframework.version}</version> 135 </dependency> 136 137 <dependency> 138 <groupId>org.springframework</groupId> 139 <artifactId>spring-aop</artifactId> 140 <version>${springframework.version}</version> 141 </dependency> 142 <!-- spring jar end --> 143 144 <dependency> 145 <groupId>org.mybatis</groupId> 146 <artifactId>mybatis</artifactId> 147 <version>${mybatis.version}</version> 148 </dependency> 149 150 <dependency> 151 <groupId>org.mybatis</groupId> 152 <artifactId>mybatis-spring</artifactId> 153 <version>${mybatis-spring.version}</version> 154 </dependency> 155 156 <dependency> 157 <groupId>mysql</groupId> 158 <artifactId>mysql-connector-java</artifactId> 159 <version>${mysql-driver.version}</version> 160 </dependency> 161 162 <dependency> 163 <groupId>com.oracle</groupId> 164 <artifactId>ojdbc14</artifactId> 165 <version>${oracle.version}</version> 166 </dependency> 167 168 <dependency> 169 <groupId>org.aspectj</groupId> 170 <artifactId>aspectjweaver</artifactId> 171 <version>${aspectjweaver.version}</version> 172 </dependency> 173 174 175 <dependency> 176 <groupId>commons-dbcp</groupId> 177 <artifactId>commons-dbcp</artifactId> 178 <version>${commons-dbcp.version}</version> 179 </dependency> 180 <dependency> 181 <groupId>commons-pool</groupId> 182 <artifactId>commons-pool</artifactId> 183 <version>${commons-pool.version}</version> 184 </dependency> 185 <dependency> 186 <groupId>commons-fileupload</groupId> 187 <artifactId>commons-fileupload</artifactId> 188 <version>${commons-fileupload.version}</version> 189 </dependency> 190 191 192 <!-- log jar --> 193 <dependency> 194 <groupId>log4j</groupId> 195 <artifactId>log4j</artifactId> 196 <version>${log4j.version}</version> 197 </dependency> 198 <dependency> 199 <groupId>org.slf4j</groupId> 200 <artifactId>slf4j-api</artifactId> 201 <version>${slf4j-api.version}</version> 202 </dependency> 203 <dependency> 204 <groupId>org.slf4j</groupId> 205 <artifactId>slf4j-log4j12</artifactId> 206 <version>${slf4j-log4j12.version}</version> 207 </dependency> 208 209 <!-- freemarker --> 210 <dependency> 211 <groupId>org.freemarker</groupId> 212 <artifactId>freemarker</artifactId> 213 <version>${freemarker.version}</version> 214 </dependency> 215 216 217 <!-- jackson --> 218 <dependency> 219 <groupId>com.fasterxml.jackson.core</groupId> 220 <artifactId>jackson-core</artifactId> 221 <version>${jackson-core.version}</version> 222 </dependency> 223 <dependency> 224 <groupId>org.codehaus.jackson</groupId> 225 <artifactId>jackson-mapper-asl</artifactId> 226 <version>${jackson-mapper-asl.version}</version> 227 </dependency> 228 229 <dependency> 230 <groupId>javax.servlet</groupId> 231 <artifactId>javax.servlet-api</artifactId> 232 <version>${javax.servlet-api.version}</version> 233 <scope>provided</scope> 234 </dependency> 235 236 <dependency> 237 <groupId>javax.servlet.jsp</groupId> 238 <artifactId>jsp-api</artifactId> 239 <version>${jsp-api.version}</version> 240 <scope>provided</scope> 241 </dependency> 242 243 <dependency> 244 <groupId>com.googlecode</groupId> 245 <artifactId>kryo</artifactId> 246 <version>${kryo.version}</version> 247 </dependency> 248 249 <dependency> 250 <groupId>org.yaml</groupId> 251 <artifactId>snakeyaml</artifactId> 252 <version>${snakeyaml.version}</version> 253 </dependency> 254 255 <dependency> 256 <groupId>redis.clients</groupId> 257 <artifactId>jedis</artifactId> 258 <version>${jedis.version}</version> 259 </dependency> 260 