Maven入门教程

GitHub仓库:Fundebug/maven-tutorial

Maven简介

Maven是Java项目构建工具,可以用于管理Java依赖,还可以用于编译、打包以及发布Java项目,类似于JavaScript生态系统中的NPM。

Maven的命令行工具为mvn,其常用命令如下表所示:

| 命令 | 说明 |
| ----------- | -----------------------|
| mvn compile | 编译Java源代码 |
| mvn package | 打包Java项目 |
| mvn deploy | 将Java项目发布到Maven仓库 |
| mvn clean | 删除构建目录 |

Maven的配置文件为pom.xml,这个文件有个很吓人的学术名字Project Object Model,但是怎么看它都只是个普通的配置文件,与NPM中的package.json没啥本质区别。

Maven的*仓库为Maven Repository,这里可以找到各种Java依赖,例如我们Fundebug的异常监控插件fundebug-javafundebug-spring

安装Maven

在MacBook上使用brew安装很方便

brew install maven

我安装的是maven版本3.5.4

mvn -version
Apache Maven 3.5.4 (1edded0938998edf8bf061f1ceb3cfdeccf443fe; 2018-06-18T02:33:14+08:00)
Maven home: /usr/local/Cellar/maven/3.5.4/libexec
Java version: 1.8.0_192, vendor: Oracle Corporation, runtime: /Library/Java/JavaVirtualMachines/jdk1.8.0_192.jdk/Contents/Home/jre
Default locale: zh_CN, platform encoding: UTF-8
OS name: "mac os x", version: "10.14.2", arch: "x86_64", family: "mac"

示例代码

本文示例代码都在GitHub仓库Fundebug/maven-tutorial

使用tree命令可以查看项目的目录结构:

tree -v
.
├── pom.xml
└── src
    └── main
        └── java
            └── com
                └── fundebug
                    └── Hello.java

pom.xml为Maven配置文件,位于项目的根目录。

Hello.java为Java源代码,位于src/main/java/com/fundebug目录中。根据Maven对目录结构的要求,Java源代码必须位于src/main/java目录。

Hello.java

package com.fundebug;

import org.json.JSONObject;

public class Hello {
        public static void main(String[] args) {
                JSONObject tomJsonObj = new JSONObject();
                tomJsonObj.put("name", "Fundebug");
                tomJsonObj.put("url", "https://www.fundebug.com");
                System.out.println(tomJsonObj.toString(4));
        }
}

Hello.java非常简单,定义了一个JSON对象,然后把它打印出来了。

package定义的包名为com.fundebug,需要与所在的目录结构相吻合,因此Hello.java位于src/main/java/com/fundebug目录中,而不是src/main/java/目录中。

代码依赖于第三方模块json,因此需要在pom.xml配置dependency:

<dependency>
    <groupId>org.json</groupId>
    <artifactId>json</artifactId>
    <version>20180813</version>
</dependency>

pom.xml

<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>
        <!-- 坐标 -->
        <groupId>com.fundebug</groupId>
        <artifactId>hello</artifactId>
        <version>1.0</version>
        <!-- 依赖 -->
        <dependencies>
                <!-- https://mvnrepository.com/artifact/org.json/json -->
                <dependency>
                        <groupId>org.json</groupId>
                        <artifactId>json</artifactId>
                        <version>20180813</version>
                </dependency>
        </dependencies>
</project>

pom.xml中,<project></project>为最外层的标签;<modelVersion>4.0.0</modelVersion>定义了所使用的POM版本。这2个标签基本上是不变的。

groupId、artifactId与version一起则定义了模块的坐标(Coordinates),每个公共模块的坐标应该是唯一的:

  • groupId:组织名称,通常是把域名反过来,例如com.fundebug
  • artifactId:模块名称,例如fundebug-java
  • version:模块版本,例如0.2.0

<dependencies></dependencies>定义了当前项目所依赖的模块:

