Maven快速入门

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Maven是Java中最为普及的包管理工具,在实际项目中由于依赖的各类jar包非常多,因此概念清晰的处理好各类Jar依赖显得非常重要,接下来通过基础知识,Jar包主要分类方式和进阶知识来介绍。

基础知识

Maven使用起来非常方便,配置卸载setting.xml中,如果是自己本地开发,推荐直接使用如下配置。

<?xml version="1.0" encoding="UTF-8"?>
<settings xmlns="http://maven.apache.org/SETTINGS/1.0.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/SETTINGS/1.0.0 http://maven.apache.org/xsd/settings-1.0.0.xsd">
<localRepository>E:\javaAssist\maven\repository</localRepository>
<pluginGroups>
</pluginGroups>
<proxies>
</proxies>
</servers>
<mirrors>
<!-- 阿里云仓库 -->
<mirror>
<id>alimaven</id>
<mirrorOf>central</mirrorOf>
<name>aliyun maven</name>
<url>http://maven.aliyun.com/nexus/content/repositories/central/</url>
</mirror>
<!-- 中央仓库1 -->
<mirror>
<id>repo1</id>
<mirrorOf>central</mirrorOf>
<name>Human Readable Name for this Mirror.</name>
<url>http://repo1.maven.org/maven2/</url>
</mirror>
<!-- 中央仓库2 -->
<mirror>
<id>repo2</id>
<mirrorOf>central</mirrorOf>
<name>Human Readable Name for this Mirror.</name>
<url>http://repo2.maven.org/maven2/</url>
</mirror>
</mirrors>
<profiles>
</profiles>
</settings>

常见命令

命令 诠释
mvn package 生成target目录,编译、测试代码,生成测试报告,生成jar/war文件
mvn tomcat7:run 运行项目于tomcat[jetty等server也OK]上
mvn compile 编译
mvn test 编译并测试
mvn deploy -Dmaven.test.skip=true 发布
mvn clean 清空生成的文件
mvn install -X 想要查看完整的依赖踪迹,包含那些因为冲突或者其它原因而被拒绝引入的构件,打开 Maven 的调试标记运行

Tip: 对于community版本的Idea就需要借助maven命令来启动tomcat容器。
此外生产环境,有时会指定特殊版本的jar,因此需要使用systemscope,如下所示

<dependency>
<groupId>com.xxxxx.security</groupId>
<artifactId>encryption</artifactId>
<version>1.0.0.2</version>
<scope>system</scope>
<systemPath>${project.basedir}/src/main/resources/lib/encryption-1.0.0.2.jar</systemPath>
</dependency>

Maven的Scope

名称 诠释
compile 编译范围,默认的范围
provided 已提供范围,比如有些web相关jar,tomcat中有,但本地没有时使用
runtime 运行时范围,比如编译时只需要slf4j-api,运行时才需要具体的实现jar
test 测试范围,例如junit,spring-test

依赖库分类

在java项目中,通常我们将所有的库归类为三种:
一方库:指当前项目中各模块间的相互依赖,其中每个模块都可以定义为该工程的一方库。(工程范围内)
二方库:指当前公司内部jar包间的相互依赖,公司内部除了当前工程之外的jar及依赖都可以定义为该工程的二方库。(公司范围内)
三方库:指公司之外的开源库, 比如apache、google、spring等第三方提供的jar及依赖。

进阶知识

项目中经常遇到jar包冲突的问题,通常的都是遇到冲突后再去检查,很被动。即使是通过 mvn dependency:tree -Dverbose 也只能是从jar层面自己分析是否有冲突。如何提前检测,如何准确定位到具体类在哪个jar包中存在冲突,这才是解决问题的根本。现推荐一款maven插件可以具体定位到哪些类有冲突,在哪些jar包中有冲突。
使用方法
在pom.xml文件build标签中添加如下代码(根据自己代码视情况添加)

<pluginManagement>
     <plugins>
            <plugin>
                   <groupId>org.apache.maven.plugins</groupId>
                   <artifactId>maven-enforcer-plugin</artifactId>
                   <version>1.1.1</version>
                   <dependencies>
                   <dependency>
                          <groupId>org.codehaus.mojo</groupId>
                          <artifactId>extra-enforcer-rules</artifactId>
                          <version>1.0-alpha-4</version>
                   </dependency>
                   </dependencies>
                   
                   <configuration>
                          <rules>
                                 <bannedDependencies>
                                        <searchTransitive>true</searchTransitive>
                                 </bannedDependencies>
                                 <evaluateBeanshell>
                                        <condition>print("[INFO] [Alibaba Enforcer Rules] parent-pom ");1==1</condition>
                                 </evaluateBeanshell>
                                 <banDuplicateClasses>
                                        <findAllDuplicates>true</findAllDuplicates>
                                      <message>[ERROR] [Alibaba Enforcer Rules] find DuplicateClasses</message>
                                 </banDuplicateClasses>
                          </rules>
                   </configuration>
            </plugin>
     </plugins>
</pluginManagement>

之后在对应项目根目录执行一下maven命令:mvn enforcer:enforce。冲突较多单屏无法显示完整时可以重定向到某文件中,如下:mvn enforcer:enforce > conflict.txt。其中Duplicate classes显示的是重复的类,Found in显示的是重复的类所在的jar包。此外,可以通过添加VM参数-verbose:class可显示每个文件加载自哪个jar包。

