Maven入门

2019-08-15  本文已影响0人  QuoVadis_k

Maven

一、初识Maven

引用来自maven官网的介绍:

Apache Maven is a software project management and comprehension tool. Based on the concept of a project object model (POM), Maven can manage a project's build, reporting and documentation from a central piece of information.

Maven 能为我们做什么？

二、安装和配置

下载地址

此教程以 3.5.4版本进行，后续版本可能会有不同

安装

Windows安装

  1. 进入下载地址，选择 Binary zip archive,下载即可。

  2. 下载完成后解压，会得到一个如下的目录：

目录

  1. 在系统中配置环境变量

    将/bin所在目录配置在系统环境变量中，我这里是D:\maven\apache-maven-3.5.4\bin

  2. 在命令行中验证安装是否成功

    打开命令行界面，执行mvn -v 或 mvn -version，出现以下界面即为安装成功，可以看到maven版本号等一系列信息。

    image

Linux安装

  1. 解压
tar zxvf apache-maven-3.6.0-bin.tar.gz

或

 unzip apache-maven-3.6.0-bin.zip
  1. 设置环境变量
[root@wangkai-centos maven]# java -version
java version "1.8.0_192"
Java(TM) SE Runtime Environment (build 1.8.0_192-b12)
Java HotSpot(TM) 64-Bit Server VM (build 25.192-b12, mixed mode)

#maven
M2_HOME=/usr/local/maven/apache-maven-3.6.0
PATH=$PATH:$JAVA_HOME/bin:$M2_HOME/bin
export PATH JAVA_HOME CLASSPATH M2_HOME

保存，退出。

source /etc/profile
  1. 验证是否安装成功

验证是否成功，出现下述情况则代表成功:

[root@wangkai-centos maven]# mvn -v
Apache Maven 3.6.0 (97c98ec64a1fdfee7767ce5ffb20918da4f719f3; 2018-10-25T02:41:47+08:00)
Maven home: /usr/local/maven/apache-maven-3.6.0
Java version: 1.8.0_192, vendor: Oracle Corporation, runtime: /usr/local/java/jdk1.8/jre
Default locale: zh_CN, platform encoding: UTF-8
OS name: "linux", version: "3.10.0-957.1.3.el7.x86_64", arch: "amd64", family: "unix"

配置

安装成功之后，在回头来看一下maven 的目录结构：

目录

下面重点看一下/setting.xml。~/.m2(用户目录下的/.m2)下的setting.xml与此类似。

进入到/conf下，有个setting.xml的文件，便是maven 的配置文件了，我在这里删去了原来文件中的注释，并做了一些修改：

<?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">

    <!-- 1.本地仓库 -->
    <!-- Default: ${user.home}/.m2/repository -->
    <localRepository>D:\maven\local_repository</localRepository>

    <!-- maven是否与用户交互 默认：true -->
    <!-- interactiveMode
      This will determine whether maven prompts you when it needs input. If set to false,
     maven will use a sensible default value, perhaps based on some other setting, for
     the parameter in question.
    -->
    <interactiveMode>true</interactiveMode>

    <!-- 是否离线模式 -->
    <!-- offline
     | Determines whether maven should attempt to connect to the network when executing a build.
     | This will have an effect on artifact downloads, artifact deployment, and others.
     |
     | Default: false  -->
    <offline>false</offline>


    <!-- 插件组 -->
    <!-- pluginGroups
      | This is a list of additional group identifiers that will be searched when resolving plugins by their prefix, i.e.
      | when invoking a command line like "mvn prefix:goal". Maven will automatically add the group identifiers
      | "org.apache.maven.plugins" and "org.codehaus.mojo" if these are not already contained in the list.
      |-->
    <pluginGroups>
        <!-- pluginGroup
             | Specifies a further group identifier to use for plugin lookup.
            <pluginGroup>com.your.plugins</pluginGroup>
            -->
    </pluginGroups>

    <!-- 代理 例如：需要设置http代理才能访问网络 -->
    <!-- proxies
       | This is a list of proxies which can be used on this machine to connect to the network.
       | Unless otherwise specified (by system property or command-line switch), the first proxy
       | specification in this list marked as active will be used.
       |-->
    <proxies>
        <!-- proxy
             | Specification for one proxy, to be used in connecting to the network.
             |
            <proxy>
              <id>optional</id>
              <active>true</active>
              <protocol>http</protocol>
              <username>proxyuser</username>
              <password>proxypass</password>
              <host>proxy.host.net</host>
              <port>80</port>
              <nonProxyHosts>local.net|some.host.com</nonProxyHosts>
            </proxy>
            -->
    </proxies>