<dependencies>
    <!-- https://mvnrepository.com/artifact/org.json/json -->
    <dependency>
        <groupId>org.json</groupId>
        <artifactId>json</artifactId>
        <version>20180813</version>
    </dependency>
</dependencies>

Maven可以根据<dependency></dependency>中定义的坐标,自动下载所依赖的模块。在MacBook上,Maven将下载的模块缓存在$HOME/.m2/目录。

使用mvn打包

执行mvn package命令,即可将源码打包为.jar文件:

mvn package
[INFO] Scanning for projects...
[INFO]
[INFO] -------------------------< com.fundebug:hello >-------------------------
[INFO] Building hello 1.0
[INFO] --------------------------------[ jar ]---------------------------------
[INFO]
[INFO] --- maven-resources-plugin:2.6:resources (default-resources) @ hello ---
[WARNING] Using platform encoding (UTF-8 actually) to copy filtered resources, i.e. build is platform dependent!
[INFO] skip non existing resourceDirectory /Users/fundebug/Desktop/maven-tutorial/src/main/resources
[INFO]
[INFO] --- maven-compiler-plugin:3.1:compile (default-compile) @ hello ---
[INFO] Changes detected - recompiling the module!
[WARNING] File encoding has not been set, using platform encoding UTF-8, i.e. build is platform dependent!
[INFO] Compiling 1 source file to /Users/fundebug/Desktop/maven-tutorial/target/classes
[INFO]
[INFO] --- maven-resources-plugin:2.6:testResources (default-testResources) @ hello ---
[WARNING] Using platform encoding (UTF-8 actually) to copy filtered resources, i.e. build is platform dependent!
[INFO] skip non existing resourceDirectory /Users/fundebug/Desktop/maven-tutorial/src/test/resources
[INFO]
[INFO] --- maven-compiler-plugin:3.1:testCompile (default-testCompile) @ hello ---
[INFO] No sources to compile
[INFO]
[INFO] --- maven-surefire-plugin:2.12.4:test (default-test) @ hello ---
[INFO] No tests to run.
[INFO]
[INFO] --- maven-jar-plugin:2.4:jar (default-jar) @ hello ---
[INFO] Building jar: /Users/fundebug/Desktop/maven-tutorial/target/hello-1.0.jar
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 2.789 s
[INFO] Finished at: 2019-01-05T15:23:02+08:00
[INFO] ------------------------------------------------------------------------

mvn package执行之后,项目中会新增一个tartget目录,编译的字节码文件位于target/classes目录,而jar包位于target/hello-1.0.jar

tree -v
.
├── pom.xml
├── src
│   └── main
│       └── java
│           └── com
│               └── fundebug
│                   └── Hello.java
└── target
    ├── classes
    │   └── com
    │       └── fundebug
    │           └── Hello.class
    ├── hello-1.0.jar

使用mvn运行

打包好的jar包,可以直接使用java命令运行时,注意需要指定所依赖的jar包。对于所依赖的jar包,Maven则会自动下载依赖,放在本地仓库中。在MacBook上,Maven本地仓库位于$HOME/.m2/目录。

java -cp target/hello-1.0.jar:$HOME/.m2/repository/org/json/json/20180813/json-20180813.jar com.fundebug.Hello
{
    "name": "Fundebug",
    "url": "https://www.fundebug.com"
}

也可以使用mvn exec:java命令执行,不需要指定依赖的jar包,更加方便:

mvn exec:java -Dexec.mainClass="com.fundebug.Hello"
[INFO] Scanning for projects...
[INFO]
[INFO] -------------------------< com.fundebug:hello >-------------------------
[INFO] Building hello 1.0
[INFO] --------------------------------[ jar ]---------------------------------
[INFO]
[INFO] --- exec-maven-plugin:1.6.0:java (default-cli) @ hello ---
{
    "name": "Fundebug",
    "url": "https://www.fundebug.com"
}
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 0.837 s
[INFO] Finished at: 2019-01-05T15:33:57+08:00
[INFO] ------------------------------------------------------------------------

参考

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