261 <dependency> 262 <groupId>commons-lang</groupId> 263 <artifactId>commons-lang</artifactId> 264 <version>${commons-lang.version}</version> 265 </dependency> 266 267 268 <dependency> 269 <groupId>org.mockito</groupId> 270 <artifactId>mockito-core</artifactId> 271 <version>${mockito-core.version}</version> 272 <scope>test</scope> 273 </dependency> 274 275 <dependency> 276 <groupId>org.powermock</groupId> 277 <artifactId>powermock-core</artifactId> 278 <version>${powermock-core.version}</version> 279 <scope>test</scope> 280 </dependency> 281 282 <dependency> 283 <groupId>org.powermock</groupId> 284 <artifactId>powermock-api-mockito</artifactId> 285 <version>${powermock-api-mockito.version}</version> 286 <scope>test</scope> 287 </dependency> 288 289 <dependency> 290 <groupId>org.powermock</groupId> 291 <artifactId>powermock-module-junit4</artifactId> 292 <version>${powermock-module-junit4.version}</version> 293 <scope>test</scope> 294 </dependency> 295 296 297 </dependencies> 298 </dependencyManagement> 299 300 <distributionManagement> 301 <repository> 302 <id>releases</id> 303 <name>public</name> 304 <url>http://59.50.95.66:8081/nexus/content/repositories/releases</url> 305 </repository> 306 <snapshotRepository> 307 <id>snapshots</id> 308 <name>Snapshots</name> 309 <url>http://59.50.95.66:8081/nexus/content/repositories/snapshots</url> 310 </snapshotRepository> 311 </distributionManagement> 312 313 314 <!--构建管理--> 315 <build> 316 <plugins> 317 318 <plugin> 319 <groupId>org.apache.maven.plugins</groupId> 320 <artifactId>maven-compiler-plugin</artifactId> 321 <version>${maven-compiler-plugin.version}</version> 322 <configuration> 323 <source>1.7</source> <!-- 源代码使用的开发版本 --> 324 <target>1.7</target> <!-- 需要生成的目标class文件的编译版本 --> 325 </configuration> 326 </plugin> 327 328 <plugin> 329 <groupId>org.apache.maven.plugins</groupId> 330 <artifactId>maven-javadoc-plugin</artifactId> 331 <version>${maven-javadoc-plugin.version}</version> 332 </plugin> 333 334 335 <plugin> 336 <groupId>org.apache.maven.plugins</groupId> 337 <artifactId>maven-release-plugin</artifactId> 338 <version>${maven-release-plugin.version}</version> 339 </plugin> 340 341 <plugin> 342 <groupId>org.apache.maven.plugins</groupId> 343 <artifactId>maven-deploy-plugin</artifactId> 344 <version>${maven-deploy-plugin.version}</version> 345 <configuration> 346 <updateReleaseInfo>true</updateReleaseInfo> 347 </configuration> 348 </plugin> 349 350 </plugins> 351 </build> 352 353 354 <pluginRepositories> 355 <pluginRepository> 356 <id>nexus</id> 357 <name>nexus</name> 358 <url>${repository-url}</url> 359 <releases> 360 <enabled>true</enabled> 361 </releases> 362 <snapshots> 363 <enabled>true</enabled> 364 </snapshots> 365 </pluginRepository> 366 </pluginRepositories> 367 368 369 </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。
1) 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。
2) modelVersion 当前pom模型的版本。
3) 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。
4) 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。
5) 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。
6) packaging定义maven项目的打包方式，可以是jar包、war包、pom。
7) 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。
8) 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。
(1)type说明依赖的类型
(2)optional标记依赖是否可选
(3)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。
可爱博主：AlanLee
博客地址：http://www.cnblogs.com/AlanLee
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