    <!-- 下载与部署仓库的认证信息 -->
    <!-- servers
       | This is a list of authentication profiles, keyed by the server-id used within the system.
       | Authentication profiles can be used whenever maven must make a connection to a remote server.
       |-->
    <servers>
        <!-- server
         | Specifies the authentication information to use when connecting to a particular server, identified by
         | a unique name within the system (referred to by the 'id' attribute below).
         |
         | NOTE: You should either specify username/password OR privateKey/passphrase, since these pairings are
         |       used together.
         |
        <server>
          <id>deploymentRepo</id>
          <username>repouser</username>
          <password>repopwd</password>
        </server>
        -->

        <!-- Another sample, using keys to authenticate.
        <server>
          <id>siteServer</id>
          <privateKey>/path/to/private/key</privateKey>
          <passphrase>optional; leave empty if not used.</passphrase>
        </server>
        -->
    </servers>

    <!-- 镜像 -->
    <mirrors>
        <!-- 2. 镜像地址 -->
        <mirror>
            <id>nexus-aliyun</id>
            <name>*</name>
            <url>http://maven.aliyun.com/nexus/content/groups/public</url>
            <mirrorOf>central</mirrorOf>
        </mirror>
    </mirrors>

    <!-- 3.多环境 -->
    <profiles>
    </profiles>

    <!-- 激活环境 -->
    <!-- activeProfiles
       | List of profiles that are active for all builds.
       |
       -->
    <activeProfiles>
        <activeProfile>alwaysActiveProfile</activeProfile>
        <activeProfile>anotherAlwaysActiveProfile</activeProfile>
    </activeProfiles>
</settings>

​ 第1处：本地仓库。默认的本地仓库地址是${user.home}/.m2/repository,如果需要更改，可以参考如上配置进行更改。

​ 第2处：镜像地址。默认是没有配置的，由于maven的中央仓库在国外，访问会比较缓慢，可以参考如上配置，配置一个国内的镜像地址，此处配置的是aliyun的镜像地址。

​ 第3处：设置多环境配置。这个在以后的文章里会详细总结

三、使用Maven构建一个简单的Java程序

pom.xml 定义了项目的基本配置和信息，描述了项目如何构建，声明了项目的依赖。

<?xml version="1.0" encoding="UTF-8"?>
<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>maven.demo</groupId>
    <artifactId>first-demo</artifactId>
    <version>1.0-SNAPSHOT</version>
</project>

这是最一个pom.xml 中最基本的元素。

编写主程序

在当前文件夹下创建 src/main/java/wk/learn/maven 目录，在此目录上创建App.java :

package wk.learn.maven;

public class App {

    public String helloWorld(){
        return "hello world";
    }

    public static void main(String[] args) {
        System.out.println(new App().helloWorld());
    }
}

在命令行中：

F:\idea\learn\maven-demo>mvn clean compile
[INFO] Scanning for projects...
[INFO]
[INFO] ------------------------< wk.learn:maven-demo >-------------------------
[INFO] Building maven-demo 1.0-SNAPSHOT
[INFO] --------------------------------[ jar ]---------------------------------
[INFO]
[INFO] --- maven-clean-plugin:2.5:clean (default-clean) @ maven-demo ---
[INFO]
[INFO] --- maven-resources-plugin:2.6:resources (default-resources) @ maven-demo ---
[WARNING] Using platform encoding (GBK actually) to copy filtered resources, i.e. build is platform dependent!
[INFO] Copying 0 resource
[INFO]
[INFO] --- maven-compiler-plugin:3.1:compile (default-compile) @ maven-demo ---
[INFO] Changes detected - recompiling the module!
[WARNING] File encoding has not been set, using platform encoding GBK, i.e. build is platform dependent!
[INFO] Compiling 1 source file to F:\idea\learn\maven-demo\target\classes
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 4.220 s
[INFO] Finished at: 2019-04-18T21:22:20+08:00
[INFO] ------------------------------------------------------------------------

这个项目就已经编译成功了。

编写测试

首先需要引入测试所依赖的jar,这里使用JUnit

在pom.xml 中加入：

<dependencies>
    <dependency>
        <groupId>junit</groupId>
        <artifactId>junit</artifactId>
        <version>4.12</version>
        <scope>test</scope>
    </dependency>
</dependencies>

然后创建 src/test/java/wk/learn/maven 的目录，在此目录下创建 AppTest.java：

package wk.learn.maven;

import org.junit.Assert;
import org.junit.Test;

public class AppTest {

    @Test
    public void helloTest(){
        App app = new App();
        Assert.assertEquals("hello world",app.helloWorld());
    }
}