附上一个基础的Maven文件Demo

<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/maven-v4_0_0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <groupId>com.bjorktech.cayman</groupId>
    <artifactId>cm-web</artifactId>
    <packaging>war</packaging>

    <parent>
        <artifactId>cayman</artifactId>
        <groupId>com.bjorktech</groupId>
        <version>1.0.0-SNAPSHOT</version>
    </parent>

    <properties>
        <!-- Web -->
        <jsp.version>2.3.1</jsp.version>
        <jstl.version>1.2</jstl.version>
        <servlet.version>3.1.0</servlet.version>
        <!-- <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding> -->
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-webmvc</artifactId>
        </dependency>
        <!-- <dependency> <groupId>javax</groupId> <artifactId>javaee-web-api</artifactId> 
            <version>7.0</version> <scope>provided</scope> </dependency> -->
        <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>jstl</artifactId>
            <version>${jstl.version}</version>
        </dependency>
        <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>javax.servlet-api</artifactId>
            <version>${servlet.version}</version>
            <scope>provided</scope>
        </dependency>
        <dependency>
            <groupId>javax.servlet.jsp</groupId>
            <artifactId>javax.servlet.jsp-api</artifactId>
            <version>${jsp.version}</version>
            <scope>provided</scope>
        </dependency>
        <!-- tx -->
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-tx</artifactId>
        </dependency>
        <!-- aop -->
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-aop</artifactId>
        </dependency>
        <dependency>
            <groupId>org.aspectj</groupId>
            <artifactId>aspectjweaver</artifactId>
        </dependency>
        <dependency>
            <groupId>org.aspectj</groupId>
            <artifactId>aspectjrt</artifactId>
            <version>1.8.5</version>
        </dependency>
        <!-- mybatis -->
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
        </dependency>
        <dependency>
            <groupId>com.google.guava</groupId>
            <artifactId>guava</artifactId>
        </dependency>
        <dependency>
            <groupId>joda-time</groupId>
            <artifactId>joda-time</artifactId>
        </dependency>
        <!-- log -->
        <dependency>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-api</artifactId>
        </dependency>
        <dependency>
            <groupId>ch.qos.logback</groupId>
            <artifactId>logback-access</artifactId>
        </dependency>
        <dependency>
            <groupId>ch.qos.logback</groupId>
            <artifactId>logback-classic</artifactId>
        </dependency>
        <dependency>
            <groupId>ch.qos.logback</groupId>
            <artifactId>logback-core</artifactId>
        </dependency>
        <!-- <dependency> <groupId>org.apache.logging.log4j</groupId> <artifactId>log4j-api</artifactId> 
            </dependency> <dependency> <groupId>org.apache.logging.log4j</groupId> <artifactId>log4j-core</artifactId> 
            </dependency> <dependency> <groupId>org.apache.logging.log4j</groupId> <artifactId>log4j-slf4j-impl</artifactId> 
            </dependency> -->
        <!-- 本地tomcat -->
        <!-- <dependency> <groupId>org.apache.tomcat</groupId> <artifactId>tomcat-servlet-api</artifactId> 
            </dependency> -->
        <!-- json -->
        <dependency>
            <groupId>com.fasterxml.jackson.dataformat</groupId>
            <artifactId>jackson-dataformat-xml</artifactId>
            <version>2.5.3</version>
        </dependency>
        <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-databind</artifactId>
            <version>2.5.3</version>
        </dependency>
        <!-- 文件上传 -->
        <dependency>
            <groupId>commons-fileupload</groupId>
            <artifactId>commons-fileupload</artifactId>
            <version>1.3.1</version>
        </dependency>
        <dependency>
            <groupId>commons-io</groupId>
            <artifactId>commons-io</artifactId>
            <version>2.3</version>
        </dependency>
        <!-- 老式soap -->
        <dependency>
            <groupId>javax.xml.rpc</groupId>
            <artifactId>javax.xml.rpc-api</artifactId>
            <version>1.1.1</version>
        </dependency>
        <dependency>
            <groupId>org.apache.axis</groupId>
            <artifactId>axis</artifactId>
            <version>1.4</version>
        </dependency>
        <!-- axis依赖包 -->
        <dependency>
            <groupId>commons-discovery</groupId>
            <artifactId>commons-discovery</artifactId>
            <version>0.2</version>
            <exclusions>
                <exclusion>
                    <artifactId>commons-logging</artifactId>
                    <groupId>commons-logging</groupId>
                </exclusion>
            </exclusions>
        </dependency>
        <dependency>
            <groupId>wsdl4j</groupId>
            <artifactId>wsdl4j</artifactId>
            <version>1.6.3</version>
        </dependency>
        <!-- xml解析 -->
        <dependency>
            <groupId>dom4j</groupId>
            <artifactId>dom4j</artifactId>
            <version>1.6.1</version>
        </dependency>
        <!-- 测试 -->
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-test</artifactId>
        </dependency>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
        </dependency>
    </dependencies>
    <build>
        <finalName>cm-web</finalName>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
            </plugin>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-war-plugin</artifactId>
                <configuration>
                    <!-- 无web.xml不报错 -->
                    <failOnMissingWebXml>false</failOnMissingWebXml>
                </configuration>
            </plugin>
        </plugins>
    </build>
</project>

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