廖雪峰Java12maven基础-2maven进阶-2模块管理

1. 把大项目拆分为模块是下降软件复杂度的有效方法

在Java项目中，咱们一般会会把一个项目分拆为模块，这是为了下降软件复杂度。

例如：咱们能够把一个大的项目氛围module-a, module-b, module-c三个模块，这样咱们就能够下降软件的复杂度。

maven能够有效管理多个模块

2.创建一个非mavend的项目，。在这个项目下新建4个maven模块。

2.1 模块greeting

不要忘了log4j2.xml文件
Greeting.java

package com.greeting;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
public class Greeting {
    public static void print(String name){
        Log log = LogFactory.getLog(Greeting.class);
        log.info("Hello,"+name+"!");
    }
}

GreetingTest.java

package com.greeting;

import org.junit.Test;
public class GreetingTest {

    @Test
    public void print() {
        Greeting.print("Test");
    }
}

pom.xml

<?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>
<parent>
    <groupId>com.csj2018</groupId>
    <artifactId>parent</artifactId>
    <version>1.0-SNAPSHOT</version>
    <relativePath>../parent/pom.xml</relativePath>
</parent>
    <artifactId>greeting</artifactId>
    <version>1.0-SNAPSHOT</version>
    <packaging>jar</packaging>
</project>

2.2 模块hellomaven

App.java

package com.hellomaven;
import com.greeting.Greeting;

public class App {
    public static void main(String[] args){
        Greeting.print("Maven");
    }
}

AppTest.java

package com.hellomaven;

import org.junit.Test;
public class AppTest {

    @Test
    public void main() {
        App.main(null);
    }
}

pom.xml

<?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>
    <parent>
        <groupId>com.csj2018</groupId>
        <artifactId>parent</artifactId>
        <version>1.0-SNAPSHOT</version>
        <relativePath>../parent/pom.xml</relativePath>
    </parent>
    <!--<groupId>com.csj2018</groupId>继承parent，能够删除-->
    <artifactId>hellomaven</artifactId>
    <version>1.0-SNAPSHOT</version>
    <packaging>jar</packaging>
    <dependencies>
        <dependency>
            <groupId>com.csj2018</groupId>
            <artifactId>greeting</artifactId>
            <version>1.0-SNAPSHOT</version>
        </dependency>
    </dependencies>
    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-shade-plugin</artifactId>
                <version>3.2.1</version>
                <executions>
                    <execution>
                        <phase>package</phase>
                        <goals>
                            <goal>shade</goal>
                        </goals>
                        <configuration>
                            <transformers>
                                <transformer implementation="org.apache.maven.plugins.shade.resource.ManifestResourceTransformer">
                                    <mainClass>com.hellomaven.App</mainClass>
                                </transformer>
                            </transformers>
                        </configuration>
                    </execution>
                </executions>
            </plugin>
        </plugins>
    </build>
</project>

2.3 模块parent

模块greeting，hellomaven的pom文件高度类似，咱们能够提取出共同部分做为parent，而模块greeting，hellomaven分别从parent继承，就能够简化greeting，hellomaven2个模块自身的配置。
parent的packaging是pom，不是jar，是由于parent自己不包含任何Java代码/
pom.xml

<?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>com.csj2018</groupId>
    <artifactId>parent</artifactId>
    <version>1.0-SNAPSHOT</version>
    <packaging>pom</packaging>
    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <java.verison>1.8</java.verison>
        <maven.compiler.source>1.8</maven.compiler.source>
        <maven.compiler.target>1.8</maven.compiler.target>
    </properties>
    <dependencies>
        <dependency>
            <groupId>commons-logging</groupId>
            <artifactId>commons-logging</artifactId>
            <version>1.2</version>
        </dependency>
        <dependency>
            <groupId>org.apache.logging.log4j</groupId>
            <artifactId>log4j-jcl</artifactId>
            <version>2.10.0</version>
            <scope>runtime</scope>
        </dependency>
        <dependency>
            <groupId>org.apache.logging.log4j</groupId>
            <artifactId>log4j-core</artifactId>
            <version>2.10.0</version>
            <scope>runtime</scope>
        </dependency>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.12</version>
            <scope>test</scope>
        </dependency>
    </dependencies>
    
</project>

运行hellomaven的App.java，结果以下

3.编译

进入hellomaven，编译提示找不到greeting的jar包

mvn clean compile

若是模块A依赖模块B，则模块须要模块B的jar包才能正常编译
中央仓库：发布者将模块B发布到maven中央仓库，模块A从中央仓库获取模块B。
私有仓库：内网中，发布者将模块B发布到私有仓库，模块A从中央仓库获取模块B。
本地仓库：发布者使用mvn clean install将模块B发布到maven本地仓库，模块A从本地仓库获取模块B。不推荐，由于每次修改模块B源码，都须要从新安装。会出现版本不一致的状况。
模块化编译：

<modules>
    <module>模块A</module>
    <module>模块B</module>
</modules>

3.1模块build

pom.xml

<?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>com.csj2018</groupId>
    <artifactId>build</artifactId>
    <version>1.0-SNAPSHOT</version>
    <packaging>pom</packaging>
    <modules>
        <module>../parent</module>
        <module>../greeting</module>
        <module>../hellomaven</module>
    </modules>
</project>

进入build根目录，再次编译成功

打包，运行jar包

mvn clean package
#进入hellomaven/target目录下，运行jar包
cd ../hellomaven/target
java -jar hellomaven-1.0-SNAPSHOT.jar

4. 总结：

• maven支持模块化管理，能够把一个大项目拆成几个模块
• 能够经过继承在parent的pom.xml同必定义重复配置
• 能够经过 编译多个模块