在命令行中执行：

F:\idea\learn\maven-demo>mvn clean test
[INFO] Scanning for projects...
[INFO]
[INFO] ------------------------< wk.learn:maven-demo >-------------------------
[INFO] Building maven-demo 1.0-SNAPSHOT
[INFO] --------------------------------[ jar ]---------------------------------
[INFO]
[INFO] --- maven-clean-plugin:2.5:clean (default-clean) @ maven-demo ---
[INFO] Deleting F:\idea\learn\maven-demo\target
[INFO]
[INFO] --- maven-resources-plugin:2.6:resources (default-resources) @ maven-demo ---
[WARNING] Using platform encoding (GBK actually) to copy filtered resources, i.e. build is platform dependent!
[INFO] Copying 0 resource
[INFO]
[INFO] --- maven-compiler-plugin:3.1:compile (default-compile) @ maven-demo ---
[INFO] Changes detected - recompiling the module!
[WARNING] File encoding has not been set, using platform encoding GBK, i.e. build is platform dependent!
[INFO] Compiling 1 source file to F:\idea\learn\maven-demo\target\classes
[INFO]
[INFO] --- maven-resources-plugin:2.6:testResources (default-testResources) @ maven-demo ---
[WARNING] Using platform encoding (GBK actually) to copy filtered resources, i.e. build is platform dependent!
[INFO] skip non existing resourceDirectory F:\idea\learn\maven-demo\src\test\resources
[INFO]
[INFO] --- maven-compiler-plugin:3.1:testCompile (default-testCompile) @ maven-demo ---
[INFO] Changes detected - recompiling the module!
[WARNING] File encoding has not been set, using platform encoding GBK, i.e. build is platform dependent!
[INFO] Compiling 1 source file to F:\idea\learn\maven-demo\target\test-classes
[INFO]
[INFO] --- maven-surefire-plugin:2.12.4:test (default-test) @ maven-demo ---
[INFO] Surefire report directory: F:\idea\learn\maven-demo\target\surefire-reports

-------------------------------------------------------
 T E S T S
-------------------------------------------------------
Running wk.learn.maven.AppTest
Tests run: 1, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.088 sec

Results :

Tests run: 1, Failures: 0, Errors: 0, Skipped: 0

[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 5.160 s
[INFO] Finished at: 2019-04-18T21:36:41+08:00
[INFO] ------------------------------------------------------------------------

可以看到，已经编译成功并且通过了Test

打包

执行打包命令：

F:\idea\learn\maven-demo>mvn clean test
[INFO] Scanning for projects...
[INFO]
[INFO] ------------------------< wk.learn:maven-demo >-------------------------
[INFO] Building maven-demo 1.0-SNAPSHOT
[INFO] --------------------------------[ jar ]---------------------------------
[INFO]
[INFO] --- maven-clean-plugin:2.5:clean (default-clean) @ maven-demo ---
[INFO] Deleting F:\idea\learn\maven-demo\target
[INFO]
[INFO] --- maven-resources-plugin:2.6:resources (default-resources) @ maven-demo ---
[WARNING] Using platform encoding (GBK actually) to copy filtered resources, i.e. build is platform dependent!
[INFO] Copying 0 resource
[INFO]
[INFO] --- maven-compiler-plugin:3.1:compile (default-compile) @ maven-demo ---
[INFO] Changes detected - recompiling the module!
[WARNING] File encoding has not been set, using platform encoding GBK, i.e. build is platform dependent!
[INFO] Compiling 1 source file to F:\idea\learn\maven-demo\target\classes
[INFO]
[INFO] --- maven-resources-plugin:2.6:testResources (default-testResources) @ maven-demo ---
[WARNING] Using platform encoding (GBK actually) to copy filtered resources, i.e. build is platform dependent!
[INFO] skip non existing resourceDirectory F:\idea\learn\maven-demo\src\test\resources
[INFO]
[INFO] --- maven-compiler-plugin:3.1:testCompile (default-testCompile) @ maven-demo ---
[INFO] Changes detected - recompiling the module!
[WARNING] File encoding has not been set, using platform encoding GBK, i.e. build is platform dependent!
[INFO] Compiling 1 source file to F:\idea\learn\maven-demo\target\test-classes
[INFO]
[INFO] --- maven-surefire-plugin:2.12.4:test (default-test) @ maven-demo ---
[INFO] Surefire report directory: F:\idea\learn\maven-demo\target\surefire-reports

-------------------------------------------------------
 T E S T S
-------------------------------------------------------
Running wk.learn.maven.AppTest
Tests run: 1, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.088 sec

Results :

Tests run: 1, Failures: 0, Errors: 0, Skipped: 0

[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 5.160 s
[INFO] Finished at: 2019-04-18T21:36:41+08:00
[INFO] ------------------------------------------------------------------------

F:\idea\learn\maven-demo>mvn package
[INFO] Scanning for projects...
[INFO]
[INFO] ------------------------< wk.learn:maven-demo >-------------------------
[INFO] Building maven-demo 1.0-SNAPSHOT
[INFO] --------------------------------[ jar ]---------------------------------
[INFO]
[INFO] --- maven-resources-plugin:2.6:resources (default-resources) @ maven-demo ---
[WARNING] Using platform encoding (GBK actually) to copy filtered resources, i.e. build is platform dependent!
[INFO] Copying 0 resource
[INFO]
[INFO] --- maven-compiler-plugin:3.1:compile (default-compile) @ maven-demo ---
[INFO] Nothing to compile - all classes are up to date
[INFO]
[INFO] --- maven-resources-plugin:2.6:testResources (default-testResources) @ maven-demo ---
[WARNING] Using platform encoding (GBK actually) to copy filtered resources, i.e. build is platform dependent!
[INFO] skip non existing resourceDirectory F:\idea\learn\maven-demo\src\test\resources
[INFO]
[INFO] --- maven-compiler-plugin:3.1:testCompile (default-testCompile) @ maven-demo ---
[INFO] Nothing to compile - all classes are up to date
[INFO]
[INFO] --- maven-surefire-plugin:2.12.4:test (default-test) @ maven-demo ---
[INFO] Surefire report directory: F:\idea\learn\maven-demo\target\surefire-reports

-------------------------------------------------------
 T E S T S
-------------------------------------------------------
Running wk.learn.maven.AppTest
Tests run: 1, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.105 sec

Results :

Tests run: 1, Failures: 0, Errors: 0, Skipped: 0

[INFO]
[INFO] --- maven-jar-plugin:2.4:jar (default-jar) @ maven-demo ---
[INFO] Building jar: F:\idea\learn\maven-demo\target\maven-demo-1.0-SNAPSHOT.jar
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 3.510 s
[INFO] Finished at: 2019-04-18T21:41:13+08:00
[INFO] ------------------------------------------------------------------------

通常还需要将项目安装到本地仓库中，这样别的项目就可以使用这个jar了，安装的命令是: mvn install

现在我们的项目已经成功编译，测试，打包 和安装，主要使用了:

四、在IDEA中使用Maven

通常我们编写代码都会使用到IDE，各个IDE也都很好的集成了maven，这里介绍一下maven在IDEA中的使用和配置。

IDEA中已经默认集成了maven，但我们总想做一些定制：

File->Settings 或者使用快捷键 Ctrl+Alt+s 打开设置，找到 Build,Execution ... -> Build Tools -> Maven

image

​ 第一处：可以自己指定maven的目录,自己下载的任意版本的maven

​ 第二处：可以自己指定 setting.xml 的位置

​ 第三处：可以自己指定本地仓库的位置

在编辑器的右侧可以打开maven 的插件，如下图，这个插件提供了maven 的生命周期，插件等的使用，非常方便。

image

五、坐标和依赖

maven 坐标为各种构件引入了秩序，任何一个构件都必须明确自己的坐标，而一组Maven坐标是通过一些元素定义的，它们是 groupId,artifactId,version,packageing,classifier等

说白了,就是每个jar包在maven的仓库中的坐标都是唯一的,我们需要引入不同的jar包,直接填写其对应的坐标即可。

<dependency>
    <groupId>cn.hutool</groupId>
    <artifactId>hutool-all</artifactId>
    <version>4.6.1</version>
</dependency>

如上, 分别指定了三个元素, groupId 指的是这个Jar包的公司或组织Id, artifactId 指的是项目名，version 指的就是jar包的版本号了。

Scope

指的是这个Jar包的依赖范围:

Scope 依赖范围 compile classpath test classpath runtime classpath example
complie Y Y Y spring-core
test N Y N Junit
provided Y Y N servlet-api
runtime N Y Y jdbc驱动实现
system Y Y N 本地的,maven仓库之外的类库文件

六、仓库

Repository 是Maven中的一个重要的概念,主要分为 本地仓库 ,远程仓库 。

本地仓库 可以通过 seeting.xml 中的 <localRepository> 这个标签项来设置具体路径,比如 <localRepository>D:\maven\local_repository</localRepository>

远程仓库 默认情况下是 maven 的中央仓库,一般企业中会搭建私服来开发,这里只需理解一下远程仓库的概念。

Maven查找依赖的流程是会先去本地仓库中查找，如果没有找到，就会向上去远程仓库拉取，然后将依赖缓存在本地；如果在本地找到了 。就不会再去远程仓库拉取了。

设置阿里云镜像

​ 默认的远程仓库为 maven的中央仓库 ，由于中央仓库的服务器在国外，我们平时下载jar包速度会很慢，可以通过 setting.xml 中的 <mirro> 标签来设置镜像提供加速服务。

​ 在 setting.xml 中找到 <mirrors> 标签，这个标签代表的是镜像的集合,在这个标签中添加

 <mirror>      
      <id>nexus-aliyun</id>    
      <name>*</name>  
      <url>http://maven.aliyun.com/nexus/content/groups/public</url>    
      <mirrorOf>central</mirrorOf>      
</mirror>
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